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On the optimal path of growth in chum salmon (Oncorhynchus keta) Wild, Alexander 1973

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ON THE OPTIMAL P A T H OF GROWTH IN CHUM SALMON (Oncorhynchus keta) by Alexander Wild B .A.Sc , University of British Columbia, 1956 A thesis submitted in partial fulfilment of the requirements for the degree of Master of Science in the Department of Zoology We accept this thesis as conforming to the required standard T H E UNIVERSITY OF BRITISH COLUMBIA July 1973 In presenting t h i s thesis i n p a r t i a l f u l f i l m e n t of the requirements for an advanced degree at the University of B r i t i s h Columbia, I agree that the Library s h a l l make i t f r e e l y available f o r reference and study. I further agree that permission fo r extensive copying of t h i s thesis for scholarly purposes may be granted by the Head of my Department or by h i s representatives. It i s understood that copying or publication of t h i s thesis for f i n a n c i a l gain s h a l l not be allowed without my written permission. Department of Zoology The University of B r i t i s h Columbia Vancouver 8, Canada Date 16 July 1973 A B S T R A C T The effects of temperatures within the optimal range for incubation of salmon, and hyperoxic and hypoxic oxygen tensions, were examined to develop an optimal path of growth during the pre-rearing stage for chum salmon (Oncorhynchus keta). During early development, and at constant oxygen tension, an elevated temperature of 55°F (1Z.8°C) led to accelerated growth and most efficient conversion of yolk compared to 50°F (10°C) or 45°F (7.2°C). With increased age, growth and efficiency were favored by decreasing temperature with its associated increase in oxygen concentration and reduced metabolic demand by the embryo. After hatching, the detrimental effect of a high temperature was not offset by the increased availability of oxygen and growth was retarded relative to lower temperatures. Oxygen tensions within the treatment range of 145 to 253 mm Hg did not contribute significantly to embryo weight when measured at equal stages of development in day-degrees. The optimal path for growth with minimal o o mortality involved a gradual reduction in temperature from 55 to 45 F during incubation, a constant temperature of 45°F after hatching to the beginning of active feeding, and an oxygen tension not in excess of air saturation. T A B L E OF CONTENTS P a g e A B S T R A C T " T A B L E OF CONTENTS U i LIST OF T A B L E S iv LIST OF FIGURES v ACKNOWLEDGMENTS vi INTRODUCTION 1 METHODS AND MATERIALS 4 RESULTS. 13 Embryo Weight, Temperature and Oxygen Tension Requirements •. 13 Yolk Conversion Efficiency 18 DISCUSSION 28 SUMMARY AND CONCLUSIONS 3 5 L I T E R A T U R E CITED 37 APPENDICES 41 iv LIST OF T A B L E S T A B L E Page I Operating conditions during the experimental interval from 0 - 1300 D ° 10 II Hatching time in day-degrees (D°) and embryo weights 21 III Suggested transfer periods for path of maximal growth in weight. Developmental age in D ° 27 IV Embryo and alevin dry weight comparison at different temperatures and oxygen tensions 31 V LIST OF FIGURES FIGURE Page l a F a c t o r i a l design of the experiment 5 l b Treatment locations within experimental trays 5 2 Stylized diagram showing the relationship between embryo growth and temperature at constant oxygen tension 14 3 Effect of temperature at constant oxygen tension on the weight of chum salmon embryos 15 4 Effect of oxygen tension at constant temperature on the weight of chum salmon embryos 19 5 Effect of temperature at constant oxygen tension on the length of chum salmon embryos 20 6 Growth and per cent accumulative gross conversion efficiency of chum salmon incubated at 141.5 mm Hg (O^) 23 7 Growth and per cent accumulative gross conversion efficiency of chum salmon incubated at 195.0 mm Hg (O2) ^5 8 Growth and per cent accumulative gross conversion efficiency of chum salmon incubated at 253.0 mm Hg (O-j). 26 ACKNOWLEDGMENTS The author would like to express his gratitude to Dr. P. A. Larkin, for his encouragement and support throughout the project and for a cr i t i c a l review of the manuscript. Appreciation is also extended to Mr. J. M. Blackburn for his able assistance and helpful suggestions during construction of the equipment. 1 INTRODUCTION The search for optimal operating conditions in salmon hatcheries is directed towards two major objectives: to achieve maximal size at the time of release, and to increase productivity in terms of fish numbers and their ability to survive. Efforts to achieve these goals have focussed on the rearing, rather than the incubating stage, with emphasis on nutrition and suitable environmental conditions to improve the stamina and growth rate of young salmon (Burrows, 1963, 1969; Burrows and Combs, 1968; Banks, et al., 1971). There is a practical reason for this choice. Hatchery conditions can exert a more direct influence on growth and development of stamina after hatching than during incubation. As a result, the full potential for growth and survival, and the conditions needed to realize this potential, have not been established for the interval prior to active feeding. In terms of the major objectives, it is necessary that optimal conditions be specified for this period in order to assess the benefits on a practical basis. Two critical differences that exist between the egg and alevin stages and that of active feeding are: (1) the influence of temperature on growth in the presence of a chorion that can limit oxygen supply; and (2) the interaction of these variables on the conversion efficiency of an endogenous food source. The relationship between temperature and oxygen tension appears to be a suitable starting point in determining optimal conditions during incubation and the immediate post-hatching stage. 2 Oxygen Tension During Incubation: Hypoxic conditions are known to retard growth and development in salmonids (Alderdice, ejt al., 1958; Wickett, 1958; Hamdorf, 1961; Garside, 1966), suggesting that the - minimal oxygen tension should be equal to air saturation to achieve optimal results. Hamdorf's (1961) experiments with rainbow trout (Salmo irideus) eggs are particularly important, for he demonstrated that hatching occurred at the point where no further embryonic growth was possible. The limit of growth was dependent upon the prevailing oxygen tension. To illustrate this point, embryos incubated at an oxygen concentration of 21 ppm at 5 0 ° F showed a 40 per cent increase in hatched dry weight, a 20 per cent greater condition factor, and an advanced stage of development compared to normal controls (10.3 ppm). The difference in hatching time between the two treatments was only one day, indicating the hyperoxic conditions accelerated growth and development. The results also suggested that, in addition to air-saturated levels of oxygen tension, hyperoxic conditions should be included as a potential optimal condition during incubation. Temperature Conditions Prior to Active Feeding: A low incidence of abnormalities and mortalities has often been used to indicate optimal developmental temperatures, and for commercial salmon the range has been established at 4 2 ° - 5 7 ° F . 1 (Brett, 1952, 1956; Burrows, 1963; Combs, 1965). ^Al l temperatures in the present study are reported in degrees Fahrenheit, the practical unit used in North American hatcheries. To convert day-degrees of development in ° F to ° C , divide by 1.8. 3 The effects on specific growth rate of varying or constant temperatures within this range, and the relationship between temperature and gross conversion efficiency, have not been clearly established. Efficiencies have usually been determined during the post-hatching stage (Gray, 1928; Merriman, 1935; Hayes, 1949; Marr, 1965). While Hayes (1949) indicated a linear increase in efficiency in the 4 1 ° - 6 l ° F interval for Atlantic salmon (Salmo salar), Marr (1965) showed that specific growth and metabolic rates were not proportional and a peak efficiency occurred at 5 0 ° F . A similar disproportionality may exist in the egg stage, suggesting that optimal conditions for growth and conversion may not be equal. Vernidub (1963) found that for Baltic salmon (Salmo salar) and trout (S. trutta), maximal growth rate and efficiency coincided with a rising temperature scheme, from fertilization to the stage of active feeding. The information given here on temperature effects on growth rate and efficiency are either partially conflicting, species specific, or dependent on the stage of development when the measurements were taken, and the problem should be examined further. The objectives of the experiments in the present study were twofold: (1) to initially examine the effects of temperatures within a narrow optimal range and various oxygen tensions on the growth and conversion efficiency of salmon embryos and alevins; and (2) to define optimal conditions for growth based on these results. 4 M E T H O D S A N D M A T E R I A L S A schematic representation of a factorial experiment involving five temperature schemes and three oxygen tensions is shown in Figure l a . E a c h combination of temperature and oxygen tension represented an indiv i -dual treatment to which chum salmon (Oncorhynchus keta) eggs were subjected f r o m ferti l ization to the onset of starvation. Nine egg trays were required for the experimental treatments. E a c h tray was partitioned into three equal-area sections, and each section contained an average of 402 eggs (range: 380 - 443). The trays and the distribution of the treatment eggs during the course of the experiment are il lustrated in F igure lb . Section one of each tray contained the eggs held at constant conditions throughout the experiment; the remaining sections were involved in egg transfers according to the following plan. At approximately 300 day-degree ( D ° ) intervals one section of eggs f r o m each tray at T^ was transferred, f i rs t to T2 at 3 4 4 D ° , and then to T3 at 6 6 3 D ° , where it was held until completion of the experiment (rising temperature scheme T^) . One third of the eggs at To were lowered to T-, at 300 D ° and then to T at 6 2 0 D ° to ^ 1 m i m i c a naturally-fal l ing temperature scheme, T ^ . The eggs at 5 0 ° F were not moved. Egg transfers took place at constant oxygen tension only, i .e., f r o m O j T j to O^T^ to O ^ T ^ . and the reverse . Chum salmon eggs were obtained f r o m the Qualicum River hatchery, Vancouver Island, on December 15, 1971. The ova f rom each of nine, incised females were placed in separate containers, dry-fert i l ized by sperm T A R G E T V A L U E S T 2 I 45 F o 50 F 55 F Transfer T4 = T | — » T 2 * T 3 Transfer T5 = T 3 — T 2 — T, 141.5 mm Hg O X Y G E N T E N S I O N 0, 195.0 m m Hg 0 , T , 0 , T 2 0 | T 3 0 , T 4 0 | T 5 0 2 T, 0 2 T 2 0 2 T 3 0 2 T 4 0 2 T 5 ofl 253.0 m m Hg 0 3 T 2 ° 3 T 3 O 3 T 4 ° 3 T 5 F IG. 1a. F a c t o r i a l d e s i g n of t h e e x p e r i m e n t s h o w i n g the 15 t r e a t m e n t s and t h e i r a b b r e v i a t e d n o m e n c l a t u r e . o, I 2 3 I 2 3 I 2 3 0 , T , O, T 4 d A 0 2 T , 0 , T , 2 '4 ° 3 T I 0 3 T 4 3 44 D 620 D 0 , T 2 0 2 T 2 3 44 D d 620 D 0 3 T 2 344 D d 6 20 D 6 63 D 6 6 3 D 6 63 D 0 , T ; I '3 300 0 0 | T 5 300 D 0 2 T 3 0 2 T 5 ° 3 T 3 300 D ° 3 T 5 F I G . 1b. T r e a t m e n t l o c a t i o n s w i t h i n e x p e r i m e n t a l t r a y s . T r a n s f e r t i m e s o 1 1 11 s h o w n in d a y d e g r e e s (D ) f a n d t e m p o r a r y o c c u p a t i o n o f d u m m y s e c t i o n s ( d ) . f r o m two males, and transported to the university campus within eight hours. During the interval, the water temperature in the containers did not increase by more than 2.5°F above the original value of 40°F. In the laboratory, fertilized eggs of approximately equal diameter from three females were pooled and arranged in a close-packed mono layer in the trays. Because of the design of the experiment, the number of eggs at each combination of oxygen and temperature could have been different at various times; i.e., more at during the intermediate period of the rising and falling temperature regimes. Accordingly, the number of eggs per tray was kept constant through-out the experiment by filling the vacant sections with fertilized eggs from additional females. These eggs were called "dummies" and the tray sections which they temporarily occupied are designated by "d" in the Figure lb. For each treatment, twenty eggs were removed at each transfer period and at each 100D° interval and preserved in four per cent glutaraldehyde for sub-sequent weight and length measurements. Five additional eggs were preserved at each 300D° interval for histological sectioning. Following each sample time the mono layer was re-established by the addition of "dummy" eggs maintained in duplicate containers fed by the overflow from each treat-ment tray. The replacement of eggs ensured that water velocities were approximately equal up to the point of hatching. At that time, all remaining "dummy" eggs and alevins were removed from the experimental sections. Mortalities were recorded and removed at three day intervals during incubation, and on a daily basis following hatching. An estimate of 7 survival that compensated for periodic removal of eggs and accidental and 2 natural deaths was determined by the method given by Seymour (rvIS 1956). The dechlorinated, f i ltered (5 (i) water supply to the equipment was based on a gravity feed system involving three 8-Imp. gal. plastic containers arranged in a pyramid. Both the top and one lower vessel were equipped with. 1000-watt, quartz-glass immers ion heater contained in a heat exchanger, the latter being suspended inside the vessel . Following initial heating to 4 5 ° F in the head tank, the single discharge s tream was divided equally between the lower containers, one volume being further heated to 5 5 ° F . One-half of the outflow f r o m each lower tank was then joined in a regulating valve to yield 5 0 ° F water, and the remaining flows provided temperatures of 4 5 ° to 5 5 ° F . Each heated water source was subsequently divided in three, fed through individual flow-meter tubes, and discharged into the top of separate absorption columns containing Raschig r ings . A metered flow of blended oxygen or nitrogen and air was delivered to the base of three columns receiving water at three individual temperatures. A total of nine columns was required to achieve the three oxygen partial pressures , one for each group of temperatures. Water was delivered to each treatment tray at 654 m l / m i n to yield an estimated, actual velocity past the eggs of 2.3 mm/sec and a flushing rate of eight times per hour. The water flow entering each tray passed upwards through an l /8 th- inch mesh nylon net supporting the eggs and overflowed by gravity into a s imi lar tray containing ^See Appendix A 8 the "dummy" eggs. A two-inch depth of water was maintained above the egg layer. Equilibration of the tray contents with the atmosphere was prevented by means of a gas seal. An 1/2-inch square, urethane foam strip was adhered to the peripheral lip of each tray and the whole covered by an over-sized heavy plate of 1/4-inch glass. A layer of black vinyl sheeting and an anchoring sheet of 1/8-inch glass prevented light from entering the tray. The protruding surfaces and edges of the heavy glass plate and the tray exterior were coated with reflective aluminum paint. By removing the anchor glass and vinyl the eggs could be observed without disturbing the gas seal. Dial-type thermometers mounted through the glass plates provided an easy reference to temperature conditions. The fungicide, malachite green, was added once daily to the incoming water supply up to hatching of the treatment eggs and discontinued thereafter. Temperatures were recorded at least four times daily and accu-mulative day-degrees calculated on the assumption of a linear temperature change between intervals. The pattern of water flow ensured that if an unexpected temperature change occurred all treatments were equally affected. A modified Winkler method was used for oxygen determinations below and above air-saturated levels, as recommended by the American Public Health Association, ejt aL, (1967), and carried out every second day or more often, as required. The average values and ranges of oxygen tension, temperature and water flow rate in the experimental interval from 0-1300 D ° appear in 9 Table I. The values for the water flow ranges do not reflect three equip-ment shut-downs for cleaning purposes, but the duration of each interruption, with zero flow, did not exceed one hour before normal conditions were restored. The failure of water flow rates to obtain the target value of 654 ml/min (Table I) or to achieve the same average values can be attributed to the effect of both supersaturated water and algal build-up in the absorption columns. The first difficulty occurred due to rapid heating of water followed by a relatively slow passage to the absorption columns. Excess air tended to be released gradually in the water lines leading to an air lock and reduced flow rates; the effect was more pro-nounced with increasing temperature. The installation of short, plastic tubes acting as disengagement chambers minimized the problem. Algal build-up in the absorption columns reduced water flows in each treatment over the same 30-day period from 654 ml/min to 536 ml/min (O^T^) o r to 460 ml/min (O^T^), with the highest temperature and oxygen tension showing the greatest decline. A linear decrease in flow rate was assumed in calculating average treatment flow rates. Due to temperature differences between treatments, the reduced flow occurred at different developmental stages; i.e., at 5 5 ° F hatching was complete when flow rates began to decline, whereas at 4 5 ° F the re-establishment of normal flows coincided with hatching. A reduction in flow rate from 654 to 460 ml/min, however, only results in a three per cent decrease in oxygen concentration Table I. Operating conditions during the experimental interval from 0-1300 D ° . . ' . . . . T R E A T M E N T ° 1 ° 2 ° 3 T l T 2 T 3 * T 4 * T 5 T l T 2 V T 4 T 5 T l T 2 T 3 T 4 T 5 Oxygen tension (mm Hg) •> Target value Average Range 95% of time 142.4 140.0-145.0 143.9 138.1-149.7 141.5 145.4 139.6-151.2 .145.0 . 140.0-150.0 . 142.7 137.7-147.7 190.0 187.6-192.4 196.2 190,6-201.8 195.0 199.0 194.8-203.2 195.3 187.4-203.2 192.4 l186.2-198.6 246.6 236.9-256.3 254.4 245.2-263.6 253.0 250.5 237.3-267.5 247.0 222.5-271.5 250.6 233.5-267.7 Temperature ( °F) Target value Average Range 95% of time 45.0 45.0 44.5-45.5 50.0 50.0 49.5-50.5 55.0 54.7 54.5-55.5 50.4 47.1 45.0 45.0 44.5-45.5 50.0 50.0 49.5-50.5 55.0 54.7 54.5-55.5 50.4 47.1 45.0 45.0 44.5-45.5 50.0 50.0 49.5-50.5 .55.0 54.7 54.5-55.5 50.4 47.1 Water flow (ml/min) Target value Average Range 95% of time 633 560-654 617 514-654 654 628 458-654 605 450-654 629 560-654 634 560-654 617 519-654 654 626 450-654 606 450-654 628 556-654 633 560-654 619 519-654 654 627 450-654 604 450-654 629 560-654 * - Rising (T ) and falling (T ) temperature schemes, respectively. 11 (Daykin, 1965) at the chorionic surface and the effect is hot serious. The oxygen tension target values were maintained throughout the period of reduced water flow. Initial hatching occurred simultaneously in treatments O^T^ and O T at 900D° , and the alevins demonstrated their ability to squeeze 1 5 through the openings of the 1/8-inch mesh supporting screens. As an emergency measure, they were transferred to smaller meshed baskets that fit snugly into the partitioned treatment sections. A l l remaining treatment eggs were similarly enclosed at the onset of their individual hatch period. Channelling of water between the vertical basket walls and tank partitions could have led to unequal flow rates between treatments and affected the data on growth comparisons. The trends in relative weight and length measurements established before hatching were nevertheless maintained to the end of the experiment. If minor flow differences did exist, they do not appear to have affected the conclusions of the experiment. After removing the chorion from the preserved eggs by means of jeweller's forceps, embryological features were noted without staining and the embryo, with its yolk sac membrane, was separated from the yolk. Lengths were measured to 1/10 mm from the nose tip to the insertion of the caudal fin (projected hypural plate) by means of a vernier scale mounted on a dissecting microscope. Both the embryo and yolk were then dried separately in small foil pans for six days at 140.0 + 1 . 3 5 ° F . Each dry embryo and yolk was weighed twice to the nearest 1/10 mg on an electrical pan balance. 1 2 The use of equal thermal units, or day degrees, to indicate equal developmental stages in poikilotherms has been criticized by Battle ( 1 9 4 4 ) , Kinne and Kinne ( 1 9 6 2 ) , Marr ( 1 9 6 5 ) , Ignat'eva ( 1 9 7 0 ) , and others. Garside ( 1 9 6 6 ) indicated that the Van't Hoff rule (Q^Q) does not hold for brook and rainbow trout, a plot of log developmental rate versus temperature being curvilinear in the range from 3 6 ° to 6 3 ° F . In the short 1 0 ° F interval used in this experiment, however, deviations from linearity are not appreciable and equal day-degree values were taken to indicate equivalent stages of development. 13 R E S U L T S E m b r y o Weight, Temperature and Oxygen Tension Relationships Growth curves for a l l of the 15 treatments were evidently non-linear in the interval f r o m 3 0 0 - 1 3 0 0 D ° , and the relationship between dry embryo weight (or length) and D ° was l inearized by means of logarithmic axes. Covariance analysis indicated that temperature and temperature-oxygen interaction effects were significant (.00 5 > P > .001, and .001 > P > .0001, respectively), whereas the effect of oxygen tension alone was not (.10 > P > .05). The interaction effect is complex. It is i l lustrated in part by the stylized d iagram (Figure 2) which shows the change in embryo weight with developmental time ( D ° ) for the three constant tem-peratures at the lowest oxygen tension O^ (141.5 m m Hg). The r i s ing (T^) and falling ( T 5 ) temperature schemes are not included in order to simplify the diagram. The weight differences between embryos at 300 D ° have been marginally exaggerated to illustrate the reversa l in weight relationships achieved by 1300 D ° . The dotted lines join points of equal Do value. 3 F igure 3, based .on actual data , may be visualized as a frontal view para l le l to the D ° - a x i s of Figure 2. A l l treatment relationships are represented and can be located by the legend. Interpretation of Figure 3 can be simplified by focussing, one at a time, on the temperature-weight data associated with one oxygen tension. See Appendix B T 2 T E M P E R A T U R E F I G . 2. S t y l i z e d d i a g r a m s h o w i n g t h e r e l a t i o n s h i p b e t w e e n e m b r y o g r o w t h a n d t e m p e r a t u r e at c o n s t a n t o x y g e n t e n s i o n . D a s h e d l i n e s j o i n e m b r y o s of e q u a l d e v e l o p m e n t a l a g e in d e g r e e d a y s ( D ° ) . V e r t i c a l s e c t i o n s t h r o u g h e q u a l D ° - l i n e s u s e d in p r e p a r i n g F I G . 3 f r o m a c t u a l d a t a . 15 141.5 mm Hg (10.77) (10.12) (9.50] 28 24 E 2 0 x o ui 5 16 o >• CC ca z > o 12 8-7 0 0 5 0 0 3 0 0 D° - O — i T 3 195 .0 mm Hg (14.83) (13.93) (13.13) H A T C H 43= 2 5 3 . 0 mm Hg (19.20) (18.IO) (I7.00) r 2 8 24 20 16 - 12 3> A 9 - A -n 1 T 2 T 3 »• o T E M P E R AT U R E , F. F I G . 3. E f f e c t of t e m p e r a t u r e at c o n s t a n t o x y g e n t e n s i o n on t h e w e i g h t of c h u m s a l m o n e m -b r y o s . L e g e n d ' - O - T, (45 ° F l . • " T 2 ( 5 0 ° F ) . • - T 3 ( 5 5 ° F >. A - i ncr ea s i ng t emp e ra t u r e ( T 4 ). • " d e -c r e a s i n g t e m p e r a t u r e ( T 5 ) . 0 ° - d e g r e e d a y s ( ° F ) . H - h a t c h w e i g h t . 9 - 9 0 0 0 ° . ( ) - o x y g e n c o n -c e n t r a t i o n , p p m . 16 Beginning at 300 D and O^, the embryo weights at Ty and are not significantly different at the five per cent probability level, and the line joining the individual weights does not appear to have a noticeable positive slope. At 500 D ° , the embryo weight at is significantly greater than at (P < .0 5, sum of squares simultaneous test procedure; Sokal and Rohlf, 1969)» although neither differs significantly f r o m the embryo weight at (P > .05). The positive slope of the 500 D ° line has been altered to a negative value by 700 D ° and the embryo weights are again not significantly different. The order of weights, however, has been reversed, T^ > T^, > T^» indicating that the initial accelerative effect of temperature on growth has been reversed . More importantly, the growth rate at 4 5 ° F has accelerated relative to both 5 0 ° and 5 5 ° F . The trend in relative growth rates established at 700 D ° is augmented at succeeding "stages" of 900, 1100 and 1300 D ° ; the slope of the line joining the three temperatures becomes increasingly negative. A s imi lar trend is noticeable under oxygen tensions and but the change in slope of the equal D ° - l i n e s is progress ively delayed in moving f r o m to O^ . This phenomenon, which illustrates the interaction component of temperature and oxygen tension, may be accounted for in terms of oxygen availability and embryonic demand. Belehradek (1930) calculated a value of 1.3 for the oxygen diffusion coefficient across the chorionic membrane of Atlantic salmon eggs. Hayes, et al . , (1951) found that its value did not change in the interval f rom 3 9 ° to 5 0 ° F , but decreased at higher temperatures. Despite the lack of agreement, the coefficient is nearly independent of temperature and indicates 17 that the oxygen diffusion rate will become limiting as the embryo develops; the critical value is also inversely proportional to temperature. The target oxygen concentrations shown in brackets at the top of Figure 3 decrease with increasing temperature at constant oxygen tension. If we now reconsider relative embryo weights at O T . and 500 D ° , it appears that 5 5 ° F accelerates growth relative to 4 5 ° F . By 700 D ° the reduced oxygen availability at 55 ° and 5 0 ° F has begun to retard embryonic growth, and the effect is lessened as oxygen concentration increases with decreasing temperature. If this reasoning is correct, an increase in oxygen tension should delay the reversal in weight relationships exhibited under O^. This appears to be the case at O (195.0 mm Hg). Embryo weights for T at 300 and 500 D ° , respectively, are not significantly different, but by 700 D ° the relative weights are such that T_ > T > T and all differ significantly (P < .0 5). Apparently, oxygen availability has become limiting at 5 5 ° F , but has not yet retarded growth at 5 0 ° F . By 900 D ° the weight relationships are fully reversed and are maintained up to 1300 D ° . The most pronounced delay occurs at the highest oxygen tension, (253.0 mm Hg), where weights for the three temperatures are not significantly different at each develop-mental stage up to 900 D ° . The weight reversal is quickly accomplished between 900 D ° and hatching 957 D ° ) , and maintained thereafter. Analysis of variance for the fifteen treatments associated with each D ° level shows that temperature and temperature-oxygen tension interaction significantly affects embryo weight (P < .0 5), but increasing oxygen tension does not (P > .05). The overlapping position of equal D ° lines at different 18 oxygen tensions (Figure 3) demonstrates the negligible effect of oxygen tension. The temperature and interaction effects are more readily visualized in Figure 4 where, after 700 D° , increased temperature is seen to depress relative growth. The same figure illustrates that for a given temperature and D ° value, increasing oxygen tension generally results in an increase in embryo weight. Deviations from this scheme are encountered at 900 D ° for O j T ; at 1 1 0 0 D ° for , and at O T and O s T 3 for 1300 D ° . The values depart from the expected trend and the reasons are not clear. Differences in water flow immediately prior to hatching, due to the channelling effect described earlier, may be the most likely cause. The important features, however, of weight reversal and the consistent order of relative weights o 4 following this event have not been obscured. The length at age (D ) data shown in Figure 5 further support this observation. No importance is attached to the relative time of hatching in the various treatments. The necessity of transferring the eggs to baskets at this critical period may have initiated the hatching process prematurely and masked the expected results. The relevant data in Table II indicate that at constant temperature increasing oxygen tension did not consistently delay the mid-hatching time or result in increased embryo weights. Yolk Conversion Efficiency A plot of average embryo and yolk weights versus time in days was 4 See Appendix C 20 141.5 mm Hg 1 9 5 . 0 mm Hg - 2 5 3 . 0 m m Hg 21 Table II. Hatching time in day-degrees (D°) and embryo weights. __ Oxygen Hatching Hatching Average "Weight at Temperature Tension Point (D°) Duration (Hrs) Hatching (mg) T O 900 183 9.93 1 ( 4 5 ° F ) O z 926 106 10.17 0 3 936 100 11.63 T O 933 109 9.92 2 ( 5 0 ° F ) O z 941 60 10.53 O s 938 93 10.50 T O 937 95 7.94 3 ( 5 5 ° F ) O z 937 143 9.80 0 3 937 138 10.14 T O 946 73 7.90 4 (rising) O z 957 94 8.50 0 3 957 77 10.02 O 899 103 10.25 5 „ „ . , O , 919 127 11.56 (falling) 2 0 3 913 113 11.66 used to calculate accumulative gross conversion efficiency for each treat-ment by means of the formula [embryo weight x (100)]/(total yolk consumed). 6 The yolk weight data required smoothing by threes to reduce variability. The use of this procedure raises a serious question about a suitable drying technique for preserved yolk material. A low drying temperature of 1 4 0 ° F was selected to reduce losses of volatile lipids and six days was required to achieve constant weights. Occasional fractured yolks were indicative of the stresses set up by the drying process and it is questionable if all free water was evaporated. The loss of variable amounts of oil when separating the embryo from the yolk could not be prevented, and would also contribute to errors in yolk weights. Both sources of error can affect the efficiency value, particularly at low embryo weights, and in interpreting the results a greater emphasis must be placed on the relative efficiencies achieved by different treatments. The relationship between accumulative gross efficiency, embryo weight and D ° for the five temperature treatments associated with oxygen tension O^ is summarized in Figure 6. The data points represent values taken from previously smoothed growth curves. Embryo weights at equal developmental time for the three constant temperatures are joined by dashed lines. The figure as a whole represents a ribbon which recedes from the viewer as an upward sloping ramp between 300 and 800 D ° , twists on itself between 800 and 1100 D ° , and intersects the vertical plane at 1300 D ° . 5 See Appendix D ^Chronological data values 1, 2 and 3 are averaged to yield a single datum point. A second point is obtained from the average of values 2, 3 and 4, etc. 23 2 4 A l l c u r v e s d e m o n s t r a t e t h a t e f f i c i e n c y i n c r e a s e s d u r i n g t h e e a r l y s t a g e s o f d e v e l o p m e n t , a c h i e v e s a m a x i m u m , a n d b e g i n s t o d e c l i n e a s m a i n -t e n a n c e c o s t s i n c r e a s e w i t h a g e . T h e m a x i m u m e f f i c i e n c y t h a t c a n b e a t t a i n e d u n d e r c o n s t a n t t e m p e r a t u r e c o n d i t i o n s i s d i r e c t l y r e l a t e d t o t e m p e r a t u r e o o i n t h e e a r l y s t a g e s . T h u s , b y 7 0 0 D t h e a c c u m u l a t i v e e f f i c i e n c i e s a t 4 5 , 5 0 ° a n d 5 5 ° F a r e 6 5 . 5 , 7 6 . 7 a n d 8 2 . 2 p e r c e n t , r e s p e c t i v e l y . B y 1 3 0 0 D ° a l l t r e a t m e n t e f f i c i e n c i e s a r e a p p r o x i m a t e l y e q u a l a t 50 p e r c e n t , b u t t h e e m b r y o w e i g h t a t 4 5 ° i s a b o u t 50 p e r c e n t g r e a t e r t h a n a t 5 5 ° F . C l e a r l y , t h e e m b r y o a t 5 5 ° F h a s f a i l e d t o m a i n t a i n i t s i n i t i a l a d v a n t a g e i n r e l a t i v e g r o w t h r a t e a n d c o n v e r s i o n e f f i c i e n c y , a n d b e y o n d 7 0 0 D ° h a s c o n v e r t e d a d i m i n i s h i n g a m o u n t o f y o l k i n t o t i s s u e . T h e r e v e r s a l i n t e m p e r a t u r e e f f e c t s o n g r o w t h r a t e s u g g e s t s t h a t a n o p t i m a l p a t h f o r g r o w t h e x i s t s b e t w e e n t h e t e m p e r a t u r e e x t r e m e s o f 4 5 ° a n d 5 5 ° F . M a i n t a i n i n g t h e e m b r y o a t a t e m p e r a t u r e t h a t c o i n c i d e s w i t h a p a t h o f m a x i m u m e m b r y o w e i g h t d u r i n g i t s d e v e l o p m e n t c a n b e e n v i s i o n e d i n F i g u r e 6 b y e m b r y o t r a n s f e r s f r o m 5 5 ° t o 5 0 ° F b e t w e e n 6 0 0 a n d 7 0 0 D ° , a n d f r o m 5 0 ° t o 4 5 ° F b e t w e e n 7 0 0 a n d 8 0 0 D ° . A d e c l i n i n g t e m p e r a t u r e s c h e m e f o r m a x i m a l g r o w t h i s c o n s i s t e n t w i t h n a t u r a l d e v e l o p m e n t i n s a l m o n a n d i s f u r t h e r c o r r o b o r a t e d b y t e m p e r a t u r e t r e a t m e n t T . T r a n s f e r s u n d e r T 5 5 o c c u r r e d a t s t a g e s e a r l i e r t h a n s u g g e s t e d , b u t t h e e m b r y o w e i g h t s a f t e r 7 0 0 D ° a r e c o n s i s t e n t l y g r e a t e r t h a n t h o s e i n c u b a t e d a t 5 5 ° o r 5 0 ° F . C h a n g e s i n e f f i c i e n c y a n d g r o w t h w i t h a g e ( D ° ) u n d e r i n c r e a s i n g o x y g e n t e n s i o n s a n d O , a p p e a r i n F i g u r e s 7 a n d 8 , r e s p e c t i v e l y . I n c o n t r a s t t o t h e h y p o x i c a n d m a r g i n a l l y h y p e r o x i c c o n d i t i o n , t h e t e m p e r a t u r e -25 26 e f f i c i e n c y r e l a t i o n s h i p s u n d e r o x y g e n t e n s i o n O a r e r e v e r s e d d u r i n g t h e t h e h i g h e s t a n d l o w e s t t e m p e r a t u r e s a r e a s s o c i a t e d w i t h t h e l o w e s t a n d h i g h e s t e f f i c i e n c i e s , r e s p e c t i v e l y . T h e s i g n i f i c a n c e o f t h i s r e v e r s a l c a n n o t b e i n t e r p r e t e d m e a n i n g f u l l y d u e t o t h e s o u r c e s o f e r r o r a t t a c h e d t o t h e e f f i c i e n c y e s t i m a t e s . F i g u r e s 7 a n d 8 d o , h o w e v e r , i n d i c a t e a d e l a y i n e m b r y o w e i g h t r e v e r s a l s d u e t o i n c r e a s e d o x y g e n s u p p l y , a n d a l t e r t h e s u g g e s t e d o p t i m a l p a t h f o r g r o w t h i n w e i g h t a s s h o w n i n T a b l e I I I . E m b r y o w e i g h t s i n t h e d e c l i n i n g t e m p e r a t u r e r e g i m e s ( T ) o f b o t h h y p e r o x i c t r e a t -5 m e n t s s u p p o r t t h e c o n c e p t o f a n o p t i m a l p a t h . T a b l e I I I . S u g g e s t e d t r a n s f e r p e r i o d s f o r m a x i m a l p a t h o f g r o w t h i n w e i g h t . D e v e l o p m e n t a l a g e i n D ° . e a r l y s t a g e s o f d e v e l o p m e n t . I n t h e 3 0 0 t o 7 0 0 D ° i n t e r v a l , f o r i n s t a n c e , O x y g e n t e n s i o n F r o m 5 5 ° t o 5 0 ° F F r o m 5 0 ° t o 4 5 ° F F r o m 5 5 ° t o 4 5 ° F O 1 6 0 0 - 7 0 0 7 0 0 - 8 0 0 6 0 0 - 7 0 0 9 0 0 - 1 0 0 0 9 0 0 - 1 0 0 0 DISCUSSION The results indicate that a path of optimal growth in weight exists for chum salmon in the interval from fertilization to the onset of starvation. The path is dependent upon the interaction effect of temperature and oxygen tension in relation to the developmental age (D°) of the embryo and alevin. F o r a given oxygen tension the oxygen demand of the embryo during early development is minimal and not limited by the diffusion coefficient of the chorionic membrane. Under these conditions, the highest temperature of 55°F appears to initially accelerate growth relative to 50° or 45°F. The beneficial effect of an elevated temperature is reversed with age, as the need for oxygen increases, but its rate of transport becomes limiting. The path of optimal growth favors a decreasing temperature scheme with its associated increase in oxygen concentration and reduced metabolic demand by the embryo. Pri o r to hatching, the duration of development at 55°F can be temporarily extended by increasing the oxygen tension, but if optimal growth is to be maintained, the temperature must be reduced when the oxygen supply becomes limiting. Accumulative gross conversion efficiency for all treatments increases during the early stages of development, but as growth proceeds, the efficiency decreases due to an increase in maintenance costs. The rate of decrease in efficiency is more pronounced with increasing, constant temperature indicating that growth is impeded and a diminishing amount of yolk is converted into tissue. This effect is particularly noticeable after h a t c h i n g a n d o c c u r s u n d e r a l l o x y g e n t e n s i o n s . I n c r e a s i n g o x y g e n t e n s i o n f o r a g i v e n t e m p e r a t u r e r e g i m e l e a d s t o a n i n c r e a s e i n e m b r y o w e i g h t a t e q u a l " s t a g e s " o f d e v e l o p m e n t , b u t t h e e f f e c t i s n o t s i g n i f i c a n t . T h e i n h i b i t i o n o f g r o w t h b y i n c r e a s i n g t e m p e r a t u r e i s c o n t r a r y t o t h e s i t u a t i o n r e p o r t e d b y B a n k s , e _ a l . , ( 1 9 7 1 ) . T h e o p t i m a l t e m p e r a t u r e f o r g r o w t h o f c h i n o o k f i n g e r l i n g s ( O n c o r h y n c h u s t s h a w y t s c h a ) r e c e i v i n g e x t e r n a l f o o d w a s f o u n d t o b e 6 0 ° F . T h e d i f f e r e n c e i n t e m p e r a t u r e o p t i m a m a y b e d u e t o t h e d i f f e r e n c e i n f o o d s o u r c e s a n d t h e i r m e t h o d o f a s s i m i l a t i o n I n A t l a n t i c a n d B a l t i c s a l m o n , V e r n i d u b ( 1 9 6 6 ) i n d i c a t e s t h a t m a c r o p h a g e s , m o n o c y t e s a n d l e u k o c y t e s t h a t y i e l d a p o s i t i v e r e a c t i o n t o p e r o x i d a s e s a n d b o u n d l i p o i d s p h a g o c y t i z e t h e y o l k a n d t h a t t h e f o r m a t i o n o f t h e l a t t e r c e l l s o c c u r s i n t w o w a v e s b e f o r e a c t i v e f e e d i n g b e g i n s . T h e p r i m a r y c e l l s f r o m t h e f i r s t p r o d u c t i o n w a v e a r e e v i d e n t b e f o r e c i r u l a t i o n b e g i n s a n d a l a r g e p r o p o r t i o n a r e m a t u r e a t t h e b e g i n n i n g o f e y e p i g m e n t a t i o n . T h e s e c o n d p r o d u c t i o n w a v e o c c u r s w i t h t h e o n s e t o f n e g a t i v e p h o t o t a x i s , b u t t h e n u m b e r o f c e l l s r a p i d l y d e c l i n e s f o l l o w i n g t h e d i s a p p e a r a n c e o f t h e y o l k s a c . I f s i m i l a r e v e n t s o c c u r i n P a c i f i c s a l m o n , a n d i f t h e w h i t e - c e l l c o u n t i s l o w d u r i n g t h e i n t e r - w a v e p e r i o d , t h e r a t e o f y o l k a b s o r p t i o n m a y b e i n a d e q u a t e t o m e e t b o t h t h e m a i n t e n a n c e a n d g r o w t h n e e d s o f t h e e m b r y o s a n d a l e v i n s r a i s e d a t h i g h t e m p e r a t u r e s . G r o w t h w o u l d b e s a c r i f i c e d i n t h i s c a s e u n l e s s t h e t e m p e r a t u r e w a s r e d u c e d a c c o r d i n g t o t h e s u g g e s t e d o p t i m a l p a t h . O n c e e x t e r n a l f e e d i n g b e g i n s , h o w e v e r , f o o d c a n b e g i v e n i n a d e q u a t e a m o u n t s t o m e e t b o t h r e q u i r e m e n t s a n d t h e t e m p e r a t u r e i n c r e a s e d t o t h e n e w , o p t i m a l v a l u e f o r g r o w t h . 3 0 I n t h e f o r e g o i n g d i s c u s s i o n t h e r e s u l t s h a v e b e e n i n t e r p r e t e d i n t e r m s o f d a y - d e g r e e s o f d e v e l o p m e n t , r a t h e r t h a n t i m e i n d a y s , a n d w i t h o u t r e f e r e n c e t o t h e i r p r a c t i c a l v a l u e . T h e s e p o i n t s w i l l n o w b e c o n s i d e r e d . T h e b e n e f i c i a l e f f e c t o f i n c r e a s i n g o x y g e n t e n s i o n o n e m b r y o w e i g h t i s l i m i t e d i n b o t h t i m e a n d i n t e n s i t y . T h e p e r t i n e n t d e t a i l s t o s u p p o r t t h i s s t a t e m e n t a p p e a r i n T a b l e I V . U n d e r o p t i m a l t e m p e r a t u r e c o n d i t i o n T ^ e m b r y o s i n c u b a t e d a t o x y g e n t e n s i o n a n d s h o w e d a n e g l i g i b l e d i f f e r e n c e i n w e i g h t a t h a t c h i n g , b u t b o t h v a l u e s w e r e s i g n i f i c a n t l y g r e a t e r , b y 10 p e r c e n t , t h a n e m b r y o s i n c u b a t e d u n d e r O T . T h e 4 0 p e r c e n t i n c r e a s e i n 1 5 w e i g h t d e m o n s t r a t e d b y H a m d o r f , ( 1 9 6 l ) u s i n g a n o x y g e n c o n c e n t r a t i o n of 2 1 p p m o n r a i n b o w t r o u t , w a s n o t d u p l i c a t e d b y c h u m s a l m o n . T h e d i f f e r e n c e m a y l i e i n t h e c h o r i o n d i f f u s i o n c o e f f i c i e n t s f o r t h e t w o s p e c i e s o r t h e w a t e r v e l o c i t i e s u s e d i n t h e e x p e r i m e n t s . I t i s a l s o c l e a r t h a t a n o x y g e n t e n s i o n i n e x c e s s o f 1 9 5 m m H g ( O ^ ) w a s n o t n e c e s s a r y . I n c o m b i n a t i o n w i t h o p t i m a l t e m p e r a t u r e T , o x y g e n t e n s i o n O a p p e a r e d t o i n c r e a s e t h e e m b r y o w e i g h t b y a b o u t 3 8 p e r c e n t a n d d e l a y e d h a t c h i n g b y 1 3 d a y s i n c o n t r a s t t o t h e c o n s t a n t r e g i m e o f 5 5 ° F . T h e b e n e f i t o f m a i n t a i n i n g t h e o x y g e n t e n s i o n a b o v e a i r s a t u r a t i o n a f t e r h a t c h i n g i s d o u b t f u l . S t r e l ' t s o v a ( 1 9 6 4 ) r e p o r t s t h a t c o n c e n t r a t i o n s u p t o 2 4 p p m r e s u l t e d i n f r a n t i c s w i m m i n g m o v e m e n t s i n y e a r l i n g a n d t w o - y e a r -o l d t r o u t f r o m p o s s i b l e d a m a g e t o t h e c e n t r a l n e r v o u s s y s t e r r i . A l t h o u g h t h e a g e o f c h u m s a l m o n r e p o r t e d i n t h i s e x p e r i m e n t d i d n o t e x c e e d f o u r m o n t h s , and abnormal swimming movements were not confined to a particular 7 oxygen tension , the growth rate at hyperoxic conditions was not main-tained. The deficiency in weight of embryos O, T_ relative to 0_T_ or 1 5 2 5 0_T C at hatching was overcome by 1200 D°, and suggests that in the equi-3 5 • valent total period of 76 days, an oxygen tension greater than air satura-tion is without benefit. Table IV. Embryo and alevin dry weight comparison at different temperatures and oxygen tensions. at hatching at 1200 D Avg. dry Avg. dry Total days Oxygen embryo Oxygen embryo to Temperature tension wt. (mg) Days tension wt. (mg) 1200 D ° 45°F °1 9.9. 68 °i 24.4 92 55°F °1 8.4 41 ° i 15.2 52 55°-> 45°(T.) o °1 10.2 52 ° i 23.8 76 V °2 11.6 54 °z 23.0 76 T 5 °3 11.7 54 °3 22.8 76 7 Whirling disease affected some alevins in all treatments. Samples were removed only after characteristic movements ceased, following light adaptation. Yolk-sac constriction disease affected all alevins and occurred after hatching, within three days at 55°F and seven days at 45°F. B u r r o w s ( 1 9 6 3 ) h a s r e c o m m e n d e d 5 5 ° F a s t h e o p t i m a l i n c u b a t i o n t e m p e r a t u r e f o r c h i n o o k s a l m o n , a t r e a t m e n t t h a t e n s u r e s t h e m o s t r a p i d t r a n s i t i o n t o t h e r e a r i n g p h a s e . S e y m o u r ( M S 1 9 5 6 ) f o u n d t h a t m o r t a l i t i e s f o r t h e s a m e s p e c i e s w e r e g r e a t e r d u r i n g t h e a l e v i n s t a g e a t t h i s t e m p e r a -t u r e t h a n a t 5 0 ° F , a n d a t t r i b u t e d t h e i n c r e a s e t o h e t e r o c h r o n y , o r a d i s -l o c a t i o n o f e m b r y o l o g i c a l e v e n t s . F o r c h u m s a l m o n , a c c u m u l a t i v e m o r t a l i t y f o r e a c h o f f i f t e e n t r e a t m e n t s d i d n o t e x c e e d 2 . 5 p e r c e n t b y 1 2 0 0 D ° . I n t h e f o l l o w i n g 1 0 0 D ° i n t e r v a l , m o r t a l i t i e s a t 5 5 ° F t r i p l e d i n c o m p a r i s o n t o e m b r y o s r a i s e d a t a c o n s t a n t t e m p e r a t u r e o f 4 5 ° F o r t h e o p t i m a l p a t h O . T . A c o n s t a n t t e m p e r a t u r e o f 5 5 ° F t h e r e f o r e r e p r e s e n t s 1 5 a c o m p r o m i s e b e t w e e n r a p i d d e v e l o p m e n t a n d i n c r e a s e d m o r t a l i t y t h a t c a n b e p a r t i a l l y o v e r c o m e b y a d e c r e a s i n g t e m p e r a t u r e s c h e m e s u c h a s O T . 1 5 T o a d e g r e e , t h e l o w e r e d t e m p e r a t u r e w i l l a l s o a v o i d t h e d i s e a s e s u s c e p t -i b i l i t y o f f i s h r e a r e d a t a h i g h t e m p e r a t u r e , a n d w i l l l e n g t h e n t h e c r i t i c a l t r a n s i t i o n p e r i o d b e t w e e n f e e d i n g o n y o l k a n d e x t e r n a l f o o d . T h e b e n e f i t o f i n c r e a s e d s u r v i v a l a n d a g r e a t e r a l e v i n w e i g h t a t t h e b e g i n n i n g o f a c t i v e f e e d i n g i s a l s o c o n s i s t e n t w i t h h a t c h e r y o b j e c t i v e s . D u r i n g t h e c o u r s e o f t h e e x p e r i m e n t , s e v e r a l p o i n t s e m e r g e d t h a t w o u l d b e u s e f u l i n e x p a n d i n g i t s s c o p e a n d i n d e f i n i n g a n o p t i m a l p a t h w i t h g r e a t e r a c c u r a c y . E a c h i t e m i s b r i e f l y e l a b o r a t e d o n b e l o w . 1. E x p e r i m e n t s d e a l i n g w i t h e m b r y o n i c g r o w t h i n s a l m o n i d s i n c u b a t e a t d i f f e r e n t t e m p e r a t u r e s h a v e n o t m e a s u r e d t e m p e r a t u r e e f f e c t s a l o n e . T h e y h a v e d e a l t w i t h a t e m p e r a t u r e i n c r e a s e t o g e t h e r w i t h a d e c r e a s e i n o x y g e n c o n c e n t r a t i o n , a n d t h e p r e s e n t e x p e r i m e n t i s n o e x c e p t i o n . T o e s t i m a t e a m o r e v a l i d t e m p e r a t u r e e f f e c t o n m e t a b o l i c r a t e , t h e o x y g e n t e n s i o n o u t s i d e t h e e g g s h o u l d b e a d j u s t e d t o m a i n t a i n t h e s a m e o x y g e n c o n c e n t r a t i o n i n t h e p e r i -v i t e l i n e s p a c e i n a l l t e m p e r a t u r e t r e a t m e n t s . O n l y u n d e r t h e s e c o n d i t i o n s w i l l t h e e m b r y o s r e c e i v e t h e s a m e a m o u n t o f o x y g e n r e l a t i v e t o t h e i r n e e d s . M i c r o - o x y g e n p r o b e s m a y b e a u s e f u l t e c h n i q u e i n m e a s u r i n g t h e d e s i r e d c o n c e n t r a t i o n s . M o r p h o l o g i c a l s t a g i n g f o r O n c o r h y n c h u s s p e c i e s c a n b e e s t a b l i s h e d i n t e r m s o f d i m e n s i o n l e s s c h a r a c t e r s , o r T D , a s r e p o r t e d b y D e t t l a f f ( 1 9 6 4 ) a n d I g n a t ' e v a ( 1 9 7 0 ) . T h e b i o l o g i c a l s i g n i f i c a n c e o f t h i s c h a r a c t e r i s t i c s h o u l d b e e x a m i n e d m o r e f u l l y , f o r i t m a y o f f e r a m o r e r e l i a b l e i n d e x f o r c o m p a r i n g d e v e l o p m e n t a l s t a g e s t h a n d a y - d e g r e e s . T h e c u r r e n t e x p e r i m e n t c a n b e r e p e a t e d a t a i r - s a t u r a t e d l e v e l s o n l y , b u t b o t h t h e n u m b e r of t e m p e r a t u r e t r e a t m e n t s a n d s a m p l i n g f r e q u e n c y s h o u l d b e i n c r e a s e d . T h e o b j e c t i v e s w o u l d b e t o d e f i n e t h e o p t i m a l t e m p e r a t u r e r a n g e m o r e c l o s e l y , a n d a l l o w s p e c i f i c g r o w t h a n d m e t a b o l i c r a t e s t o b e c a l c u l a t e d a t c l o s e i n t e r v a l s . D r y e m b r y o a n d y o l k w e i g h t s s h o u l d b e t a k e n f r o m f r e s h m a t e r i a l o n l y t o i n c r e a s e t h e a c c u r a c y o f t h e r e s u l t s . T h e o p t i m a l p a t h f o r g r o w t h c o u l d t h e n b e d e t e r m i n e d o n t h e b a s i s o f m a x i m a l , s p e c i f i c 34 g r o w t h r a t e . A f u r t h e r r e f i n e m e n t w o u l d i n v o l v e a l o w e r i n g o f t e m p e r a t u r e i n s m a l l d e c r e m e n t s s u c h t h a t t h e o x y g e n c o n c e n -t r a t i o n w a s k e p t i n b a l a n c e w i t h t h e i n c r e a s i n g n e e d s o f t h e e m b r y o . T h e u p p e r a n d l o w e r t e m p e r a t u r e s w o u l d s t i l l b e d e f i n e d b y t h e o p t i m a l r a n g e . T h e e x p e r i m e n t c o u l d a l s o b e e x t e n d e d t o i n c l u d e a l l c o m m e r c i a l s a l m o n t o e x p l o r e t h e i r d i f f e r e n c e s a n d o p t i m a l r e q u i r e m e n t s . E x p e r i m e n t s i n w h i c h c h u m , s o c k e y e ( O . n e r k a ) a n d c o h o ( O . k i s u t c h ) s a l m o n ( C a n a g a r a t n a m , 1 9 5 9 ) w e r e r e a r e d i n w a t e r u p t o 12%, s a l i n i t y s h o w e d t h a t g r o w t h i s m o r e r a p i d t h a n i n f r e s h w a t e r . R o c k w e l l ( M S 1 9 5 6 ) a c h i e v e d s i g n i f i c a n t l y g r e a t e r g r o w t h d u r i n g i n c u b a t i o n w i t h p i n k ( O . g o r b u s c h a ) a n d c h u m s a l m o n i n w a t e r o f m i l d s a l i n i t y ( £ 8 % o ) . I t i s n o t k n o w n i i t h e i m p r o v e d g r o w t h i s d u e t o t h e i n c r e a s e d i o n i c c o n t e n t o f s e a w a t e r a n d r e d u c e d e n e r g y l o s s i n o s m o - r e g u l a t i o n , b u t t h e b e n e f i t o f s a l i n i t y i n c o m b i n a t i o n w i t h a n o p t i m a l p a t h o f g r o w t h s h o u l d b e f u r t h e r e x a m i n e d . E n d o g e n o u s r h y t h m s o f g r o w t h w h i c h f l u c t u a t e o n a b i - w e e k l y b a s i s h a v e b e e n r e p o r t e d b y B r o w n ( 1 9 5 7 ) i n S a l m o t r u t t a . S i m i l a r c y c l e s m a y e x i s t i n s a l m o n . If t h e p e r i o d o f g r o w t h d e c l i n e c o u l d b e o f f s e t b y a l t e r a t i o n s i n l e n g t h o f d a y l i g h t o r t e m p e r a t u r e , a s u s t a i n e d m a x i m a l g r o w t h r a t e m a y b e a c h i e v e d . 35 SUMMARY AND CONCLUSIONS Optimal conditions in salmon hatcheries can be applied during both incubation and rearing to achieve an increase in size and survival rate. In contrast to the rearing phase, in which nutrition and suitable environmental conditions have been emphasized in reaching these goals, the optimal conditions and the benefit that may be derived from their application during incubation have not been explored in detail. As an initial approach to this problem, the effects of temperature and oxygen tension on the growth and yolk conversion efficiency of chum salmon have been determined experimentally. The oxygen tensions were represented by a marginally hypoxic (141.5 mm Hg) and hyperoxic (195.0 mm Hg) situation as well as an extreme hyperoxic (2 53.0 mm Hg) condition. Three constant temperatures of 45°, 50° and 55°F, and a declining and rising temperature treatment within this optimal range were associated with each oxygen tension. The experimental results afforded the following conclusions. 1. At constant oxygen tension, elevated temperatures accelerate growth of chum salmon initially, but this effect is reversed with age as the need for oxygen increases. The path of optimal growth then favors a decreasing temperature scheme with its associated increase in oxygen concentration and reduced metabolic demand by the embryo. 2. Increasing oxygen tension did not contribute significantly to embryo weight when measured at equal stages of development in day-degrees. P r i o r to hatching, increasing oxygen tension retards, but does not eliminate, the change in optimal growth conditions. During ear ly incubation, accumulative gross conversion efficiency is also favored by an elevated temperature under marginally hypoxic and hyperoxic conditions. A s development and growth proceed, efficiency decreases due to increased maintenance costs, but the decline is inversely related to temperature. After hatching, the detrimental effect of a high temperature is not offset by the increased availability of oxygen. The embryo may convert yolk efficiently into tissue, but the rate of conversion decreases and growth is retarded relative to that at a lower temperature. Oxygen tensions in excess of air saturation have a significant and beneficial effect on embryo weight at hatching, but the margin is eliminated by 1200 D ° of development. Under these conditions, the suggested optimal path of growth is restr icted to a decreasing temperature at air saturation. Relative to a constant temperature of 55 ° F , the optimal path wi l l delay active feeding by about one month, but it wi l l provide for increased survival and a greater alevin weight when external feeding begins. L I T E R A T U R E C I T E D A l d e r d i c e , D . F . , W . P . W i c k e t t , J . R . B r e t t . 1 9 5 8 . S o m e e f f e c t s o f t e m p o r a r y e x p o s u r e t o l o w i d s s o l v e d o x y g e n l e v e l s o n P a c i f i c s a l m o n e g g s . J . F i s h . R e s . B d . C a n a d a , 1 5 ( 2 ) : 2 2 9 - 2 4 9 . A m e r i c a n P u b l i c H e a l t h A s s o c i a t i o n , A m e r i c a n W a t e r W o r k s A s s o c i a t i o n , W a t e r P o l l u t i o n C o n t r o l F e d e r a t i o n . 1 9 6 7 . S t a n d a r d m e t h o d s  f o r t h e e x a m i n a t i o n of w a t e r a n d w a s t e w a t e r . 1 2 t h e d i t i o n . A m e r . P u b l . H e a l t h A s s ' n . I n c . , N e w Y o r k . 7 6 9 p p . B a n k s , J . L . , L . G . F o w l e r , J . W . E l l i o t . 1 9 7 1 . E f f e c t s o f r e a r i n g t e m p e r a -t u r e o n g r o w t h , b o d y f o r m a n d h e m a t o l o g y o f f a l l c h i n o o k f i n g e r l i n g s . P r o g . F i s h C u l t . , 3 3 ( l ) : 2 0 - 2 6 . B a t t l e , H . I . 1 9 4 4 . T h e e m b r y o l o g y o f t h e A t l a n t i c s a l m o n . C a n . J . R e s . , D 2 2 ( 1 0 ) : 1 0 5 - 1 2 5 . B e l e h r a d e k , J . 1 9 3 0 . T e m p e r a t u r e c o e f f i c i e n t s i n b i o l o g y . B i o l . R e v . , 5 : 3 0 - 5 8 . B r e t t , J . R . 1 9 5 2 . T e m p e r a t u r e t o l e r a n c e i n y o u n g P a c i f i c s a l m o n , g e n u s O n c o r h y n c h u s . J . F i s h . R e s . B d . C a n a d a , 9 ( 6 ) ; 2 6 5 - 3 5 3 . . 1 9 5 6 . S o m e p r i n c i p l e s i n t h e t h e r m a l r e q u i r e m e n t s o f f i s h e s . Q u a r t . R e v . B i o l . , 3 1 ( 2 ) : 7 5 - 8 7 . B r o w n , M . E . , 1 9 5 7 . E x p e r i m e n t a l s t u d i e s o n g r o w t h . I n : T h e P h y s i o l o g y  o f f i s h e s . E d . b y M . E . B r o w n , V o l . 1 . A c a d e m i c P r e s s , N e w Y o r k . 4 4 7 p p . 3 8 B u r r o w s , R . E . 1 9 6 3 . W a t e r t e m p e r a t u r e r e q u i r e m e n t s f o r m a x i m u m p r o -d u c t i v i t y o f s a l m o n . P r o c . 1 2 t h P a c . N o r t h w e s t S y m p . o n W a t e r P o l l u t i o n R e s e a r c h . U . S . D e p t . H e a l t h , E d . a n d W e l f a r e , C o r v a l l i s , O r e g o n . . 1 9 6 9 . T h e i n f l u e n c e o f f i n g e r l i n g q u a l i t y o n a d u l t s a l m o n s u r v i v a l s . T r a n s . A m . F i s h . S o c , 9 8 ( 4 ) : 7 7 7 - 7 8 4 . a n d B . C . C o m b s . 1 9 6 8 . C o n t r o l l e d e n v i r o n m e n t s f o r s a l m o n p r o p a g a t i o n . P r o g . F i s h C u l t . , 3 0 ( 3 ) : 1 2 3 - 1 3 6 . C a n a g a r a t n a m , P . 1 9 5 9 . G r o w t h o f f i s h e s i n d i f f e r e n t s a l i n i t i e s . J . F i s h . R e s . B d . C a n a d a , 1 6 ( 1 ) : 1 2 1 - 1 2 9 . C o m b s , B . C . 1 9 6 5 . E f f e c t o f t e m p e r a t u r e o n d e v e l o p m e n t o f s a l m o n e g g s . P r o g . F i s h C u l t . , 2 7 ( 3 ) : 1 3 4 - 1 3 7 . D a y k i n , P . N . 1 9 6 5 . A p p l i c a t i o n o f m a s s t r a n s f e r t h e o r y t o t h e p r o b l e m o f r e s p i r a t i o n o f f i s h e g g s . J . F i s h . R e s . B d . C a n a d a , 2 2 ( 1 ) : 1 5 9 - 1 7 1 . D e t t l a f f , T . A . 1 9 6 4 . C e l l d i v i s i o n s , d u r a t i o n o f i n t e r - k i n e t i c s t a t e s a n d d i f f e r e n t i a t i o n i n e a r l y s t a g e s o f e m b r y o n i c d e v e l o p m e n t . I n : A d v a n c e s i n M o r p h o g e n e s i s , V o l . 3 . E d . b y M . A b e r c r o m b i e a n d j . B r a c h e t . A c a d e m i c P r e s s , L o n d o n . 4 0 8 p p . G a r s i d e , E . T . 1 9 6 6 . E f f e c t s o f o x y g e n i n r e l a t i o n t o t e m p e r a t u r e o n t h e d e v e l o p m e n t o f e m b r y o s o f b r o o k t r o u t a n d r a i n b o w t r o u t . J . F i s h . R e s . B d . C a n a d a , 2 3 ( 8 ) : 1 1 2 1 - 1 1 3 4 . G r a y , J . 1 9 2 8 . T h e g r o w t h o f f i s h I I . T h e g r o w t h r a t e o f t h e e m b r y o o f S a l m o f a r i o . J . E x p . B i o l . , 6 : 1 1 0 - 1 2 4 . H a m d o r f , K . 1 9 6 1 . T h e i n f l u e n c e o f t h e e n v i r o n m e n t a l f a c t o r s O ^ . ; p a r t i a l p r e s s u r e , a n d t e m p e r a t u r e o n t h e e m b r y o n i c a n d l a r v a l d e v e l o p m e n t o f t h e r a i n b o w t r o u t ( S a l m o i r i d i u s G i b b ) . Z e i t s c h r i f t f u r v e r g l e i c h e n d e p h y s i o l o g i e , 4 4 : 5 2 3 - 5 4 9 . H a y e s , F . R . 1 9 4 9 . T h e g r o w t h , g e n e r a l c h e m i s t r y a n d t e m p e r a t u r e r e l a t i o n s h i p s of s a l m o n i d e g g s . Q u a r t . R e v . B i o l . , 2 4 ( 4 ) : 2 8 l - 3 0 8 . , I . R . W i l m o t a n d D . A . L i v i n g s t o n e . 1 9 5 1 . T h e o x y g e n c o n s u m p t i o n o f t h e s a l m o n e g g i n r e l a t i o n t o d e v e l o p m e n t a n d a c t i v i t y . J . E x p . Z o o l . , 1 1 6 ( 3 ) : 3 7 7 - 3 9 5 . I g n a t ' e v a , G . M . 1 9 7 0 . R e g u l a r i t i e s o f e a r l y e m b r y o g e n e s i s i n s a l m o n i d f i s h e s a s r e v e a l e d b y t h e m e t h o d o f d i m e n s i o n l e s s c h a r a c t e r i z a t i o n o f d e v e l o p m e n t a l t i m e . T r a n s l a t e d i n : T h e S o v i e t J . D e v e l o p . B i o l . , l ( l ) : 2 0 - 3 2 . K i n n e , O . , a n d E . M . K i n n e . 1 9 6 2 . R a t e s o f d e v e l o p m e n t i n e m b r y o s of a c y p r i n o d o n t f i s h e x p o s e d t o d i f f e r e n t t e m p e r a t u r e - s a l i n i t y - o x y g e n c o m b i n a t i o n s . C a n . J . Z o o l . , 4 0 : 2 3 1 - 2 5 3 . M a r r , D . H . A . 1 9 6 5 . I n f l u e n c e o f t e m p e r a t u r e o n t h e e f f i c i e n c y o f g r o w t h o f s a l m o n i d e m b r y o s . N a t u r e , 2 1 2 : 9 5 7 - 9 5 9 . M e r r i m a n , E . 1 9 3 5 . T h e e f f e c t o f t e m p e r a t u r e o n t h e d e v e l o p m e n t o f t h e e g g s a n d l a r v a e o f t h e c u t - t h r o a t t r o u t ( S a l m o c l a r k i i c l a r k i i R i c h a r d s o n ) . J . E x p . B i o l . , 1 2 ( 4 ) : 2 9 7 - 3 0 5 . R o c k w e l l , J . J r . M S 1 9 5 6 . S o m e e f f e c t s o f s e a w a t e r a n d t e m p e r a t u r e o n t h e e m b r y o s o f t h e P a c i f i c s a l m o n , O n c o r h y n c h u s g o r b u s c h a ( W a l b a u m ) a n d O n e o r h y n c h u s k e t a ( W a l b a u m ) . P h . D . T h e s i s , U n i v . W a s h i n g t o n . 2 2 3 p p . S e y m o u r , A . H . M S 1 9 5 6 . E f f e c t s o f t e m p e r a t u r e u p o n y o u n g c h i n o o k s a l m o n . P h . D . T h e s i s , U n i v , . W a s h i n g t o n . 1 2 7 p p . S o k a l , R . R . a n d F . J . R o h l f . 1 9 6 9 . B i o m e t r y . W . H . F r e e m a n a n d C o . , S a n F r a n c i s c o . 7 7 6 p p . S t r e l ' t s o v a , S . V . 1 9 6 4 . A d a p t a t i o n o f c a r p a n d r a i n b o w t r o u t t o d i f f e r e n t o x y g e n c o n t e n t s o f t h e w a t e r . I n : F i s h p h y s i o l o g y i n a c c l i m a t i z a - t i o n a n d b r e e d i n g . E d . b y T . I . P r i v o l ' n e v , L e n i n g r a d , V o l . 5 8 . I s r a e l p r o g r a m f o r s c i e n t i f i c t r a n s l a t i o n s , J e r u s a l e m , 1 9 7 0 . V e r n i d u b , M . F . 1 9 6 3 . E x p e r i m e n t a l e v i d e n c e f o r t h e t e c h n i q u e o f a n a c c e l e r a t e d e m b r y o n i c d e v e l o p m e n t i n s a l m o n a n d i t s s i g n i f i c a n c e f o r s a l m o n c u l t i v a t i o n . V e s t n i k L e n i n g r a d s k o g o U n i v e r s i t e t a , S e r i y a b i o l o g i s c h e s k a y a , 3 . . 1 9 6 6 . C o m p o s i t i o n o f t h e r e d a n d w h i t e b l o o d c o r p u s c l e s o f e m b r y o s o f A t l a n t i c a n d B a l t i c s a l m o n ( S a l m o s a l a r L . ) a n d c h a n g e s i n t h i s c o m p o s i t i o n d u r i n g t h e g r o w t h o f t h e o r g a n i s m . P r o c . M u r m a n s k I n s t . M a r i n e B i o l o g y ( 1 2 - l 6 ) : l 3 9 - l 6 2 . W i c k e t t , W . P . 1 9 5 8 . R e v i e w o f c e r t a i n e n v i r o n m e n t a l f a c t o r s a f f e c t i n g t h e p r o d u c t i o n o f p i n k a n d c h u m s a l m o n . J . F i s h . R e s . B d . C a n a d a , 1 5 ( 5 ) : 1 1 0 3 - 1 1 2 6 . 41 A P P E N D I X 42 APPENDIX A — Accumulative Mortality Calculation The following method, derived by Seymour (MS 1956), was used to calculate accumulative mortality. The losses were separated into two categories: (1) natural mortality, and (2) removals and accidental deaths. The accumulative mortality took into account losses from both categories and was computed for each three-day period before hatching, and on a daily basis thereafter The accumulative mortality for the three-day period n was the sum of three items: (1) the accumulative mortality for period n-1; (2) the sum of the mortalities during period n; and (3) the natural mortality that would have occurred in period n among those removed for samples or killed accidentally. Item (3) was calculated by multiplying the natural mortality rate for period n by the sum of the number of individuals that were removed for samples or had died accidentally during period n and the number of individuals that would have survived to the end of period n-1, having previously been removed for samples or having died accidentally. The per cent accumulative mortality was equal to 100 times the accumulative mortality divided by the number of eggs at the start of the experiment. 4 3 A P P E N D I X B - A v e r a g e , D r y E m b r y o W e i g h t s ( m g ) O x y g e n T e n s i o n O j D ° n T l n T x 2 n T 3 n T 4 n T 5 3 0 0 1 9 0 . 4 2 ( 0 . 1 3 6 ) 1 9 0 . 3 5 ( 0 . 1 0 5) 1 9 0 . 3 3 ( 0 . 1 0 6 ) 1 9 0.29 ( 0 . 1 3 9 ) 1 9 0 . 3 6 ( 0 . 1 4 5 ) 3 4 4 1 9 0 . 3 4 ( 0 . 1 0 2 ) 1 9 - 1 9 - 1 9 0 . 2 9 ( 0 . 0 7 4 ) 1 9 - • 5 0 0 10 1 . 3 7 ( 0 . 1 9 8 ) 10 1 . 5 4 ( 0 . 1 5 4 ) 10 1 . 6 5 ( 0 . 1 6 7 ) 10 1 . 4 1 ( 0 . 1 4 1 ) 10 1 . 7 8 ( 0 . 2 3 9 ) 6 2 0 - - - - 10 3 . 1 4 ( 0 . 2 0 1 ) 6 6 3 - - - 10 3 . 1 2 ( . 0 2 4 1 ) -7 0 0 10 4 . 5 6 ( 0 . 3 0 2 ) 10 4 . 5 5 ( 0 . 0 8 5 ) 10 4 . 3 2 ( 0 . 1 6 1 ) 10 4 . 0 2 ( 0 . 2 4 6 ) 10 4 . 9 5 ( 0 . 1 4 1 ) 9 0 0 10 9 . 9 3 ( 0 . 7 0 4 ) 10 8 . 7 8 ( 0 . 1 6 2 ) 10 8 . 0 5 ( 0 . 5 7 5 ) 10 7 . 4 6 ( 0 . 8 0 6 ) 1 0 1 0 . 2 5 ( 0 . 3 9 0 ) 5 0 % h a t c h 10 a s a b o v e 10 9 . 9 2 ( 0 . 5 2 4 ) 1 0 7 . 9 4 ( 0 . 5 3 2 ) 10 7 . 9 0 ( 0 . 4 9 2 ) 10 a s a b o v e 1 1 0 0 10 1 9 . 1 2 ( 2 . 0 7 7 ) " 10 1 6 . 2 2 ( 1 . 4 2 1 ) 10 1 2 . 5 4 ( 1 . 6 2 3 ) 10 1 4 . 0 0 ( 1 . 5 1 0 ) 10 1 9 . 1 6 ( 2 . 1 3 1 ) 1 3 0 0 1 9 2 7 . 3 5 ( 3 . 4 8 6 ) 1 9 2 1 . 8 3 ( 1 . 9 3 5 ) 1 9 1 7 . 9 6 ( 2 . 2 2 5 ) 1 9 2 0 . 0 2 ( 3 . 1 0 6 ) 1 9 2 7 . 8 1 ( 3 . 6 9 7 ) n = n u m b e r o f s a m p l e s ; ( ) = s t a n d a r d e r r o r 44 APPENDIX B - continued Oxygen Tension O D° n T l n T2 n T A3 n T4 n T 5 300 19 0.26 (0.103) 19 0.30 (0.120) 19 0.28 (0.094) 19 0.27 (0.107) 19 0.29 (0.087) 344 19 0.31 (0.104) 19 - 19 - 19 0.29 (0.044) 19 -500 10 1.42 (0.269) 10 1.57 (0.209) 10 1.71 (0.124) 10 1.33 (0.178) 10 1.68 (0.884) 620 - - - - 10 3.22 (0.358) 663 - - - 10 3.08 (0.241) -700 10 4.07 (0.387) 10 4.78 (0.158) 10 4.42 (0.277) 10 3.90 (0.30 5) 10 4.72 (0.263) 900 10 10.23 (0.526) 10 9.60 (0.420) 10 8.34 (0.443) 10 7.54 (0.528) 10 10.34 (0.277) 50% hatch 10 10.17 (0.804) 10 10.54 (0.423) 10 9.80 (0.477) 10 8.50 (0.687) 10 11.56 (0.292) 1100 10 20.08 (1.696) 10 16.76 (1.765) 10 14.72 (1.856) 10 14.84 (1.518) 10 20.02 (2.188) 1300 19 24.56 (2.568) ^ 19 22.99 (3.271) 19 21.35 (3.862) 19 18.38 (1.332) 19 23.87 (2.572) n = number of samples; ( ) = standard error 45 APPENDIX B - continued Oxygen Tension O D° n T l n T2 n T 3 n T4 n T 5 300 19 0.32 (0.096) 19 0.29 (0.085) 19 0.32 (0.100) 19 0.27 (0.084) 19 0.31 (0.090) 344 19 0.27 (0.071) 19 - 19 - 19 0.30 (0.080) 19 -500 10 1.42 (0.112) 10 1.51 (0.159) 10 1.84 (0.218) 10 1.28 (0.225) 10 1.58 (0.271) 620 - - - - 10 3.50 (0.250) 663 - - - 10 3.09 (0.360) -700 10 4.50 (0.345) 10 4.66 (0.320) 10 4.86 (0.265) 10 3.80 (0.234) 10 5.02 (0.292) 900 10 9.52 (0.288) 10 9.48 (0.371) 10 9.67 (0.399) 10 8.16 (0.40 7) 10 11.30 (0.508) 50% hatch 10 11.36 (0.719) 10 10.50 (0.676) 10 10.14 (0.525) 10 10.02 (0.386) 10 11.66 (0.503) 1100 10 19.20 (1.733) 10 17.26 (1.622) 10 16.08 (1.600) 10 14.32 (1.293) 10 18.51 (1.924) 1300 19 24.33 -(2.276) 19 23.09 (3.833) 19 19.12 (2.830) 19 19.53 (2.383) 19 27.64 (3.523) n - number of samples; ( ) = standard error APPENDIX C - Average Embryo Lengths (mm) Oxygen Tension O D° n T l n T 2 n T 3 n T4 n T 5 300 10 6.44 10 6.73 10 7.27 10 6.36 10 7.41 (0.220) (0.236) (0.177) (0.288) (0.242) 344 19 7.71 - - 19 7.71 -500 10 11.55 10 11.63 10 11.89 19 11.45 10 12.18 (0.263) (0.250) (0.179) (0.237) (0.228) 50% hatch 10 21.35 10 21.39 10 20.57 10 20.66 10 21.44 (0.574) (0.598) (0.380) (0.679) (0.420) 1100 10 26.21 10 24.90 10 23.20 10 23.65 10 25.84 (0.178) (0.162) (0.187) (0.210) (0.188) 1300 19 27.58 19 26.09 19 24.56 19 25.33 19 26.81 (0.584 (0.665) (0.717) (0.673) (0.547) Oxygen Tension O^ 300 10 6.50 10 6.63 10 7.36 10 6.48 10 7.29 (0.200) (0.116) (0.252) (0.144) (0.129) 344 19 7.61 - - 19 7.61 -500 10 11.52 10 11.65 10 11.88 10 11.17 10 11.89 (0.362) (0.250) (0.300) (0.157) (0.305) 50% hatch 10 21.87 10 21.71 10 21.43 10 21.08 10 22.02 (0.566) (0.436) (0.353) (0.516) (0.432) 1100 10 26.54 10 25.03 10 23.54 10 23.67 10 26.29 (0.153) (0.086) (0.203) (0.158) (0.098) 1300 19 27.14 19 25.98 19 24.88 19 24.88 19 27.11 (0.567) (0.361) (0.792) (0.712) (1.054 n = number of samples; ( ) = standard error 47 APPENDIX C - continued Oxygen Tension O D° n T l n T2 n T 3 n T4 n T 4 300 10 6.46 10 6.91 19 7.43 10 6.35 10 7.43 (0.241) (0.213) (0.125) (0.184) (0.377) 344 19 7.59 - - 19 7.63 -500 10 11.25 10 11.50 10 12.10 10 11.05 10 12.20 (0.201) (0.294) (0.1911) (0.276) (0.211) 50% hatch 10 22.47 10 21.86 10 21.42 10 21.93 10 22.18 (0.742) (0.435) (0.329) (0.663) (0.609) 1100 10 26.30 10 24.82 10 23.85 10 23.80 10 25.92 (0.187) (0.147) (0.173) (0.254) (0.158) 1300 19 27.11 19 26.11 19 24.66 19 24.72 19 27.36 (0.592) (0.627) (0.7 56) (1.516) (0.662) n = number of samples; ( ) = standard error APPENDIX D - Accumulative, Per Cent Gross Conversion Efficiency Degree Days (°F) 300 344 500 620 663 700 900 hatch 1100 1300 ° 1 T 1 61.9 42.2 57.5 65.5 68.2 68.2 65.1 50.0 T 2 50.1 - 58.1 - - 76.7 72.9 72.6 67.2 47.7 T 3 81.8 - 73.3 - - 82.2 76.1 75.4 65.4 48.2 T 4 88.4 70.0 58.8 - 65.7 70.5 76.9 77.2 77.6 51.4 T 5 36.3 - 67.7 76.3 - 82.5 81.6 81.6 63.8 52.3 ° 2 T 1 9.5 9.0 19.6 _ 36.0 55.3 59.9 70.3 49.8 T2 12.4 - 22.9 - - 41.3 54.4 55.8 60.2 49.5 T 3 28.4 - 69.0 - - 80.5 69.2 68.8 62.4 49.5 T4 30.8 30.1 52.2 - 65.1 69.9 76.5 76.9 60.7 53.0 T 5 56.8 — 55.0 69.2 - 67.4 75.5 77.3 76.1 45.5 ° 3 T 1 71.4 47.0 64.5 70.8 59.5 61.9 59.9 47.2 T2 39.3 - 55.7 - - 71.8 76.3 76.4 72.6 49.7 T 3 14.2 - 37.2 - - 57.1 71.0 71.6 79.0 43.4 T4 45.1 37.5 54.9 - 67.3 69.1 68.6 70.2 64.1 48.4 T 5 41.6 - 48.9 53.5 - 59.2 72.7 74.0 63.3 51.6 

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