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UBC Theses and Dissertations

Age, growth, and sexual development of the exploited stocks of eastern Pacific albacore, Thunnus alalunga. Partlo , John Middleton 1953

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AGE, GROWTH, AND SEXUAL DEVELOPMENT OF THE EXPLOITED STOCKS OF EASTERN PACIFIC ALBACORE (Thunnus alalunga) by JOHN MTDDLETON PARTLO A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF ARTS, i n the Department of Zoology We accept t h i s thesis as conforming to the standard required from candidates f o r the degree of MASTER OF ARTS. 'Members of the Department of Zoology The University of B r i t i s h Columbia A p r i l , 1953 ABSTRACT Age determinations of albacore are based on concentric marks on the centra of vertebrae. These are shown to be annual by several tests. The 1950 B r i t i s h Columbia albacore fishery was supplied by four age classes (III, IV, V, and VI , whose mean lengths at the time of capture (53*^, 61.3, 71.0, and 80.5 centimeters coincide with the mean lengths of size groups in the commercial catch (5^.3, 62.3, 71.3, 79.7 centimeters . The relationship of body length to vertebral radius i s shown to be rectilinear, and reveals a correlation coefficient of 0.9^8. The body length weight relation i s expressed by the formula, log W « 5.088 3.13 log L, where ¥ i s the weight in kilograms and L Is the length in centimeters. A histological study of the gonads indicates that the fishery i s supported by immature-stocks. Male f i s h showed greater sexual develop-ment than female f i s h of comparable size and age. Gradients of germ c e l l development were observed within the testis and ovary. Larger gonads showed a centripetal and anterior-posterior degree of spermato and oogenesis. TABLE OP CONTENTS Page I. INTRODUCTION 1 II . DISTRIBUTION 2 I I I . THE FISHERY 3 IV. AGE . 5 Material and methods. 5 Relationship of body length and vertebral radius. 10 Length frequency d i s t r i b u t i o n s . 12 V. GROWTH 21 Growth i n length. 21 Growth i n weight. 2l± VI. SEXUAL DEVELOPMENT ' 29 Material and methods. 29 The t e s t i s . 30 The ovary. 32 VII. DISCUSSION 35 VIII. SUMMARY 37 IX. ACKNOWLEDGEMENTS 1+0 X. REFERENCES IjJ. XI. PLATES ' I[4 U .1  VCORE Frontispiece. Th e Albacore (Thunnus alalunga). Drawing from "Marine game fishes of the P a c i f i c Coast from Alaska to the Equator" by Lionel A. Walford. Drawing by Malmquist. INTRODUCTION • Any e f f o r t directed toward sound f i s h e r i e s management impinges on what i s known of the l i f e h i s t o r y of the species under consideration. In the Eastern P a c i f i c albacore (Thunnus alalunga). fundamental age, growth, and sex data are e n t i r e l y absent. Furthermore, i t i s evident from studies of related species (S e l l a 1930: Aikawa and Kato 1938) and from examinations during t h i s study, that albacore scales and o t o l i t h s are not suitable f o r age and growth deductions. Accordingly growth rings on vertebrae centra were examined f o r evidence of age i n an e f f o r t to l i n k the data to well established methods of determining growth rates. The lack of data describing growth h i s t o r i e s i n d i f f e r e n t calendar years, and the persistance of strong year classes l i m i t e d the number of applicable methods f o r v a l i d a t i n g age deductions. An understanding of the sexual development attained by component age classes of the f i s h e r y i s an important c o r o l l a r y to age and growth studies, p a r t i c u l a r l y as a basis f o r future fecundity studies. The present study, therefore, includes a h i s t o l o g i c a l account of the gonads. DISTRIBUTION The P a c i f i c albacore occurs i n varying abundance along the P a c i f i c coast of North America from Southern Lower C a l i f o r n i a to Northern i n waters adjacent to Japan, the Hawaiian Islands, and i n Oceania. In the A t l a n t i c Ocean i t has been found along the coast of Europe northward to the B r i t i s h I s l e s , o f f the coast of A f r i c a , i n the Mediterranean, and on rare occasions o f f the A t l a n t i c coast of North America and the West Indies. I. McT. Cowan f i r s t recorded the species from B r i t i s h Columbia waters on the basis of a specimen taken August 17, 1937 near Kyuquot, west coast of Vancouver Island (Clemens and Wilby 19A6). Albacore are generally found i n offshore waters adjacent to B r i t i s h Columbia during the summer months. They have been caught as early as mid-July and as l a t e as the fourth week of September, but t h e i r period of maximum abundance i n these waters i s i n August. In more southern waters adjacent to C a l i f o r n i a and Lower C a l i f o r n i a they may be found as early as A p r i l and as l a t e as January (Walford 1937). B r i t i s h Columbia. I t i s a pelagic(oceanic)species which i s also found - 3 -THE FISHERY According to Brock (194-3) the development of the P a c i f i c Coast alba-core f i s h e r y began about 1910 and was confined to C a l i f o r n i a waters u n t i l 1936. Since 1938 the f i s h e r y has increased i n i n t e n s i t y o f f the B r i t i s h Columbia coast. This new industry has become of considerable economic importance to the province. The magnitude and value of the f i s h e r y over the t h i r t e e n year period 1939 to 1951 r e f l e c t s i t s sporadic nature, (Table I ) . Since the albacore i s a pelagic species inhabiting offshore waters, f i s h i n g i s l i m i t e d to large vessels which are capable of t r a v e l l i n g to the f i s h i n g grounds and remaining f o r several days. T r o l l i n g vessels of f o r t y feet or more i n length are used extensively as w e l l as some halibut vessels normally employed i n the f l a g - l i n e f i s h e r i e s . The method of f i s h i n g i s exclusively surface t r o l l i n g at speeds from s i x to seven knots. Lures are used for bait and are varied as to shape, s i z e , material, and colour. With the exception of bone or p l a s t i c j i g s , which are r i g i d structures, the lures resemble a squid, one of the p r i n c i p l e items of the albacore's d i e t . Each t r o l l i n g l i n e (6 to 15 per boat) i s equipped with a single lure and double barbless hook. Upon capture the f i s h are hand-lined to the vessel, disengaged from the hook, and a f t e r a period of cooling are iced i n the "round" to await transfer to cold storage at the vessel's port of c a l l . Almost the entire commercial catch i s canned. The major portion i s processed by Canadian companies but some shipments of frozen albacore are made to the United States, and a small portion of the catch i s sold fresh, . presumably f o r the purpose of home canning. Year Quantity Landed Value Landed Value Per (cwts) Ton & 1939 2,838 14,190.00 100.00 1940 45 225.00 100.00 1941 760 6,840.00 180.00 1942 1943 288 5,760.00 400.00 1944 4,636 76,676.00 330.00 1945 14,287 297,983.00 85,113.00 420.00 1946 4,316 395.00 1947 7,965^ 211,650.00 530.00 1948 21,747 598,000.00 550.00 1949 22,310 363,000.00 325.00 1950 '21,188 372,711.00 350.00 1951 189* * To end of October TABLE I - Round weights of albacore landed at B r i t i s h Columbia ports with estimated value of the catch i n do l l a r s 1939-1951. AGE The usefulness of various bony structures f o r determining age has been known f o r the past century (Williamson 1851). Reibisch (1899) described the vertebrae of p l a i c e , and noted t h e i r possible use f o r age determinations, but i t remained for Hiencke (1904) to determine the age of f i s h successfully from vertebrae. The u t i l i z a t i o n of vertebrae and other bony structures by subsequent investigators has been reviewed by Graham (1928) and Menon (1950). To establish that growth marks evident on the centra of albacore were true year marks, the data calculated from the deduced age of 531 f i s h and vertebral measurements of 99 f i s h were examined i n several ways. I f age deductions are correct: ( l ) there should be agreement between the mean length of f i s h assigned to each age class and the mean length of each component size group i n the sample; (2) the lengths of young f i s h calculated from the vertebral measurements of older f i s h should agree with the observed lengths of young f i s h . Materials and methods The material f o r t h i s study consisted of fork lengths, weights, and vertebrae from commercial stocks of Eastern P a c i f i c albacore caught by B r i t i s h Columbia fishermen. Length measurements of 29,4-74- f i s h from the 1950 commercial catch were made by port representatives of the Fisheries Research Board of C anada at the ports of Vancouver, V i c t o r i a , and Prince Rupert. Samples of 20 to 750 f i s h were taken from catches of the majority of vessels landing alba-core at these ports. The weights of 505 albacore from the vertebral samples were measured -6-to the nearest ounce using a Ch a t i l l o n spring scale. Vertebrae from 531 f i s h , captured during the 1950 f i s h i n g season and stored, were collected at processing plants i n Vancouver during December 1950 and January 1951. The ninth prehaemal vertebra was selected f o r study. Selection of t h i s thoracic vertebra was based on i t s access-i b i l i t y , uniform shape, and l e g i b i l i t y of concentric rings on the centrum. These f i s h were sampled without conscious bias during canning operations. Their l o c a l i t y of capture i s uncertain, but since B r i t i s h Columbia f i s h -ermen confine t h e i r operations to the offshore waters from south of San Francisco to the Queen Charlotte Islands,- the samples may be classed as Eastern P a c i f i c albacore from offshore waters adjacent to C a l i f o r n i a , Oregon, Washington, and B r i t i s h Columbia. Samples of vertebrae collected p r i o r to-1950 have not been included i n t h i s study because size selection rendered them incomparable with the 1950 camples. Data collected i n 1949 were u t i l i z e d f o r a cursory examination of the vertebral . method of age determination. The material i s considered reasonably representative of the albacore population inhabiting the offshore waters of the Eastern P a c i f i c adjacent to Canada and the United States during 1950. Some size selection may have occurred i n the vertebral samples when cannery operators removed the f i s h from cold storage f o r processing, but selection i n samples of the comraer-c i a l catch at the ports of landing* should be n e g l i g i b l e . Since surface t r o l l i n g was used~ exclusively i t was assumed that size selection by f i s h i n g gear d i d not occur. Length measurements were made to the nearest centimetre using measuring - 7 -boards standardized at the P a c i f i c B i o l o g i c a l Station f o r albacore studies. This measuring device was a simple board, bevelled from each side toward the center, with a head stop and a graduated r u l e . Measurements could be r e a d i l y and accurately effected by placing the f i s h on the board with the anterior portion of the upper jaw resting against the head stop and the caudal f i n p a r a l l e l to the board. Lengths throughout the study were measured from the t i p of the snout (most anterior part of upper jaw) with jaws closed, to the cartilagenous median part of the caudal fork (Schaefer and Marr 194-9). No allowance was made for shrinkage i n any of the samples. Shrinkage from the time the f i s h were captured u n t i l they were landed at the port of c a l l was considered ne g l i g i b l e since the f i s h were iced during the intervening period. However, shrinkage due to freezing of the catch p r i o r to the c o l l e c t i o n of vertebral samples may have been a source of length v a r i a t i o n between the commercial samples and the vertebral samples. The length data were segregated into, normal frequency d i s t r i b u t i o n s by the method described by Harding (194-9), using p r o b a b i l i t y graph paper de-vised by Hazen (1913). The application of t h i s graphical method i s based on the assumption that the component size groups are themselves normally d i s t r i b u t e d . Sectioning of the vertebrae and accentuation of the growth marks (rings) on the centra was required f o r vertebral examination. Each verte-bra was sectioned f r o n t a l l y i n t o two unequal segments with the aid of a f i n e toothed c i r c u l a r saw. The larger of the two segments was sanded on a motor driven disc sander u n t i l the center of the centrum was revealed. The growth marks were accentuated by immersing the vertebrae i n aqueous -1% KOH -3-f o r 36 hours, washing i n tap water, and preserving i n 95% alcohol (Fig. 1, 2, and 3). The vertebrae were retained i n alcohol u n t i l examined. An e a r l i e r attempt to accentuate the growth marks by d i f f e r e n t i a l s t a i n i n g , using a method described by Crumley, Crow, and G r i f f i n (1939) was unsuccess-f u l . The amphicoelus albacore vertebra, sectioned i n the above manner, reveals two segments of two hollow cones whose vertices meet at the centre of the centrum and whose bases form the anterior and posterior margins of the vertebra. Upon the inner surface of these respective cones are rings running p a r a l l e l to the base of the cone and completely e n c i r c l i n g the centrum. They are i n the form of narrow translucent zones separated by broad opaque zones as described by Freidenfelt (1922) f o r Lucioperca. However, the narrow zones on the albacore centrum were observed, not only as translucent bands, but also as eruptions or ridges on the exposed inner surface of the centrum. The ri n g measurements were made to the mid-point of each ridge. The method of measuring the rings on the vertebrae was the same as that developed by Freidenfelt (1922) and applied to scombrids by Aikawa and Kato (1938). The rings on each of the 531 vertebrae represented i n the sample were counted with the aid of a low power dissecting microscope having 12X magnification. Measurements of 99 vertebrae were made to the nearest tenth of a millimetre with the aid of a r u l e , graduated i n 0.5 mm. i n t e r v a l s , attached to the transparent stage of the microscope. Reflected l i g h t was used f o r a l l readings. Each vertebra was placed on the under surface of the stage with the newly exposed surface uppermost. The distance F i g . 3 S a g i t t a l section of a vertebra a f t e r alcohol f i x a t i o n -10-from the centre of the centrum to each ri n g and to the outer edge of the centrum were measured along the four newly exposed edges of the cones and the corresponding measurements averaged. These averaged measurements w i l l hereafter be referred to as r i n g r a d i i and vertebral r a d i i respectively. The vertebral r a d i i of 200 f i s h were u t i l i z e d to determine the relationship of vertebral radius and f i s h length. Relationship of body length and vertebral radius The establishment of a relationship between the body length,and the length of a body part was recognized f i r s t by Walter (1901) as a fundamental prerequisite f o r age and growth studies based on annual increments i n length evident on the body part. Many subsequent investigators have reaffirmed Walter's s i g n i f i c a n t contribution. Freidenfelt (1922), investigating the age and growth of Perca lucioperca found a positive correlation between the growth of f i s h and the growth of scales and vertebrae. He also established that the f i r s t annulus on a vertebra, unlike that on a scale, remained unchanged af t e r i t s formation. In the present study, the radius of the ninth prehaemal vertebra was compared with the body length f o r each of 200 f i s h i n the vertebral sample. The vertebral r a d i i were plotted against the fork lengths a r i t h m e t i c a l l y and a r e c t i l i n e a r regression was calculated by the method of least squares (Fig. 4-). The regression f i t s the data s a t i s f a c t o r i l y and may be described by the general formula: L -0.069 0.1271^ where L equals the vertebral radius i n millimeters and equals the fork length i n centimeters. The correlation c o e f f i c i e n t of the two variables -11-F i g . 4 Body-vertebra relationship of Eastern P a c i f i c albacore collected from the 1950 B r i t i s h Columbia commercial catch. -12-i s 0.94.8 and the constant, 0.069, i s not s i g n i f i c a n t l y d i f f e r e n t from zero. Extrapolation of the regression l i n e beyond the l i m i t s of the data may not be j u s t i f i e d , but since vertebral growth, unlike scale growth, begins during the embryonic stages of l i f e i t would be expected that when a f i s h i s of measurable length i t would have vertebrae of measurable radius. The value of the "Y" intercept of the l i n e of regression has been used f o r growth calculations. Length frequency d i s t r i b u t i o n s In order to make a comparison of the length d i s t r i b u t i o n of the verte-b r a l sample with the length d i s t r i b u t i o n of each assigned age class i t was necessary to separate the vertebral sample into i t s component size groups. This was accomplished by applying the p o r t a b i l i t y graph method of analys-ing polymodal length frequency d i s t r i b u t i o n s (Harding 194-9) to the length frequency data of the vertebral sample. I t was assumed that each component size group of the sample was normally distributed as to length. On the basis of t h i s assumption the accumulated percent frequency of each c e n t i -metre length class was plotted on Hazen's pr o b a b i l i t y graph paper (Fig. 5). The graph paper has a percentage scale along the bottom, reading from 0.1% on the l e f t to 99.9$ on the r i g h t , and the reverse scale along the top. The scale divisions are not equal but decrease toward the center of the paper. This gradation i s arranged so that when any normally distributed population i s plotted as a cumulative percentage, the points f a l l on a straight l i n e . The position of the l i n e i s determined by i t s mean and i t s slope by the standard deviation. I f the cumulative percentage of a poly-—I—i 1 — I — i 1 1 i 1 — i — I — i — i r—'—i 1 1 — i — i 1 — i 0.1 0-2 OS I 2 S 10 20 50 40 50 60-70 80 90 95 98 99 99.5*98 99.9 . _ . A C C U M U L A T E D P E R C E N T F R E O U E M C V F i g . 5 The accumulated percent length frequency of the vertebral sample plotted on Hazen's proba b i l i t y graph paper. - I l l -.... ^ modal d i s t r i b u t i o n , composed of several normal d i s t r i b u t i o n s , i s plotted on the p r o b a b i l i t y graph paper the plotted points w i l l form sigmoidal curves which are the resultant of two or more straight l i n e s . The point of i n f l e c t i o n of each curve (where the sigmoidal curvature changes sign from positive to negative) i s , according to Harding, the d i v i s i o n point expressed i n percentage of the proportionate d i s t r i b u t i o n s . For example, the i n f l e c t i o n points of the three sigmoidal curves were selected at the 1.1%, 32.0$, and 94.0$ v e r t i c a l s (Fig. 5). This suggests that the poly-modal frequency d i s t r i b u t i o n of the vertebral sample i s composed of four normally distributed size groups. The group; of smaller individuals make up 1.1% of the sample; the remaining size groups make up 30.9%, 62.0$,, and 6.0$ respectively. The l i n e s CD, EF, GH, I J (Fig. 5) were drawn to represent the four normal size groups represented i n the sample. The l i n e CD i s f i t t e d by multiplying the cumulative percent frequency of the smaller individuals by 100/1.1 and the l i n e s EF, GH, and I J by multiplying the cumulative percent frequency of each remaining size group by 100/30.9, 100/62.0, and 100/6.0 respectively. The resultant of the four l i n e s i3 the l i n e AB. The ordinate values i n centimetres of length f o r the intercept of the 50$ v e r t i c a l and the four l i n e s i s the mean f o r the respective d i s t r i b u t i o n s , and s i m i l a r l y % the difference between the ordinate values f o r the i n t e r -cepts of the 15.87$ and 84.13$ v e r t i c a l s with each l i n e i s the standard deviation f o r the respective d i s t r i b u t i o n s . When analysed, the length frequency d i s t r i b u t i o n of the vertebral smaple, (Fig. 5) i s composed of four size groups, mixed i n the proportions 1.1:30.9:62.0:6.0 with mean -15-lengths of 53.40 cms., 61.3 cms., 71.0 cms., and 80.55 cms., respectively, and with respective standard deviations of 2.20, 1.95, 2.87, and 2.52. The standard error of the mean (^p)> where ^ equals the standard deviation, and N equals the number of variates i n the d i s t r i b u t i o n , was calculated f o r each size d i s t r i b u t i o n . (Table I I ) . To present the analysed data graphically, points on the abscissa of each normal d i s t r i b u t i o n , expressed as cumulative percentages, were select-ed and the proportion of the d i s t r i b u t i o n l y i n g between each point and the mean was expressed as a f r a c t i o n of a standard deviation i n accordance with the tables of cumulative normal frequency d i s t r i b u t i o n (Snedecor 194-6). These values were used to determine the ordinate value from the tables of ordinate values of the normal curve (Snedecor 1946) f o r each selected point on the normal curve and the derived values f o r the ordin-ates m u l t i p l i e d by the constant, Number of variates i n % , f o r each Standard deviation size d i s t r i b u t i o n . The resultant values of the ordinates, expressed as percent, were plotted f o r each abscissal length i n centimetres corres-ponding to the symmetrical points which were o r i g i n a l l y expressed as cumulative percentages (Fig. 6). Comparison of mean lengths of component size groups with mean lengths of r i n g classes i n the vertebral sample show considerable agreement (Table I I j F i g . 7). The v a r i a t i o n between the mean length of r i n g class I I I i n the vertebral sample expressed by the two methods of analysis i s a result of the difference i n length range between the observed data and that expressed by the graphical method. The comparison of calculated lengths at the time of r i n g formation - 1 6 -AGE GROUPS PERCENT OF TOTAL DISTRIBUTION Age Analysis Vertebral Sample Commercial Catch Length Analysis Length Analysis I I I 1.3 1.1 P.4 IV 29.6 30.9 11.9 V 61.6 62.0 80.7 VI 7.5 6.0 7.0 MEAN LENGTH (Centimeters) I I I 54.28 53.40 54.27 IV 61.22 61.30 62;35; V 70.83 71.00 71.35 VI 79.85 80.55 79.70 STANDARD DEVIATION I I I 2.21 2.20 1.75 IV 1.90 1.95 2.05 V 2.70 2.87 2.62 VI 2.54 2.52 2.37 STANDARD ERROR I I I 0.85 0.91 0.16 TV 0.15 0.15 0.03 V 0.15 0.16 0.02 VI 0.40 0.45 0.05 TABLE I I - The percent composition, mean length, standard deviation, and standard error of component age groups of the 1950 vertebral sample, determined by age analysis, and length frequency analysis. Similar s t a t i s t i c s of the 1950 commercial catch determined by length frequency analysis are included. - 1 7 -1950 COMMERCIAL FISHERY : J y ( i i i \ \ \ \ \ N= 29,474 — i — \ — - — i 1950 VERTEBRAL SAMPLE n -i tj2^ 1 \ \ j { 1 i C: \ \ \ \ ( i i N» 531 _ _ | ^ r ^ • • • , • — — • • • , • . . . . . . . . . • • -i-p • 45 50 55 60 65 70 75 80 85 LENGTH (cm.) F i g . 6 The length frequency d i s t r i b u t i o n s of the 1950 commercial catch and vertebral sample. The histogram represents the frequency d i s t r i b u t i o n before analysis. The normal length frequency curves represent the length d i s t r i b u t i o n of each component size group as determined by the pr o b a b i l i t y graph method. - 1 8 -3 4 5 6 : A G E GROUPS F i g . 7 A comparison of the mean length, standard deviation,i ^ standard t e r r o r , and length range of component size groups (A) and assigned age classes (B) i n the vertebral sample. Each per-pendicular l i n e represents the length range; the s o l i d rectangle the standard deviation; the clear rectangle represents two standard errors of the mean which i s represented by the horiz-ontal l i n e separating the two l i g h t rectangles. - 1 9 -and observed lengths of f i s h of each r i n g class at time of capture show agreement (Table I I I ; F i g . 7). Exact agreement i s not observed because the f i s h were captured during the intervening period of r i n g formation and the observed lengths are greater than the calculated lengths. Since a r e c t i l i n e a r relationship was shown between f i s h length and vertebral radius, a d i r e c t proportion between the observed values of f i s h length and t o t a l vertebral radius was assumed f o r the purpose of t h i s comparison and |n-lawhere 1 i s the length of f i s h , S i s the radius of the vertebra, n It 5t represents any given r i n g on the vertebra, and T represents the time of capture. The youngest r i n g class (ring class I I I ) was not represented i n the subsample of vertebral data used f o r vertebral r i n g measurements and therefore was not included i n t h i s comparison. Since the two c r i t e r i a used to validate age deductions have been s a t i s f i e d i t may be stated that r i n g classes are analogous with age classes and subsequent reference to r i n g classes I I I , IV, V, and VI w i l l be expressed as assigned age classes I I I , IV, V, and VI. A length frequency analysis of the 1950 commercial catch has been included to provide a comparison of r i n g classes i n the vertebral sample with size groups i n the commercial catch (Table I I ; F i g . 6). The r e s u l t s show s i g n i f i c a n t > s t a t i s t i c a l agreement and suggest that the 1950 B r i t i s h Columbia albacore f i s h e r y was supported by four age classes, I I I , IV, V, and VI i n r e l a t i v e proportions of 0.4$, 11.9$, 80.7$, and 7.0$. Age No. of Average Length Year of L i f e Class F i s h at Capture (cm.) 1 2 3 4 - 5 6 IV 5 63.40 15.71 28.29 41.11 53.72 V 86 70.75 15.16 27.31 39.68 51.85 62.91 VI 8 79.63 15.14- 27.27 39.63 51.77 62.82 72.13 Average Calculated Length (cm.) 15.34 27.62 40.14 52.45 62.86 72.13 TABLE I I I - Calculated length at time of annulus formation f o r f i s h of known age -21-GROWTH Growth i n length The growth i n length during successive years of l i f e was determined from the average radius of each vertebral annulus using the equation of regression, L=-Q069+0.127Li. The calculated fork lengths at each verted b r a l annulus, the observed fork lengths of each assigned age cl a s s , and the annual length increment f o r each year of l i f e are presented i n tabu-lated form (Table IV). The youngest age class (age class I I I ) i s not considered representative because of the small number of invididuals involved. In addition, the average observed length of the age class exceeds the average calculated length at the formation of the next annulus. The growth curve (Fig. 8) i s a graphical presentation of c a l c u l -ated fork lengths at each vertebral annulus. From these data i t may be seen that the albacore attains an average length of 72.10 centimetres a f t e r s i x years of l i f e . The average length a f t e r one year i s 15.57 centimetres. This l a t t e r length c o n f l i c t s with the findings of Aikawa and Kato (1938), who calculated the f i r s t years growth to be 35.00 centimetres f o r albacore of the Western P a c i f i c . Yearly increments of length (Table IV) indicate a f a i r l y uniform growth rate during the f i r s t , second, t h i r d , and fourth years, and the beginning of a decline i n growth during the f i f t h and s i x t h years. S e l l a (1930) observed a s i m i l a r growth pattern over a fourteen year period f o r the blue f i n tuna (Thunnus thynnus). Menon (1950) i n his review of Sella*s age and growth investigations suggests that the use of data of combined sexes i s perhaps the reason f o r t h i s apparent uniformity of growth. -22-AGE CLASS I I I I I I IV V VI Average Vertebral 1.913 3.445 5.006 6.541 7.937 9.112 r i n g radius (mms.) Average Fork Length 54.28 61.22 70.83 79.85 at capture (cms.) Calculated Fork Length 15.57 27.60 39.86 51.91 -62.87 72.10 at each annulus (cms.) Average Annual 15.57 12.03 12.26 12.05 10.96 9.23 Increment (cms.) TABLE TV - The average vertebral r i n g radius, the average fork length at capture, the calculated fork length at each annulus formation, and the average annual length increments f o r albacore sampled from the 1950 commercial catch. - 2 3 -T 1 1 1 1 1 r 1 2 3 4 5 6 7 RING N U M B E R 1 I _ F i g . 8 Length-Age relationship of Eastern P a c i f i c Albacore - 2 4 -Brock (1943) on the basis of samples of the 1940 Eastern P a c i f i c albacore catch, suggests that the sex r a t i o closely approximates one to one, and that probably there was no s i g n i f i c a n t difference i n length between the sexes. I f t h i s were the case f o r the 1950 samples the uniform growth described by the data i s probably a feature common to the albacore. Growth i n weight Weights and lengths of both sexes were used to determine the weight-length relationship of Eastern P a c i f i c albacore. The cal c u l a t i o n of constants and the expression of variables i n logarithmic form resulted i n the equation: LogW = 5.088 + 3.13 log L where W= weight i n kilograms and L= length i n centimetres. A comparison of actual and calculated weights expressed i n pounds and kilograms (Fig. 9) show that the equation f i t s the observed data reasonably w e l l . The greatest difference between actual weights and calculated weights occurs at lengths that are poorly represented i n the data. The average difference between the actual and calculated weights amounts to only 0.198 kilograms. The growth i n weight of albafiore caught i n Eastern P a c i f i c waters increases at a rate greater than the cube of the length. The relationship between age and body weight (Table V) has been graphically i l l u s t r a t e d (Fig. 10). Calculations of body weight were determined by substituting the calculated average fork length of each assigned age class (Table IV) i n the logarithmic equation expressing the -2£-3 9 4 7.87 11.81 15.75 1969 2162 27.56 31.50 35.43 (In.) FORK LENGTH 10 2 0 30 4 0 5 0 6 0 7 0 SO 9 0 (cm.) j F i g . 9 Actual weights (dots) and calculated weights ( s o l i d l i n e ) of Eastern P a c i f i c Albacore. - 2 6 -relationship of body length and weight. From these data i t may be seen that a 15.57 centimetre f i s h , one year of age, weighs 0.07 kilograms (0.15 l b s . ) . The albacore does not a t t a i n a length of 72.10 centimetres u n t i l s i x years of age. At t h i s length and age the weight has increased to 7.98 kilograms (17.60 l b s . ) . Aikawa and Kato (1938) indicate that the growth i n weight of Western P a c i f i c albacore during t h e i r f i r s t year of l i f e i s 1.0 kilogram and that a f t e r s i x years of growth they a t t a i n a weight of 9.2 kilograms. With the exception of age class I I I , which was poorly represented i n the sample, the observed weights of each age class at the time of capture show good agreement with the calculated weights at the time of annulus form-ation. I t appears, as i n the length data, that only the larger individuals of age class I I I were represented, since the average observed weight of t h i s class exceeds the average calculated weight of the next older age class. Agreement between actual and calculated weights f o r any one age class i s not exact since the actual weights are f o r f i s h captured during the intervening period of annulus formation. This difference suggests that the major portion of the annual growth i n weight takes place before the time of capture. -27-AGE CLASS Observed Weight I I I I I I IV V VI at capture (lbs.) 7.56 10.41 14.83 23.64 Observed Weight 3.43 4.72 6.73 10.72 at capture (kilograms) Calculated Weight 0.15 0.88 2.77 6.32 11.77 17.60 (lbs.) Calculated Weight 0.07 0.40 1.26 2.87 5.34 7.98 (Kilograms) Annual Increment 0.15' 0.73 1.89 3.55 5.45 5.83 (lbs.) Annual Increment 0.07 0.33 0.86 1.61 2.47 2.64 (Kilograms) TABLE V - The average observed and calculated weights at annulus formation f o r each assigned age class of the 1950 vertebral sample of Eastern P a c i f i c Albacore and the annual calculated increments i n weight. -28-1 2 3 4 5 6 RING NUMBER P i g . 10 Age-Weight relationship of Eastern P a c i f i c Albacore. - 2 9 -SEXUAL DEVELOPMENT To provide further information on t h e l i f e history of the albacore stocks exploited by B r i t i s h Columbia fishermen, i t was considered necessary to examine the gonads of f i s h from the commercial catch and ascertain the degree of sexual development attained by the respective component size groups i n the f i s h e r y . Early investigations of f i s h gonads have dealt with the o r i g i n and migration of germ c e l l s . More recent studies of the structureiand seasonal changes of gonads have been undertaken f o r a number of species. Hann (1927) described the s t r u c t u r a l development of the r a d i a l type testes as well as the histor y of the germ c e l l s i n Cottus. Mature gonads of either males or females have been described by a number of investigators f o r several species. James (194-6) has ably tabulated the date, investigator, and species of f i s h studied. Material and methods During September 1950 and August 1951, 26 and 18 albacore respectively were sampled f o r gonads. The fork length of each f i s h was recorded and the gonads f i x e d i n Bouin's f l u i d . Accommodations of the research vessel would not permit weighing either f i s h or gonads. After dehydration and clearing, segments of each gonad were embedded i n p a r a f f i n . The tissues were sectioned at 6/> to 10ft and regressively stained with Ehrlich's acid hematoxylin and counterstained with eosin. In a few specimens Heidenhain's i r o n alum hematoxylin was used. F i s h were selected as to size to corres-pond to mean lengths of age classes i n the f i s h e r y . Unfortunately gonad samples of the smallest size group (age class I I I ) i n the fisher y were not -30-obtainable for this study. The testis The testes of the albacore are slender elongate organs lanceolate in transverse section, situated in the postero-dorsal part of the body cavity. In every specimen examined, both male and female, a lobulated mass of fat tissue was attached to each gonad. The size of this fat body increased with the size of the fish and reached its greatest development on the right gonad. Usually i t extended the length of the gonad, but occasionally i t continued for a variable distance both anteriorly and posteriorly. Each testis is attached to the swim bladder and dorsal wall of the body cavity by a short mesorchium. The testis is covered with a sheath of connective tissue which extends into the testis on the exterior lateral side. Thin septa of connective tissue extend radially from the centre of the testis and divide i t into tubules. Each tubule is lined with germ cells under-going development. The primary spermatic duct lies on the median side near the attachment of mesorchium and fat body (Fig. L4-). Near the anter-ior part of the testis i t is slit-like in cross section and lined with columnar epithelium. Near the posterior end of the gonad the duct is oval (Fig. 16). Secondary sperm ducts extend from the seminiferous tubules lined with spermatogenic cells to the primary spermatic duct (Fig. 13). Examination of a mid-segment of the testis of a male, 62.0 cms. in length (age class IV) captured in August 1951 (Fig. 17) reveals numerous seminferous tubules containing spermatogenic cells in various stages of development. The stages of development appear similar for a l l cells - 3 1 -within each section of the tubule, p a r t i c u l a r l y i n tubules containing c e l l s i n l a t e r maturation stages. A greater magnification of the same section of the t e s t i s (Fig. 18) shows mature spermatozoa with f l a g e l l a i n close proximity to one another and the heads spread out i n a fan shape toward the periphery of the tubule. Tubules containing masses of spermatids are also di s c e r n i b l e . Spermia were not observed i n the primary spermatic duct of f i s h of t h i s size group. Sections of successive transverse segments of the t e s t i s from a male, 70.5 cms. long (age class V) captured i n August 1951, show a gradient of germ c e l l development from anterior to posterior (Fig. 11, 12, 13, 1A> 15, and 16). The most anterior segment of the t e s t i s (Fig. 11) i s made up of tubules containing spermatogonial c e l l s undergoing early stages of spermatogenesis. The segment posterior to the l a t t e r (Fig. 12) reveals the f i r s t i n d i c a t i o n of c o l l e c t i n g ducts which appear to be secondary to the primary sperm duct. These are f i l l e d with spermatozoa as i s the primary spermatic duct i n more posterior segments. Sections of these progressive segments indicate that the tubules near the periphery of the t e s t i s at the posterior end of the gonad contain germ c e l l s i n more ad-vanced stages of maturation than those i n more anterior segments. The primary spermatic duct i s almost oval at the posterior end of t e s t i s (Fig. 16). I t i s well supplied with blood vessels and numerous v i l l i . Mature spermia may be observed within the duct. The increase i n t e s t i s size from that of the 62.0 centimetre male, previously described, i s due mainly to the swollen condition of ducts and tubules which are f i l l e d with spermatozoa. This degree of gonad development was not evident i n the - 3 2 -testes of a l l f i s h of t h i s s i z e . The t e s t i s of an i n d i v i d u a l 74.0 cms. i n length caught i n September 1950 (Fig. 20) did not show the same degree of development, but was s i m i l a r to the condition described f o r the 62.0 centimetre male caught i n August 1951. From these observations of albacore testes taken from f i s h caught i n August and September, i t i s believed that some of the males, whose lengths correspond to five-year-old f i s h , are approaching spawning condition. A l l testes of f i s h i n the largest size group showed a degree of germ c e l l development s i m i l a r to those of the 70.5 centimetre specimen (Plate I ) . A male 78.8 centimetres i n length (age class VI) (Fig. 21 and 22) i s representative of t h i s size and age group. The ovary" The ovaries of the albacore, l i k e the testes, are situated i n the postero-dorsal part of the body cavity on either side of the swim bladder. They are covered externally with a layer of peritoneum beneath which i s a t h i n tunica albuginea of connective tissue. Numerous ovigerous lamellae project into the lumen of the ovary. The lumen leads p o s t e r i o r l y to a thick non-muscular oviduct. The oogonia, l i k e spermatogonia, undergo periods of m u l t i p l i c a t i o n , growth, and maturation. Since seasonal observations were not made i n t h i s study, the time periods required f o r these phases of development could not be determined. Several premeiotic stages of oocyte growth could be recog-nized i n each ovary. Successive transverse segments of the ovary from a specimen 61.0 cms. i n length (age class IV) (Fig. 23, 24, 25, 26, and 27) indicate that oocytes - 3 3 -near the posterior of the gonad are larger than those at the anterior end. In f i s h of t h i s s i z e , early growth i s s t i l l i n progress and oogonia may be discerned near the surface of the lamallae i n addition to primary oocytes possessing a quantity of yolk. The l a t t e r d i f f e r from the former primarily i n s i z e . M i t o t i c stages of development were not discernible, but early accumulation of yolk and the presence of f o l l i c l e c e l l s were evident (Fig. 25). During t h i s l a t t e r growth phase of the primary oocyte, which seems to be the most advanced i n the f i s h of t h i s s i z e , several n u c l e o l i are observed around the periphery of the nucleus. Due to the accumulation of yolk and enlargement of the nucleus, the oocytes are very conspicuous and vary i n size from 2.5ff to 52// i n diameter. From the examination of these ovarian sections i t i s apparent that albacore 61.0 centimetres long, which correspond to f i s h four years of age, are immature. Several growth stages of germ c e l l development were observed i n each ovary. A transverse section of the ovary (Fig. 28) of a female f i s h 63.5 cms. i n length (age class IV) which i s comparable i n size and age to the 61.0 centimetre female mentioned above, shows an e a r l i e r phase of oocyte growth. Oogonia and a few primary oocytes are evident. The ovaries from a female f i s h , 69.1 cms. i n length (age class V) taken i n August, are characterized by occasional oocytes with either very granular or vacuolated peripheral cytoplasm (Fig. 29 and 30). The egg i s enveloped i n a f o l l i c u l a r membrane, two rows of flattened c e l l s i n thickness, and a d i s t i n c t l a y e r , the zona pel l u c i d a , as described by James (1946). The nucleus of the egg i s d i s t i n c t l y oval i n shape with many n u c l e o l i about i t s periphery. This oocyte growth stage varied i n size from 104// to 180// i n diameter as compared with the l e s s mature oocytes present, which vary from 6.5// to 104//in diameter. The ovigerous lamellae are well f i l l e d with growing oocytes of different sizes. The ovary diameter i s much greater than that of f i s h of the younger size group (61.0 cms.). The ovaries of f i s h 69.0 centimetres long were V r ~ 7 - ^ more than twice the size of f i s h 61.0 centimetres i n length. The gonad i s opaque and pale yellow i n colour, while that of the younger f i s h i s opaque and almost white. The gonads of a female 84.9 cms. long (age class VI) caught i n September 1950, had hot developed to the same degree as the 69.0 c e n t i -metre specimen caught i n August 1951. No oocytes with granular or vac-uolated cytoplasm were present, but the i n t e r s t i t i a l tissue was i n a si m i l a r stage of reduction and the number of oocytes and size of the ovary were s i m i l a r . I t i s believed that females captured i n September i n t h e i r s i x t h year of l i f e (84.9 cms. long) may mature at the same time as the few five-year-old f i s h (69.0 cms. long) displaying more advanced stages of sexual development a month e a r l i e r . Completely.ripe eggs were not observed i n any of the sampled ovaries, but the vacuolated cytoplasmic stage of oocyte growth evident i n the ovaries of five-year-old f i s h (69.0 cms. long) caught i n August, suggests that spawning may occur within a matter of months. Four-year-old f i s h (61.0 cms. long) l i k e the older age groups are immature, but the condition of the ovaries suggests that t h i s period of sexual development i s one of m u l t i p l i c a t i o n and early growth. - 3 5 -DISCUSSION The examination of Eastern P a c i f i c albacore vertebrae has provided a basis f o r estimating the age and growth of commercial stocks. Since the-examined f i s h consist of intermediate age classes ( I I I , IV, V, and VI), the lengths and weights of younger age classes (I and I I ) were determined by back calculations of e x i s t i n g data. The r e s u l t s obtained are at v a r i -ance with those of other workers. Two Japanese investigators (Aikawa and Kato 1938) examined the verte-brae of Western P a c i f i c albacore and estimated the average radius of the f i r s t vertebral annulus to be 3.2 millimeters. This measurement agrees closely with the average radius of the second vertebral annulus (3.4- mm.) determined i n t h i s study. The average radius of the f i r s t vertebral annulus i s 1.9 millimeters. Unfortunately i t has not been possible, i n either study, to substantiate the calculated growth during early devel-opment by actual observations. During the current study, the l e g i b i l i t y of the f i r s t annulus was clear and w e l l defined on a l l vertebrae examined, and i t i s f e l t that since the observations were consistent, that the i n c l u s i o n of t h i s growth mark provides a v a l i d interpretation of the age and growth of Eastern P a c i f i c albacore. H i s t o l o g i c a l examination of albacore gonads has indicated that the commercial f i s h e r y i s dependent upon an immature population. None of the f i s h examined had sexually r i p e gonads, nor was there evidence of ova i n an a t r e t i c condition. The observation that the older age groups i n the population were approaching sexual maturity provides s u f f i c i e n t e v i -dence f o r speculation on the dominance of component age classes i n the . . -36-commercial fishery. Of the four age classes (III, IV, V, and VI) represented in the fishery (Pig. 6 and 7), examination of the gonads reveals that some males and females of age class V are more mature than others of the group. Furthermore, a l l indiv-iduals of age c l a s s VI that were examined were approaching a mature state. It may be noted that age class VI i s a minor size group i n the fishery. It i s believed,, that since there was no evidence of individuals in the sample with atretic ova that the small relative proportion of age class VI i s a result of a small proportion of individuals of age class V that did not spawn i n the interval between fishirg seasons and have entered the fishery the following year as the next larger size group (age class VI). Similarly, since gonad examination indicates that a l l individuals of age class VI are approaching sexual maturity and older age classes are not observed in the fishery i t i s believed that individuals do not enter the fishery after spawning^ -37-SUMMARY 1. The Eastern P a c i f i c albacore (Thunnus alalunga. Gmelin) occurs season-a l l y i n offshore waters adjacent to B r i t i s h Columbia as f a r north as the northern extremity of the Queen Charlotte Islands. More prolonged occurrences are observed i n offshore waters adjacent to the United States and Lower C a l i f o r n i a . 2. Vertebral examinations are a v a l i d means of determining age of Eastern P a c i f i c albacore. 3. The graphical method of analysing polymodal length frequency d i s t r i -butions i s a v a l i d means of segregating the commercial albacore catch into component age classes. 4. The 1950 albacore f i s h e r y i n waters adjacent to the P a c i f i c Coast of Canada and the United States was dependent upon four age classes of f i s h , and almost e n t i r e l y upon the dominant five-year-old f i s h which contributed over 80 per cent of the t o t a l catch. Fish less than three years of age did not enter the commercial f i s h e r y . The oldest f i s h f o r which a d e f i n i t e age could be determined had completed s i x winters. 5. Albacore a t t a i n average fork lengths of approximately 15.57, 27.60, 39.86, 51.91, 62.87, and 72.10 centimetres at 1, 2, 3, 4, 5, and 6 years of age. 6. The weight of Eastern P a c i f i c albacore increases at a rate greater than the cube of the length. The average weight attained at the time the s i x t h annulus i s formed i s 7.98 kilograms (17.60 l b s . ) . 7. Several stages of sexual development were observed i n albacore testes sampled from the 1950 B r i t i s h Columbia commercial catch. Testes of - 3 8 -the two larger size groups (age classes) contained cysts of spermatozoa i n secondary and primary spermatic ducts. Only a proportion of the indiv i d u a l s belonging to the second oldest age class (age class V) had testes i n l a t e r stages of spermatogenesis, while the^testes of a l l individuals of the oldest age class (age class VI) were approaching l a t e r stages of spermatogenesis. 8. During germ c e l l development, which was evident i n a l l testes examined, the seminiferous tubules of the testes were f i l l e d with germ c e l l s i n various stages of spermatogenesis. 9. Within the testes, centrepetal and anterior-posterior gradients of germ c e l l development occur. Advancement i n spermatogenesis was ob-served from the periphery of the gonad toward the center as well as from anterior to posterior along the length of the organ. 10. Ovaries of albacore sampled from the commercial f i s h e r y were immature. The ovaries of f i s h 69.0 centimetres i n length (age class V) captured i n August exhibit oocytes i n advanced stages of development. Some of the c e l l s were much enlarged with each enveloped i n a f o l l i c u l a r mem-brane and a d i s t i n c t zona pel l u c i d a . The cytoplasm of the c e l l was either granular or vacuolated with an oval nucleus i n the center which contained many neucleoli about i t s periphery. This l a t t e r growth stage of oogenesis was not observed i n a specimen 84.9 centimetres i n length captured i n September of the previous year but there were many oocytes present which were approaching the vacuolated cytoplasmic stage. None ,of the ovaries examined showed signs of a t r e t i c germ c e l l s . 11. A centripetal as well as an anterior-posterior gradient of germ c e l l - 3 9 -development occurs within the ovary. More advanced stages of growth and development were observed near the lumen than near the periphery of the organ. Germ c e l l s were further advanced near the posterior end than near the anterior end of the ovary. AGKNOWLEDGEMENTS Thanks are expressed to Dr. J . L. Hart, Director of the P a c i f i c B i o l o g i c a l Station, who gave permission f o r the abacore material to be used as a th e s i s . The author g r a t e f u l l y acknowledges the help and en-couragement given him by Dr. W. A. Clemens and Dr. W. Hoar of the Depart-ment of Zoology, under whose d i r e c t i o n th^e manuscript was prepared. Special assistance by Mrs. K. Herlinveaux of the P a c i f i c B i o l o g i c a l Station and Dr. P. Ford of t i f ^ Department of Zoology, University of B r i t i s h Columbia, on h i s t o l o g i c a l technique and examination of the histo-l o g i c a l material i s g r a t e f u l l y acknowledged. Catch samples were obtained through the courtesy of Tulloch Fisheries Ltd. and Canadian Fishing Co. Ltd. Assistance i n c o l l e c t i n g the samples was rendered by Messrs. R. M. Wilson, D. Odium, R. Grubb, and R. J. Kar-j a l a . The ready cooperation of other members of the s t a f f of the P a c i f i c B i o l o g i c a l Station and members of the s t a f f at the University of B r i t i s h Columbia has added to the pleasure of t h i s work. Aikawa, H. and M. Kato 1938 Brock, Vernon E. 1943 Clemens, W. A. and G. V. Wilby 1946 Crumley, R. W., J. F. Crow and •A. B. G r i f f i n . 1939 Freidenfelt, Av. T. 1922 Graham, Michael. 1928 H arm, Harry W. 1927 Harding, J . P. 1949 -41-REFERENCES Age determination of f i s h . 1... B u l l . Japan. Soc. S c i . F i s h . , 7 ( l ) : 79-88. Contribution to the biology of the albacore (Germo alalunga) of the Oregon coast and other parts of the North P a c i f i c . Stanford Ich. B u l l 2 (6): 199-243. Fishes of the P a c i f i c Coast of Canada. B u l l . Fish. Res. Bd. C nada. (68): a 166-167. Clearing specimens f o r the demonstra-t i o n of bone. Stain Techn., 14 ( l ) : 7-11. Undersokninger over Gosens t i l l v a n t s a r s k i l t i Hjalmeren. Medd. Kungl. Lantbruks t y r e l s i n , Nr. 235: 1-75. Studies of age determination i n f i s h . Part 2. A survey of the l i t e r a t u r e . Min. Agric. F i s h . Invest. Series 2, 11=(3): 1-50. The germ c e l l s of Cottus B a i r d i i . Jour. Morph. 1£ (2); 427-297. The use of pr o b a b i l i t y paper f o r the graphical analysis of polymodal frequency d i s t r i b u t i o n . Jour. Mar. Bio. - 4 2 -Hazen, A. 1913 Heincke, F. R. 1904 James, Marian F. 1946 Marr, John C. and Milner B. Schaefer 1949 Menon, M. D. 1950 Assoc., 28: LU-153. Storage to be provided i n impounding resevoirs f o r municipal, water supply. Proc. Amer. Soc. C i v i l Eng., 3J2.: 1943-2044. The occurrence and d i s t r i b u t i o n of the eggs, larvae and various age groups of food fishes i n the North Sea. Cons. Perm. Internat. Explor. Mer., Rapp. et Proc. Ver., General Report, 1902-1904, Appendix E: 1-39.. Histology of gonadal changes i n the blue g i l l (Lepomis macrochirus rafinesque), and the largemouth bass (Huro Salmoides Lacpede). Jour. Morph. 79_ (1): 63-91. Definitions of body dimensions used i n describing tunas. U. S. F i s h and Wild-l i f e Service, F i s h . B u l l . , %1 (47): 241-244. The use of bones, other than o t o l i t h s i n determining the age and growth rate of fishes. Cons. Perm. Internat. Explor. Mer., Jour, du Consl, 16 (3): 311-355. Reibisch, J . 1899 S e l l a , M. 1930 Snedecor, George W. 194-6 Walford, L i o n e l A. 1937 Walter, E. 1901 Williamson, W.C. 1851 TJber die E i z a h l b e i Pleuronectes  platessa und die Altersbestimmung dieser Form aus den Otolithen. K i e l . N.F., £ : 233-248. D i s t r i b u t i o n and migration of the Tuna (Thuhnus thynnus L.) studied by" the method of hooks and other observations. Internat. Rev. Hydro-biol. u Hydorgi., Bd. 2k' 446-466. S t a t i s t i c a l methods. Iowa State C o l l . Press, Ames, Iowa. Marine game fishes of the P a c i f i c Coast from Alaska to the Equator. University of C a l i f o r n i a Press, Berkely: 14-17. Die Altersbestimmung des Karpfens nach der Schuppe. In Knauthe: "Die Karp-fenzucht." pp. 88-132. Neudamm. Investigations into the structure and development of the scales and bones of f i s j i e s . P h i l . Trans. Roy. S o c , Part 1 : 6 43-702. PLATE I Photomicrographs of sections of s i x progressive segments from anterior to posterior of a t e s t i s from a specimen 70.5 cms. i n length (age class V). Hematoxylin and Eosin 7^ x 100; M, mesorchium; St, seminiferous tubule; Ssd, secondary spermatic duct; V, v i l l i s ; Bv, blood vessel; Spa, sperma-tozoa; Spd, spermatids; Spm, spermatogonium; Sf, spermatozoa f l a g e l l a . F i g . 11 Cross-section of the anterior t i p of a t e s t i s showing the mesor-chium and seminiferous tubules with t h e i r central lumen and surr-ounding spermatogenic c e l l s . F i g . 12 Cross-section of a segment showing secondary spermatic ducts f i l l e d with spermatozoa. F i g . 13 Cross-section of a segment showing a secondary spermatic duct con-tai n i n g spermia (top of figure) opening into the primary duct. Note primary spermatic duct f i l l e d with spermatozoa. F i g . 14- Cross-section of a segment showing the primary sperm duct and the attachment of mesorchium to t e s t i s . Note germ c e l l s near the t e s t i s periphery are i n e a r l i e r stages of growth and maturation than those more i n t e r i o r , also that the walls of the. primary spermatic duct are s l i g h t l y v i l l i f o r m . F i g . 15 Cross-section of a segment showing large secondary sperm ducts near periphery of t e s t i s as well as tubules containing sperma-togenic c e l l s i n l a t t e r stages of development. Note v i l l i f o r m l i n i n g of the primary spermatic duct with numerous blood vessels i n each v i l l u s . F i g . 16 Cross-section of the s i x t h segment (posterior segment) showing oval primary spermaticduct containing many spermia. Note that the large secondary spermatic ducts f i l l e d with spermia at the top of the fig u r e . - 4 7 -.PLATE I I Photomicrographs of sections of testes from specimens of various sizes. Hematoxylin and Eosin; M, mesorchium; St, seminiferous tubule; Psd, primary spermatic duct; Ssd, secondary spermatic ductj V, v i l l u s ; Bv, blood vessel, ,Spa, spermatozoa; Spd, spermatids; Spm, spermatogonium; Sf, spermatozoa f l a g e l l a . F i g . 17 Cross-section of a mid segment of a t e s t i s from a specimen 62.0 cms. i n length (age class IV1) showing numerous tubules containing spermatogenic c e l l s i n several stages of development. Note that no s j j e r i i are evident i n the primary spermatic duct. 8^/x 100. Fi g . 18 Enlarged section Figure 1 showing mature sperm and spermatids. Note f l a g e l l a on spermia. 8^/x 4-50. Fi g . 19 Spermia i n a t e s t i s section taken from a specimen 62.0 cms. i n length (age class IV). Bfj x 1000. Fi g . 20 Cross-section of mid-segment of a t e s t i s taken from a specimen 74.0 cms. i n length (age class V) showing tubules containing germ c e l l s i n early stages of development. Some tubules contain spermia. 8// x 100. Fi g . 21 Cross-section of mid-segment of a t e s t i s from a specimen 78.8 cms. i n length (age class VT) showing many tubules containing spermia, spermatids, and primary germ c e l l s . The primary spermatic duct i n the upper l e f t corner of the figure i s f i l l e d with spermia.^x>0o F i g . 22 Enlarged section of Figure 5 showing spermatogenic c e l l s i n several stages of development. Note groups of spermatozoa with f l a g e l l a v i s i b l e . 7p x 450. - 4 9 -.PLATE III Figures 23 , 24, 2$, 26, and 27 are photomicrographs of f i v e progressive segments from anterior to posterior of an ovary from a specimen;6l.0 cms. i n length (age class IV); Figure 28 i s a photomicrograph of a mid-ovarian segment from a specimen 63 .5 cms. i n length (age class IV). Hematoxylin and Eosin; Osl, ovigerous lamella; Ot, oocyte; 01 ovary lumen, P, peritoneum; Od, oviduct; Gt, connective t i s s u e . Pig. 23 Cross-section of a segment (anterior tip) showing a few ovigerous lamellae and oogonia i n early stages of development. 7/> x 100. F i g . 24 Cross-section of a segment. Oocytes i n the grovjing stage are located near periphery of each lamella and the central lumen of the ovary i s l i n e d with epith-e l i a l c e l l s . The peritoneum covering the ovary i s evident. 8// x 100. F i g . 25 Cross-section of a segment (medial) showing greater ; numbers of ovigerous lamellae and a corresponding increase i n the number of growing oocytes. 8 x 100. F i g . 26 Cross-section of a segment with many ovigerous lamellae and growing oocytes. 7f x 100. F i g . 27 Cross-section of a posterior segment shows the o v i -duct.- Surrounding tissue i s dense collagen with an outer peritoneal sheath. Qf/ x 100. F i g . 28 The ova are In early stages of growth. A few primary - 5 0 -o o c y t e s may be o b s e r v e d near the p e r i p h e r y of some l a m e l l g Iff x 100. ' ; " - 5 2 -PLATE IV Figures 29 and 30 are photomicrographs of mid-ovarian segments from a specimen 69.0 cms. i n length (age class V) captured i n August 1951. Figure 31 i s a microphotograph of a mid-ovarian segment from a specimen 84-.9 cms. i n length (age class VIO captured i n September 1950. Hemotoxylin and Eosin; 0t, oocyte; Ct, connective tissue; Zp, zona pellucida; Fe, f o l l i c l e c e l l s ; N, nucleus; Cy, cytoplasm; No, n u c l e o l i . F i g . 29 Numerous growing oocytes and one oocyte i n an advanced stage of growth. Note the decreased thickness of connective tissue surrounding ova and the d i s t i n c t f o l l i c u l e surrounding the large ovum. Ij/ x 100. F i g . 30. Enlarged section of Figure 1 showing the characteristics of an ovum. Note the oval nucleus with n u c l e o l i about i t s periphery. Two layers of f o l l i c l e -cells surround the egg. A Bona pellucida may be observed i n t e r i o r from the f o l l i c u l a r epithelium. 7^ x 4-00. F i g . 31 Thin strands of connective tissue and growing ova of various sizes may be observed. &y x 100. 

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