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Some effects of thyroxine on developing Chum salmon, Oncorhynchus keta, and the comparative action of… Dales, Samuel 1953

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SOME EFFECTS OF THYROXINE ON DEVELOPING CHUM SALMON, Oncorhynchua keta, AND THE COMPARATIVE ACTION OF THIO-UREA, THE HALIDES AND ADRENALIN by SAMUEL DALES A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF ARTS in 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 THE UNIVERSITY OF BRITISH COLUMBIA A p r i l , 1953 ABSTRACT Chum salmon eggs were Immersed In thyroxine, i n thiourea, i n halide s a l t s , and i n adrenalin on the day of f e r t i l i z a t i o n and were maintained in these solutions u n t i l several months aft e r hatching. A l l treatments affected growth eith e r favourably or adversely, but only thyroxine and chloride changed body proportions. The changes due to chloride were s i g n i f i c a n t l y smaller than those following thyroxine treatment and i t i s postulated that they are.not 'thyroxine-like' in nature. Thiourea inhibited c o l l o i d function with the usual hypertrophy and hyperplasia of the gland. Chloride and bromide depressed the heart rate s i g n i f i c a n t l y , whilst the other treatments had no e f f e c t . Iodide and bromide dispersed melanin pigment but thyroxine concentrated I t s l i g h t l y and adrenalin maximally so that adrenalin treated l i v e f i s h were very pale. Thyroxine Increased markedly the deposition of guanine and must, therefore, accelerate the hydrolysis of nuclear purines. It is concluded that s p e c i f i c effects pro-duced by thyroxine in developing chum salmon are not d u p l i -cated by the halides and adrenalin. - I I -ACKNOWLEDGEMENTS The writer wishes to thank Dr. W. S. Hoar, Pro-fessor, Department of Zoology, f o r guidance, invaluable help and c r i t i c i s m throughout. He also wishes to thank Dr. W. A. Clemens, Head of the Department of Zoology, f o r permission to work on the problem and for c r i t i c i s m of the manuscript and Dr. W. M. Cameron, Professor, Department of Zoology, for advice in s t a t i s t i c a l analysis. I am indebted to Mr. G. J. Robertson for help in f e r t i l i z i n g the eggs, to my wife, Laura, for help i n pre-paration of slide s and to Mrs. H. R. Pulton f o r typing the thes i s • TABLE OF CONTENTS ABSTRACT. I ACKNOWLEDGEMENTS I I INTRODUCTION 1 MATERIALS AND METHODS 3 RESULTS 5 A. HEART RATE 5 B. BODY PARTS . 7 C. THYROID GLAND 16 D. PIGMENTATION 21 I. MELANIN . 21 i i . GUANINE 21 DISCUSSION 26 THYROID GLAND 26 GUANINE DEPOSITION 29 GROWTH AND BODY PROPORTIONS 31 * MELANOPHORE DISPERSAL 35 HEART RATE 36 CONCLUSION 37 SUMMARY . 39 LITERATURE CITED 40 INTRODUCTION Since Gudematsch (1913) observed that feeding mammalian thyroid to frog larvae produced a precocious metamorphosis, much work has been done on the role of the thyroid In development of the vertebrate (Lynn et a l 1951). The effect of administering thyroxine to develop-ing Oncorhynchua keta p r i o r to hatching was f i r s t studied by the author (Dales 1951)jWho found that i t exerted a s t r i k i n g e f f e c t on growth and protein metabolism. In the present experiment It was decided to study the possible action of thyroxine on growth and development of chum salmon f o r a longer period and extend the treatment. Thereby, i t waa hoped to elucidate further the role of the thyroid hormone in metabolism and development of f i s h and to determine whether Its effects are s p e c i f i c or general. Thiourea has long been used i n a l l e v i a t i n g the effects of excessive quantities of thyroid hormone i n humans and experimental animals. The drug la thought to prevent iodination of the thyroxine molecule by i n t e r f e r i n g with the oxidative enzyme systems, which bring about iodine incorpora-tion and by combining with part of the elemental iodine. A controversial literature,regarding the administration of thiourea to f i s h j i a diacusaed by Pleiachmann (1947). Some workers find that thiourea accelerates, others that i t has no effect whatso-ever and othera yet that i t i n h i b i t s thyroid gland a c t i v i t y . The author found e a r l i e r that thiourea produced effects antago-n i a t i c to thyroxine and i n the present experiment It waa desired - 2 to confirm these r e s u l t s . The thyroxine molecule, OH" contains four atoms of iodine. U n t i l recently i t was believed that of the halogens only iodine, when bound with s p e c i f i c proteins, could produce b i o l o g i c a l l y active thyroid hormone compounds. Experiments have demonstrated, however, that iodine can be replaced by other halogens and the hormone thus produced i s b i o l o g i c a l l y active i n amphibian metamorphosis and mammalian metabolism, though the a c t i v i t y Is greatly reduced (Salter 1950). A test was made, i n the present experiment, to determine whether developing chum salmon take up bromide, chloride and iodide from the aquatic medium. I f , from these halogens, the embryos could elaborate 'thyroxine-like' compounds, i t might be anticipated that these compounds would produce 'thyroxlne-like' effects on development. i t was of Interest to study the effect of another metabolic accelerator, adrenalin, on development. To I l l u s t r a t e the s p e c i f i c i t y of action of thyroxin, MATERIALS AND METHODS The eggs of several ripe females were stripped and f e r t i l i z e d with sperm from several ripe males, on the spawning grounds, Sardis, B. C , November 10, 1951. They were then transported i n glass containers to the University hatchery and 5000 were placed in each of seven enamel buckets of eight l i t r e s capacity, f i l l e d with the desired solutions. The enamel buckets stood In a cement trough, with running water around them, ensuring equal temperatures for eggs of a l l t r e a t -ments. The temperatures ranged from 5.5°C to 12.0°C but at no time waa there a change greater than - 2°C In any 24 hours. Ample oxygen waa bubbled i n from compressed a i r hoaea and aolutiona were aerated continuously. To prevent the accummu-l a t i o n of tox i c materiala and to prevent fungua growth i n the containera the aolutiona were changed weekly by aiphoning off the old l i q u i d and aimultaneoualy pouring i n freah water. Thia method enaured that the eggs were not expoaed to a i r at any time. The aolutiona uaed were thyroxine aodium (B.D.H.) 1:12-gr m i l l i o n , thiourea 0.05$, aodium iodide, bromide and chloride 1:7,500 and adrenalin chloride (Parke Davia and Oo.) 1:60 m i l l i o n . Adrenalin waa.administered d a i l y by a dropper becauae i t la e a s i l y oxidized and thua loaea i t a b i o l o g i c a l a c t i v i t y . Shortly p r i o r to hatching and soon after^three eggs were removed from each treatment on several occaasiona. The capsule waa peeled off c a r e f u l l y with fine forceps and the embryos were placed In a glass d i s h containing some of the solution i n which they were being treated. .The dish was placed i n a constant temperature bath standing on a binocular microscope stage. After the temperature in the dish became constant the rate of heart beats of each embryo was recorded f o r three minutes. P r i o r to hatching three eggs from each treatment were preserved on alternate days. On the f i n a l day of the experiment, 121 days after f e r t i l i z a t i o n and 56 days after hatching, a l l f i s h were k i l l e d and fixed in Bouin's p i c r i c -acid-formol-acetic-acid mixture. Measurements were made on the same day to prevent errors due to shrinkage by the f i x a -t i v e . Body length was measured from the snout t i p to the fork i n the t a i l and the pectoral f i n length from the fleshy base to the furthest extremity of the rays. Two f i s h , k i l l e d on the las t day of the experiment, were selected at random from each treated group. After imbedding i n p a r a f f i n , by the dioxan method, s e r i a l sections 15 thick were cut transversely and s a g i t a l l y . Staining was done with Harri's haematoxylin and eosin. TABLE' I AVERAGE HEART RATE OF 5 EMBRYO FISH. COUNTED FOR 3 MINUTES 9 RECORDED PRIOR TO HATCHING AND SOON AFTERWARDS Days From TPfl T»t; 111 TP.— Temper-ature °C Treatment L \D J. u X JL J- _C1 t i o n Control Thyroxine Thiourea Iodide Bromide Chloride Adrenalin 54 8 54 56 68 55 46 65 56 57 7 51 52 58 53 51 59 55 63 11 65 56 61 - 68 65 60 61 70 7 60 58 51 51 46 51 53 74 10 61 72 61 76 65 62 61 75 8 66 62 57 58 53 55 60. 75 8 65 61 58 62 52 60 64 76 8 68 62 58 61 56 54 65 76 8 63 59 54 56 56 58 60 79 9 67 75 72 70 73 87 81 Average of a l l Observat ions 62.0 61.3 59.8 61.0 56.3 55.1 61.6 - 6 -Ld 62 • cr 60 CL c o < UJ 00 < U J 52 56 56 54 •O: • QL. •\-::z--I:.' •:co:i :-'Hi'-: i :</)•;_ • L L . ' . -:<;: .UJ :• •••X-: .in-•.UJ'-::Q.'i vO: X CO U_ Mil'; : 9 -•:o-VT; VUJ': >ta_:-v. ;;<•.•••. •'•<y Figure 1.- Histogram shows the average heart rate calculated from a l l observations. TABLE I A t TEST OF SIGNIFICANCE BETWEEN THE MEAN HEART RATE IN CONTROL AND TREATED FISH Treatment Mean Heart Mean t Calculated Rate Difference X 1 - X 2 / S I Control 62.0 Thyroxine 61,3 0.7 0.8 Thiourea 59.8 1.2 1.6 Iodide 61.0 1.0 1.0 Bromide 56.3 5.7 5.1 # Chloride 55.1 6.9 6,6 # Adrenalin 61.6 0.4 0.4 k Johnson 1950 t Tabled at p.01 Is 3.35 # Indicates s i g n i f i c a n t difference - 7 -Table I and figure 1. show the averages of ten sets of observations taken from three f i s h i n each treat-ment for a period of three minutes. This means that i n a l l , beats from t h i r t y f i s h , sampled at random from each treat-ment group, were recorded. Table IA reveals that a s i g n i -f i c a n t l y depressed heart rate resulted from treatment with bromide and chloride. B. BODY PARTS Approximately seventy f i s h were measured in each treatment group, for t h e i r body length and l e f t pectoral f i n length. A logarithmic and arithmetical length frequency plot indicated that the individuals within a group approximated more closely a binomial d i s t r i b u t i o n , i f plotted logarithmically. Scatter diagrams (figures 2 . -8 . ) show the d i s t r i b u t i o n of points of each treatment group. A c a l c u l a t i o n of the c o r r e l a t i o n c o e f f i c i e n t revealed that there was no correlation between these two measurements within any of the groups. An analysis of variance revealed a s i g n i f i c a n t difference at P .01 between the populations of each group treated, both for the body length and for the pectoral f i n length. To find where the s i g n i f i c a n t difference occurred, the means of each treatment group were compared with those of the controls by the t t e s t . The results of this test are shown i n tables I I and I I I . F i d u c i a l l i m i t s on either side of the mean were calculated (table IV) and i l l u s t r a t e d graphically (figure 9 . ) . - 8 -C O N T R O L F I S H < cr o i -u UJ CL o o •• • • •*>. •*• .*. 330 3 .40 SiO LOG e BODY LENGTH Figure 2. Scatter diagram shows plot of body length and pectoral f i n length of control f i s h . z UJ < CE O (-U Ld Q. o 13 O _) 3.20 T H Y R O X I N E F I S H 1.40 1.30 Q90 083 330 3 4 0 3.50 L O G e BODY LENGTH 3.60 Figure 3» Scatter diagram shows plot of body length and pectoral f i n length of thyroxine f i s h * THIOUREA FISH • • • • • • • • • • • • • \ • •I • • • • • • • t • - t 1.20 0 8 0 3.20 3 3 0 3.40 3 . 5 0 LOGe BODY L E N G T H Figure 4 . Scatter diagram shows plot of body length and pectoral f i n length of thiourea f i s h . IODIDE FISH i i-z UJ _J < tr O t-u UJ 0-<n O A • s ' *: A * • s . . ' . H . . •• , % •• t • • • • • • a 3 ° 3.40 3.5o LOGe BODY L E N G T H Figure 5 . Scatter diagram shows plot of body length and pectoral f i n length of iodide f i s h . X o z _ l < CE o i-u UJ Q_ <D o o - 10 -BROMIDE FISH • •• • • •• % 3:25 350 3"4G 350" 3^ 0" LOGe BODY L E N G T H oso Figure 6 . Scatter diagram shows plot of body length and pectoral f i n length of bromide f i s h . CHLORIDE FISH 326! 330 ! 340 35"0 3.60 LOGe BODY L E N G T H 0B0 Figure 7. Scatter diagram-shows plot of body length and pectoral f i n length of chloride f i s h . - 11 -ADRENALIN FISH •? it t $ - -* ** t> * 3.20 330 3.40 L O G e BODY L E N G T H 3.50 360 LOO 080 Figure 8 . Scatter diagram shows plot of body length and pectoral f i n length of adrenalin f i s h * TABES V t TEST OF SIGNIFICANT DIFFERENCE BETWEEN THE MEANS OF CHLORIDE TREATED FISH MEASUREMENTS AND THOSE OF CONTROLS AND THYROXINE GROUPS Treatment Mean of Body Length mms Mean Difference t Calculated* *l-X2/sa-Mean of Pectoral Fin Length mms Mean Difference xi-X2 t Calouiated Chloride Control Thyroxine 32.2 33.1 29.7 0.9 2.5 3.3 # 12 .8 # 3.25 2.96 3.62 0.29 0.37 4.3 # 7 . 8 # _ Johnson 1950 t Tabled at p.01 i s 2.61 # Indicates s i g n i f i c a n t difference - 12 -TABLE I I t TEST OP SIGNIFICANT DIFFERENCE BETWEEN MEANS OF CONTROL FISH BODY LENGTH (33.1 mms) AND TREATED FISH Treatment Mean of Body Length Mean Difference t Calculat ed mms Xj-Xg x l " x 2 / s d _ Thyroxine 29.7 3.4 13.6 Thiourea 30.6 2.5 10.0 Iodide 29.3 3.8 13.6 # Bromide 35.5 2.4 9.6 # Chloride 32.2 0.9 3.3 Adrenalin 34.4 1.3 5.2 # Johnson 1950 t Tabled at p .01 is 2.61 # Indicates s i g n i f i c a n t difference TABLE I I I t TEST OF SIGNIFICANT DIFFERENCE BETWEEN MEANS OF CONTROL FISH PECTORAL FIN LENGTH (2.96 mms) AND TREATED FISH Treatment Mean of Pectoral F in Length mms . Mean Difference t Calculated xl- x2/scT * Thyroxine 3.62 0.64 9.5 # Thiourea 3.04 0.05 0.7 Iodide 2.71 0.25 3.9 #, Bromide 3.45 0.50 -7.5 # Chloride 3.25 0.29 4.3 # Adrenalin 3.69 0.73 11.4 # & Johnson 1950 t Tabled at p.01 is 2.61 # Indicates s i g n i f i c a n t difference. TABLE IV FIDUCIAL LIMITS, AT t .01, ON EITHER SIDE OF THE MEAN OF CONTROL AND TREATED FISH Treatment Body Length mms Pectoral F i n Lensth mma S— Standard Error of Mean F i d u c i a l Limits msT t 3 _ X Upper and Lower Limits S^ Standard Error of Mean F i d u c i a l Limits m-~: t a _ X Upper and Lower Limits Controls 0.18 0.48 +33.58 -32.62 0.05 0.13 +3.09 -2.83 Thyroxine 0.17 0.45 +30.15 -29.25 0.05 0.13 +3.75 -3.49 Thiourea 0.16 0.42 +31.02 -30.18 0.06 0.16 +3.20 -2.88 Iodide 0.21 0.55 +29.85 -28.75 0.09 0.24 +2.95 -2.47 Bromide; 0.18 0.48 +35.98 -35.02 0.05 0.13 +3.59 -3.33 Chloride 0.21 0.55 +32.75 -31.65 0.05 0.13 + 3.38 -3.12 Adrenalin 0.18 0.48 +34.88 -33.92 0.08 0.21 + 3.90 -3.48 - 14 -1.40 I h-CD Z UJ _J _J < or O u UJ Q_ <D o _J 2 0 100 •080 THYROXINE ADRENALIN —(H THIOUREA ^ IODIDE BROMIDE CHLORIDE - ^ C O N T R O L -0-3.30 3.40 FIDUCIAL-LIMITS ABOUT THE MEAN CALCULATED AT "b.01 3. ,50 $£0 LOGe BODY L E N G T H Figure 9© F i d u c i a l l i m i t s , on eit h e r side of the mean,of body length and pectoral f i n length f o r control and treated f i s h . - 15 -Figure 10. Photograph i l l u s t r a t i n g the slov/er growth of body length and accelerated growth of pectoral f i n length i n thy-roxine f i s h (lower) as compared with control f i s h (upper). - 16 -Analysis of the means shows that f i s h developing i n bromine and adrenalin had an accelerated growth of both body and pectoral f i n length and those. developing i n Iodine a reduced one. A s l i g h t decrease i n body length with no s i g n i f i c a n t d i f -ference i n f i n length Is shown in thiourea treated f i s h . Both chloride and thyroxine groups had a decreased body length and an increased pectoral f i n length compared with the controls (tables I I I and IV and figure 9.). A s i g n i f i c a n t difference between the means of the body length and pectoral f i n length of chloride and thyroxine treated groups indicates that a de-celerated body growth and increased pectoral f i n growth were much more marked following the l a t t e r treatment (table V, figure 10.) C. THE THYROID GLAND Hi s t o l o g i c a l transverse and s a g i t a l sections containing thyroid f o l l i c l e s were examined from f i s h selected at random from each treatment group. A t y p i c a l section was chosen to i l l u s t r a t e the state of a c t i v i t y of the gland, i n each case. Observations were recorded in tabular form (table VI) and i n photographs (figures 11.-17.). Increased a c t i v i t y of the thyroid gland i s reflected by the presence of peripheral vacuoles (artefacts In themselves) and more basophilic and granular c o l l o i d r e s u l t i n g from enzymatic hydrolysis (De Robertis 1949). Applying these c r i t e r i a to the results obtained in the present experiment (table VII and figures 11.-17.) we f i n d that: a) Control f i a h have a moderately active gland reflected by a low - 17 -c u b o i d a l e p i t h e l i u m , s l i g h t l y b a s o p h i l i c and g r a n u l a r c o l l o i d and the presence of small p e r i p h e r a l v a c u o l e s . A small amount of c o l l o i d was found i n the lymph t i s s u e ( f i g u r e 11.). b) The f o l l i c l e s i n t h y r o x i n e f i s h ( f i g u r e 12.) are l a r g e and c o l l o i d Is markedly s t o r e d In them. Absence of p e r i p h e r a l v acuoles and abundance of c o l l o i d in the lymphatics suggests an overabundance of hormone which Is not b e i ng u t i l i z e d as f a s t as i t i s produced. The squamous or low c u b o i d a l e p i t h e l i u m f u r t h e r i n d i c a t e s i n a c t i v i t y . c) Thiourea t r e a t e d f i s h had h y p e r p l a s t i c , h y p e r t r o p h i e d f o l l i c l e s , the lumina of which were v e r y sma l l and almost completely devoid of c o l l o i d . The columnar f o l l i c u l a r e p i t h e l i u m f u r t h e r i n d i c a t e s s t i m u l a t i o n and i n h i b i t e d c o l l o i d p r o d u c t i o n ( f i g u r e 13.). d) A l l of the o t h e r treatments ( a d r e n a l i n and the h a l i d e s ) , p r o -duced on l y mfjJdly a c t i v e glands. The number of f o l l i c l e s and height of f o l l i c u l a r e p i t h e l i u m i n c r e a s e d i n c h l o r i d e t r e a t e d f i s h . A d r e n a l i n produced an enlargment of the f o l l i c l e s and abundance of s t o r e d e o s i n o p h i l i c c o l l o i d i n them. Many s m a l l p e r i p h e r a l vacu-o l e s i n d i c a t e m i l d a c t i v i t y ( f i g u r e s 14.-17.)• TABLE VII STATE OP ACTIVITY OP THE THYROID FOLLICLES IN CONTROL AND TREATED FISH Treatment Height of F o l l i c u l a r Epithelium i n Microns Approximate Size of Typical F o l l i c l e i n Microns Presence of Vacuoles Presence of Co l l o i d i n Lymphatics C o l l o i d Granular (G) or Clear (C) Co l l o i d Basophilic (B) Eosinophilic (E) Controls 4 30 F a i r l y Small # G S l i g h t l y E/B Thyr oxine 2 55 None ### G E ? Thiourea 14 13 None C • Iodide 4 20 Small # C ? E Bromide 5 35 Small # C E Chloride 8 25 Small # G S l i g h t l y ? Adrenalin 3 60 F a i r l y Small # C E ### Extensive # Slight Figure l l * Section showing thyroid f o l l i c l e s i n control f i s h , x 330 Figure 12, Section show-ing thyroid f o l l i c l e s i n thyroxine f i s h , x 200 Figure 13. Section showing thyroid Figure 14. Section show-f o l l i c l e s In thiourea f i s h , x 200 ing thyroid f o l l i c l e s i n iodide f i s h , x 200 - 20 -F i g u r e 15. S e c t i o n showing t h y r o i d f o l l i c l e s i n bromide f i s h , x 200 F i g u r e 16, S e c t i o n showing t h y r o i d f o l l i c l e s i n c h l o r i d e f i s h , x 200 F i g u r e 17. S e c t i o n showing t h y r o i d f o l l i c l e s i n a d r e n a l -i n f i s h , x 330 - 21 Do PIGMENTATION  Melanin St r i p s of skin,taken from preserved f i s h , were mounted on glass slides for microscopical examination. In each case the s t r i p was removed from an area below the dorsal f i n . The state of dispersal of the melanophores i s shown i n figures 18.-24. It should be noted (figure 18.) that melano-phores normally become more dispersed v e n t r a l l y away from the dorsal f i n . Parr marks in f i s h are produced by close aggregations of melanophores i n regularly arranged areas of the s k i n . After f i x a t i o n i n Bouin's f l u i d an overlaying mat of guanine crystals was washed off and revealed that parr marks were absent i n the thyroxine and adrenalin treated groups. In addition adrenalin caused an extreme concentration of pigment and a reduction i n the number of pigment c e l l s , so that l i v e f i s h appeared very pale, whilst thyroxine caused only s l i g h t concentration (figures 19. and 24.). Iodide produced an extreme expansion of pigment and bromide increased the number of melanophores so that bromide treated f i s h appeared very dark when a l i v e . L i t t l e difference was noted between the controls, chloride and thiourea treated f i s h . Guanine Several weeks a f t e r the commencement of hatching, a notably accelerated guanine deposition and covering of.the yolk sac by the body w a l l , was recorded In thyroxine treated f i s h . This became very pronounced 51 days from the commence-ment of hatching, when the photographs (figures 25.-27.) were - 22 -taken, A s l i g h t l y Increased guanine deposition in bromide and adrenalin treated f i s h was also noted (figure 25.) but this may be considered as only a manifestation of accelerated growth of the organism as a whole (tables I I and IV and figure 9,), A s l i g h t l y decreased guanine deposition was observed i n thiourea treated f i s h , but no differences were recorded with iodide and chloride treatments weBO compared with controls. - 2 3 P i g , 18 Con- P i g . 19 Thy-t r o l s : r e t i c u - r o x i n e : s t e l -l o - s t e l l a t e x50 l a t e x 50 P i g . 20 T h i o u r e a : r e t i c u l o - s t e l l a t e x 50 WW P i g , 21 i o d i d e : r e t i c u l a t e x 50 1 J IS • • • • « »• • •. » *•.» P i g . 22 Bromide: r e t i c u l o : s t e l l a t e x 50 i P i g , 23 C h l o r i d e : s t e l l a t e x 50 F i g , 24 A d r e n a l i n : punctate x 50 F i g u r e s 18.-24, Showing the d i s p e r s a l of dermal melanophores In c o n t r o l and t r e a t e d f i s h . Arrows p o i n t to p a r r marks. D e s c r i p t i o n s of d i s p e r s a l are based on a melanophore index by Slome and Hogben (1936). - 24 -CONTROL THIOUREA THYROXINE: (Note S i l v e r i n g ) IODIDE BROMIDE ADRENALIN Figure 25, Control and treated f i s h photo graphed 51 days a f t e r commence ment of hatching, x 1^ Figure 26. Control f i s h photographed 51 days aft e r commencement of hatching. Note that the yolk sac i a only p a r t i a l l y covered by body wall and that guanine deposit i s s l i g h t * x 2-| Figure 27. Thyroxine treated f i s h photo-graphed 51 days after commence-ment of hatching. Note that the yolk sac i s almost completely covered by the body wall and guanine deposition i s pronounced. - 26 -DISCUSSION THYROID GLAND Following studies with radioactive iodine, It is now believed that the thyroid hormone functions at c e l l u l a r l e v e l . C i r c u l a t i n g iodide Is removed from the blood and con-centrated in the thyroid c e l l s . Through enzymatic processes the iodine i s combined with protein to form several protein-iodide compounds, of which thyroxine i s believed to be the b i o l o g i c a l l y active component. The hormone i s passed into tiie blood stream and combines with a f r a c t i o n of the plasma protein. Gradually I t passes through the c a p i l l a r y walls into tissue spaces and thence bathes the c e l l s . The 'spent' hormone drains into the lymphatics and f i n a l l y undergoes enzymatic decomposi-t i o n . The iodine which is liberated can recombine i n the gland to produce fresh thyroid hormone. Stimulated thyroid f o l l i c l e s show a liquefaction of the f o l l i c u l a r c o l l o i d , granular inclusions, presence of vacuoles and basophilic staining properties. A gland whose f o l l i c l e s are f i l l e d with c l e a r , homogeneous, acidophilic c o l l o i d , lacking vacuoles, i s quiescent. Upon stimulation f o l l i c u -l a r c e l l s produce and release c o l l o i d Into the lumen. By a change In the absorptive and enzymatic processes of the c e l l , the c o l l o i d i s reabsorbed into the epithelium and released as thyroid hormone Into the blood and surrounding lymph. A control f i s h which i s producing adequate hormone for i t s normal life-processes would be expected to store any additional thyroid hormone which i t does not require. It Is not - 27 -su r p r i s i n g , therefore, that following immersion i n thyroxine, the thyroid f o l l i c l e s increase i n s i z e , have low, inactive epithelium and show marked storage of c o l l o i d . When thyroid hormone i s abundant, c o l l o i d i s evident i n the lymphatics. The mechanism of i n h i b i t i o n i n c o l l o i d formation by thiourea Is discussed above. Hypertrophy and hyperplasia of the f o l l i c u l a r c e l l s i s a compensatory mechanism on the part of an organism attempting to produce a hormone necessary for normal function. Recent studies have revealed a balance be-tween the concentrations of thyroid and thyreotrophic hormones. When thiourea i n h i b i t s the formation of the former hormone the p i t u i t a r y secretes a greater amount of the l a t t e r which, i n turn, activates the thyroid f o l l i c u l a r c e l l s and gives r i s e to the hyperplastic state. Similar thyroid i n h i b i t i o n to the one shown In figure 13. has been produced i n different vertebrate classes. Thus Adams et a l (1949) working with chick embryos, Gordon et a l (1945) with Rana plpiens larvae, Tinnacci (1948) with a selachian Mustelus l a e v l s , Lever et a l (1949) and Vivien et a l (1952) with Lebistes reticulatus» a l l found hypertrophy and hyperplasia of the gland following administration of goi-trogens. Oliverau (1950), however, treated both young and adults of two selachian species with antithyroid agents and found no changes i n the gland. The a c t i v i t y of the thyroid can also be changed by treatment with various halide s a l t s . Thus Oliverau (1950b) obtained an i n h i b i t i o n of the thyroid of Tinea tinea during the spring, a time of the gland's greatest a c t i v i t y , by - 28 -immersing the f i s h i n water of - A »85 s a l i n i t y , hut could not obtain s i m i l a r I n h i b i t i o n i n Cyprinus carpio and Ameiurus  nebulosus . Following injections of potassium iodide into salmon parr Hoar (1951) noted increased c o l l o i d storage and changed a c t i v i t y i n the gland, as w e l l as increased s i l v e r -ing and thus proved that t h i s s a l t increased the quantity of thyroid hormone produced. In the present experiment the halides had only s l i g h t effect on glandular a c t i v i t y and brought about no increased s i l v e r i n g . I t i s possible that growing alevins, before the commencement of feeding, do not have available any additional tyrosine, for combination with the abundant halides, to produce more hormone. On the other hand the osmotic gradient In the halide solutions was too s l i g h t to produce either the type of i n h i b i t i o n shown by Oliverau or act i v a t i o n shown by a group of French workers i n the eel thyroid (see discussion below). Increased size of the f o l l i c l e s and storage of hor-mone noted i n adrenalin treated f i s h i s due, perhaps^to an interference, by adrenalin, i n the u t i l i z a t i o n of thyroid hor-mone In the body. The effect may be through the p i t u i t a r y , which, i f activated by adrenalin, could secrete additional thyreo-trophic hormone. This, In turn, could stimulate thyroid into production, but need not increase i t s u t i l i z a t i o n . Lynn et al (1941) report that metamorphosis of the amphibian Amblystoma  tigrinum i s accelerated by the thyroid stimulating hormone of the p i t u i t a r y and even more accelerated by treatment with adrenalin, as w e l l . A cursory examination of the anterior p i t u i t a r y In control and adrenalin treated chum salmon revealed 29 -no obvious h i s t o l o g i c a l changes i n the g l a n d . GUANINE DEPOSITION Although mammalian t h y r o i d e x t r a c t and t h y r o x i n e w i l l i n c r e a s e the m e t a b o l i c r a t e i n the mammal as measured by oxygen consumption, (Donhoffer 1947), i t f a i l s to do so i n f i s h e s (Root and E t k i n 1940, Smith et a l 1943). I t has been demonstrated t h a t f i s h t h y r o i d has p h y s i o l o g i c a l a c t i v i t y s i n c e It can Induce p r e c o c i o u s metamorphosis i n t a d p o l e s . I t has a l s o been shown that oxygen consumption can be Increased w i t h d i n i t r o p h e n o l and decreased w i t h a d r e n a l i n i n j e c t i o n s i n f i s h e s (Smith and Mathews 1942). The same authors (1948) i n -creased s i g n i f i c a n t l y the oxygen consumption of Bathystoma by i n j e c t i n g t h y r o i d from the p a r r o t f i s h and thereby demon-s t r a t e d that a c a i o r i g e n i c e f f e c t In f i s h i s p o s s i b l e i f the t h y r o i d i s obtained from w i t h i n the c l a s s P i s c e s . Although the f u n c t i o n of t h y r o i d hormone In . metabolism of the c o l d blooded v e r t e b r a t e s i s s t i l l obscure, It s f u n c t i o n i n amphibian and, to a l e s s e r degree, In f i s h metamorphosis Is somewhat c l e a r e r . During metamorphosis a c t i v i t y of the gland i n tadpoles i s at i t s h e i g h t and the a d m i n i s t r a t i o n of hormone can a l s o b r i n g about pre c o c i o u s changes. Whether increased t h y r o i d a c t i v i t y i s concomitant w i t h metamorphosis i n a l l species of f i s h i s not yet c l e a r . Means (1948) b e l i e v e s that the a n a b o l i c and c a t a b o l l c a c t i o n of t h y r o x i n e i s slow, exerted over a long p e r i o d of time and t h a t : - 30 "the thyroid hormone should be considered as accelerating en-zymic a c t i v i t i e s of the c e l l i n a l l departments." One of these "accelerating a c t i v i t i e s " and indications of metamorphosis i n the Salmonoidea is the accelerated deposition of guanine which produces a s i l v e r y appearance in the f i s h . Chum salmon, following thyroxine treatment, show such s i l v e r i n g (figures 25. and 27.). That thyroxine increases guanine deposi-tion i n chum salmon was shown also i n a previous experiment (Dales 1951) when, following immersion of developing eggs In the hormone, a precocious s i l v e r i n g occured even before hatching in treated embryos, whilst the controls were completely devoid of guanine. Hoar (1951) found intense s i l v e r i n g In chum salmon alevins following thyroxine treatment and also some increased s i l v e r i n g i n coho f i n g e r l i n g s a f t e r treatment with thyroid ex-t r a c t , thyroxine and sodium Iodide. No increased s i l v e r i n g was noted i n the present experiment a f t e r treatment with the halides and adrenalin possibly because no additional hormone was being circulated In the ti s s u e s . Some diadromous f i s h become s i l v e r y at stages of t h e i r maturation, concomitant with an Increased a c t i v i t y of the' thyroid. Several species of P a c i f i c salmon become s i l v e r y smolt following the onset of downstream migration and at the same time their thyroids are activated (Hoar and B e l l 1950). In a s i m i l a r way Robertson (1948, 1949) and Landgrebe (1941) report s m o i t i f i c a t i o n in several species of Salmo following thyroid treatment. Hoar, however, reports that such treatment does not always produce marked changes in the A t l a n t i c salmon, Salmo sa l a r . On the - 31 -other hand a group of French workers, Including V i l t e r , (1946) correlated the Increased activity of the thyroid in the European eel with changes In environmental salinity and not with the appearance of a silvery coat. Since the purines are usually broken down to waste products, such as uric acid, i t Is possible that the mechanism of guanine deposition in the salmonoids f i t s the statement by Baldwin (1949): "Not a l l animals possess a l l of three enzymes necessary to carry out the complete series of changes, so that free adenine and guanine may appear in the excreta." Following immersion in thiourea Smith (1950) and Hoar (1951) found no decreased silvering in chum salmon alevins. Since thiourea inhibits formation of the thyroid hormone, the latter author concludes that silvering Is not brought about by the action of the thyroid hormone alone. On the other hand, Dales (1951), found in a previous experiment that chum salmon alevins which had been developing in thiourea became very markedly silvery after being transferred to thyroxine solution for several weeks. It is possible that guanine deposition is not stopped by thiourea because this goitrogen is unable to inhibit a l l of the hormone production at the non-toxic experi-mental doses commonly used. It would be of interest to find the effect,on guanine deposition, of administering one of the new synthetic antimetabolites of thyroxine. GROWTH AND BODY PROPORTIONS Several writers have attempted to explain changes in body proportions elicited by the thyroid hormone during - 32 -metamorphosis. In an e a r l y e x p l a n a t i o n Huxley (1929) b e l i e v e d that l a r v a l t i s s u e s , which are adapted to l i v e at a low meta-b o l i c r a t e , are a f f e c t e d a d v e r s e l y when the metabolic l e v e l Is r a i s e d (by t h y r o x i n e , f o r example), w h i l s t t i s s u e s charac-t e r i s t i c of the a d u l t are favoured by such changes. Since i t i s not proved that t h y r o x i n e i s able t o increase the oxygen consumption of f i s h , t h i s hypothesis i s not admissable. Another theory i s that the Increased m i t o t i c d i v i s i o n s i n organs used i n the t e r r e s t r i a l h a b i t a t , f o r example, the limbs, of a metamorphosing t a d p o l e , and a r e g r e s s i o n i n those nec-es s a r y f o r the a q u a t i c one, i s c o n t r o l l e d by the t h y r o i d hor-mone. More r e c e n t e x p l a n a t i o n s are based on t h e o r i e s of em-b r y o l o g i c a l d i f f e r e n t i a t i o n (Lynn et a l 1951). Thus responses of the v a r i o u s t i s s u e s depend on f a c t o r s inherent i n the t i s s u e s themselves and the m o r p h o l o g i c a l changes d u r i n g metamorphosis are determined by the r e a c t i n g t i s s u e s as w e l l as by the a c t i v a -t i n g substance i n d u c i n g these changes. I t i s p o s s i b l e that some organs have a g e n e t i c a l l y low t h r e s h o l d of s u s c e p t i b i l i t y to the t h y r o i d hormone, as are, f o r example, the limbs of a maturing tadpole or the p e c t o r a l f i n s of d e v e l o p i n g chum salmon. Perhaps the t h y r o i d hormone c o n t r o l s a sequence of events which c o n s t i t u t e the metamorphic p a t t e r n , so that an increased q u a n t i t y of hormone upsets t h i s sequence and produces d i s p r o p o r t i o n a t e growth i n the body p a r t s of a d e v e l o p i n g a l e v i n . C o n t r o v e r s i a l r e s u l t s of the e f f e c t of t h y r o i d gland products on growth i n f i s h e s have been r e p o r t e d . An adverse e f f e c t on growth of young brook t r o u t i s r e p o r t e d by Lynn et - 33 -a l ( 1 9 5 1 ) , a d e c r e a s e d g r o w t h o f i m m a t u r e P l a t y p o e c l l u s i s c i t e d by G r o b s t e i n and B e l l a m y ( 1939 ) and a d e c r e a s e d g r o w t h o f c o h o f l n g e r l i n g s i s r e p o r t e d b y S m i t h ( 1 9 5 0 ) , who t r e a t e d t h e s e f i s h w i t h t h y r o i d e x t r a c t and t h y r o x i n e . S m i t h e t a l (1943) n o t e d no d i f f e r e n c e i n t h e g r o w t h o f L e b l s t e s r e t i c u l a ' t u s g u p p i e s , w h i l s t H o p p e r ( 1952 ) w o r k i n g w i t h t h e same s p e c i e s f o u n d a n i n c r e a s e o f 40$ t o 90% i n g r o w t h o f f e m a l e s and 20% t o 50% i n m a l e s . T h e m a r k e d l y d e c r e a s e d g r o w t h r a t e o f t h y r o x i n e t r e a t e d chum s a l m o n may be due t o : a . t h e u p s e t g r o w t h p a t t e r n d i s c u s s e d a b o v e . b . t h e p r e c o c i o u s g r o w t h o f b o d y w a l l o v e r t h e y o l k s a c c . t h e i n c r e a s e d n u c l e o p r o t e i n c a t a b o l i s m m a n i -f e s t e d i n i n c r e a s e d g u a n i n e d e p o s i t i o n o r due t o a c o m b i n a t i o n o f t h e s e f a c t o r s . L a R o c h e ( 1950 ) and S m i t h (1950 ) r e p o r t d e c r e a s e d g r o w t h o f A t l a n t i c s a l m o n p a r r and c o h o s a l m o n f l n g e r l i n g s f o l l o w i n g i o d i d e t r e a t m e n t , r e s u l t s s i m i l a r t o t h o s e f o u n d i n t h e p r e s e n t e x p e r i m e n t . C h l o r i d e a l s o r e d u c e d b o d y l e n g t h , w h i l s t b r o m i d e and a d r e n a l i n i n c r e a s e d I t m a r k e d l y . I n c r e a s e d g r o w t h f o l l o w i n g b r o m i d e and a d r e n a l i n t r e a t m e n t was c o u p l e d w i t h g r e a t e r u t i l i z a t i o n o f t h e y o l k s a c f o o d r e s e r v e , i n d i c a t i n g t h a t t h e s e c h e m i c a l s s p e e d up f o o d c o n s u m p t i o n and f a v o u r g r o w t h . S i n c e a d r e n a l i n a l s o d e c r e a s e s t h e o x y g e n c o n s u m p t i o n i n f i s h ( d i s c u s s e d a b o v e ) , i t may h a v e b e n e f i c i a l e f f e c t s o n t i s s u e b u i l d i n g . B e c a u s e o f t h e a n t a g o -n i s t i c e f f e c t s o f t h e h a l i d e s o n g r o w t h r a t e and b e c a u s e an e x a m i n a t i o n o f t h e g i a n d s showed no i n c r e a s e d a c t i v i t y o f t h e t h y r o i d i t must be c o n c l u d e d t h a t t h e h a l i d e s and a d r e n a l i n do n o t h a v e • t h y r o x i n e - l i k e * a c t i o n on f i s h g r o w t h . - 34 -The i n h i b i t i o n of growth by thiourea may be due to a slower u t i l i z a t i o n of the y o l k sac food reserve (Hoar 1951), or due to t o x i c e f f e c t s of t h i s compound. Hopper (1952) found a decrease from 5% to 15% i n l e n g t h of Leblstes r e t l c u l a t u a t r e a t e d w i t h t h i o u r a c l l . S i m i l a r r e s u l t s are reported by Goldsmith et a l (1944) on other species of f i s h . An e x p l a n a t i o n f o r the r e s u l t i n g change i n body proportions f o l l o w i n g thyroxine treatment of chum salmon a l e v i n s should be looked f o r i n the t h e o r i e s of the metamorphic mechanism, discussed above. Grobstein and Bellamy (1939), noted a s i m i l a r decrease In body length and e l o n g a t i o n i n the f i n s of immature P l a t y p o e c l l u s f o l l o w i n g the feeding of dessicated mammalian t h y r o i d . The change i n body proportions r e s u l t i n g from c h l o r i d e treatment cannot, however, be the e f f e c t of Increased hormonal, ' t h y r o x i n e - l i k e ' a c t i o n . C h l o r i n a t i o n of the thyroxine mole-cule produces a hormone which, i n the mammal, has only one tenth of the a c t i v i t y of a s i m i l a r brominated compound and only one two hundredth of the a c t i v i t y of 1 thyroxine i t s e l f (Means 1948). N e i t h e r bromine nor iodine treatment produced d i s p r o p o r t i o n a t e growth, although these h a l i d e s are capable of producing hormones w i t h g r e a t e r b i o l o g i c a l a c t i v i t y than c h l o r i n e . Lynn et a l (1951) report that tadpole metamorphosis, which can be induced by i o d i d e , cannot be a c t i v a t e d by the sane q u a n t i t i e s of bromide. Thus, assuming that growth of the pec-t o r a l f i n can be l i k e n e d to that of a tadpole limb, responses which cannot be e l i c i t e d by bromide treatment are not l i k e l y to be produced by c h l o r i d e . The unchanged shape of the f i n - 35 -i n the c h l o r i d e group when compared w i t h t h e s t r i k i n g l y f a l c a t e f i n o f the t h y r o x i n e group of f i s h ( f i g u r e 10.) and the s i g n i f i -c a nt d i f f e r e n c e i n l e n g t h of t h i s appendage between these two e x p e r i m e n t a l groups f u r t h e r s u b s t a n t i a t e s the t h e o r y t h a t c h l o r i d e d i d n ot have a • t h y r o x i n - l i k e ' e f f e c t on growth o f body p a r t s I n d e v e l o p i n g chum salmon. MELANOPHORE DISPERSAL Melanophore pigment c o n t r o l Is v a r i a b l e i n the d i f f e r e n t v e r t e b r a t e c l a s s e s . In amphibia the c o n t r o l Is l a r g e l y hormonal and based on a q u a n t i t a t i v e r a t i o between two sub s t a n c e s B. and W. The f o r m e r , ( t h o u g h t t o be i n t e r m e d i n ) b r i n g s about an e x p a n s i o n and the l a t t e r a c o n t r a c t i o n of p i g -ment g r a n u l e s . On the b a s i s of s u r g i c a l e x p e r i m e n t s Hogben and W i n t o n (1922) have shown t h a t hormones B. and W. are p r o -duced by the p a r s i n t e r m e d i a and p a r s t u b e r a i i s r e s p e c t i v e l y . I n f i s h , on the o t h e r hand, melanophore c o n t r o l can be e i t h e r nervous o r hormonal o r b o t h . P a r k e r (1950) c l a s s i f i e s these i n t o the d i n e u r o n i c , mononeuronic and a - n e u r o n i c c a t e g o r i e s . T e l e o s t s a re almost u n i v e r s a l l y i n the d i n e u r o n i c and hormonal c l a s s . N e i l l (1940) d i f f e r e n t i a t e s hormonal c o n t r o l from nervous on the speed o f change i n pigment d i s p e r s a l , i n response to s t i m u l i and c o n c l u d e s t h a t the speedy c o n t r o l i n genus Salmo i s p r i m a r i l y n e r v o u s . R o b e r t s o n (1951) found t h a t a d r e n a l i n r a p i d l y c o n c e n t r a t e s dermal melanophores i n rainbow t r o u t and thus s u b s t a n t i a t e s the work o f N e i l l . Doses as low as one p a r t i n t e n m i l l i o n s were e f f e c t i v e i n c o n c e n t r a t i n g melanophore pigment i n Ameiurus and Fuhdulus ( P a r k e r 1950). A l t h o u g h 36 a d r e n a l i n produced maximal c o n c e n t r a t i o n i n chum salmon a l e v i n s , no such marked c o n c e n t r a t i o n was produced by t h y r o x i n e . Thyroxine d i d , however, prevent the formation of p a r r marks, an e f f e c t not produced by the h a l i d e s or t h i o u r e a . Hoar (1951) a l s o found that f o l l o w i n g t h y r o x i n e treatment, p a r r marks i n coho salmon f l n g e r l i n g s disappeared.. The i n a b i l i t y of the h a l i d e s i n the present experiment to prevent p a r r mark f o r m a t i o n i s another proof of t h e i r non. ' t h y r o x i n e - l i k e ' e f f e c t . Robertson (1951b) r e p o r t s t h a t a prompt c o n c e n t r a t i o n of dermal melanophores followed I n j e c t -i o n of t h y r o i d e x t r a c t but no such c o n c e n t r a t i o n was e l i c i t e d by i o d i d e or th y r o x i n e i n rainbow t r o u t . In the present ex-periment i o d i d e and bromide produced d i s p e r s a l of melanin i n pronounced and moderate degrees, r e s p e c t i v e l y . I t i s p o s s i -b l e that bromide i o n , which blocks impulses from the sensory to the motor neurones (see d i s c u s s i o n of heart r a t e below) a l s o b l o c k s impulses to the a d r e n e r g i c i n n e r v a t i o n and accentu-ates the e f f e c t o f the c h o l i n e r g i c one. No e x p l a n a t i o n i s apparent f o r the e f f e c t produced by i o d i d e . HEART RATE Thyroxine i n c r e a s e s the r a t e of p u l s a t i o n i n explanted c h i c k heart muscle p r o g r e s s i v e l y (Markowitz et a l 1932). No e f f e c t on the he a r t r a t e of de v e l o p i n g chum salmon, at the time of h a t c h i n g , was noted i n the present experiment. Two of the h a l i d e treatments, bromide and c h l o r i d e d i d , how-ever, s i g n i f i c a n t l y reduce the heart r a t e . Roche (1951) found that bromination of thyroxine reduced i t s c a r d i a c a c t i v i t y i n - 37 -the mammal by r e d u c i n g the degree of t a c h y c a r d i a i n the r a t . The bromine i o n has a g e n e r a l l y depressant e f f e c t on the c e n t r a l nervous system, depresses the motor i r r i t a b i l i -t y and r e f l e x a c t i v i t y , so t h a t the passage of impulses from sensory to motor c e l l s of the s p i n a l cord i s delayed or i n t e r -r u p t e d . I t was observed that bromine t r e a t e d f i s h , s e v e r a l months a f t e r h a t c h i n g , were g e n e r a l l y s l u g g i s h i n t h e i r move-ments, so that a slower heart r a t e may be due to the s e d a t i v e a c t i o n of t h i s h a l i d e . Sollmann (1948) r e p o r t s that s e d a t i v e doses of bromide reduce the h e a r t r a t e i n humans, i n d i r e c t l y . On the other hand, when a mammalian heart was perfused w i t h s a l t s i n which the bromide i o n had r e p l a c e d the c h l o r i d e , o n l y a s l i g h t e f f e c t on the heart r a t e was reported (Grollman 1951). Wo e x p l a n a t i o n can be g i v e n f o r the decreased h e a r t r a t e due to c h l o r i d e treatment. Apart from B r i n d l e y ' s (1935) work on Fundulus embryos, i t i s g e n e r a l l y found that a d r e n a l i n does not a l t e r the heart r a t e of t e l e o s t s . Jampolsky (1951) s t u d i e d the e f f e c t of a d r e n a l i n on sockeye salmon a l e v i n s and other species but found that i t d i d not a c c e l e r a t e the h e a r t , a r e s u l t s u b s t a n t i a t e d i n the present experiment. He thus concludes t h a t sympathetic i n n e r v a t i o n i n the t e l e o s t h e a r t i s absent. The d i f f e r i n g e f f e c t s on the heart r a t e of chum salmon embryos obtained w i t h t h y r o x i n e , a d r e n a l i n , t h i o u r e a and i o d i d e on the one hand, and c h l o r i d e and bromide on the other, adds f u r t h e r proof that the e f f e c t o f h a l i d e s i s not • t h y r o x i n - l i k e * In n a t u r e . CONCLUSION In c o n c l u s i o n i t may be s t a t e d t h a t t h y r o x i n - 38 -exerts s p e c i f i c effects on body proportions and nucleo-protein catabolism and that these effects cannot be duplicated by the halides or adrenalin. 39 SUMMARY Only bromide and chloride depress the heart rate s i g n i f i -cantly* The other treatments have no e f f e c t . A l l treatments a f f e c t growth rate either favourably or adversely. a. Bromide and adrenalin increase body length. b. Iodide and thiourea decrease body length. c. Thyroxine and chloride decrease body length and Increase pectoral f i n length. The change i n body parts produced by chloride i s discussed and concluded to be d i f f e r e n t from the one produced by thyroxine. a. Thiourea i n h i b i t s c o l l o i d formation and causes hypertrophy and hyperplasia of the thyroid f o l l i -cles • b. Thyroxine increases c o l l o i d storage in the f o l l i -cles and lymphatics. c. The other treatments affect the a c t i v i t y of the gland only s l i g h t l y . a. Adrenalin produced p a l l o r i n l i v e f i s h by con-centrating maximally the dermal melanophores. b. Iodide and bromide disperse melanin pigment. c. Thyroxine produces a disappearance of parr marks, but the same effect is not produced by the halides Only thyroxine increases guanine deposition and must, there fore, act in:'-the hydrolysis of the purine f r a c t i o n of the nucleoproteins. It i s concluded that the action of thyroxine Is s p e c i f i c and d i f f e r s from that of the halides and adrenalin In developing chum salmon. 40 -LITERATURE CITED Adams, A* E, and A. L. B u l l , The effects of antithyroid drugs on chick embryos, Anat, Rec. 104: 421-441, 1949 a Baldwin, E, "An introduction to comparative biochemistry". Cambridge U. Press, 1949. B r i n l e y , P. J . Evidence f o r sympathetic innervation of the teleost heart: with a note on a method of trans-planting the heart of Fundulua embryos. Phys. Zool. 8: 360-373, 1935. Dales, S. Some effacta of thyroxine and thiourea on early development of chum salmon, Oncorhynchua keta, Theaia i n Dept. Zool., University of B. C, 1951. De Robertis, E. Cytological and cytochemical bases of thyroid function. Ann. N.Y. Acad. S c i . 50: 317-335, 1949. Donhoffer, S. and J . Vonotzky. The effect of thyroxine on food intake and s e l e c t i o n . Amer. J . P h y s i o l , 150: 334-339, 1947. E t k i n , W. The phenomena of anuran metamorphosis I I I . The development of the thyroid gland, J . Morph. 59: 69-89, 1936, E t k i n , W. Growth of the thyroid gland of Rana piplens i n r e l a t i o n to metamorphoals. B i o l . B u l l . 59: 285-292, 1930. Pleiachmann, W. Comparative phyaiology of the thyroid hormone. Quart. Rev. B i o l . 22: 119-140, 1947. Goldamlth, E. D., P. N. N i g r e l l i , A. S. Gordon, H. A. Charipper and M. Gordon. Effect of thiourea upon f i s h devel-opment. Endocrinology 35: 132-133, 1944, Grollmam, A. "Pharmacology and therapeutics". Lea and Pebiger, Philadelphia, 1951. Gudernatsch, J. P. Feeding experiments on tadpoles. I . The influence of s p e c i f i c organs given as food on growth and d i f f e r e n t i a t i o n , A contribution to knowledge of organs with intern a l secretions* Arch. Entwmech. Org. 35: 457-501, 1913. Hoar, W. S» The thyroid gland of the A t l a n t i c aalmon. J . Morph. 65: 257-290, 1939. - 41 Hoar, W. S. and G. M. B e l l . The thyroid gland i n r e l a t i o n to the seaward migration of P a c i f i c salmon. Canad. J . Res. 28D: 126-136, 1950, Hoar, W. S . , V. S . Black and E. C. Black. Some aspects of the physiology of f i s h . Univ. Toronto B i o l . Ser. 59, Publ. Ont. P i s h . Res. Lab. 71: 1-51, 1951 Hoar, W. S« Thyroid function i n some anadromous and landlocked t e l e o s t a . Trans. Roy. Soc. Can. 46, aer. 3: 39-53, 1952. Hogben, L. and F. R.. Winton. Hypoplasia and amphibian colour change. Proc. Roy. Soc. Long. B 93: 318-329, 1922. Hopper, A. P. Growth and maturation reaponse of Leblatea r e t i c u l a t u s to treatment with mammalian thyroid pow-der and t h i o u r a c i l . J . Exp. Zool. 119: 205-220, 1952. Huxley, J . So Thyroid and temperature i n cold blooded verte-brates. Nature, Lond., 123:712, 1929. Jampolaky, M. The autonomic control of the teleoat heart. Theaia i n Dept. Zool., University of B. C , 1951. Johnaon, L. P.. V. "An introduction to applied biometrics". Burgeaa Publ. Co., Minneapolia, U.S.A*, 1950. Landgrebe, P. W. The role of the p i t u i t a r y and the thyroid i n the development of teleosta. J . Exp. B i o l . 18: 162-169, 1941. LaRoche, G«, C. P. Leblond and G. Prefontaine. •Effects of thyroid hormone on the A t l a n t i c salmon parr atage. Rev. can. b i o l . 9: 101-103, 1950, Lever,. J . , J . Miltenburg and G. J. Van Oordt. Effect of a short treatment with thiourea on the f l a h thyroid gland. Proc. Koninkl. Nederland. Akad. Wetenachap. 52: 296-300, 1949. Lynn, W. G. and H. E. Wachowaki. The thyroid gland and i t a func-t i o n in cold-blooded vertebratea. Quart. Rev. B i o l . 26: 123-168. 1951. Markowitz, C. and W. M. Yater. Reaponae of explanted cardiac muacle to thyroxine. Amer. J . Phyaiol. 100: 162-166, 1932. Means, J. H. "The function of the thyroid gland". Amer. Lecture Series #40, S p r i n g f i e l d , 111., U.S.A., 1948. 42 -N e i l l , R. M. Colour change In young fiahea. Colour change In Anguilla J• Exp. B i o l . 17: 74-94, 1940. Oliverau, M. Influence of Increase i n s a l i n i t y on the a c t i v i t y of thyroida of varioua freah water teleoateana. Compt. Rend. Soc. B i o l . 144: 775-776, 1950. Oliverau, M. (b) Action de divers antlthyroidiena sur l a glande thyroide des Selaciens Scylllum a t e l l a r e (Plem.) et Scyllium canlcula, L. Compt. Rend. Soc. B i o l . 144: 832-834, 1950. Parker, G„ H. "Chemical control of nervoua a c t i v i t y " . In 'The Hormones', ed. Pincus and Thimann. Academic Press, N. Y., 1950* Robertson, 0. H. The occurence of increased a c t i v i t y of the thyroid i n rainbow trout at the time of transformation from parr to s i l v e r y smolt. P h y s i o l . Zool. 21: 282-295, 1948. Robertson, 0. H. Production of the s i l v e r y smolt stage i n r a i n -bow trout by Intramuscular Injection of mammalian thyroid extract and thyrotropic hormone. J . Exper. Zool. 110: 337-355, 1949. Robertson, 0. H. Factors influencing the state of dispersion of the dermal melanophores in rainbow trout. Physio-l o g i c a l Zool. 24: 309-325, 1951. Robertson, 0. H. (b) A atudy of the melanophore concentrating effect of mammalian thyroid extract i n rainbow trout. Endocrinology 48: 658-668, 1951. Roche, J., G. H. Delatour and R. Michel. Recherches sur l ' a c t i o n comparee de l a thyroglobuline et de proteines a r t i f i c e l l e m e n t iodees et bromees aur le rhythme cardiaque du r a t . Ann. Endocrinol. I I : 321-328, 1950. Root, R. W. and W. E t k i n . Effect of thyroxine on oxygen consump-ti o n of the toadflsh. Pro. Soc. Exp. B i o l . 37: 174-175, 1940. S a l t e r , W. T. Chemistry and physiology of thyroid hormone. In 'The Hormonea', ed. Pincua and Thimann. Academic Press, N. Y., 1950. Smith, S. B. Effects of thyroxine and related compounds on young salmon and trout. Thesis i n Dept. Zool., University of B. C , 1950. - 43 -Smith, D* C, and S, A, Matthews. The ef f e c t of adrenalin on the oxygen consumption of the f i s h G l r e l l a  n igricans. Amer. J. Phys. 137: 533-538, 1942. Smith, D. C. and G. M. Everett. The effect of thyroid hormone on the growth rate, time of sexual, d i f f e r e n t i a t i o n and oxygen consumption on the f i s h , Labiates  r e t i c u l a t u a . J. Exp. Zool. 94: 229-240, 1943. Smith, D.C. and S. A. Matthews. Parrot f i s h thyroid extract and i t s effect upon oxygen consumption i n the f i s h , Bathystoma. Amer. J . Phys., 155: 215-221, 1948. Sollmann, T. "A manual of pharmacology". W. B. Saunders, Philadelphia and London, 1948. Ti n a c c i , P. The action of some antithyroid substances ( t h i o u r a c i l methylthiouracil and aminothiozol) on Mustelus laevis Publ, Staz. Napoli 21: 124-131, 1948. A Cited by abstract. V-ilter, V. Action of thyroxine on the metamorphosis of eel larvae Compt, Rend. Soc. B i o l , 140: 783-785, 1946. Vi v i e n , J. and M. L. Guser. Action of prolonged treatment with thiourea on the structure and function of the thyroid and p i t u i t a r y of Leblstes r e t i c u l a t u s . Compt. Rend. 234: 1643-1645, iVW, 

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