HAYDOCK : GONAD MATURATION OF GULF CROAKER 



no response to 0.1 and 0.5 mg salmon pituitary, 

 5 mg carp pituitary, 50 lU HCG, 20 lU oxy- 

 tocin, and 5 mg DOCA. On the other hand, 1 

 to 5 mg salmon, 10 mg carp, and 100 lU HCG, 

 gave uniformly positive results, all fish showing 

 weight gains of 5 to 13 %. Variable results 

 were observed with 50 and 100 lU PMS. Al- 

 though most PMS fish which were weighed 

 showed some gain in weight, this was in general 

 less than that observed with carp, salmon, and 

 HCG. In fact, it was noted that two fish in- 

 jected with 100 lU PMS spawned freely without 

 ever appearing grossly bloated, a characteristic 

 of all fish which were spawned with other prep- 

 arations. 



The time scale of weight gain. — A comparison 

 was made of the weight gained by fish given 

 one injection of 5 mg salmon, 10 mg carp, and 

 50 III PMS (Table 8). The time span of hy- 

 dration was arbitrarily divided into the weight 

 gained between 7 and 23 hr post-injection and 

 the total weight gained, including that added 

 between 23 and 30 hr. At 30 hr ovulated eggs, 

 if present, were stripped from the fish. Gen- 

 erally, all fish lost weight in the first 7 hr, pro- 

 bably because of handling and lack of feeding 

 during the experiment. The weight gains are 

 due mostly to water uptake and movement of 

 water into the gonad. 



Table 8. — Effects of hormones on time-course of weight 

 gain. 



fleets some fundamental difference in the way 

 these preparations afl!"ect the physiological mech- 

 anism causing hydration. The time-course of 

 hydration (Table 8) may be important in de- 

 termining the condition of eggs at ovulation 

 (Table 7). It should be noted that among the 

 three groups tested for the time-course of hy- 

 dration, viable eggs were obtained only from 

 the PMS-injected fish (Table 7) ; unfortunately, 

 there is no comparable data on the time-course 

 of weight gain in fish given 1 mg salmon, which 

 also produces viable eggs. 



Factors Affecting Hydration 



GSI. — It is apparent from Table 7 that the 

 gonad must be close to 5 % of the body weight 

 to respond to an otherwise adequate dose of 

 hormone. Although GSI could not be measured 

 prior to injection, almost all fish which failed to 

 respond had final GSI's below 5 %. Table 9 

 presents further confirmation of this. These 

 fish, injected with 1 mg salmon, came from a 

 stock which had shown a general decline in GSI, 

 because of being kept on a long photoperiod for 

 an extended time. Of four injected fish, three 

 hydrated and one of these subsequently spawned. 

 The fish that neither hydrated nor spawned had 

 a final GSI of just under 3 %. Only 1 of 11 un- 

 infected fish from this same stock showed a GSI 

 above 5 %, while 3 more were above 4 %. 



Table 9. — GSI of Bairdiella icistia measured on 26-VI-70. 



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