FISHERY BULLETIN: VOL. 69, NO. I 



Hormone dosage. — In general, there appears 

 to be a threshold response to dosage. Fish with 

 high GSI values and between 50- and 100-g body 

 weight hydrated after one injection of 10 mg 

 carp but not 5 mg (Table 7) . With salmon, 1 to 

 5 mg were adequate doses for 50- to 350-g fish 

 while 0.1 and 0.5 mg were inadequate except in 

 one case. In the case of HCG, 100 lU caused 

 hydration while 50 lU did not except in a single 

 case. Note, however, the low GSI value meas- 

 ured for three of the fish given 50 lU HCG. 



It must be noted that the highest dosages used 

 were adequate for hydration but inhibited 

 spawning (see section following on ovulation). 

 This was true for 10 mg carp, 5 mg salmon and, 

 especially, 100 lU HCG where the fish continued 

 to gain weight and eventually died in the tank 

 without ovulating a single egg. These results 

 would suggest that it is important to determine 

 the lowest possible dosage which will consistently 

 bring about hydration. 



Temperahire. — A temperature threshold un- 

 derlies the entire spawning process. Between 

 14° and 17° C the fish did not hydrate in re- 

 sponse to an otherwise adequate dosage of 1 mg 

 salmon pituitary. Two days later these same 

 fish spawned within 30 hr when given a second 

 1-mg-salmon injection 24 hr after being trans- 

 ferred to 22° C water. 



OVULATION 



Ovulation and Hydration as Separate Events 



Some early results with 100-IU-PMS and 100- 

 lU-HCG injections led to speculation that the two 

 hormones were acting on different physiological 

 processes. PMS brought about ovulation with- 

 out gross hydration while HCG hydrated fish 

 to the point of death without ovulation (Table 

 7). This result was not confirmed with 50-IU 

 doses, but, in general, the impression gained was 

 that PMS produced high quality eggs with less 

 hydration than either HCG or salmon pituitary. 



In sharp contrast to the PMS results, HCG 

 caused uniform hydration but, with one excep- 

 tion, failed to bring about ovulation. In a pre- 

 liminary test, it was found that oxytocin (20 lU) 



or salmon (1 mg) caused some eggs to be ovu- 

 lated when the injection was given 24 hr after 

 the fish were injected with HCG. Oxytocin and 

 salmon pituitary had the same effect on carp- 

 injected fish which otherwise did not ovulate. 



Ovulation without apparent hydration was 

 also achieved by using multiple, subthreshold 

 doses of 0.1 and 0.5 mg salmon pituitary, but the 

 time of ovulation could not be accurately pre- 

 dicted, and therefore the eggs obtained usually 

 were not viable. (The importance of obtaining 

 eggs just at ovulation is discussed in the section 

 on fertilization.) 



In summary, carp pituitary, HCG, DOCA, and 

 oxytocin were uniformly inadequate for bring- 

 ing on ovulation except in the case of one fish 

 treated with HCG. Both carp- and HCG-in- 

 jected fish hydrated, some becoming grossly 

 distorted. On the other hand, salmon pituitary 

 and PMS regularly brought about ovulation. 

 Dosage appeared to be critical in the case of 

 salmon pituitary, as nonviable eggs resulted 

 from injections of 5 mg and no spawn could 

 be obtained with a single dose of 0.1 and 0.5 mg. 

 A 1-mg-salmon dosage seems to be optimal for 

 fish of 50- to 100-g total weight. Both 50- and 

 100-IU dosages of PMS gave good results with 

 remarkably clear eggs obtained from all fish. 

 In one case, a 50-IU dose of HCG was adequate 

 for spawning, but 100 lU appeared to be inhib- 

 itory to ovulation. 



The Time Scale of Ovulation 



The combined results from 28 fish which pro- 

 duced viable eggs following injection with a 

 single dose of salmon (1-3 mg) showed that the 

 average time elapsed from injection to spawning 

 was 30.4 hr, with a standard deviation of 3.3 hr 

 and a range of 24.5 to 35.5 hr (Fig. 3). This 

 30-hr latent period following injection gener- 

 ally held regardless of the type of hormone used, 

 its dosage, or the time of day the injection was 

 made. In the case of a few large fish (100 to 

 300 g) given 1 mg salmon, a second 1-mg in- 

 jection was given 24 hr later, but this did not 

 affect the time of spawning. Five fish given 5 

 mg salmon spawTied 28 hr after injection, but 

 their eggs were not viable. In one experiment. 



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