FISHERY BULLETIN: VOL. 73, NO. 2 



Table 2.— Effects of hormones on Pseudopleuronectes americanus. Temperature range 3°-5°C {i 3.2°C). Photoperiod 9L/15D. Symbols 



( + = Did, = Did not hydrate or ovulate). 



'Gonadosomatic index. 



^Human chorionic gonadotropin. 



3Plug formed, fish became grossly bloated and died, eggs were water hardened in ovaries. 



mullet, Mugil cephalus, while attempting induced 

 spawning. 



The findings at the conclusion of the second 

 series of experiments indicated that the injection 

 of HCG, although more effective at the lower 

 water temperatures, resulted in poor egg quality 

 and egg survival, the formation of membranous 

 plugs, and gross hydration causing death. 



Oxytocin at all three dosage levels tested had 

 little effect when water temperatures were above 

 5°C. Three fish hydrated but none ovulated or 

 contained matured eggs (Table 3). 



DOCA administered at the lower dosage levels 

 of 5 and 10 mg/454 g fish and at water tempera- 

 tures above 5°C, resulted in several fish hydrating 

 but none ovulating. At the higher dosage level of 

 20 mg/454 g fish, two test fish hydrated, and 

 although their GSI levels were high, no ovulation 

 occurred and no mature eggs were present in their 

 ovaries. 



PMSG at the three dosage levels of 55, 110, and 

 220 IU/454 g fish showed low activity when ad- 

 ministered at water temperatures above 5°C. 

 Although some fish had hydrated, none ovulated 

 and GSI levels were low in all of the test groups. 



HCG was ineffective at the dosage levels of 100 

 and 200 lU. Dosage levels of 400 lU resulted in 

 three fish hydrating at low GSI levels. Another fish 

 ovulated and was stripped 3 days after the last 

 injection. Egg fertilization was high and 

 approximately 80% of the eggs hatched. The larvae 



obtained from this induced spawning appeared to 

 be normal in all respects and several were reared 

 through metamorphosis. 



The data gleaned from this trial at water 

 temperatures in the 6°-7.5°C range substantiated 

 results derived from earlier experiments, sug- 

 gesting that water temperatures above 6°C 

 inhibit maturation of winter flounder, and for the 

 most part hormones are ineffective. The manner 

 in which hormones exert their effects on fish is 

 poorly understood, and dosage levels are probably 

 meaningless as the largest fish may not neces- 

 sarily be the most sexually mature and may differ 

 in receptibility to hormone injections. 



Haydock (1971) has observed a temperature 

 threshold of 17°C below which the gulf croaker, 

 Bairdiella icistia, would not hydrate or ovulate. It 

 is very probable that a similar temperature 

 threshold exists for winter flounder above 6°C. 

 Observations in the past at our laboratory have 

 noted that gravid female flounder perished in 

 water temperatures of 10°C, and ova from these 

 fish were stunted and misshapen. Male flounder 

 held under the same conditions suffered no ap- 

 parent ill effects. 



In the lower temperature range tested (range 

 3°-5°C, mean 3.2°C), oxytocin produced slightly 

 better results (Table 4). Three fish hydrated but 

 none ovulated nor contained mature eggs. GSI 

 levels were higher at the lower temperatures at all 

 dosage levels tested. No abnormal hydration was 



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