FISHERY BULLETIN: VOL. 70, NO. 4 



of 25 °C does not, however, block mitotic prolif- 

 eration of spermatogonia. 



Experiment IV (Table 3) indicates that 27°C 

 blocks the initiation of testicular recrudescence. 

 Testicular regression is initiated within 14 days 

 at 27°C (Experiment V); the testes of all fish 

 were in the regression phase (Stage 0). More- 

 over, Experiment VI suggests that testicular re- 

 gression is initiated within 8 days at 27°C; the 

 testes of all fish were regressing (Stage 0) . 



When initial controls are undergoing testicu- 

 lar regression, 28°C stimulates a more rapid 

 completion of regression than does 24°C (Ex- 

 periment VII). This is evident since the testes 

 of a majority of the fish at 28°C were in the 

 quiescent phase (Stage 1) whereas those of the 

 24 °C group were in Stage 0. A 30°C tempera- 

 ture (Experiment VIII) causes a more complete 

 testicular regression than does a 24°C tempera- 

 ture (i.e., testicular weights of the 30°C group 

 were significantly lower (P < 0.01) than those 

 of the 27 °C group). Both of these treatments 

 caused the completion of testicular regression 

 within 21 days; the testes of a majority of fish 

 in both groups were in the quiescent phase 

 (Stage 1). Similarly, 32°C stimulates a more 

 rapid and more complete testicular regression 

 than 28°C (Experiment IX) ; testicular weights 

 after 8 days were significantly lower (P < 0.01) 

 in the 32°C group than those of the 28°C group. 

 Testes of all fish at both temperatures were re- 

 gressing (Stage 0). After 14 days at 28°C, 

 testicular weights were still significantly higher 

 (P < 0.05) than testicular weights after 8 days 

 at 32°C (Experiment IX). 



With the exception of the experiments in 

 which the initial controls were fish with regres- 

 sing gonads, all high temperature treatments 

 summarized in Table 3 caused a significant de- 

 crease in testicular weights. These data indicate 

 that the rate of testicular regression and the 

 degree of testicular regression are temperature 

 dependent. These data also indicate that under 

 laboratory conditions testicular involution is in- 

 itiated relatively soon after exposure to high 

 temperatures and that regression can be com- 

 pleted rapidly in this species. 



Experiments similar to those discussed above 

 were conducted with female Gillichthys (Table 



4). Beginning with fish in active vitellogenesis 

 (Stage III), 25°C initiates ovarian regression 

 (Stage I) within 21 days, independent of photo- 

 period (Experiment 1). Ovarian weights in the 

 two photoperiod groups were not significantly 

 different. Beginning with fish having regres- 

 sing ovaries (Experiment 2), 27°C caused the 

 completion of ovarian risgression. Experiment 

 3 suggests that ovarian regression is complete 

 within 21 days at 30°C; the ovaries of a majority 

 of the initial controls were in phases of active 

 vitellogenesis (Stage III), whereas following 

 treatment, the ovaries of all fish were in the 

 quiescent phase (Stage II). 



Experiment 4 (Table 4) indicates that 32°C 

 stimulates a more rapid rate of ovarian regres- 

 sion than does 28°C; ovarian weights of the 32° 

 and 28°C groups were significantly difl^erent 

 (P < 0.01) after 8 days of treatment. Ovarian 

 regression was occurring in all fish. After 14 

 days at 28°C, further ovarian regression oc- 

 curred, but involution had still not been com- 

 pleted. 



Therefore, temperatures between 25° and 

 32°C initiate ovarian regression within a rel- 

 atively short time; all high temperature treat- 

 ments caused a significant decrease in ovarian 

 weights. Apparently the completion of ovarian 

 regression is temperature dependent, 



EFFECTS OF 21°-22°C AND PHOTOPERIOD 

 TREATMENT ON GONADAL FUNCTION 



The previous experiments suggest that gonad- 

 al regression occurs at 24°C but not at 20°C. To 

 define more precisely the thermal threshold for 

 gonadal involution, the efl^ects of 21°-22°C treat- 

 ments were examined in April, May, September, 

 and November. The conditions employed and 

 results obtained in these experiments are sum- 

 marized in Table 5. 



Beginning in April with fish in active sperm- 

 atogenesis or in the prespawning condition 

 (Stage 3 or 4), there was no change in testes 

 after 17-day treatment at 22°C (15L/9D) . How- 

 ever, after 30-day treatment at 22°C and a short 

 photoperiod (10L/14D), there was a significant 

 decrease (P < 0.01) in both ovarian and testic- 

 ular weights (Experiment 11 — Table 5) . Testes 



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