de VLAMING: CONTROL OF REPRODUCTION IN GILLICHTHYS 



S 4 



a_ 



_B_ 



3_ 



_s_ 



_B- 



H R 



N' I5L 8L ISL 8L I5L BL 

 27° 20° 13° 



15 Feb'uory 2'' feb 



Figure 6.— EflFect of 27°, 20°, and 13°C treatments at 

 short (8L/16D) and long (15L/9D) photoperiods on 

 testicular histology in Gillichthys mirabilis. I.C. refers 

 to initial controls (15 January) and N, to sample from 

 natural population. Each box represents the testicular 

 condition of one fish. 



Testicular weights in the 20°C groups re- 

 mained at approximately the initial level. Both 

 groups at 20°C had significantly heavier 

 (P < 0.01) testes than those of the 27°C groups. 

 The testes of all fish at 20°C advanced to Stages 

 3 or 4 by 24 February, and there was no clear 

 photoperiod eflfect. Testicular weights of the 

 13°C groups did not diflfer significantly from the 

 initial January controls but were significantly 

 greater than those of the 20 °C group at a short 

 photoperiod (P < 0.05) and those of the 27°C 

 groups (P < 0.01). Spermatogenic condition 

 of the testes in the 13°C groups was essentially 



the same as in the January controls and Febru- 

 ary sample from nature (Figure 6). 



The results of this experiment indicate that 

 spermatogenesis is maintained at 13°C and 20°C 

 (independent of photoperiod) but that this pro- 

 cess may occur at a slower rate at 20°C than at 

 13°C. This difference in effect of these two tem- 

 peratures must be accepted with some reserva- 

 tion because the variability of gonadal develop- 

 ment in the initial controls could introduce a 

 degree of bias into the results. Regardless of 

 photoperiod, testicular regression occurred at 

 27°C. 



EFFECTS OF HIGH TEMPERATURES ON 



GONADAL FUNCTION IN 



DIFFERENT SEASONS 



Experiments using high temperatures were 

 initiated at different times during the year to 

 determine whether there is a seasonal variation 

 in gonadal susceptibility to such treatment. The 

 conditions employed and results obtained in these 

 experiments are summarized in Table 3. 



Experiments I and II indicate that 24°C is a 

 sufl^ciently high temperature to initiate testic- 

 ular regression within a relatively short period. 

 With either a long (15L/9D) or a short 

 (8L/16D) photoperiod (Experiment III), 25°C 

 stimulates the completion of testicular regres- 

 sion within 21 days; testes of these fish were in 

 the quiescent phase ( Stage 1 ) . A temperature 



Table 3. — EflFect of various high temperature and photoperiod treatments on testicular weight in Gillichthys mirabilis. 



•Significantly less {P < 0.05) than initial controls. 

 "•Significantly less {P < 0.01) than initial controls. 



1143 



