de VLAMING: CONTROL OF REPRODUCTION IN GILLICHTHYS 



sing (Stages and I) . Following 80-day treat- 

 ment at 16°C, ovarian and testicular weights 

 were significantly greater (F < 0.01) than those 

 of the initial controls. Testes of the experimen- 

 tal fish were in Stage 3 or 5. Ovaries of fish in 

 the 16°C group were in Stage II or III. 



The results of these experiments indicate that 

 spermatogenesis and vitellogenesis are main- 

 tained at 16° C. In fish with regressing gonads 

 (collected in July), 16°C treatment initiates 

 spermatogenesis and oogenesis. 



EFFECTS OF LONG PHOTOPERIOD 



TREATMENT (15°C) ON FISH WITH 



REGRESSING TESTES 



In July 1969 an experiment was initiated to 

 determine whether a long photoperiod could 

 block recrudescence at an "intermediate" tem- 

 perature. All of the initial controls were under- 

 going testicular regression (Stage 0); the mean 

 (±: SE) testicular weight (mg) in this sample 

 was 32.3 it 2.2. Fish were exposed to 15°C for 

 30 days at a 15L/9D photoperiod. At the ter- 

 mination of the experiment a sample of fish was 

 taken from nature; the mean testicular weight 

 (± SE) in this group was 20.7 ± 3.2, and the 

 testes of these fish were regressing (Stage 0). 

 Testicular weights (x ± SE = 58.3 ± 7.3) of 

 the 15°C group were significantly greater 

 (P < 0.01) than those of the initial July controls 

 and the September sample from nature. The 

 testes of nine fish in the 15°C group were in 

 Stage 3, and those of three were in Stage 4. 

 These data suggest that 15°C treatment initiates 

 testicular recrudescence, even when the photo- 

 period is long. 



Table 6.— Effect of 16°C treatment (12L/12D) on 

 testicular and ovarian weight in Gillichthys mirahilis. 



EFFECTS OF 12° AND 20°C TREATMENT 



ON FISH IN STAGES OF 



ACTIVE GAMETOGENESIS 



Data presented above suggest that gameto- 

 genesis may be maintained more efl^ectively at 

 13°C than at 20°C. Beginning in March 1968, 

 fish were exposied to 20° and 12°C for 21 days to 

 examine this possibility (Table 7). The ovaries 

 of the initial March controls were in phases of 

 active vitellogenesis (Stage III) or the pre- 

 spawning or postspawning condition (Stage IV 

 or V) ; the testes of this group were in Stage 3. 



Table 7.— Effect of 21-day 12° and 20°C treatments on 

 ovarian and testicular weights in Gillichthys mirabilis. 



**Significantly greater [P < O.Ol) than initial controls. 



*Significantly greater (P < 0.05) fhan initial controls. 



Ovarian weights in the two experimental 

 groups did not differ significantly from those 

 of the initial March controls, but they were sig- 

 nificantly less (P < 0.01) than ovarian weights 

 of the sample taken from nature at the time of 

 sacrifice (April). Ovaries of the 20° and 12°C 

 groups were in Stage III or IV; the ovaries of 

 a majority of the April sample from nature were 

 in Stage IV. 



Testicular weights in the 20°C group were 

 not significantly altered by treatment, but those 

 of the 12°C group were significantly greater 

 (P < 0.05) than the testicular weights of the 

 initial March controls. The testes of fish in the 

 12°C group were in Stage 3 or 4; however, the 

 testes of four of seven fish at 20°C were in Stage 

 2 and the remainder in Stage 3. 



These data indicate that at a 12L/12D photo- 

 period, vitellogenesis and spermatogenesis will 

 occur at both 12° and 20°C but that the lower 

 temperature is more eff'ective. Neither of these 

 treatments, however, was as effective in promot- 

 ing vitellogenesis as the factors acting on the 

 natural population. 



1147 



