FISHERY BULLETIN: VOL. 70, NO. 4 - 



lower (P < 0.01) than those of the initial No- 

 vember controls. 



In spring spermatogenesis occurs at 22°C only 

 if the photoperiod is long and in autumn only if 

 the photoperiod is short. This temperature 

 causes ovarian regression regardless of photo- 

 period, suggesting that females may be more 

 sensitive to temperature than males. Similarly, 

 21°C will promote the initiation of testicular and 

 ovarian recrudescence only if photoperiod is 

 short. Apparently then, the effects of photoperi- 

 od at these temperatures are seasonally variable. 



EFFECTS OF PHOTOPERIOD AT 20oC ON 



FISH WITH REGRESSING OR 



QUIESCENT GONADS 



Experiments reported above showed that go- 

 nadal recrudescence will not occur at 20°C if 

 treatment is initiated in July but that gameto- 

 genesis is maintained at this temperature at 

 other times during the year. Thus, the influence 

 of 36-day 20°C treatment at various photope- 

 riods on gonadal recrudescence was examined in 

 August 1968 (Figure 7). The gonads of the 

 initial August controls were in Stages and 1. 

 Neither testicular nor ovarian weights in any 

 of the experimental groups varied significantly 

 from gonadal weights in the initial August con- 

 trols, and there were no significant differences 

 in gonadal weights among the experimental 

 groups. Differences in gonadal histology were, 

 nonetheless, evident. Testes of all fish collected 

 from nature in August and September were in 

 the regression phase (Stage 0). In all photo- 

 period groups testicular regression was com- 

 plete, and spermatogonial proliferation (Stage 

 2) or spermatogenesis (Stage 3) was occurring. 

 The testes of 4 of 10 fish at a 15L/9D photo- 

 period, however, were in the quiescent phase 

 (Stage 1). A majority of ovaries from fish col- 

 lected from nature in August and September 

 were in the quiescent phase (Stage II) . In each 

 experimental group, the ovaries of some fish 

 were in the early phases of vitellogenesis (Stage 

 III); with the exception of one fish, vitellogen- 

 esis was initiated in all females at 15L/9D. 



These results indicate that gonadal recrudes- 

 cence is initiated at 20°C if treatment is begun 





30 



20 



it) 



.J« 



J<8) 



(8) 



^Jrt 



(Id) rti 



w 



l&l 200 « 



Initial 

 Controls 

 (15 August) 



Nature 8L/I6D I2L/I2D I5L/9D 

 Sorriple 



21 September 



Figure 7.— Effect of 36-day 20 °C treatment at various 

 photoperiods on ovarian and testicular weight in Gil- 

 lichthys mirabilis. Shaded histograms illustrate mean 

 ovarian weights ; open histograms illustrate mean testic- 

 ular weights; the means are bracketed by one standard 

 error. Photoperiod treatments are given below the his- 

 tograms. Sample sizes are indicated atop each histo- 

 gram. 



in August. Recrudescence was initiated after 

 36 days in all photoperiod groups, but a long 

 photoperiod (15L/9D) was most eflfective in 

 females and least effective in males. 



EFFECTS OF 16° C TREATMENT 

 ON GONADAL FUNCTION 



Gonadal recrudescence does not normally oc- 

 cur if Gillichthys is exposed to 20°C in July. To 

 examine whether recrudescence could be initi- 

 ated in July at a slightly lower temperature, the 

 eflfect of 16°C treatment was determined. Before 

 examining the effects of this temperature treat- 

 ment on recrudescence, an experiment was con- 

 ducted in January to be certain that gametogen- 

 esis could be maintained at this temperature. 

 The ovaries of the initial January controls 

 (Table 6) were in Stage III, IV, or V; the testes 

 of fish in this sample were in Stage 4 or 5. 

 Neither testicular nor ovarian weights were sig- 

 nificantly altered by this 90-day treatment, nor 

 was there an evident change in gonadal activity 

 as judged by histological examination. 



The testes and ovaries of the initial controls 

 of the July experiment (Table 6) were regres- 



1146 



