FISHERY BULLETIN: VOL. 70, NO. 4 



Figure 4.— Effect of 27° and 13°C treat- 

 ments at short (8L/16D) and long (15L/9D) 

 photoperiods on testicular and ovarian weight 

 in Gillichthys mirabilis. Mean gonadal 

 weight is represented by histograms; the 

 mean is bracketed by one standard error. 

 Shaded histograms represent gonadal weight 

 of samples collected in nature; open histo- 

 grams, experimental groups. Light (hours 

 given per 24 hr), temperature, and dates 

 on which fish were sacrificed are recorded 

 below the histograms. Sample sizes are in- 

 dicated atop each histogram. 



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 27° 13° 



20 July 



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 Control 

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20 July 



and those of the 13°C group at a short photo- 

 period. Ovaries in both 13°C groups were, how- 

 ever, in active vitellogenesis (Stage III). These 

 results could indicate a photoperiod influence 

 in vitellogenesis. But one must observe caution 

 in interpreting these data since this difference 

 in ovarian condition may simply be a problem 

 of beginning experiments with fish in various 

 stages of oogenesis. Data presented by de Vlam- 

 ing (1972b) revealed the nonsynchrony of ga- 

 metogenesis in this species (i.e., fish in different 

 stages of gonadal development were common in 

 monthly samples between November and June) . 

 High temperatures apparently cause testicular 

 and ovarian regression in spring, at least when 

 the photoperiod is long, whereas low tempera- 

 tures prevent gonadal regression and are re- 

 quired for spermatogenesis and vitellogenesis. 



EFFECTS OF CONSTANT TEMPERATURES 



AND PHOTOPERIOD ON FISH IN 

 STAGES OF ACTIVE SPERMATOGENESIS 



(JANUARY) 



In the previous experiment the influence of 

 temperature and photoperiod was examined 

 during the spawning season in spring. Whether 

 fish respond similarly in winter (near the onset 

 of the spawning season) is also of interest, so 

 in January 1968 fish were exposed to 27°, 20°, 

 and 13°C, at a short (8L/16D) or a long 

 (15L/9D) photoperiod for 30-39 days. The in- 

 fluence of these treatments on testicular weight 



and histology is presented in Figures 5 and 6, 

 respectively. 



Testes of the initial January controls were in 

 Stages 3, 4, or 5. As observed in May, testes 

 regressed rapidly at 27°C; testes weights were 

 significantly less (P < 0.01) than those of the 

 January controls and February sample from 

 nature. Histological examination confirmed that 

 regression had occurred (testes in Stage 1). No 

 photoperiod effect was seen at 27 °C. 



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Figure 5.— Effect of 27°, 20°, and 13°C treatments at 

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

 testicular weight in Gillichthys mirabilis. Mean testic- 

 ular weight is represented by histograms; the mean is 

 bracketed by one standard error. Shaded histograms 

 represent testicular weight of samples collected in na- 

 ture; open histograms, experimental groups. Light 

 (hours given per 24 hr), temperature, and dates on 

 which fish were sacrificed are recorded below the histo- 

 grams. For example sizes, see Figure 6, 



1142 



