de VLAMING: CONTROL OF REPRODUCTION IN GILLICHTHYS 



Figure 3.— Effect of 24°, 20°, and 13°C 

 treatments at short (8L/16D) and long 

 (15L/9D) photoperiods on testicular his- 

 tology in Gillichthys mirabilis. I.C. refers 

 to initial controls (15 July) and N, to 

 samples from natural population. Each 

 box represents the testicular condition of 

 one fish. 



1=1 



_H_ 



_H_ 



P P 



.M. 



H R 



I5L BL 15L 9L l5L 

 24° 20° 13° 



28 Auqust 



I5L 8L I5L BL I5L 

 24° 20° 13° 



22 SepiemDef 



ISL 6L I5L BL I5L 

 24° 20° 13° 



with one exception. Testicular weights of the 

 20 °C group at 8L/16D sacrificed in August were 

 significantly greater (P < 0.05) than those of 

 the July controls. With the exception of this 

 same group, active spermatogenesis was not in- 

 itiated in fish exposed to 20°C. Mitotic prolifer- 

 ation of spermatogonia was, however, stimulated 

 by this treatment. In contrast, active spermato- 

 genesis was initiated by August at 13°C, regard- 

 less of photoperiod. Active spermatogenesis 

 was not initiated in the natural population until 

 after 22 September. Testicular weights of 

 both groups at 13°C sacrificed in September 

 were significantly greater (P < 0.01) than 

 those of the initial July controls and those 

 of the September sample from nature. Some 

 photoperiod effect was evident at 13°C since 

 testicular weights at 8L/16D were significantly 

 higher (P < 0.05) than those of the 15L/9D 

 group by September. By November, the testes 

 of a majority of the fish in the 13°C-8L/16D 

 group were in the prespawning condition (Stage 

 4) whereas the testes of all fish in the 13°C- 

 15L/9D group were in Stage 3; testicular 

 weights of these two groups were also signifi- 

 cantly diflferent (P < 0.01). 



These data indicate that 24°C inhibits testic- 

 ular recrudescence by blocking the transforma- 

 tion of spermatogonia to spermatocytes and also 

 retards mitoses in the spermatogonia. Low tem- 

 peratures promote testicular recrudescence; the 

 rate of recrudescence at a low laboratory tem- 

 perature was faster than in the natural popula- 



tion. At low temperatures, short photoperiods 

 accelerate testicular recrudescence. With the 

 exception of the one sample at 20°C-8L/16D 

 sacrificed in August, 20°C stimulates little or no 

 testicular recrudescence, only mitotic prolifer- 

 ation of spermatogonia. 



EFFECTS OF CONSTANT TEMPERATURES 



AND PHOTOPERIOD ON FISH IN 



STAGES OF ACTIVE GAMETOGENESIS 



(MAY) 



Responses of fish in phases of active gameto- 

 genesis (in May) were examined by exposing 

 two groups of fish for 67 days to 13°C, at a short 

 (8L/16D) and a long (15L/9D) photoperiod, 

 and 27°C at a long photoperiod (15L/9D) . The 

 efl["ects of these treatments on gonadal weights 

 are summarized in Figure 4, 



At the beginning of treatment, testes and ov- 

 aries were in Stages 3 and III, respectively. In 

 the July sample from nature, sacrificed with the 

 experimentals, ovarian (Stage I) and testicular 

 (Stage 0) regression was occurring. Testes and 

 ovaries of fish at 27°C regressed as in nature; 

 in both sexes gonad weights were significantly 

 lower (P < 0.01) than initial levels. 



In both groups at 13°C spermatogenetic ac- 

 tivity remained at the initial levels and the testes 

 did not show the regression seen in nature or at 

 27°C. Ovarian weights in the 13°C group at a 

 long photoperiod were significantly lower 

 (P < 0.05) than those of the initial May sample 



1141 



