Histological changes of gonads in the white spotted rabbit fish (Siganus sutor) under photoperiod fluctuations

In this study, the effects of photoperiod alternation on the maturational progress of the white spotted rabbit fish (Siganus sutor) were investigated. A hundred adult fish (total length: 306.4 ± 2.12 mm; body weight 401.5 ± 8.45 g) were caught from Lavan Island. They were divided in 300 l tanks (n = 5) and exposed to tree different day length including 8, 12 and 16 h combined with constant 2000 lux light intensity with three replicates during prespawning season. After 60 days, the GSI mean values were 2.03± 0.34%, 5.83± 0% and 10.39± 0.80%, respectively, for females and 8.15± 0.43%, 13.91± 1.52% and 14.56± 0.41%, respectively, for males according to photoperiods. These results showed significant differences between fishes were reared under 8 h and 16 h photoperiods (P<0/05). In the case of gonad histology, the maturity stages of ovaries along with photoperiod increasing were 3, 4 and 5; whereas testes of males reared in all treatments reached to stage 5. These results clear that increasing of light duration from 8 h to 16 h in combination with 2000 lux light intensity have positive relation with the gonadal progress of white spotted rabbit fish in both sexes. Thus, rearing of fish fewer than 16 h day length obtains the highest level of sexual maturity.