Effect of different light regimes on the maturational progress of the whitespotted rabbitfish (Siganus sutor)

In this study, the effects of different light regimes on the reproductive activity of a typical Indo- Pacific coral reef rabbitfish, Siganus sutor, were evaluated. Forty- five adult fish were exposed to nine different photoperiod (۸L: ۱۶D, ۱۲L: ۱۲D, ۱۶L: ۸D) and light intensity (۱۰۰۰, ۲۰۰۰, ۳۰۰۰ lux) combinations with three replicates and five other fishes reared under indoor light condition (Control). Gonadosomatic Index (GSI) and Hepatosomatic Index (HSI) were calculated after ۶۰ days and compared among different experimental regimes in males and females. In the control group, GSI and HSI mean values were ۴.۶۷ and ۳.۲۴%, respectively, for females and ۱۰.۰۵ and ۲.۱۰%, respectively, for males, and these fish showed differences in comparison with the exposed fish. Females kept under ۱۰۰۰ and ۲۰۰۰ lux light intensities had a higher GSI mean value (۹.۲۶ and ۱۰.۳۹%, respectively) and also lower average HSI (۲.۱۰ and ۲.۳۱%, respectively) in ۱۶L: ۸D treatment. A similar result was also obtained for males, whereas the ۳۰۰۰ lux light intensity, ۸L: ۱۶D day length combination led to more gonadal development (GSIs of ۱۶.۴۱% in females and ۱۲.۰۳% in males). A comparison of results among different photoperiods also confirmed that maturation was induced better in fish maintained under ۱۶L: ۸D in both sexes. This investigation revealed the visible role of both photoperiod and light intensity on inducing maturity in the whitespotted rabbitfish, S. sutor. Thus, rearing of adults exposed to an artificial light regime, including ۱۶L: ۸D and ۲۰۰۰ lux light intensity, promotes more gonadal development than that occurring in the wild.

Keywords:

Photoperiod , Light intensity , GSI , HSI , rabbitfish , Siganus sutor , Persian Gulf