The effects of different photoperiods on body growth, gonadal growth and hypothalamic monoamine content in juvenile Oreochromis niloticus (Linnaeus, 1757)

Abstract

The effects of different photoperiods (12/12; 24/0 and 0/24 Light/Dark) on body growth, gonadal development and monoamine concentration in the hypothalamus of male and female tilapia, Oreochromis niloticus, were studied. Standard body length and total weight were similar in male and female maintained under different photoperiods. The gonadosomatic index (GSI) was higher in female maintained under 0/24 conditions than in 12/12. The concentration of norepinephrine (NE) in the hypothalamus of males kept at 0/24, was higher than the male kept under 12/12 and 24/0. The content of dopamine (DA) in the hypothalamus of males at 24/0 was higher than in all other treated animals. The concentration of serotonin (5-HT) in the hypothalamus of male and female O. niloticus showed no statistical differences. The highest DA/NE relationship was observed in males maintained under 24/0 light/dark condition. The 5-HIAA/5-HT ratio in males kept under 24/0 light/dark condition was significantly lower than those maintained at 12/12 and 0/24. The present results suggest that there are sex differences in the neuroendocrine mechanisms regulating gonadal growth in O. niloticus, as well as in the participation of the light/dark conditions.