Seasonal changes in hepatosomatic index,gonadosomatic index and plasma estradiol‐17β level in captively reared female rabbit fish (Siganus guttatus)

The seasonal changes in hepatosomatic index (HSI), gonadosomatic index (GSI) and plasma estradiol‐17β (E₂) level in female rabbit fish (Siganus guttatus) were investigated. The relationship between plasma E₂ levels with these indices and ovarian growth was also evaluated. Each month, at least 10 female broodfish were sacrificed to collect liver, ovary and blood for HSI, GSI and plasma E₂, respectively. GSI and HSI were calculated as percentage (%) of relative weight of gonad and liver to total body weight, respectively. Plasma E₂ level was measured using enzyme‐linked immunosorbent assay method (ELISA). Ovaries were cut and stained for histological observation. The results included seasonal changes in plasma E₂ levels, stages of ovarian development, GSI and HSI. The highest level of E₂ was observed in June (1,445.62 pg/ml) and during vitellogenesis (2,305 pg/ml). GSI and HSI values significant fluctuated monthly. The highest HSI and GSI were 1.72% in May and 3.58% in June, respectively. The pattern of plasma E₂ levels showed a relationship with GSI and different stages of ovarian development. HSI was associated with ovarian stages. During vitellogenesis, the highest value (1.9%) of HSI was observed. Histological sections showed that rabbit fish is a multiple spawner. These results contribute to further understanding of female rabbit fish reproductive biology in captivity. Important reproductive parameters such as HSI, GSI and E₂ can be used to indicate maturation status of this fish species.