Different dissolved oxygen effects on growth and O2-sensing pathway in juvenile bighead carp (Hypophthalmichthys nobilis)

Dissolved oxygen is one of the crucial determinants affecting production and welfare of fish in aquaculture. This study aimed to study the effects of varying levels of dissolved oxygen under normoxia on growth performance, biochemical activity and gene expression in bighead carp (Hypophthalmichthys nobilis). Juvenile bighead carp were raised in three groups of tanks for 60 days with O2 concentrations of 4 mg/L, 5 mg/L and 6 mg/L, respectively. In the fish group of 6 mg/L, we harvested the highest body weight (19.30 +/- 0.29 g) and the highest SGR (specific growth rate) (0.45 +/- 0.01%) among three groups. The mRNA levels of the oxygen -sensing pathway genes including epas1a (HIF-2 alpha), hif3a (HIF-3 alpha) and egln1a (PHD2) were highest at 4 mg/L, indicating a negative correlation with growth rate. Plasma catalase (CAT) activity was significantly higher in 6 mg/L group than in the other two groups. Furthermore, the fish of 6 mg/L group showed the highest transcription level in gh (GH). These results demonstrated that increasing water oxygen under normoxia condition positively improve growth and antioxidant, and this further extended our understanding how effective aeration strategies affect outcome of integrated aquaculture in bighead carp and other food fish.