Effects of thermal stress and hypoxia on skin mucus immune and stress responses in blue gourami ( Trichogaster trichopterus ) cultured in intensive recirculation aquaculture system and semi‐intensive systems

Abstract

The current study evaluated the effects of thermal stress and hypoxia on skin mucus immune and stress responses in an ornamental fish, blue gourami (Trichogaster trichopterus), reared in intensive recirculation aquaculture system (RAS) and semi-intensive traditional pond system (TPS). Fish were derived from RAS and TPS and exposed to thermal (T1: 32 ± 2°C; T2: 12 ± 1°C) and hypoxia (DO: 3–3.5 mg L-1, over 0, 4, 8, 12 and 24 h) stresses. The results showed that the lysozyme and alkaline phosphatase (ALP) activities and the soluble protein contents of skin mucus were significantly higher in fish cultured in RAS than those of TPS, while the lactate dehydrogenase (LDH) and lactate were significantly lower in RAS compared with those of TPS (p < 0.05). Lysozyme activity and the amount of soluble protein showed a significant decrease after exposure to low temperature in both RAS- and TPS-reared fish, while the skin mucus complement activity revealed a significant increase (p < 0.05) at low temperature. Hypoxia condition significantly increased the LDH activity, and the lactate content of fish reared in both RAS and TPS 12–24 h after exposure (p < 0.05). Glucose levels significantly increased after 4 h of exposure to hypoxia (p < 0.05) and then returned to the initial level at 8–24 h after exposure. The results of this study demonstrate that both RAS condition and environmental challenges can affect mucosal immune and stress responses in blue gourami.