Physio-biochemical and immunological responses of Etroplus suratensis (Cichliformes) to chronic ammonia exposure

Ammonia is one of the deleterious water quality parameters that must be managed for successful aquaculture production. The present study evaluated the impact of chronic ammonia exposure on the physio-biochemical and immunological responses of Etroplus suratensis. Fish (n = 120, 24 ± 3 g) were exposed to four different ammonia concentrations (0, 1, 2, and 4 mg L⁻¹ of Total ammonia nitrogen (TAN)) at 27.5 to 29.7⁰C for 30 days. The unionized ammonia concentrations are 0, 0.014, 0.028, 0.057 mg L⁻¹. The lowest haemoglobin (Hb) level was observed in fish exposed to the highest level of TAN (4 mg L⁻¹). The serum glucose, cortisol, liver superoxidase dismutase, catalase activities, enzymes such as alkaline phosphatase, Serum Glutamic- Oxaloacetic Transaminase, and Serum Glutamic- Pyruvic Transaminase were higher in fish exposed to 4 mg L⁻¹ TAN than the control group. The serum total protein and albumin levels were substantially decreased with TAN exposure. Immune parameters such as Immunoglobulin M and Tumour Necrosis Factor—alpha were significantly (P < 0.05) lower in the groups exposed higher ammonia concentrations than the unexposed group. The heat shock protein 70 gene expression was significantly higher at 1 mg L⁻¹ TAN, and the Insulin-like growth factor-1 gene expression was lower (P < 0.05) at 4 mg L⁻¹ TAN. This is the first detailed investigation on the impact of chronic ammonia exposure in the culture fish E. suratensis. This study reveals that a chronic exposure to TAN even at lower concentrations, such as 1 mg L⁻¹ TAN in fresh water can have a negative impact on E. suratensis physico-biochemical and immunological responses. Hence, it is important to manage TAN levels below 1 mg L⁻¹ in the culture system of E. suratensis to ensure good health.