Haemato-immunological and stress responses of Labeo rohita (Hamilton) fingerlings: effect of rearing temperature and dietary gelatinized carbohydrate

A feeding trial of 70‐days was carried out to study the haemato‐immunological and stress responses of Labeo rohita fingerlings reared at two water temperatures [ambient (Amb) – 27 °C and 32 °C] fed with graded levels of gelatinized corn carbohydrate (GC). Two hundred and sixteen fingerlings were randomly distributed into six treatment groups in triplicate. Three semi‐purified diets were prepared containing 30% crude protein with graded levels of GC 40%, 50% and 58%. The six treatment groups were T₁ (40% GC × Amb), T₂ (40% GC × 32 °C), T₃ (50% GC × Amb), T₄ (50% GC × 32 °C), T₅ (58% GC × Amb) and T₆ (58% GC × 32 °C). The blood glucose level was significantly (p < 0.05) lowered in groups fed with 58% GC level. Neither dietary GC levels nor temperature had a significant (p > 0.05) effect on serum cortisol and superoxide dismutase activity. Lysozyme activity was significantly higher (p < 0.05) in T₁ during pre‐ and post‐challenge period while temperature alone had a significant (p < 0.05) effect on post‐challenge Nitroblue Tetrazolium and found higher at 32 °C. A significant effect of GC levels and rearing temperature was recorded on WBC in the pre‐ and post‐challenge period. Highest pre‐challenge WBC was observed in T₄ group and in the post‐challenge period T₁ group recorded maximum. Water temperature had significant effect on pre‐challenge haemoglobin content, highest being at 32 °C (T₂). A significant (p < 0.05) effect of rearing temperature and dietary GC level on total serum protein and albumin was also observed. Highest total serum protein and albumin was recorded in T₁ and globulin in T₂. Percentage survival after challenging with Aeromonas hydrophila was highest in T₁ followed by T₃ group and lowest in T₆. The results obtained in the present study suggest that L. rohita fingerlings may utilize higher levels of dietary GC at higher temperature (32 °C) but may affect its immunity status.