Effect of stocking density and feeding regimes on haematology, stress and histological recovery in stunted Lebeo rohita fingerlings reared in cage culture

Abstract

A 330-day field trial was conducted to evaluate the effect of stocking density and feeding ration on stunted Labeo rohita (Hamilton, 1822) fingerling reared in floating net cages. The stunted fingerling of L. rohita with an average body weight 38.23 ± 1.90 g were stocked in cages (3 × 3 × 3 m) at different densities viz. T1 (10), T2 (15), T3 (20) and T4 (25) fish/m3 and fed with varying levels of feeding rations at 3, 4, 5 and 6% at each stocking density. The 4×4 factorial design was used, and each density and feeding level kept in triplicate, and fed with commercial pellet feed (crude protein 28% and fat 5%) twice in a day. The significant recovery was observed in the T1 (10*5 and 10*6) treatment groups, which showed highest Hb, RBC, PCV and lowest WBC content at the end of experiment. Similarly, significant changes were observed in glucose, cortisol and lactate dehydrogenase (LDH), which were highest in higher stocking density (T4), and normalized in lower stocking T1 (10*5 and 10*6) treatment groups. Histological examination showed, almost complete recovery of structural changes such as swelling/ edema primary lamellae, hyperplasia of basal epithelium between the secondary lamellae of gill and necrosis in liver of lower stocking densities (10 and 15 fish/m3). In contrast, greater structural changes in both the organs were observed in the higher stocking density groups (20 and fish nos/m3). Based on the results, it can be concluded that maximum growth and complete recovery (in term of haematology, stress and histological changes) were observed in lower stocking density (10 fish/m3) fed with 5 to 6% feeding levels. Hence, in an Indian reservoir cage-based cultures, 10 fish/m3 fed with 5 to 6% feeding rations can be recommended at commercial scale to get maximum and sustainable profit by using the stunted L. rohita fingerling.