Substituting palm oil for fish oil in feeds for juvenile rohu, Labeo rohita: effects on growth performance, fillet fatty acid composition, and antioxidant capacity

The study aims were to test the effects of partial or total replacement of dietary fish oil (FO) by palm oil (PO) on growth, antioxidant capacity, lysozyme activity, muscle fatty acid composition, and fillet quality of rohu (Labeo rohita) fingerlings. The rohu fingerlings (3.25 +/- 0.13 g) were stocked in 18 circular (water volume 55 L) polyvinyl tanks in triplicate groups (30 fish per tank). Six iso-proteic (400 g/kg) and iso-lipidic (97 g/kg) purified diets were formulated in which FO was replaced by 0, 20, 40, 60, 80, and 100% PO (0 PO, 20 PO, 40 PO, 60 PO, 80 PO, and 100 PO). The diets were fed to the fish for 8 weeks, with meals being given at 8:00, 12:00, and 16:00 h. There were no significant (P > 0.05) treatment effects on growth (19.32-22.58 g gain/fish), feed conversion ratio (1.32-1.68), and protein efficiency ratio (1.48-1.89). However, protein retention efficiency was highest (33.25-34.99%) in fish fed the 0 PO and 60 PO diets, and lipid retention efficiency was highest (53.09%) in the fish fed the 100 PO diet. Muscle eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) levels and n-3/n-6 ratio were highest in fish fed the 100% FO diet and decreased as increasing proportions of FO were replaced by PO. Serum superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), and lysozyme activity did not change significantly (P > 0.05) up to 60% replacement of FO with PO. Further replacement of FO with PO (80 PO and 100 PO) resulted in decreased serum antioxidant capacity and lysozyme activity. Although muscle atherogenicity and thrombogenicity indices did not change significantly (P > 0.05) among treatments, the highest hypocholesterolaemic-to-hypercholesterolaemic (H/H) ratio and fillet lipid quality (FLQ) were found in fish receiving the 0 PO (with 100% FO and no PO). H/H and FLQ values did not differ significantly up to 60% replacement of FO with PO but decreased upon further replacement of FO with PO. FO can be replaced by PO to a level of 60% without hampering the growth and fillet quality of fingerling rohu provided with such diets for a period of a few weeks, but the long-term effects of FO replacement remain to be studied.