Dietary lecithin ameliorates endosulfan-induced stress responses and promotes growth, immunity, and disease resistance in fingerlings of the milkfish, Chanos chanos

A 45-day trial was conducted in a static-renewal system to investigate the potential of lecithin in mitigating the stress response of milkfish (Chanos chanos) exposed to a low concentration of endosulfan (0.52 ppb, 1/40th of LC50). Fingerlings (12.65 +/- 1.25 g) (n = 225) were evenly distributed among five treatments, each with three replicates of 15 fish. The fish were reared in 150 L FRP tanks and fed ad libitum (similar to 3 % of BW) a basal diet (CP 35.87 % and DE 388 Kcal/100 g) without or with lecithin, forming groups as: a control, an endosulfan-exposed (EE), and EE fish fed diets containing 1 %, 1.5 %, and 2 % lecithin. Endosulfan exposure significantly increased (P < 0.01) cortisol (29 %), blood glucose (34 %), antioxidant enzymes in the liver, gill, and brain (2- to 2.65- fold catalase, 1.5- to 1.75- fold SOD, and 1.4- to 1.79-fold GST), as well as stress markers in the liver and gill (HSP70 by 1.5 fold) and caspase activity in the liver and gill (1.2 to 1.3 fold). It also decreased (P < 0.01) ascorbic acid in muscle and brain tissues (35 % to 46 %). However, lecithin supplementation reversed these effects, with 2 % supplementation resulting in 17% lower cortisol, 0.3 to 0.7-fold reductions in antioxidant enzymes, over 0.5-fold reductions in HSP70 and caspase, and 33 % to 47 % higher ascorbic acid levels in tissues compared to the control group. Endosulfan also decreased (P < 0.01) intestinal protease, amylase, and alkaline phosphatase, and branchial ATPase activity, while increasing dehydrogenases (LDH, MDH, G6PDH) and transaminases (ALT and AST) levels, which were restored by lecithin. Fish fed 1 and 1.5 % dietary lecithin resisted endosulfan-induced effects on hematological parameters (RBC, WBC, phagocytic activity/NBT, and Hb) and serum protein (P < 0.01), with 2 % lecithin performing better than the control (P < 0.01). Lecithin ameliorated endosulfan-induced chromosomal aberrations and histopathological changes in the liver and gills. Endosulfan exposure significantly decreased (P < 0.01) specific growth rate(SGR) (by 25 %) and protein efficiency (PE) (by 0.36 points), while increasing (P < 0.01) feed conversion ratio (FCR) (by 0.83 points) and cumulative mortality (by 17 %) due to increased susceptibility to Vibrio parahaemolyticus. Lecithin supplementation not only reversed these adverse effects but also yielded superior results compared to the control group. Specifically, 2 % supplementation improved SGR by 22 %, FCR by 0.38 points, PE by 0.22 points, and relative survival by 22 %. These findings suggest that dietary 2 % lecithin protects against endosulfan-induced stress, triggers immune response in C. chanos, and alleviates stress even in pathogen-challenged fish.