Dietary chitosan supplementation in Litopenaeus vannamei reared in a biofloc system: Effect on antioxidant status facing saline stress

This study evaluated the effects of dietary supplementation with different concentrations of chitosan from shrimp tailings on the antioxidant and immune systems of juvenile Litopenaeus vannamei cultivated in a biofloc system (BFT) and subjected to abrupt salinity reduction. The experiment was performed with juvenile shrimp fed diets supplemented with four levels of chitosan: C0 (0 g kg(-1) diet - control), C1 (1 g kg(-1) diet), C3 (3 g kg(-1) diet), and C5 (5 g kg(-1) diet). After 35 days, the shrimp were exposed to an acute reduction in salinity from 30 to 5 for 24 h, and the hemolymph, gills, and hepatopancreas were collected. No significant differences were found in the growth performance and survival among treatments. In the gills, acute salinity reduction increased the activity of catalase (CAT), although this effect was reversed by the 5 g kg(-1) diet (C5). Furthermore, glutathione-S-transferase (GST) activity was maintained at the basal level in shrimp fed a 1 g kg(-1) diet (C1) but reduced in those fed C3 and C5. We also identified a reduction in lipid peroxidation in shrimp fed the C3 and C5 diets. In the hepatopancreas, the GST activities and glutathione (GSH) levels were higher in shrimp supplemented with chitosan, which showed a protective effect. Saline stress and chitosan supplementation did not affect differential hemocyte counts. In conclusion, the results of this study suggest that dietary intake of chitosan could enhance some antioxidant defenses of L. vannamei farmed in a BFT system. Thus, the inclusion of at least 1 g kg(-1) chitosan could represent a good alternative to improve defense mechanisms and stress resistance, and it could also contribute to the development of sustainable aquaculture.