Dietary Chlorella vulgaris modulates the performance, antioxidant capacity, innate immunity, and disease resistance capability of Nile tilapia fingerlings fed on plant-based diets

This study assessed the impacts of dietary Chlorella vulgaris (ChV) on the growth, digestive en-zymes activity, antioxidant status, immune responses, expression of hepatic cytokines and growth-related genes, and disease resistance capability of Nile tilapia (Oreochromis niloticus) fingerlings fed on plant-based diets. For this purpose, six tested diets were formulated to include 0.0 (control), 2.5, 5, 10, 15, and 20 g ChV/kg diet and were offered to the fish in triplicated groups for 70 days. A dose-dependent increase was observed in feed intake, specific growth rate, and weight gain (%) in ChV-fed fish but feed conversion ratios and survival rates % were not significantly changed among different ChV groups. Significantly higher serum protease, amylase, and lipase enzyme levels were detected in ChV-fed fish than the control group, especially in treatments of 10 - 15 g/kg diet. Feeding the fish with 10-20 g ChV/kg diet markedly increased serum total proteins, total lipids, and globulin levels. Similarly, glutathione peroxidase, super-oxide dismutase, and catalase activities as well as serum lysozyme and respiratory burst activities, and total IgM levels were also elevated. On the other hand, lowest malondialdehyde levels were recorded in fish groups fed diets with 10 - 20 g ChV/kg diet compared with the control group. Bactericidal activities against Aeromonas hydrophila, Pseudomonas fluorescens, and Vibrio anguil-larum were significantly higher as levels of dietary ChV increased up to 15 and 20 g/kg diet. Dietary ChV also upregulated the transcription of hepatic growth hormone, insulin-like growth factor 1, interleukin-1 beta, and tumor necrosis factor-alpha genes, particularly at 15 - 20 g/kg diet. However, feeding Nile tilapia fingerlings with 15 g ChV/kg diet is adequate to promote the performance and support antioxidant capacity, immune response, and resistance capability to bacterial infections.