The green microalga Scenedesmus quadricauda modulates the performance, immune indices, and disease resistance of Nile tilapia fingerlings

Abstract

Microalgae have been efficiently used as a feed supplement to enhance the fish performance and welfare because of their unique nutritional properties and functional bioactive ingredients. In this context, the current study assessed the effects of enriching fish diets with the green microalga Scenedesmus quadricauda (SQ) on the growth, digestive enzymes, antioxidant status, mucosal and innate immunity biomarkers, and serum bactericidal activities in Nile tilapia (Oreochromis niloticus) fingerlings. However, SQ was mixed with the ingredients of the basal diet in a dose of 0.0 (defined as control), 5.0, 10.0, 15.0, and 20.0 g/kg diet and then fed to fish daily for 60 days. Supplementing diets with SQ significantly prompted the growth and feed utilization indices of Nile tilapia with optimum results at 15 g/kg diet. Dietary SQ significantly (P < 0.05) improved activities of digestive enzymes (lipase, α-amylase, and protease), blood proteins (albumin, globulin, and total protein), antioxidant enzymes (glutathione peroxidase, superoxide dismutase, and catalase), and skin mucosal and serum innate immunity indices (lysozyme, total immunoglobulins, and complement C3). Conversely, serum malondialdehyde levels and activities of alanine and aspartate transaminase were significantly (P < 0.05) declined in fish fed with SQ-enriched diets. Serum bactericidal activities against Streptococcus agalactiae, Vibrio vulnificus, Pseudomonas fluorescens, and Aeromonas sobria were significantly higher at SQ-fed treatments, reaching their highest inhibition activities in the treatments of 15–20 g/kg diet. The present study evoked that enriching fish diets with 15 g SQ/kg diet provided marked enhancements in growth, antioxidant, and immune responses of Nile tilapia fingerlings.