Enhancing growth performance, antioxidant capacity, and immunological responses of Siberian sturgeon (Acipenser baerii) by dietary substitution of fishmeal with Chlorella vulgaris

The increasing demand for sustainable and cost-effective fishmeal alternatives in aquaculture has led to growing interest in using microalgae, such as Chlorella vulgaris (CV), as a novel protein source. The present study investigated the effect of substituting fishmeal with CV meal on performance, muscle composition, digestive enzyme activities, antioxidant capacity, and immune responses of Siberian sturgeon ( Acipenser baerii ). A total of 240 fish (50.12 ± 0.31 g) were randomly allotted in triplicate to one of five dietary groups, in which 0.0 (CV0.0), 2.5 (CV2.5), 5.0 (CV5.0), and 10.0 (CV10.0) percent of fishmeal in the basal diet was substituted with CV meal. The results indicated that increased dietary CV supplementation exhibited a significant linear effect on FBW, WGR, SGR, and PER, with the highest values of 118.3 ± 11.05 g, 136.03 ± 7.17 %, 1.23 ± 0.26 % d −1 , and 2.03 ± 0.39 %, respectively, in fish fed the CV10.0 supplemented diet (p < 0.05). A significant linear increase in muscle protein content was also observed, while lysine levels significantly decreased. However, no significant difference was found in the muscle amino acid content of fish fed diets supplemented with different levels of CV (p > 0.05), except for lysine content in the muscle of fish that linearly declined as the dietary CV supplementation increased (p < 0.05). Digestive enzymes activities - including trypsin, chymotrypsin, amylase, and lipase - were linearly enhanced by increasing dietary CV supplementation. The activities of T-AOC, CAT, and SOD showed both linear and quadratic increases with increasing dietary CV supplementation and reached the highest values of 22.31 ± 0.72, 73.18 ± 3.20 and 50.32 ± 1.39 L −1 , respectively, in fish fed with CV10.0 supplemented diet (p < 0.05). Serum lysozyme activity, immunoglobulin M content as well as C3 and C4 complements were linearly and quadratically stimulated as the dietary CV supplementation increased to the highest values in fish fed the CV10.0 supplemented diet (p < 0.05). The present findings underscore the potential of CV as a sustainable alternative protein source at 10 percentage substitution with fishmeal for enhancing growth, antioxidant defenses, and immune responses in Siberian sturgeon. These results support further research on optimizing microalgae-based diets and exploring their long-term benefits for aquaculture sustainability. • CV meal improved growth performance of Siberian sturgeon (CV10.0). • CV10.0 substitution group showed the highest final weight and weight gain ratio. • Digestive enzyme activities peaked in fish fed CV10.0 supplemented diet (p < 0.05). • Fish on CV10.0 had the highest antioxidant capacity (T-AOC, CAT, SOD, GPX). • Higher immune responses (LA, IgM, C3, C4) were found in fish on CV10.0 diets.