Effect of dietary supplementation with filamentous microalga Tribonema ultriculosum on growth performance, fillet quality and immunity of rainbow trout Oncorhynchus mykiss

The present study was to investigate the effect of dietary Tribonema ultriculosum supplementation on growth performance, fillet nutritional quality and immunity of rainbow trout Oncorhynchus mykiss (165.26 ± 0.57 g, mean ± SD). Three diets containing 0 (control), 50 g/kg and 100 g/kg T. ultriculosum (TU) were introduced to triplicate groups of the experimental fish for 90 days. Then, a lipopolysaccharide (LPS) stress experiment was conducted to evaluate the effect of microalgal addition on fish immune response. Compared to the control, microalgal addition significantly increased fish feed intake and growth. Dietary T. ultriculosum supplementation significantly increased the contents of palmitoleic acid, eicosapentaenoic acid (EPA) and docosahexaenoic acid in fillet. The addition of T. ultriculosum significantly increased the activity levels of spleen glutathione peroxidase (before LPS stress) and superoxide dismutase (after LPS stress), and simultaneously decreased the spleen malondialdehyde content compared to the control. In terms of the immune response, fish fed diets containing T. ultriculosum had a higher level of lysozyme activity (before LPS stress), immunoglobulin M content (before and after LPS stress) and hepcidin expression (after LPS stress) compared to the control. These results suggest that T. ultriculosum can be used to increase fish growth, fillet nutritional quality and immunity.