ß-glucan modulates non-specific immune gene expression, thermal tolerance and elicits disease resistance in endangered Tor putitora fry challenged with Aeromonas salmonicida.

An eight-week feeding trial was performed to assess the effect of different dietary levels (0, 0.5, 1.0, and 1.5%) of ß-glucan (sourced from Saccharomyces cerevisiae) on growth, survival, immunological parameters (immune gene expression, lysozyme, and antiprotease), total antioxidant status, thermal tolerance, and disease resistance of Tor putitora fry. Feeding of moderate doses (0.5 and 1.0%) of ß-glucan significantly improved survival but not weight gain percentage as compared to that received unsupplemented control and highest dose (1.5%) of glucan. Supplementation of ß-glucan in diets differentially influenced the mRNA expression of cytokine and other immune genes. For instance, transcripts of cytokines such as tnf-α and il-1ß were significantly upregulated, while ifn-γ and il-10 were unaffected by ß-glucan intake. Also, the relative mRNA expression of tlr-5 and hepcidin1 along with lysozyme and antiprotease activities were remained largely unchanged by dietary glucan administration. In contrast, ß-glucan induced mRNA expression of defensin1 and c3 while decreased the transcript level of mhc-1. On the other hand, dietary inclusion of ß-glucan markedly improved total antioxidant levels and extended the thermal tolerance limits at both the ends, as shown by increased CTmax and lower CTmin than the control group. After feeding ß-glucan for eight weeks, the fish were bath challenged with a bacterial pathogen, Aeromonas salmonicida. The challenge study results revealed that ß-glucan intake improved most of the studied immune parameters, resulting in lower mortality. Overall, dietary inclusion of ß-glucan (0.5-1.0%) was efficient in improving the immune responses, thermal tolerance, and disease resistance of T. putitora fry.