Dietary soy lecithin augments antioxidative defense and thermal tolerance but fails to modulate non-specific immune genes in endangered golden mahseer (Tor putitora) fry.

A 70-day experiment was carried out to assess the effect of different levels (0, 1 and 2%) of soy lecithin in the diet on growth, survival, antioxidant defense markers, immune gene expression and thermal tolerance limits of golden mahseer, Tor putitora fry. Percentage weight gain, specific growth rate (SGR %) and survival of mahseer fed lecithin supplemented diets were not significantly different from those of the control group. Also, the mRNA expression levels of different immune related genes such as tnfα, il-1β, il-10, complement-3, interferon-gamma (ifnγ) and tlr4 were unaffected by dietary lecithin supplementation. Nevertheless, superoxide dismutase (SOD) activity was significantly greater in the lecithin-fed groups than the control fish. The glutathione-S-transferase (GST) activity was exceptionally high in the 2% lecithin supplemented group compared to the rest two groups. This increase in antioxidant status with dietary lecithin supplementation, however, was not reflected in the whole body malonaldehyde (MDA) levels, as it did not vary significantly among the dietary groups. Importantly, dietary inclusion of soy lecithin significantly increased upper thermal tolerance limits as evidenced by higher CT and LT values. Likewise, golden mahseer fry fed with lecithin supplemented diets (both 1 and 2%) registered significantly lower critical and lethal thermal minimum (CT and LT) values than the control group, indicating higher cold tolerance capacity. Our results thus demonstrate that the dietary inclusion of soy lecithin could enhance the upper and lower thermal tolerance limits and antioxidant status of golden mahseer fry and failed to enhance immune related gene expression.