Dietary microbial levan enhances tolerance of Labeo rohita (Hamilton) juveniles to thermal stress

A preliminary study was conducted to determine the ameliorating effect of dietary microbial levan against thermal stress in Labeo rohita juveniles. Six purified diets were prepared with different levels of microbial levan: basal (no levan), T1 (basal + 0.25%), T2 (basal + 0.50%), T3 (basal + 0.75%), T4 (basal + 1%) and T5 (basal + 1.25%), fed to six groups of fish in triplicate, reared at 26 °C. After feeding for 60 days, critical temperature maxima (CTMax), lethal temperature maxima (LTMax), and the level of heat shock protein (HSP) 70 in the liver and muscle tissues of fish under normal and after heat shock treatment at 35 °C was determined in each group. Results indicated significant increase in the temperature tolerance (CTMax and LTMax) of the group fed diets supplemented with 1.0 and 1.25% microbial levan compared to other experimental groups. In the sub-lethal thermal stress test, significantly higher level of HSP70 was observed in the liver of fish fed diet supplemented with 1.0 and 1.25% and in the muscle of fish fed diet supplemented with 1.25% microbial levan compared to that of other experimental groups. Overall results indicated that dietary microbial levan can confer protection against thermal stress in L. rohita juveniles.