Dietary microbial levan ameliorates stress and augments immunity in Cyprinus carpio fry (Linnaeus, 1758) exposed to sublethal toxicity of fipronil

A 45-day feeding trial was conducted to study the stress ameliorating and immunomodulatory role of microbial levan in Cyprinus carpio fry exposed to sublethal dose (1/10th LC50) of fipronil [(+/-)-5-amino-1-(2,6-dichloro-alpha,alpha,alpha-trifluoro-p-tolyl)-4-trifluoromethylsulfinylpyrazole-3-carbonitrile]. Two hundred and twenty-five fry were randomly distributed in five treatments in triplicates. Four purified diets were prepared with graded levels of microbial levan. Five different treatment groups were levan control L0P0 (basalfeed+0% levan without exposure to pesticide); pesticide control L0P1 (basalfeed+0% levan with exposure to pesticide); L0.25P1 (basalfeed+0.25% levan with exposure to pesticide); L0.50P1 (basalfeed+0.50% levan with exposure to pesticide) and L0.75P1 (basalfeed+0.75% levan with exposure to pesticide). Lactate dehydrogenase (LDH), malate dehydrogenase (MDH) and fructose-1,6-diphosphatase (FDPase) activites were significantly (P<0.05) increased, whereas alkaline phosphatase (ALP), adenosine triphosphatase (ATPase) and acetyl choline esterase (AchE) activities were significantly (P<0.05) reduced in higher levan-fed groups. RBC, haemoglobin and WBC counts were significantly (P<0.05) increased in the levan-fed groups. Similar trends were also observed for the total serum protein, globulin, NBT and lysozyme activities. Blood glucose and serum cortisol exhibited a third order polynomial relationship with increasing level of dietary levan. Overall result showed stress ameliorating, immunostimulating and protective role of microbial levan against fipronil-induced stress in C. carpio fry at 0.75% level of dietary levan supplementation.