Microbial levan in the diet of Labeo rohita Hamilton juveniles: effect on non‐specific immunity and histopathological changes after challenge with Aeromonas hydrophila

Abstract

A 60-day feeding trial was conducted to study the immuno-protective effect of microbial levan on Labeo rohita juveniles challenged with Aeromonas hydrophila. Six purified diets were prepared with different levels of microbial levan: control (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. Among the treatment groups the haemoglobin content and total leucocyte count were increased with a dietary supplementation of levan at 1% or more. An increasing trend for total erythrocyte count was observed with increasing level of dietary levan. Lower levan-supplemented groups showed a higher albumin/globulin ratio. As the levan supplementation was increased, there was a gradual increase in serum lysozyme activity and respiratory burst activity [nitroblue tetrazolium (NBT) assay] reduction values. The highest lysozyme activity and NBT were observed in the T5 group although this was similar to the T4 group (P > 0.05). No significant histo-architectural changes were associated with dietary levan levels. After challenge with A. hydrophila, moderately degenerated hepatocytes, oedema and leucocytic infiltration in parenchymatous tissues, and extensive haemorrhage and haemosiderosis in the kidney were observed in the control group. However, the T5 group supplemented with 1.25% levan showed infiltrating leucocytes in the liver while the kidney showed only moderate degeneration of renal tubules. The relative survival per cent of juveniles after challenge with A. hydrophila was the highest in the T5 group followed by T4. This suggests that microbial levan at 1.25% can be used as dietary immunostimulant for L. rohita juveniles.

Immunostimulant effects of Cotinus coggyria on rainbow trout (Oncorhynchus mykiss)

“…Lysozyme level increased with microbial levan in Lobeo rohita [28], with dietary Astragalus radix and Ganoderma lucidum in carp (C. carpio) [10], with Solanum trilobatum in Oreochromis mossambicus [9], and with fish protein hydrolyzate in Lateolabrax japonicus [29]. In some case, no lysozyme level changes were observed with vitamin C in rainbow trout [30,31].…”

Prebiotics and Fish Immune Response: A Review of Current Knowledge and Future Perspectives

“…Levan when incorporated at 5 and 10 g kg ¡1 in the feeds of juvenile common carp Cyprinus carpio, improved the serum lysozyme activity (Rairakhwada et al, 2007). The juveniles of another carp variety, L. rohita were found to have high serum lysozyme activity and highest relative survival percentage against Aeromonas hydrophila upon levan inclusion in the feed at 12.5 g kg ¡1 (Gupta et al, 2008). In a recent investigation, serum lysozyme activity and survival rate of orangespotted grouper (Epinephelus coioides H.) after challenge with Vibrio harveyi were significantly, higher in the 25 g kg ¡1 levan supplemented group compared to the control group (Huang et al, 2014).…”

Non-starch polysaccharides and their role in fish nutrition – A review

“…Levan, a natural polymer of fructose with b (2,6) linkages produced extracellularly by many microorganisms like Zymomonas mobilis, Bacillus subtilis, Bacillus polymyxa, and Acetobacter xylinum, is shown to have immunostimulating properties in fish (Gupta et al, 2008;Rairakhwada et al, 2007). Dietary levan supplements at a concentration of 0.5% have been reported to activate non-specific phagocytes in Cyprinus carpio juveniles which resulted in higher survival rate when challenged with Aeromonas hydrophila (Rairakhwada et al, 2007).…”