The polysaccharide fraction (PF) isolated from the hemiparasitic mistletoe, Dendrophthoe falcata (L.f.) Ettingsh (DF) leaves was tested for its immunostimulatory properties in Oreochromis niloticus (Linn.). Different groups of experimental fish were fed for 1, 2 or 3 weeks with three different doses [low (0.01%), mid (0.1%), or high (1%)] of D. falcata polysaccharide fraction (DFPF) - supplemented diet. After every feeding regimen, the fish were assessed for non-specific immunological parameters, immune related gene expression and disease protection. The DFPF treated groups showed significant (P < 0.05) enhancement of non-specific immune parameters. Significant (P < 0.05) upregulation of lysozyme and TNF-α gene expression was observed in DFPF treated groups. In pathogen challenge studies using Aeromonas hydrophila, the DFPF treated groups displayed significant (P < 0.05) decrease in percentage mortality and the consequent increase in relative percent survival (RPS). Supplementation of 1% DFPF in the feed for a week conferred the maximum protection against the virulent pathogen challenge, recording a RPS of 100. These results suggest that DFPF has the potential to be used as an immunostimulating feed additive in finfish aquaculture.
Keywords: Challenge test; Dendrophthoe falcata; Immune gene expression; Immunostimulation; Non-specific immunity; Polysaccharide fraction.
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