Dietary modulation of immune response and related gene expression profiles in mirror carp (Cyprinus carpio) using selected exotic feed ingredients

Abstract

An investigation was conducted to evaluate the effect of feeding selected exotic ingredients on immune responses and expression of immune related genes in mirror carp (Cyprinus carpio). Fish were fed diets for a total of 56days. Fishmeal served as the main protein source in the control diet and two experimental diets consisted of fishmeal fixed at 34% provision of protein and the remaining 66% protein was provided either by earthworm meal (EW diet) or a combination of whey protein concentrate (8%) and casein (58%) (WPC diet). At the start of the trial fish were injected intraperitoneally with Aeromonas hydrophila bacterin and samples of carp blood were taken for gene expression, haematological and serological analysis. Compared to fish fed fishmeal, a significant increase in mRNA expression of the pro-inflammatory cytokines IL-1β (24h post injection) and TNFα (at 12h and 48h post injection) was observed in fish fed EW. Moreover a similar trend was observed for complement 3 (C3) gene, where fish fed EW showed significant elevations in mRNA expression values at both 12 and 48h post injection compared to control fed fish. In contrast, fish fed WPC showed a significant decrease in C3 and TNF-α mRNA expression compared to fish fed fishmeal (48 h post injection). Fish fed EW and WPC showed a significant increase in peripheral leukocyte levels compared to fish fed fishmeal 14d post injection. Fish fed fishmeal presented significantly higher circulatory IgM levels at 7d post injection compared to fish fed EW and WPC. In contrast, fish fed EW and WPC showed a significant increase in IgM levels at 28d post injection. The present study shows an up-regulation of all immune related genes in fish fed EW, compared to fish fed fish meal, which is indicative of an acute inflammatory response. In contrast it appears feeding WPC has an immunosuppressive effect towards TNFα and C3 expression in carp blood. This may be offset by the fact that feeding WPC to carp appears to aid in the increased production of circulatory IgM and leukocyte levels compared to fishmeal fed fish.