Impact of feed additives on surface mucosal health and columnaris susceptibility in channel catfish fingerlings, Ictalurus punctatus

Authors: ZHAO, HONGGANG - Auburn University; LI, CHAO - Auburn University; Beck, Benjamin; ZHANG, RAN - Auburn University; THONGDA, WILAWAN - Auburn University; DAVIS, D. ALLEN - Auburn University; PEATMAN, ERIC - Auburn University

Submitted to: Fish and Shellfish Immunology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/6/2015
Publication Date: 7/9/2015
Citation: Zhao, H., Li, C., Beck, B.H., Zhang, R., Thongda, W., Davis, D., Peatman, E. 2015. Impact of feed additives on surface mucosal health and columnaris susceptibility in channel catfish fingerlings, Ictalurus punctatus. Fish and Shellfish Immunology. 46(2):624-637.

Interpretive Summary: Flavobacterium columnare, the causative agent of columnaris disease, is among the most prevalent of all freshwater disease-causing bacteria, impacting global aquaculture of catfish, salmonids, baitfish and aquaria-trade species. We were interested in examining whether the feeding of a standard catfish diet supplemented with Alltech dietary additives Actigen®, a product derived from yeast cell wall mannan oligosaccharides and/or Allzyme® SSF, a fungus-based product, could offer protection against columnaris disease. A nine week feeding trial revealed significantly higher survival following the eight day challenge period in B+Actigen® when compared with the other two diets. Given the superior protection provided by the B+Actigen® diet, we next examined the differences in gene expression in mucosal tissues of fish fed that diet and the standard diet before and after columnaris infection. We found that the B+Actigen® diet led to reduced levels of markers of inflammation, and higher levels of genes related to healing and wound repair. Future studies will evaluate the ability of these dietary compounds to protect against other important diseases of U.S. farmed-raised fish.

Technical Abstract: One of the highest priority areas for improvement in aquaculture is the development of dietary additives and formulations which provide for complete mucosal health and protection of fish raised in intensive systems. Far greater attention has been paid to dietary impact on gut health than to protective effects at other mucosal surfaces such as skin and gill. These exterior surfaces, however, are important primary targets for pathogen attachment and invasion. Flavobacterium columnare, the causative agent of columnaris disease, is among the most prevalent of all freshwater disease-causing bacteria, impacting global aquaculture of catfish, salmonids, baitfish and aquaria-trade species among others. We were interested in examining here whether the feeding of a standard catfish diet supplemented with Alltech dietary additives Actigen®, a second generation product derived from yeast cell wall mannan oligosaccharides and/or Allzyme® SSF, a fermented strain of Aspergillus niger, could offer protection against F. columnare mortality. A nine-week feeding trial of channel catfish fingerlings with basal diet (B), B+Allzyme® SSF, B+Actigen® and B+Actigen®+Allzyme® SSF revealed good growth in all conditions (FCR < 1.0), but no statistical differences in growth between the treatments. At nine weeks, based on pre-challenge trial results, basal, B+Actigen®, and B+Allzyme® SSF groups of fish were selected for further challenges with F. columnare. Replicated challenge with a virulent F. columnare strain, revealed significantly longer median days to death in B+Allzyme® SSF and B+Actigen® when compared with the basal diet (P < 0.05) and significantly higher survival following the eight day challenge period in B+Actigen® when compared with the other two diets (P < 0.05). Given the superior protection provided by the B+Actigen® diet, we carried out transcriptomic comparison of gene expression of fish fed that diet and the basal diet before and after columnaris challenge using high-throughput RNA-seq. Pathway and enrichment analyses revealed changes in mannose receptor DEC205 and IL4 signaling at 0 h (prior to challenge) which likely explain a dramatic divergence in expression profiles between the two diets soon after pathogen challenge (8 h). Dietary mannose priming resulted in reduced expression of inflammatory cytokines, shifting response patterns instead to favor resolution and repair. Our results indicate that prebiotic dietary additives may provide protection extending beyond the gut to surface mucosa.