Phytogenic feed-additive effects on channel catfish rhamnose binding lectin levels and susceptibility to Edwardsiella ictaluri

Authors: Peterson, Brian; PEATMAN, ERIC - Auburn University; OURTH, DONALD - University Of Memphis; Waldbieser, Geoffrey - Geoff

Submitted to: Diseases of Aquatic Organisms
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/12/2018
Publication Date: 7/5/2018
Citation: Peterson, B.C., Peatman, E., Ourth, D., Waldbieser, G.C. 2018. Phytogenic feed-additive effects on channel catfish rhamnose binding lectin levels and susceptibility to Edwardsiella ictaluri. Diseases of Aquatic Organisms. 129:99-106.

Interpretive Summary: We investigated the effects of a phytogenic feed additive on growth performance, disease susceptibility to Edwardsiella ictaluri, and regulation of six rhamnose binding lectin (RBL) genes. Two hundred and fifty juvenile channel catfish (13.4 ± 0.1 g) were allotted to the following treatments: Control (floating diet, Fishbelt Feeds, Inc.) and EO (floating diet supplemented with essential oils). The fish were fed their respective diets for 6 weeks. Following subjection to different feed treatments, all fish were exposed to virulent E. ictaluri by bath immersion. Another group of similarly sized fish were not challenged (non-challenged controls fed control feed). Mucosal tissue samples were taken to quantify gene expression levels of RBL on days 1 and 2 post challenge. Weight gain and food conversion ratio were similar between treatments. After challenge, survival was higher (64.4 vs 48.0%) in fish fed EO compared to controls. Relative to non-challenged controls, gill RBL 1a mRNA was higher in fish fed EO on day 1 while gill RBL 3b was higher in fish fed EO on days 1 and 2, respectively. Rhamnose binding lectin 5a in the skin and small intestine did not change significantly relative to non-challenged fish on days 1 and 2 of the disease challenge. The results demonstrate that essential oils improved survival of channel catfish challenged with E. ictaluri. One of the mechanisms through which essential oils may improve survival during exposure to E. ictaluri is through an upregulation of RBL 1a and RBL 3b in the gill.

Technical Abstract: We investigated the effects of a phytogenic feed additive (Digestarom® P.E.P. MGE) on growth performance, disease susceptibility to Edwardsiella ictaluri, and regulation of six rhamnose binding lectin (RBL) genes. Two hundred and fifty juvenile channel catfish (13.4 ± 0.1 g) were allotted to the following treatments: Control (floating diet, Fishbelt Feeds, Inc.) and EO (floating diet supplemented with essential oils; Digestarom® P.E.P. MGE at 200 g/ton). The fish were fed their respective diets for 6 weeks. Following subjection to different feed treatments, all fish were exposed to virulent E. ictaluri by bath immersion. Another group of similarly sized fish were not challenged (non-challenged controls fed control feed). Mucosal tissue samples were taken to quantify gene expression levels of RBL on days 1 and 2 post challenge. Weight gain and food conversion ratio were similar between treatments. After challenge, survival was higher (64.4 vs 48.0%) in fish fed EO compared to controls (P < 0.05). Relative to non-challenged controls, gill RBL 1a mRNA was higher in fish fed EO (P < 0.05) on day 1 while gill RBL 3b was higher in fish fed EO (P < 0.01) on days 1 and 2, respectively. Rhamnose binding lectin 5a in the skin and proximate small intestine did not change significantly relative to non-challenged fish on days 1 and 2 of the disease challenge. The results demonstrate that the essential oils in the feed additive, Digestarom® P.E.P. MGE improved survival of channel catfish challenged with E. ictaluri. One of the mechanisms through which essential oils may improve survival during exposure to E. ictaluri is through an upregulation of RBL 1a and RBL 3b in the gill.