ARS | Publication request: Roles for mannose binding lectin and rhamnose binding lectin in channel catfish fed essential oils and challenged with Edwardsiella ictaluri

Submitted to: Aquaculture America Conference
Publication Type: Abstract Only
Publication Acceptance Date: August 31, 2012
Publication Date: N/A

Technical Abstract: A major problem in the catfish farming industry has been high disease loss to enteric septicemia of catfish (ESC), caused by the bacterium Edwardsiella ictaluri. Methods to control this disease include vaccination, antibiotic therapy, and restricted feeding. Another method that has been examined is the addition of essential oils to the diet. Essential oils are aromatic compounds extracted from plants. Mechanisms through which essential oils may improve disease resistance are poorly understood. The objectives of the study were to examine the roles of mannose binding lectin and rhamnose binding lectin in channel catfish fed essential oils and challenged with E. ictaluri. Two hundred and fifty juvenile channel catfish (7.2 ± 0.1 g) were stocked into 76 L aquaria with flow-through water. There were 5 replicate tanks per treatment and the treatments were: Control (32% crude protein floating diet, Fishbelt Feeds, Inc.) and EO (32% crude protein 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. At the end of the study, all fish were exposed to virulent E. ictaluri by bath immersion. Fish from both treatments were sampled on d 1, 7, and 14 of the challenge. Plasma and liver were taken to quantify protein levels of mannose binding lectin (MBL) and gene expression levels of MBL and rhamnose binding lectin 1 (RBL1) and RBL2. Survival was recorded daily for 21 d and fish were fed their respective diets during the challenge. Survival was higher (69.5 vs 48.4%) in fish fed essential oils compared to controls (P < 0.05). Plasma levels of MBL were 3 fold higher (P < 0.05) in EO fish on d 1 but were similar to control on d 7 and 14. In contrast, MBL mRNA was increased 2.5 fold (P < 0.05) in treated fish on d 14. RBL1 mRNA was upregulated 6.5 and 3.3 fold on d 7 and d 14, respectively (P < 0.01) in the EO fish relative to controls. RBL2 mRNA levels were similar between treatments at all sampling points. The results demonstrate that essential oils improved survival of channel catfish challenged with E. ictaluri. The mechanisms through which essential oils improve survival are not known but may involve MBL and RBL1, binding to carbohydrate moieties on the surface of E. ictaluri, leading to bacterial killing.