Submitted to: Journal of Applied Aquaculture
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/14/2006
Publication Date: 6/1/2007
Citation: Shelby, R.A., Lim, C.E., Aksoy, M., Klesius, P.H. 2007. Effects of probiotic bacteria as dietary supplements on growth and disease resistance in young channel catfish, Ictalurus punctatus (Rafinesque). Journal of Applied Aquaculture. 19(1) pgs. 81-91. Interpretive Summary: Probiotics are non-pathogenic bacteria or yeasts which can be added to feed to improve growth and disease resistance in livestock. Recent literature has provided evidence that probiotics may be beneficial in aquaculture applications as well. We conducted several experiments to determine if commercially available probiotics could be added to channel catfish feed and if these provided any benefit in terms of growth enhancement or immunity to disease. Seven different commercial probiotic bacterial formulations were used and these were applied to feed at the rates recommended by the manufacturers. We fed juvenile catfish in aquaria for periods of 5 to 8 weeks, depending on the size and number of fish per tank. Before feeding, an initial experiment was conducted to confirm that 2 bacterial probiotics remained viable at the prescribed level. We measured weight gain and feed conversion on a biweekly basis. After the prescribed feeding period, we measured immune parameters such as serum protein, immunoglobulin, lysozyme and complement. We then subjected the catfish to a disease challenge by immersion using virulent Edwardsiella ictaluri bacteria, the causative agent of enteric septicemia (ESC). Our data confirmed that the treated diet contained sufficient numbers of viable bacteria, but that there was no measurable enhancement of growth or feed conversion when compared to control diets. Similarly, we could not show any differences in immune response nor disease resistance in treated fish. We conclude that these probiotics applied in this manner do not enhance growth or disease resistance in channel catfish.
Technical Abstract: Three separate experiments were conducted to determine the beneficial effects of probiotic bacteria added to commercial catfish diets. These commercial probiotics, singly and in combination, were incorporated into a commercial diet fed to juvenile channel catfish, Ictalurus punctatus (Rafinesque), in aquaria. Microbial analyses were conducted to confirm viability of the bacteria under storage conditions. Fish were fed twice daily to apparent satiation, and weighed biweekly for a periods of 5 to 8 weeks. After that time, representative fish were bled for serological analysis of protein, immunoglobulin, complement, and lysozyme. Disease resistance was additionally determined in the remaining fish by observing mortality after immersion challenge with pathogenic Edwardsiella ictaluri, the causative agent of enteric septicemia (ESC). Specific anti-ESC antibody was measured by ELISA after 15 days in the fish which survived challenge. The viability of the probiotic bacteria was between 106 and 107 colony forming units per gram (CFU/g) of probiotic diet after storage for 4 weeks at 50 C. No significant differences in levels of protein, immunoglobulin, complement, or lysozyme were noted between fish consuming probiotic diets and the control diet. In one feeding trial weight gain per fish was significantly less in the fish receiving a combination of Pediococcus and Enterococcus probiotic bacteria when compared to those consuming either bacterial supplement diet alone or the control diet. We conclude that these particular commercial dietary supplements lack specific growth promoting or immune stimulating effects in juvenile channel catfish.