Effects of Probiotic Bacteria as Dietary Supplements on Growth and Disease Resistance in Young Channel Catfish, Ictalurus punctatus (Rafinesque)

Abstract

ABSTRACT Three separate experiments were conducted to determine the beneficial effects of probiotic bacteria added 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 period 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 bacteria did not decline in storage at 5°C and could be recovered between 106 and 107 colony forming units per gram (CFU/g) of diet after storage for 4 weeks. No significant differences in levels of protein, immunoglobulin, complement, or lysozyme were noted between fish consuming probiotic diets or 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.