Evaluation of dietary immunostimulants and probiotics on growth performance and health indices of channel catfish, tilapia, and shrimp.

Abstract

Channel catfish, Nile tilapia, and whiteleg shrimp are three major aquaculture species worldwide. Growth performance and disease mortality are common bottlenecks within these culture systems. Feed supplementation with microorganisms or their byproducts is one approach to mitigate these challenges. Two studies investigated the effects of a commercial Saccharomyces cerevisiae-derived DVAQUA (postbiotic) at 0, 1, or 4 % inclusion levels in channel catfish and Nile tilapia diets over a 10-week feeding period. Immune-related gene expression, lysozyme activity, blood chemistry, and growth metrics were measured at the end of the feeding period. Tilapia were subsequently challenged by immersion of Streptococcus iniae (ARS-98-60) and catfish by immersion of Edwardsiella ictaluri (S97-773) or virulent Aeromonas hydrophila (ML09-119) to assess the potential of the postbiotic against common aquaculture pathogens. Nile tilapia resistance to S. iniae infection appeared to increase proportionally to the inclusion of DVAQUA, with up to 19 % relative percent survival for the 4 % inclusion (P=0.054). There was no significant mortality reduction for channel catfish with both pathogens (P>0.05). The impact of DVAQUA on channel catfish growth performances and blood chemistry was also measured over a 6-month feeding period. No differences were observed across lysozyme activity, blood chemistry, and growth metrics. In a third trial, Whiteleg shrimp were fed a Bacillus velezensis AP193 wild-type strain (1 × 107 CFU g-1), an AP193 high-antimicrobial-producing strain (1 × 107 CFU g-1), or BiOWiSH Feedbuilder Syn3®, a commercial B. subtilis probiotic (2 × 105 CFU g-1) amended diet for two months. Shrimp were then challenged by immersion with Vibrio parahaemolyticus (A3). No significant differences were observed in growth performance, immune-related gene expression, or blood chemistry at the end of the feeding period. There was no apparent mortality reduction at the end of the pathogen challenge (P=0.988) among the different treatment groups. Further research is needed to evaluate different concentrations of probiotics and their performance in high-production aquaculture systems.