Production of food size largemouth bass (LMB) has received more attention in recent years driven by the demand from Asian markets in north America while production in China has jumped from 150 thousand MT in 2013 to over 450 thousand MT in 2017. Commercial feeds for LMB still appear to contain high levels of costly fish meal (FM); whereas recent studies have shown that most of the dietary FM can be effectively replaced by plant-protein ingredients . Supplementation of nutritive or non-nutritive compounds to plant-protein based diets may have significant effects on the production performance and/or health status of LMB. Based on literature information and due to the lack of evaluations in LMB, t he objective of this 10-week study was to investigate the potential effects of supplemental glycine, a commercial prebiotic (GroBiotic® -A; GBA), and a nucleotide mix on the production performance, antioxidant status, and intestinal micromorphology of LMB fed soybean meal (SBM) -based diets.
Six experimental diets (a FM-based and five SBM-based diets) were formulated to contain 42% crude protein (CP) and 12% lipid. Four SBM-based diets (GLY, GBA, NCTDs, and COMB) were supplemented either with glycine (2%), GBA (2%), the nucleotide mix (0.15%), or all three supplements combined (respectively). Twenty feed-trained LMB (6.0 g/fish) were stocked in each of 24, 110-L glass aquaria operating as a recirculating aquaculture system. Each experimental diet was randomly assigned to four groups of fish and fed to apparent satiation twice daily. Statistically significant differences between treatments were considered at P < 0.05.
Survival of LMB in the study averaged 98.8% and was unaffected by diet. Final weight of the fish ranged from 48 to 61g and weight gain from 712 to 913% of initial weight. Within SBM treatments, growth of LMB fed the GBA, NCTDs and COMB diets was outperformed by that of fish fed the GLY diet. While a similar growth performance of LMB was observed between GLY and SBM-based control treatments, GLY was the only dietary treatment that did not differ from the FM-based control group (FM-C). Although no improvements in FCE were observed within SBM-based treatments in response to the test ingredients, no differences were found among GLY and FM-C fed groups. Our results showed a slightly but positive effect of supplemental glycine in improving growth performance and FCE of LMB when dietary FM is almost completely replaced (reduced from 44% to 4%) by SBM. Results for intestinal micromorphology and antioxidant status of LMB fed the experimental diets will be presented.