Uthpala M. Padeniya, Donald A. Davis, Timothy J. Bruce
School of Fisheries, Aquaculture and Aquatic Sciences, Auburn University, Auburn, AL,36849, USA
Biofloc systems are regarded as an environmentally friendly and sustainable method of rearing aquatic organisms that utilize recycled nutrients, organic matter, and microbes. Biofloc systems supply an array of advantages, such as improved biosecurity, better feed conversion, efficient water usage, and increased health and survival of rearing organisms. Exogenous supplementation of probiotics in biofloc systems helps enhance the benefits these systems supply.
The present study was done using two probiotics (AP193 and BiOWiSH FeedBuilder Syn 3) top coated in commercial feed and the commercial feed being the control on evaluating the health and immune status of Nile tilapia. Nine individual tanks (three replicates per treatment) were stocked with 120 juvenile fish of average size 71.4 ±4.4 g, and the growth trial was conducted for 16 weeks. At the end of the 14th week of the feeding trial, fish were challenged with a low dose of Streptococcus iniae (ARS-98-60, 7.2 × 107 CFU mL-1), and after the 16th week of the feeding trial, a high dose of the same strain was used (ARS-98-60- 6.6 × 108 CFU mL-1) via intraperitoneal injections in a common garden setup. At the end of the challenge, the cumulative percent mortality (CPM),serum lysozyme activity and the expression of 4 genes il1β, il6, il8, and tnfα from the spleen were measured. In both low-dose and high-dose challenges, the mortalities of the probiotic-fed groups were significantly lower (P<0.05) than in the control diet though the overall CPM in the high dose challenge for all treatments were greater than the low dose challenge. The serum lysozyme activity had no significant differences between the treatments in pre challenge (P=0.290) or when the post low dose and high dose challenge were compared for treatment via two-way ANOVA (P=0.410). The gene expression data from pre challenge among the treatments also did not show any significant difference for il1β (P=0.462), il6 (P=0.213), il8 (P=0.186), or tnfα (P=0.126). But the overall the expression of probiotic treated groups were higher than commercial diet fed fish. The post challenge data were also compared between the treatment, trials, and treatment x trial. Some differences were found although not found significant. For il1β there was a significant difference in treatment (P=0.042). However, when post hoc testing was performed differences were not detected significant between commercial diet and AP193 diet (P=0.052) and AP193 and BiOWiSH FeedBuilder Syn 3 (P=0.087). A similar trend was also observed in the expression of tnfα gene which was nearly significant (P=0.052). When the gene expressions were compared between the trials the tnfα expression was significantly higher in the high dose challenge than the low dose challenge. The opposite trend was observed in il6 where the expression was significantly lower in the high dose challenge. No differences were observed in il8 expression for treatment, trial or treatment x trial.
The results of this study demonstrates that the probiotics fed Nile tilapia in biofloc systems increases the survival rates against S. iniae related diseases. This is explained by the increase in the expression of some of the pro inflammatory cytokines tested during this study in probiotic diet fed fish. Overall. This suggests that tilapia raised in biofloc systems may benefit from probiotic feeding.