Growth performance, survival, blood chemistry, and immune gene expression of channel catfish (Ictalurus punctatus) fed probiotic-supplemented diets

Authors: NGUYEN, KHANH - Auburn University; BRUCE, TIMOTHY - Auburn University; OLUWAFUNMILOLA, E - Auburn University; LILES, MARK - Auburn University; Beck, Benjamin; DAVIS, ALLEN - Auburn University

Submitted to: Veterinary Sciences
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/14/2022
Publication Date: 12/16/2022
Citation: Nguyen, K.Q., Bruce, T.J., Oluwafunmilola, E.A., Liles, M.R., Beck, B.H., Davis, A.D. 2022. Growth performance, survival, blood chemistry, and immune gene expression of channel catfish (Ictalurus punctatus) fed probiotic-supplemented diets. Veterinary Sciences. 9(12):701. https://doi.org/10.3390/vetsci9120701.
DOI: https://doi.org/10.3390/vetsci9120701

Interpretive Summary: The channel catfish farming industry is the largest and one of the oldest aquaculture industries in the United States. Despite being an established industry, production issues stemming from disease outbreaks remain problematic for producers. Supplementing probiotics to enhance the immune system and growth potential is one of the approaches for mitigation. Although considerable laboratory data demonstrate efficacy, these results do not always translate to production-scale environments and involvement with more natural modes of disease transmission. Hence, the present work was conducted in the laboratory but incorporated flow-through water from large catfish pond production systems. Two feeding trials were conducted in an 18-tank aquaria system housing two different sizes of channel catfish. Catfish in the first trial were fed three experimental diets over eight weeks, using six replicate tanks. Commercial diets were top-coated with two selected probiotics, AP193 and BiOWiSH and a third diet with no additive was included in the study. In the second trial, diets were top-coated with BiOWiSH at three concentrations. At the completion of these studies, growth performance, survival, hematocrit, blood chemistry, probiotic concentrations within the distal intestine, and the expression of relevant immune genes were analyzed. Trial results revealed no differences among treatments concerning growth, survival, and bloodwork parameters for both trials. For immune gene expression, interesting trends were observed with substantial changes in gene expression observed in select tissues of AP193-fed fish. Based on these findings, more research on utilizing probiotics in flow-through systems with natural infection conditions is crucial to ensure consistency from a controlled laboratory scale to real-world practices.

Technical Abstract: The channel catfish (Ictalurus punctatus) farming industry is the largest and one of the oldest aquaculture industries in the United States. Despite being an established industry, production issues stemming from disease outbreaks remain problematic for producers. Supplementing probiotics to enhance the immune system and growth potential is one of the approaches for mitigation. Although considerable laboratory data demonstrate efficacy, these results do not always translate to production-scale environments and involvement with more natural modes of disease transmission. Hence, the present work was conducted in the laboratory but incorporated flow-through water from large catfish pond production systems. Two feeding trials were conducted in an 18-tank aquaria system housing two different sizes 34.8 ± 12.5 g and 0.36 ± 0.03 g channel catfish. Catfish in the first trial were fed three experimental diets over eight weeks, using six replicate tanks. Commercial diets were top-coated with two selected probiotics, AP193 and BiOWiSH, at a concentration of 0.025 g kg-1 and 0.5 g kg-1 of feed, respectively, and a control group (no additive) was included in the study. In the second trial, diets were top-coated with BiOWiSH at concentrations of 0, 0.25, 0.5, 1 g kg-1. At the completion of these studies, growth performance, survival, hematocrit, blood chemistry, probiotic concentrations within the distal intestine, and immune expression of interleukin 1ß (il-1ß), tumor necrosis factor-alpha (tnf-'), Interleukin-8 (il-8), transforming-growth factor ß1 (tgf-ß1), and toll-like receptor 9 (tlr9) were evaluated using qPCR. Trial results revealed no differences (p>0.05) among treatments concerning growth, survival, and hematological parameters for both trials. For immune gene expression, interesting trends were discerned with substantial downregulation observed in AP193-fed fish for il1ß, tnf-a, and tlr9 expression within splenic tissue, compared to that of the basal and BiOWiSH diets (p<0.05). However, the results were not statistically significant for anterior kidney tissue in the first trial. In the second trial, varied levels of probiotic inclusion revealed no significant impact of BiOWiSH's products on the expression of il1ß, tnf-a, il8, and tgf-ß1 in both spleen and kidney tissue at 0.25, 0.5, 1 g kg-1 inclusion (p>0.05). Based on these findings, more research on utilizing probiotics in flow-through systems with natural infection conditions is crucial to ensure consistency from a controlled laboratory scale to real-world practices.