Practical diets for California yellowtail, Seriola dorsalis: Use of advanced soybean meal products on growth performance, body composition, intestinal morphology, and immune gene expression.

California yellowtail (CYT), Seriola dorsalis, is a promising candidate for aquaculture due to its rapid growth and high-quality flesh, particularly in markets like Japan, Australia, China, and the United States. Soy protein has shown success as a replacement for marine protein sources in CYT diets, reducing fishmeal levels, though concerns about potential intestinal inflammation persist with the inclusion of solvent-extracted soybean meal. To address this, processing strategies like fractionation, enzymatic treatment, heat treatment, and microbial fermentation have been employed to mitigate the negative impacts of soybean meal on fish nutrition and immune systems. This study focuses on optimizing soybean meal inclusion levels by incorporating advanced soy variants into CYT diets. The eight-week feeding trial, conducted in a recirculation system, featured six diets with sequential inclusion levels (0, 50, 100%) of high protein low oligosaccharide soybean meal (Bright Day, Benson Hill, St Louis, MO) and enzyme-treated soybean meal (HP 300, Hamlet Protein Inc., Findlay, OH), replacing solvent-extracted soybean. The study compares these formulations against a soy-free animal protein-based diet. At the end of the trial, fish were sampled for growth performance, body proximate composition, intestinal morphology, and immune response from gut samples. Results showed consistent FCR (P = 0.775), weight gain (P = 0.242), and high survival rate (99.4 ± 0.5%) among dietary treatments (P>0.05). Histological evaluations revealed no gut inflammation and gene expression analysis demonstrated no significant variations in immune, physiological, and digestive markers apn (P = 0.687), mga (P = 0.397), gpx1 (P = 0.279), atpase (P = 0.590), il1ß (P = 0.659). The study concludes that incorporating advanced soybean meal products, replacing up to 20% of fishmeal does not negatively affect CYT's growth and intestinal health. This suggests that all three soy sources, contributing 35% of total protein (15.4 g 100 g-1 diet), can be included in practical diets without compromising CYT's intestinal integrity or growth. These findings have positive implications for the commercial production of CYT and future research on the incorporation of plant-based proteins in aquaculture diets.

Investigation of dietary exogenous protease and humic substance on growth, disease resistance to Flavobacterium covae and immune responses in juvenile channel catfish (Ictalurus punctatus).

Many bacterial pathogens impact the US catfish industry, and disease control can be challenging for producers. Columnaris disease in channel catfish, Ictalurus punctatus, is primarily caused by Flavobacterium covae (formerly F. columnare). Immunostimulants may enhance nonspecific immune responses and offer an alternative to antibiotic treatments in catfish. Furthermore, dietary protein sources and inclusions are also essential to fish health and nutrition and may enhance overall fish performance in pond culture. The current project evaluated two immunostimulants: a protease complex (PC) and a humic substance (HS) derived from a reed-sedge peat product. A 60-day trial examined the effects of five diets on growth performance, immune response and resistance to experimental F. covae infection in channel catfish. Diets included a high-quality fishmeal diet (32%; CF32), a high-protein soy-based diet (32%; C32), a low-protein soy-based diet (28%; C28; predominately used in industry), a low-protein soy diet supplemented with C28 + PC at 175 g metric ton-1 and C28 + HS in a low-protein diet at 23 g metric ton-1 . Following feeding for 60 d, juvenile channel catfish were sampled for growth performance and baseline health indicators (n = 3; body mucus, blood for sera, kidney and spleen). A subset of fish was then subjected to an immersion-based in vivo challenge trial with F. covae (ALG-00-530; 106 CFU mL-1 exposure). At 60d post-initiation, there were no dietary differences in the relative growth rate (p = .063) or thermal growth coefficient (p = .055), but the 32% diets generally appeared to perform best. Post-challenge, the C32 group's mortality was higher than the C28 + PC (p = .006) and C28 + HS diets (p = .005). Although not significant, the C28 and CF32 groups also demonstrated higher mortality compared to both PC and HS diets. Sera lysozyme concentration was found to increase following pathogen challenge (p < .001) and in comparison with mock-challenged catfish (p < .001). Elevated expression levels of proinflammatory cytokines (il-1ß, il-8, tnf-α and tgf-ß) were observed at trial midpoint and post-infection when compared to 60d. The C28 treatment was found to have lower tnf-α expression than the C28 + PC (p = .042) and C28 + HS (p = .042) groups following exposure to F. covae. These challenge data suggest that the immunostimulants (PC and HS) in plant-based protein may be beneficial in protecting against F. covae when offered in low-protein channel catfish diets.