California yellowtail (CYT) Seriola dorsalis , renowned for its rapid growth, desirable texture, and flavor, holds substantial potential for aquaculture production. Species of this genera have a well-established production history in Japan, Australia, and China. It also has a robust market presence in the United States, making it an appealing candidate for commercial aquaculture. The utilization of soy protein in CYT diets has demonstrated success, with a significant reduction in fishmeal levels . Despite this level of soy protein inclusion , concerns about potential intestinal inflammation related to varying soybean meal levels in fishmeal replacement have emerged. Various soy improvement strategies, including fractionation, enzymatic treatment, heat treatment, and microbial fermentation, have been consistently investigated to mitigate the negative impact of soybean meal on the nutrition and immune systems of various fish species. While advanced soy variants have proven beneficial, the effects are species-dependent and may contribute to improved alternative diet formulation if beneficial to CYT.
This study aimed to optimize soybean meal inclusion levels by incorporating advanced soybean meal variants in the CYT diet. Six isonitrogenous and isolipidic diets, featuring high protein low oligosaccharide soybean meal (Bright Day , Benson Hill, St Louis, MO) and an enzyme-treated soybean meal (HP 300 , Hamlet Protein Inc., Findlay, OH) at sequential inclusion levels (0, 50, 100%) replacing solvent-extracted soybean, were formulated for an eight-week feeding trial in a recirculation system. 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.
After eight weeks of dietary treatment, the results showed consistent FCR (P=0.775), weight gain (P=0.242), and high survival rate (99.4 ± 0.54%) among dietary treatments (P >0.05). Histological evaluations of the intestine revealed no significant gut inflammation, and gene expression analysis of immune and digestive markers apn (P=0.687) , mga (P=0.397) , gpx1 (P=0.279) , atpase (p=0.590) , il1β (P=0.659) shows no significant differences, affirming the health of CYT on the formulated diets. These findings indicate that the inclusion of advanced soybean meal products, replacing up to 20% of fishmeal, does not negatively affect CYT’s growth, intestinal morphology, or immune gene expression. A dvanced soybean meal products can be incorporated into CYT diets, limiting fishmeal inclusion to 10% and replacing up to 100% of commercial SE soybean meal without compromising intestinal integrity.
This has positive implications for the commercial production of C YT and future research.