As global fishmeal demand outpaces capture fisheries supply, the aquaculture industry has made alternative protein feedstuffs, especially from plant sources, a focus to support the continued expansion of world aquaculture. However, extensive replacement of fishmeal in aquatic diets may lead to a limiting availability of some amino acids (AAs), especially in high- protein diets for carnivorous fish. As industry standard inclusion levels of fishmeal decrease, traditionally classified dispensable AAs could become limiting, leading to both decreased growth and metabolic disorders. Therefore, an 8-week comparative feeding trial followed by an immune challenge was conducted to assess the effects of glycine supplementation as a functional AA in soybean-meal (SBM)-based diets fed to hybrid striped bass with a mean initial body weight of 1.6 g/fish. The basal diet (38% crude protein (CP), 2.23% glycine, and 10% crude lipid) was composed of practical ingredients with SBM contributing 75% of total CP. Along with the basal diet, experimental diets were supplemented with either 2% glycine, 0.2% glutathione, 0.1% buthionine sulphoximine (GSH inhibitor), and combinations thereof. At the conclusion of the comparative feeding trial, 100 µg of 2,4,6-trinitrophenyl lipopolysaccharide (TNP-LPS) or phosphate buffered saline were injected intraperitoneally into fish fed the basal and 2% glycine diets, which were then sampled for superoxide anion and hydrogen peroxide production 7 days post injection to assess innate immune responses.
Groups of 15 juvenile HSB (~1.6 g/ fish initial weight) were stocked into 36 , 38-L aquaria fashioned as a recirculating aquaculture system with sextuplicate aquaria randomly assigned to each dietary treatment. Fish were fed to apparent satiation twice daily for 8 weeks. HSB fed the diet supplemented with 2% glycine exhibited significantly (P<0.05) higher weight gain compared to fish fed diets without supplementation of this AA (Figure 1), although feed efficiency was not affected by experimental diets. Analysis of A A and glutathione concentrations in plasma and v arious other tissues of HSB is currently ongoing, along with determination of whole-body proximate composition.
Additionally, protein synthesis in tissues, measured using the [3H]phenylalanine flooding dose technique, is in progress. HSB head kidney-derived leukocytes presented no statistical differences in respiratory burst or hydrogen peroxide production when injected with TNP-LPS for either experimental group. Results of the current study suggest positive effects of glycine supplementation to HSB based on growth performance. More data are required to determine the functionality of this AA in a SBM-based diet for the fish.