Evaluation of solvent extracted, dehulled soybean meal in diets fed to largemouth bass micropterus salmoides
Global harvest regulations on marine species are increasing and so to are the demand for the fish meal (FM) derived from such fish. Therefore it is paramount for alternative protein sources to FM if aquaculture is to be sustainable. Integral to sustainability, future culture species must be fed diets containing significantly less FM. Largemouth bass (LMB) could be such a candidate. Largemouth bass domestic availability is associated with their popularity in sport fishing and more recently in fish production associated with Asian markets. Because there is a growing interest in culturing LMB, more research is needed to assess their potential as a culture species. Therefore, the purpose of this study was to evaluate the effects of graded levels of soybean meal (SBM) in practical diets fed to largemouth bass Micropterus salmoides. Solvent extracted, dehulled SBM was substituted into the diets for an isonitrogenous amount of FM. Soybean meal concentrations were added in increments of 10 % of the control diet, and ranged from 0 to 60 %. Ten fish (initial average weight 30.2 g) were stocked into each of 21 tanks (190 L per tank) with water temperature held at 25° C. Triplicate groups were randomly assigned to one of seven different dietary treatments (n = 3). Each tank was fed to satiation twice daily for 8 weeks. At the end of the study, fish were euthanized, and serum, muscle, liver, and intestines from three fish per tank were collected and immediately flash frozen in liquid nitrogen and stored at -80° C until processing. The corresponding tissue and serum samples were then used for metabolomic profiling. Additional intestine samples were preserved in 10 % neutral buffered formalin for histological examination. Mean consumption of diet 1 (0 % SBM) was significantly higher than diet 4 (30 % SBM). There were no other significant differences among consumption values. Weight gain of fish fed diets 2 and 3 (10 and 20 % SBM, respectively) were significantly higher than in fish fed diet 4; there was no other significant difference in weight gain among treatments. Hepatosomatic index of fish fed diet 2 was significantly higher than that in fish fed diet 4 and diet 5 (40 % SBM). Feed conversion ratio, specific growth rate, and visceral fat index were not significantly different among treatments. Results of blood serum response parameters were not statistically significant with the exception of alkaline phosphatase which was significantly lower in diet 4 relative to diet 1. Potential biomarkers of lysine degradation (2-piperidinecarboxylic acid, pentanedioic acid, and alpha-aminoadipic acid) were identified in muscle, liver, serum, and intestine samples. Histological analysis showed potential signs of mild enteritis in the distal intestine of fish fed diets 6 and 7 (50 and 60 % SBM, respectively). Overall, results of this study indicate that LMB seem to tolerate high levels of SBM in practical diets. Further research is needed to evaluate FM free diets containing high SBM inclusion in production size LMB.
Brown, Purdue University.
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