Evaluation of Bacillus pumillus SE5 fermented soybean meal as a fish meal replacer in spotted seabass (Lateolabrax maculatus) feed

Abstract

The impacts of fish meal (FM) substitution with Bacillus pumillus SE5 fermented soybean meal (FSM) were investigated in spotted seabass juveniles. A diet containing 35% FM was considered as the basal diet, then 20, 40, 60 and 80% of FM was replaced with FSM (FM, FSM20, FSM40, FSM60 and FSM80 diets). The experimental diets were fed to three replicate groups of fish (14.3 ± 0.35 g) for eight weeks. The results showed linear and quadratic decrease of growth performance by increasing FM replacement level (P < 0.05). Feed consumption decreased linearly, and feed efficiency decreased linearly and quadratically by increasing FSM level. Furthermore, negative linear and quadratic trends were observed between FSM levels and protein efficiency ratio, and digestibility of protein, calcium and phosphorous. Serum total protein, cholesterol and triglyceride concentrations and alkaline phosphatase activity decreased linearly by increasing FSM level, and a linear increase was observed for alanine aminotransferase activity. Serum superoxide dismutase and lysozyme activities decreased linearly and quadratically with increasing FSM level while an opposite trend was observed for serum malondialdehyde concentration. Significant negative linear and quadratic trends were observed between FSM levels and intestinal protease and lipase activities. Increasing FSM level led to linear decrease of foregut villus height, and linear and quadratic decrease of villus and muscular thicknesses. Increasing FSM level led to linear increase of serum D-lactate concentration, and linear and quadratic enhancement of diamine oxidase activity. Expression of intestinal HSP70, IL-1β and TNF-α increased linearly and quadratically with increment of FSM level. The optimum replacement level of FM with the FSM was estimated to be in the range of 26.9–37.1% by broken-line and second-order polynomial regression analyses based on weight gain, feed efficiency, and lysozyme and superoxide dismutase activities.