Alterations in feeding preference and gastric emptying of giant freshwater prawn (Macrobrachium rosenbergii) following administration of varying quantities of fermented soybean meal

Abstract

This study aimed to investigate the impact of partially substituting fish meal (FM) and soybean meal (SBM) in the diet with fermented soybean meal (FSBM) on growth, feeding preference, protease activity, and their correlation with gastric evacuation in giant freshwater prawn, Macrobrachium rosenbergii. A 55-day feeding trial was conducted with eight isonitrogenous and isoenergetic diets, followed by a gastric emptying experiment. The results showed that the control group (containing 30% FM and 18% SBM) exhibited the highest feeding preference index, and the SBM-free group (almost devoid of soybean antigen proteins) showed the lowest preference index. Moreover, all diets displayed an initial decrease in preference index followed by an increase and subsequent decline with increasing levels of supplemental fermented soybean meal. This pattern was also observed in terms of digestive enzymes and stomach emptying rates. Notably, there was the same tendency in feeding preference before and after short-term domestication (55 days), and it was consistent with the trend of feeding rate. All the presented findings indicated that the inclusion of fish meal is a crucial factor influencing the feeding preference of M. rosenbergii. The substitution of fish meal and soybean meal in feed with fermented soybean meal would induce feed aversion in M. rosenbergii, which significantly contributes to the decline in growth rate. However, when fermented soybean meal replaced fish meal and soybean meal, the individual action or interaction between antigenic proteins and other anti-nutritional factors resulted in varying changes in digestive enzyme activity and gastric evacuation dynamics.