Glutamate and serotonin enhance feeding performance, digestive enzyme activity, and immunity in the female giant freshwater prawn, Macrobrachium rosenbergii

Abstract

This study investigated the presence of glutamate (Glu) and serotonin (5-HT) in the digestive organs and their effects on feeding performance, digestive enzyme activity, and immunity throughout the ovarian cycle in female giant freshwater prawns (Macrobrachium rosenbergii). By high-performance liquid chromatography (HPLC), Glu and 5-HT were detected in the foregut, midgut, hindgut, and hepatopancreas, at the highest concentrations in the late ovarian stage and the lowest concentrations in the early ovarian stage. Through immunohistochemistry, the presence of Glu-immunoreactivity (-ir) and 5-HT-ir were observed in all digestive organs, and their intensities were shown to correlate with the levels detected by those observed via HPLC. Prawns injected with Glu and 5-HT at the doses of 2.5 × 10⁻⁶ and 2.5 × 10⁻⁷ mol/prawn, markedly increased food consumption, gastric emptying, and midgut index as well as enhanced amylase, protease, and lipase activities, compared with the control group (P < 0.05). Glu and 5-HT also enhanced epithelial cell height, villi height, and crypt depth and promoted the reactivity of PAS/AB in the digestive organs. In addition, treatment with Glu or 5-HT significantly upregulated M. rosenbergii NPF (MrNPF) and immune-related transcripts (P < 0.05). Collectively, these findings demonstrated the promising effects of Glu and 5-HT at a dose of 2.5 × 10⁻⁶ mol/prawn in stimulating feeding, digestive activities, and immunity, which could potentially be used to enhance feeding, growth, and maintain the health status of female prawn in aquaculture.