Effects of Dietary Soya-Saponins on Growth Performance and Intestinal Health in Juvenile Largemouth Bass (Micropterus Salmoides)

Abstract

This study investigated the effects of dietary soya-saponins (SS) on the growth and intestinal health of juvenile largemouth bass (Micropterus salmoides). Four isonitrogenous and isolipidic diets were formulated: a fish meal (FM)-based control diet and three experimental diets supplemented with 0.1%, 0.2%, and 0.6% SS (denoted as SS0.1, SS0.2, and SS0.6, respectively). Each diet was randomly assigned to triplicate tanks (20 fish per tank, initial body weight: 7.60 ± 0.03 g), and the feeding trial lasted for 8 weeks. The results demonstrated that SS significantly impaired the growth performance of largemouth bass in a dose-dependent manner. Hematoxylin-eosin and transmission electron microscope analyses revealed that SS severely damaged intestinal morphology, characterized by significantly reduced plica height (PH), plica width (PW), and muscular layer thickness (MLT), along with a notable decrease in goblet cell (GC) numbers. Additionally, SS induced pathological alterations in intestinal cells and organelles, including sparse and disorganized microvilli, vacuolization of GC, nuclear pyknosis, loss of mitochondrial cristae, and dilation of the endoplasmic reticulum. SS reduced intestinal antioxidant capacity, as evidenced by markedly decreased activities of superoxide dismutase (SOD), glutathione peroxidase (GSH-PX), catalase (CAT), total antioxidant capacity (T-AOC), and increased malondialdehyde (MDA) levels. Furthermore, SS compromised immune function and induced hepatic damage, supported by significantly reduced serum acid phosphatase (ACP) and alkaline phosphatase (AKP) activities and elevated alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels. Meanwhile, SS increased intestinal permeability, indicated by significantly higher serum concentrations of lipopolysaccharide (LPS), D-lactate (D-Lac), and diamine oxidase (DAO). Furthermore, 16S rRNA sequencing indicated that SS disrupted gut microbiota homeostasis, increasing the abundance of potentially pathogenic bacteria (Acinetobacter, Pseudomonas, Escherichia-Shigella, and Serratia). Transcriptomic analysis revealed that the SS0.6 group exhibited significant down-regulation of the PI3K-Akt signaling pathway and B cell receptor signaling pathway compared to the FM group. Group SS0.6 significantly downregulated intestinal barrier-related genes (claudin3, claudin8, and nectin4) while up-regulating pro-inflammatory factors (cox2) and chemokines (ccl4). In conclusion, dietary SS adversely affects the growth performance and intestinal health of juvenile largemouth bass, potentially mediated by gut microbiota dysbiosis and inflammatory responses.

Keywords: Micropterus salmoides, Soya-saponin, Inflammation, Gut microbiota, Transcriptomic