Dietary soyasaponin and prebiotics modulate intestinal health and function in the cleaner fish Ballan wrasse (Labrus bergylta)
This paper presents data from a 5-week feeding trial in which Ballan wrasse was fed either a reference diet, or the identical diet supplemented with i) the antinutrient soya saponin (0.7%) ii) a commercial prebiotic (Aquate™ SG, 0.4%) or iii) a combination of soya saponin and prebiotics. Blood, tissue and gut content from four separate intestinal segments were sampled from 6 fish per duplicate tank. Gut health and digestive functions were evaluated by various endpoint measurements employing biochemical and histomorphological tools as well as global gene expression profiling. No significant differences in fish growth were seen between the four dietary groups. Saponin supplementation, both alone and in combination with prebiotics, increased weight indices of two mid gut segments (IN2 and IN3) and decreased blood plasma glucose, cholesterol and total protein. Dry matter of intestinal content and activity of digestive enzymes were not affected by diet. Histomorphological analyses revealed clear structural alterations in the gut of fish fed saponin, both alone and in combination with prebiotics. The results indicated a progressing inflammation with increased infiltration by immune cells particularly into the distal parts of the intestine. Gene expression profiles obtained by RNA sequencing and quantitative PCR mirrored the histological and biochemical changes induced by the saponin load. The work has provided novel basic knowledge on the anatomy, digestive and immune function of the Ballan wrasse intestine. Additionally, the study demonstrated that Ballan wrasse gut health and digestive function may be markedly affected by diet composition. Overall design: Five week feeding trial with ballan wrasse fed fed either a control diet, controll+sapanonis, controll+prebiotics og controll+saponins+ prebiotics.