Tuna (<i>Thunnus alalunga</i>) Gill Extract Alters Gut Microbiota Composition and Increases Fecal Immunoglobulin A Levels in Male Mice

Intake of fish and fish-derived collagen degradants improves immunity and intestinal microbiota composition. In this study, we aimed to examine the effects of tuna gill extract (TGE) on intestinal immunity and the amino acid composition of mice. TGE was prepared and administered to male mice and splenocytes were collected from the spleen. Then, its effects on the intestinal immune system were compared between salmon collagen peptide (SCP) and TGE. Supplementation of TGE or SCP at 1% significantly increased fecal immunoglobulin A (IgA) levels and the relative Lactobacillus spp. abundance in male murine intestines. Supplementation did not affect intestinal organic acid levels; however, hydroxyproline was detected in the feces from TGE- and SCP-supplemented mice. These results indicate that TGE, a byproduct of fisheries, could be used to improve intestinal immunity in mice.