Abstract
INTRODUCTION: Histamine commonly accumulates in animal-derived feed ingredients and is detrimental to aquaculture species, but the adverse consequences of dietary histamine remain inadequately characterized. Here, we explored the physiological influences of different dietary histamine levels on the growth performance, as well as the intestinal and hepatic health, of American eels, a fish species intolerant to histamine. METHODS: Five diets were prepared with total histamine levels of 48.94, 198.19, 355.31, 492.44, and 641.37 mg kg(-1), respectively. Following a 10-week feeding trial, growth performance, intestinal and hepatic morphology, antioxidant capacity, intestinal microbiota composition, and hepatic metabolites were analyzed. RESULTS: American eels receiving diets with histamine levels exceeding 355.31 mg kg⁻¹ exhibited reduced growth performance, feed utilization, immune competence, intestinal mucosal and hepatocellular integrity, intestinal and hepatic antioxidant capacity, and intestinal digestive enzymes activities, along with elevated intestinal and hepatic malondialdehyde contents, compared to those fed the diet containing 48.94 mg kg(-1) histamine. Omics profiling further indicated that, relative to the dietary histamine level of 48.94 mg kg(-1), the 641.37 mg kg(-1) dietary histamine restructured intestinal microbiota composition by reducing the abundance Enterococcus and Rhodococcus while increasing the levels of Haliangium, Stenotrophomonas, and Blastomonas; and affected hepatic aminoacyl-tRNA biosynthesis, glycine/serine/threonine metabolism, nicotinate/nicotinamide metabolism, and valine/leucine/isoleucine biosynthesis in American eels. Broken-line regression analysis of weight gain rate identified 260.11 mg kg(-1) as the maximum tolerable dietary histamine level for American eels. CONCLUSION: These findings provide crucial insights regarding dietary histamine levels and underscore the importance of restricting histamine content in American eel diets.