Macrophytes mitigate Microcystis aeruginosa-induced fish appetite suppression via intestinal metabolite regulation

Cyanobacterial blooms and aquatic macrophytes can affect the health, physiology, and behavior of freshwater fish. Changes in food intake can be a key indicator of stress in teleost fish, while changes in metabolite abundance in the gut can indicate a shift in metabolic priorities, including response to environmental stressors. Here, we exposed stone moroko (Pseudorasbora parva) to the cyanobacterium Microcystis aeruginosa and/or the macrophyte Ottelia acuminata and analyzed changes in fish health, appetite regulation, and intestinal metabolome after 96-h exposures. We found that O. acuminata treatment didn't change the tested indicators, while exposure to M. aeruginosa increased concentrations of appetite-inhibiting factors, such as CART and GLP-1, and decreased concentrations of stimulatory factors like orexin. Exploration of the metabolome following exposure revealed that the appetite-inhibiting influence of M. aeruginosa was positively correlated with key metabolites of lipid, amino acid, and cholesterol metabolism, especially those associated with bile acid synthesis and secretion. Further, the presence of O. acuminata decreased the adverse effects of M. aeruginosa among neuro-endocrine regulatory factors, which could be explained by altered regulation of intestinal amino acid metabolites. The deeper mechanism by which O. acuminata moderates the harmful effects of M. aeruginosa remains to be identified.