Diet-induced impairments in taurine flux affect the osmoregulatory and cardiac response to hypoxia in seawater acclimated brook char (Salvelinus fontinalis)

The accumulation of anaerobic end products under hypoxia can cause cardiac swelling, which impairs heart function. Cardiac taurine efflux prevents this from occurring in freshwater fish, but its importance in marine fish is unclear. Seawater acclimated brook char (Salvelinus fontinalis Mitchill, 1814) were fed either a control diet or one enriched in β-alanine to inhibit taurine flux. Dietary β-alanine reduced cardiac taurine levels to a greater extent than in freshwater brook char and its precursor hypotaurine accumulated in multiple tissues. In contrast to freshwater brook char, dietary β-alanine tended to increase resting heart rate in seawater fish. Neither heart taurine, nor plasma osmolality were affected by hypoxia in control animals, but plasma osmolality increased significantly in hypoxic taurine deficient fish. The mean heart rate response to hypoxia was not affected by β-alanine, but the hypoxic bradycardia was eliminated in some fish. Cardiac taurine flux appears less important to hypoxic heart function in seawater but is critical for whole animal osmoregulation. We additionally illustrate multiple salinity-specific effects of dietary β-alanine on the physiology and biochemistry of this species. These findings improve our understanding of osmoregulatory mechanisms in fish and how stress tolerance may be affected by shifts in diet.