<p>Taurine is the most abundant free amino acid in heart and is important in tissue volume regulation. β-alanine, a common dietary amino acid, decreases cardiac taurine flux in fish and negatively impacts their responses to stress. Brook char (<i>Salvelinus fontinalis</i>) fed a β-alanine enriched diet to induce taurine deficiency (TD) have lower heart rates and less pronounced decreases in heart rate (bradycardia) under hypoxia, but impacts on blood flow in vivo have not been examined. We aimed to determine if changes in taurine flux constrain cardiac output under hypoxia and to characterize the role of autonomic control in this response. We measured rates of oxygen consumption (<i>Ṁ</i>O₂) and cardiorespiratory parameters in brook char acutely exposed to hypoxia (partial pressure of oxygen of 8.33&#xa0;kPa). Resting heart rate and the magnitude of the bradycardia were lower in TD fish, as was the effect of hypoxia on <i>Ṁ</i>O₂. Diet did not influence stroke volume, but cardiac output was consistently lower in TD brook char. Heart rate variability was higher in TD fish due to subtle changes in cholinergic and adrenergic tones on the heart. A lack of lactate accumulation indicated that the hypoxic stress was insufficient to challenge fluid volume regulation, but resting heart function and its response to hypoxia were still altered by dietary β-alanine. The influence of diet on cardiorespiratory function is poorly understood in fish and the nutritional landscape of aquatic ecosystems is changing; our results illustrate potential mechanisms by which diet can impact stress tolerance in fish.</p>