The aim of the present study was to evaluate the effect of halquinol, an antimicrobial used as a growth promotor in poultry, on the fresh water fish Catla catla in terms of growth promotion, protein profile, and physiology as the rate of oxygen consumption. A synergic increment in the free amino acid level and total protein concentration suggested enhanced anabolic metabolism resulting in weight gain. When compared with an untreated control group, fishes treated with 0.1% halquinol (T1) showed a higher weight gain than those treated with 0.2% halquinol (T2). Variations in the rate of oxygen consumption among the three groups (control, T1, T2) expressed the physiological response of the animals toward the chemical along the time factor. After 7 days of treatment, the absence of halquinol revealed by post-withdrawal residual HPLC studies suggests its biosafety.