Growth and physiology were compared in giant gourami (Osphronemus goramy) larvae reared in constant (25, 30, and 35 °C) and daily fluctuating (25–35 °C) temperature regimes. Larvae aged eight days post-hatching were reared indoors for 21 days in four closed recirculating systems (four aquaria per system) in the different temperature regimes. Samples of larvae were collected every week from each temperature regime for growth measurements. At the end of the experiment, cortisol and glucose concentrations, as well as oxygen consumption and ventilation rates, were determined in fish from each temperature regime. Results showed that the fluctuating temperature regime did not affect survival or abnormality, but significantly impaired growth in giant gourami larvae. Physiological responses, assessed using cortisol and glucose levels and oxygen consumption, corroborate previous findings, suggesting that a stable temperature of 30 °C is optimal for rearing giant gourami larvae. Our experimental approach demonstrated that temperature variations observed in larval rearing structures on small-scale fish farms are likely to impair the production of giant gourami fry.