Changes in the environmental temperature mediate oxidative stress state that affects the survival rate of fishes. In general, stressors could affect directly as fish death or indirectly through inhibiting immunity thus allowing pathogen invasion and disease incidence. Rapid temperature fluctuations cause severe physiological stress on fish so any temperature change affects the immune system. Fishes elicit generalized physiological and immunological stress response against heat stress. As in other vertebrates, this generalized stress response comprises physiological responses that are common to a wide range of environmental, physical and biological stressors. This mini review provides insight into the effect of heat stress on the fishes and the immune response against heat stress.