Total dissolved gas, dissolved oxygen, dissolved nitrogen, pH, conductivity, temperature, and turbidity were monitored to determine diel and annual changes in a mariculture pond and in aquaria supplied with water discharged from a power plant. The diel and annual ranges of all hydrological parameters were greater in the pond than in aquaria. Diel patterns were similar in both cases but the amplitude was attenuated in the laboratory aquaria. Gas bubble disease (OBD) developed in 17 marine and estuarine fishes and in grass shrimps in the laboratory. GBD was more prevalent in aquaria at higher temperatures than in aquaria at lower temperatures. The disease occurred only in the winter months and was simultaneously found in fish in aquaria and in fish cultured in cages in the discharge canal. GBD was attributed to nitrogen supersaturation produced as water passed through the power plant and also to pump cavitation and to changing fish from water of high saturation to water oflow saturation during cleaning of tanks. Degassing technology must be applied to heated effluents and aquaculture facilities incorporated into power plant design if their full potential for aquaculture is to be realized.