Abstract: Apparatus and a method for obtaining and maintaining life-sustaining water conditions in tanks carried on trucks to keep fish alive for relatively long periods during transport. A flow of air from a blower is cooled in a heat exchanger by a stream of air from a refrigeration unit used also to cool a space enclosing the tanks, and the flow of air thus chilled in the heat exchanger is released into the water in the tanks through diffusers, cooling and aerating the water. Rising air from a diffuser can also be used instead of a pump to circulate water from a tank through purifiers. The blower used to provide the flow of air to the diffusers is driven by the engine associated with the refrigeration unit, providing a highly reliable, simple, system.