In fish, water enters and leaves through the gills. Oxygen from the water passes through a thin membrane and into the blood-stream. Carbon dioxide passes the blood into the water in the gills. What organ-systems are interacting in the fish? Explain.

Gills which are responsible for fishes' respiration process, the gas exchange.

Respiratory system is the system responsible for an organismic gas exchange, to exhale carbon dioxide and inhale oxygen vital for the many cellular activities of an organism, this mainly happens in heterotrophs. On the other hand, autotrophs inhale carbon dioxide and exhale oxygen.