Provided is a fish farming system whereby fish can be efficiently farmed. A fish farming system comprising a feeding tank (10) in which water supply and discharge, feeding and the discharge of farmed fish (5) are conducted through a pipeline (13) provided at the bottom thereof, a vertically movable feed-discharge unit (50) which drops into the feeding tank (10) for washing or suspending feed residues with the use of a washing brush being driven by a driving motor (65) and provided with a water jet spraying nozzle (62a), and a vertically movable buffer tank (80) which receives the farmed fish (5) in the feeding tank (10) and returns the same due to the spontaneous flow down.