Fish jump in order to move through their habitat, catch flying prey and escape predators. Leaping allows them to travel upstream and avoid obstacles. Fish caught on a hook by fisherman often jump out of the water in an effort to dislodge it. Aquarium fish jump out of their tanks due to fear, to escape dirty water or to amuse themselves.
Aquarium fish that remain habitually near the surface are the most likely to jump. They often try to catch flying insects. Bottom-dwelling aquarium fish are less likely to jump, although when they reach the corner in the tank, they are curious and sometimes follow it upwards in hopes of finding food. They are easily startled by movements outside the tank, and they sometimes jump in fear.
Jumping is not risky behavior for fish in their natural habitat because they possess the ability to wriggle back to the water if they land on the shore. Jumping can be fatal for aquarium fish because they cannot get back into the tank if they land outside. In order to prevent this, aquariums should have covers. Since small aquarium fish can fit through openings designed for filters and heaters, all openings should be blocked.