It is a natural unconditional reflex, and there is too little oxygen. The oxygen a fish breathes is brought by the water in its gills, and it has no nose. If there is too little oxygen in the water, it will jump.

Most fish breathe through gills. When a fish breathes, it regularly sucks water from its mouth and forces it to flow out through its gills. At this time, gills will absorb oxygen through contact with water flow, and the flow of water can also ensure that fish will not lose their breathing ability because of the mutual adhesion between gills.