Why do mullet leap?

Mullet are commonly seen leaping out of the water. Why do they do this?

Over the years there have been numerous theories concerning the leaping of mullet. There seems to be two categories of leaping: predator avoidance and aerial respiration.

Leaping to avoid predators usually involves more than one fish jumping simultaneously, retaining an upright posture and entering the water cleanly.

The second type of leaping involves a single fish that does a slower, shorter leap, often flipping onto its side or even onto its back. They may also roll at the surface or move with their head above the water.

The research of Hoese (1985) suggests that Sea Mullet use this second category of movements to fill the pharyngobranchial organ (an area at the back of the throat) with air.

The trapped air is believed to allow the fish to remain active in water of low oxygen concentration for about five minutes.

Several interesting lines of evidence support this theory. The number of jumps is correlated with the concentration of oxygen in the water. The less oxygen, the more jumps.

Secondly, Sea Mullet feed during the day often in bottom sediments that have low oxygen concentrations. Jumping occurs much more commonly during the day. Sea Mullet rarely jump at night.

Further reading

1. Hoese, H.D. 1985. Jumping mullet - the internal diving bell hypotheses. Environmental Biology of Fishes. 13(4): 309-314.