If you've spent any amount of time boating, fishing, or bird-watching at lakes and rivers, you have most likely seen fishes jumping out of the water. I have seen it many times. Certainly, fishes will exit water in desperate attempts to escape enemies. Dolphins take advantage of the behavior, forming a circle and catching the frightened fishes in midair. But just as we may run fast from fun or from fear, different emotions might motivate fishes to jump.
Mobula rays (蝸鲼) aren't motivated by fear when they throw their impressive bodies—up to a seventeen-foot wingspan (the distance from the end of one wing to the end of the other) and a ton in weight—skyward in leap (跳跃) of up to ten feet. They do it in schools (鱼群) of hundreds. They usually land on their bellies, but sometimes they land on their backs. Some scientists think it might be a way of removing parasites (寄生虫) . But I think that the rays are enjoying themselves.
In the clear waters of Florida's Chassahowitzka National Wildlife Refuge, I watched several schools of fifty or more mullets (鲻鱼) moving in beautiful formation. Their well-built bodies were most evident when they leaped from the water. Most of the time I saw one or two leaps by a fish, but one made a series of seven. They usually land on their sides. Each jump was about a foot clear of the water and two to three feet in length.
Nobody knows for sure why the fish leaps. One idea is that they do it to take in oxygen. The idea is supported by the fact that mullets leap more when the water is lower in oxygen, but is challenged by the likelihood that jumping costs more energy than is gained by breathing air. It is hard to imagine they will feel any fresher when back in water.
Might these fishes also be leaping for fun? There is some new evidence. Gordon M. Burghardt recently published accounts of a dozen types of fishes leaping repeatedly, sometimes over floating objects—sticks, plants, sunning turtle—for no clear reason other than entertainment.
