There are about 28,000 species of bony fishes — the largest taxonomic group of vertebrates — and they have been around for a very long time (over 400 million years). So it’s no surprise that they have evolved a diverse array of ways to get around, some of them very specialized.
Many fishes, such as herring and trout, swim by flexing mainly the rear part of their muscular bodies, so that it and the tail fin press back against the water, pushing the fish forward. A streamlined body shape and a slippery body surface reduce friction and ease the forward motion. Other fishes propel themselves forward by using their fins — undulating the long dorsal or anal fins or paddling with the pectoral fins or some combination of those (e.g. boxfish). Sea horses, with their vertical orientation and tail used for grasping vegetation, swim forward by using their dorsal fin.
Although they lack legs and wings, some fishes “fly” or walk or climb. Flying fish (over 60 species in the tropics and subtropics) do not have powered flight, using wings as birds and bats do. They are really gliders, swimming fast to generate a strong leap from the water into the air, then gliding on outstretched pectoral and pelvic fins. The spine is reinforced in several ways that enhance a smooth glide. They are reported to stay aloft for almost a minute, gliding about 50 meters, although if they catch updrafts from waves they can sail up to about 400 meters, sometimes traveling at speeds over 40 miles per hour. This ability is thought to help the fish get away from predators.
Other fishes walk (or crawl), some in the water and some on land. For example, the walking catfish of Asia breathes air and propels itself on land by wriggling its body while supported by its pectoral fins. Mudskippers occur in intertidal habitats around the world. Their pectoral fins are unusual, having a “shoulder” and an “elbow” joint, which somehow gives them the ability to skitter over the mud and even jump (with the aid of the tail). This ability is used not only for travel but also for courtship, and at least some species can also climb low tree branches (presumably for short distances) using their pectoral and pelvic fins. African lungfish have long, filamentous pectoral and pelvic fins that are used to raise the submerged body above the substrate. These fins can be moved in patterns that resemble walking by a creature with legs, but the actual propulsion of the lungfish is said to come from body movement.
Some famous climbing fishes known as climbing gobies live in Hawai’i. The most impressive of these is called the ‘o’opu ‘alamo’o or Hawaiian freshwater goby (Lentipes concolor). This tiny fish, less than seven centimeters long (or 13 centimeters, says another source), is anadromous, breeding in fresh water but migrating to the sea as larvae to feed and grow, then returning to fresh waters as juveniles. Those little fish can climb waterfalls, reportedly as tall as a thousand feet, perhaps preferring parts of the waterfalls with weaker flow. Some of its close relatives can climb rocks too, perhaps not as steep and tall. They share the trait of fused pelvic fins that provide suction on the rock and presumably a brace for starting an upward push by the pectoral fins. That brace detaches as the fish undulates up, and then reattaches.
• Mary F. Willson is a retired professor of ecology. “On The Trails” appears every Wednesday in the Juneau Empire.
