Bony Tongues and Relatives: Osteoglossiformes
BONY TONGUES AND RELATIVES: Osteoglossiformes
Bony tongues are called that because most of their teeth are on the tongue and the roof of the mouth. They are odd-looking fishes. The head structure varies according to the way the different types of bony tongues feed. The tail fins of bony tongues have fewer rays, or supporting rods, than the tails of other fishes. Some bony tongues have long heads, and some have trunklike snouts, or nose areas. Bony tongues are 1.6 inches to 5 feet (4 centimeters to 1.5 meters) long.
Many bony tongues and their relatives live near the surface of slow-moving rivers and lakes or ones that are stagnant, or still and stale. Some live at all depths in large rivers and lakes. Others prefer habitats with dense, or thick, plant life. Some bony tongues live in muddy water, sometimes in swift currents.
Bony tongues and their relatives eat plankton, that is, microscopic plants and animals drifting in the water; insect adults and larvae (LAR-vee), or young insects in the early stage of growth before becoming adults; crustaceans (krus-TAY-shuns), or shelled animals with jointed legs, such as shrimp; earthworms; snails; and other fish. Some even eat frogs and mice. Some bony tongues feed at the water surface, at middle depths, and others are bottom feeders. The bony tongues with long snouts find their prey in holes and crevices (KREH-vuh-suhz).
BEHAVIOR AND REPRODUCTION
Some bony tongues and their relatives are nocturnal (nahk-TER-nuhl), often hiding during the day in dense plant cover or under other kinds of cover and coming out to hunt in the evening. Others are active during the day, spending most of their time patrolling very close to the surface. During the summer, when the water surface becomes very hot, the fishes stay in deeper, cooler areas.
Most bony tongues and their relatives breed during the rainy season, usually the spring. The size of the eggs, or female reproductive cells, ranges from 0.07 inches (1.8 millimeters) to 0.6 inches (16 millimeters). Eggs number between a few hundred and more than one thousand, depending on the species, or type of fish. Some bony tongues spawn, or produce and release eggs, every few days, and others spawn once every several weeks. Some bony tongues are mouth brooders: the female or the male, depending on the species, takes the fertilized (FUR-teh-lyzed) eggs, the ones that have joined with sperm, or male reproductive cells, and have begun development, into its mouth and keeps them there until they hatch. In some species the males and, in others, the females guard and fan the nest, that is, use their fins to move water over the eggs to keep them clean and give them oxygen.
BONY TONGUES AND THEIR RELATIVES AND PEOPLE
Most bony tongues and their relatives, particularly the larger species, are important food fishes. Bony tongues are used in public and home aquariums.
THE VARIETY OF BONY TONGUES
There are many species of bony tongues. Only one of them, the mooneye, lives in North America. The arapaima, which lives in the Amazon region of South America, is one of the largest freshwater fishes, weighing as much as 441 pounds (200 kilograms) and reaching a length of 15 feet (4.5 meters). The elephantfish is weakly electric. Other bony tongues are the arowana, the clown knifefish, and the elephantnose fish.
The World Conservation Union (IUCN) lists one species of bony tongue, the Asian arowana or dragon fish, as Endangered, meaning that it faces very high risk of extinction in the wild.
Physical characteristics: Freshwater butterflyfishes (also called but-terflyfishes) are called that because their large pectoral (PECK-ter-uhl)fins, the front set of paired fins, look like the wings of a butterfly. The pelvic fins, the rear set of paired fins, have long rays that are not covered with skin. The fanlike tail fin is quite large. Freshwater butterfly-fishes reach a length of 3.9 inches (10 centimeters). The upper part of the body is olive green, and the bottom is silvery yellow with touches of red. Freshwater butterflyfishes are not related to the butterflyfishes that live in coral reefs.
Geographic range: Freshwater butterflyfishes live in central Africa.
Habitat: Freshwater butterflyfishes live near the surface in stagnant water.
Diet: Freshwater butterflyfishes eat crustaceans, insects, and small fishes.
Behavior and reproduction: Freshwater butterflyfishes can jump out of the water. They do this for feeding or to escape predators (PREH-duhters). They have been seen gliding 13 to 16 feet (4 to 5 meters), but scientists want more proof of this behavior, because they do not believe the muscles that support the pectoral fins are large enough for lengthy flight. These fishes can use the swim bladder, an internal sac that fishes use to control their position in the water, to breathe air.
Freshwater butterflyfishes have a long spawning season. Each night they lay between eighty and two hundred buoyant eggs, or eggs that can float on the water. The embryos hatch after thirty-six hours. These fishes grow quickly, reaching their adult length within one year.
Freshwater butterflyfishes and people: Freshwater butterflyfishes are used in home aquariums.
Conservation status: Freshwater butterflyfishes are not threatened or endangered. ∎
FOR MORE INFORMATION
Berra, Tim M. Freshwater Fish Distribution. San Diego, CA: Academic Press, 2001.
Ricciuti, Edward R. Fish. Woodbridge, CT: Blackbirch, 1993.
Butler, Rhett Ayers. "Pantodontidae Family." http://fish.mongabay.com/pantodontidae.htm (accessed on September 4, 2004).