Channoidei

(Snakeheads)

Class: Actinopterygii

Order: Perciformes

Suborder: Channoidei

Number of families: 1

Evolution and systematics

The single-family (Channidae) suborder Channoidei (snakeheads) is composed of only two genera, Channa, which includes all Asian species, and Parachanna, which includes all African species. The two genera differ mainly in the morphology of the air-breathing (suprabranchial) organ; that of the latter being less developed. Currently, 25 species of Channa and three species of Parachanna have been recognized. Although snakeheads have been considered a sister group of the Anabantoidei (climbing gouramies) or the Synbranchiformes (swamp eels), the relationship of snakeheads to other fish groups still remains uncertain. The earliest fossil record of snakeheads is Eochanna chorlakkiensis from the Kuldana Formation, Pakistan (middle Eocene).

Physical characteristics

Snakeheads form a morphologically unique group of primarily freshwater fishes, which greatly vary in size at maturity. Some species have distinctively small pelvic fins, while a few others lack them completely. Generally, snakeheads have an elongated cylindrical body; flattened head; long, entirely soft-rayed dorsal and anal fins; a large mouth with well-developed teeth on both upper and lower jaws; tubelike anterior nostrils; a round to somewhat truncate caudal fin; cycloid or ctenoid body scales; shield-like scales on a head that superficially resemble that of a snake; a lengthy, elongated swim bladder reaching to the caudal peduncle region; and an accessory air-breathing apparatus (suprabranchial organ) in the head region. This suprabranchial organ is mainly composed of three parts: a suprabranchial chamber, epibranchial respiratory fold, and hyomandibular process.

Species of snakeheads can be distinguished based on coloration, meristics, and morphometrics, as well as the distribution of scales on the underside of the lower jaw, the shape of the head, and the morphology of the suprabranchial organs. Much taxonomic confusion has resulted from the fact that coloration in each species changes dramatically during growth, and in many cases, the color of juveniles is completely different from that of adults. One such case is the giant snakehead (Channa micropeltes), a popular aquarium fish that has striking black and red "racing stripes" as a juvenile, but variegated blackish markings as an adult. Many species have distinct adult coloration, such as ocellus (ocelli) on the body and/or caudal fin, vertical bands on the pectoral fins, and small spots on the body.

Distribution

Members of the genus Channa are widely distributed, occurring from Iran in the west, to China and southeastern Russia in the east, and throughout Southeast Asia, extending downward into the Philippines and Indonesia (Java being the southernmost location). Species of the genus Parachanna are restricted to central West Africa. Species are most diverse in tropical Asia. Some species are endemic to restricted areas that include special features such as tropical rainforests, such as the walking snakehead (Channa orientalis) from southern Sri Lanka, and the orange-spotted snakehead (Channa aurantimaculata) and rainbow snakehead (Channa bleheri) from northern Assam. Some species are now found outside their natural distributions, apparently as a result of human introduction. These include established populations of the northern snakehead (Channa argus) in Japan, the United States, and Aral Sea basin; the blotched snakehead (Channa maculata) in Japan; the bullseye snakehead (Channa marulius) in the United States; and the striped snakehead (Channa striata) in the islands of Indonesia east of Wallace's line, Papua New Guinea, New Caledonia, Fiji, Hawaii, Mauritius, and Madagascar. In Madagascar the striped snakehead has had a severely detrimental effect upon the island's endemic freshwater fish fauna.

Habitat

Most snakeheads prefer stagnant or slow-running waters, usually hiding under vegetation, rocks, and sunken trees. However, large species such as the northern snakehead, bullseye snakehead, and giant snakehead can usually be found inhabiting relatively deep waters with somewhat heavy vegetation in low, open country such as large rivers, swamps, ponds, and reservoirs. One species, the banka snakehead (Channa bankanensis), has been found only in peat swamps, which have dark brown, highly acid water. Most small species, such as the walking snakehead, usually live in mountain streams, but can also be found in lowland habitats. The northeastern Indian barca snakehead (Channa barca), a large species attaining 35.4 in (90 cm), is reported to live in holes within the banks of ponds and rivers. Many snakeheads are highly adaptable, being tolerant to a wide range of environments, including polluted waters.

Behavior

Highly territorial, snakeheads usually stay hidden, and migrate only short distances. Fry of some species have been reported to be cannibalistic, opportunistically eating eggs from a later spawn. Generally, the young tend to school. Snakeheads appear to need to breach the water surface periodically to exchange the air in their suprabranchial chamber. Experiments have shown that breathing surface air is far more important to them than using their gills. This is supported by evidence from the drowning deaths of fishes that have been caught in nets under water, and could not surface to breathe. Some species of snakeheads can live out of water for several days if their bodies are wet, amazingly migrating on land during the raining season by using their bodies, pectoral fins, and caudal fins. However, no one has reported them feeding while moving on land. The striped snakehead (Channa striata) has been reported to survive in the bottom mud of lakes, swamps, and canals that have dried up; fishermen using long knives to cut away the mud in layers have found these fishes singly or in clusters within cavities of the mud.

Feeding ecology and diet

Active during the day, although the dwarf snakehead (Channa gachua) has been reported to be nocturnal, all snakeheads are predatory, ambush feeders, eating almost any animal smaller than their mouths. Usually solitary feeders as adults, as juveniles they actively migrate in schools, hunting foods such as zooplankton, small insects, and crustaceans. Adult snakeheads feed on everything from insects (both terrestrial and aquatic) to young birds, including fishes, frogs, tadpoles, lizards, geckos, mice, rats, and ducks. They primarily hunt by sight, but smell and other senses may also be involved. They sometimes jump up from the water surface to grasp their prey.

Reproductive biology

Although the reproductive biology of many species of snakeheads is still unknown, it does appear that they are monogamous, exhibit parental care, and become aggressive, especially so during breeding. Many are known to be nest breeders, the parents first clearing vegetation and then building a simple circular nest at the water surface. In these species, there is a spawning embrace with the male encircling the female, squeezing the eggs out, and fertilizing them. The eggs float upward into the nest, usually guarded. After hatching, the fry will be cared for by either parent, dependent on species. The giant snakehead, with its strong canine-like teeth, has been known to attack and seriously injure humans who disturb it, especially while guarding its brood. On the other hand, two small species, the walking and dwarf snakeheads, are known to be mouth brooders, with the male reported to keep the fertilized eggs, and later fry (for a few days), in his mouth.

Conservation status

Although generally not threatened, the status of populations of some species are poorly known. No species are included on the IUCN Red List.

Significance to humans

Most channid species are important food fishes in southern Asia and China and the flesh is considered delicious. Some medium-to-large species are cultured in ponds or in cages set in slow-running rivers. Although sold fresh and sun-dried, several species, northern snakehead (C. argus) and striped snakehead (C. striata), are known as intermediate hosts of parasites harmful to humans, including Gnathostoma (jaw worms), and should be cooked thoroughly at a high temperature before eating. Two species have even been used as predators to control tilapia in aquaculture ponds. Larger species are popular game fishes in Asia, and several species feature in local beliefs or myths. In October 2002, the U.S. Fish and Wildlife Service passed a rule that prohibits the importation of live snakeheads into the United States except by scientific, medical, or educational organizations, which would be required to obtain a permit to import the fishes.

Species accounts

Resources

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[Article by: Prachya Musikasinthorn, PhD]

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