Clown Knifefish

The clown knifefish belongs to the family Notopteridae, which can be found in Africa and Asia (including India). Notopterids can be characterized by their laterally compressed bodies accompanied by an elongated anal fin. The origin of notopterids can be traced back to the Early Cretaceous when the African and Asian clades split, redistributing the genus between both regions.

Clown knifefish are ectotherms native to tropical fresh waters in Southeast Asia, specifically the Mekong, Chao Phraya, and Mae Klong Basins surrounding Laos, Thailand, Cambodia, and Vietnam. They are nocturnal, remaining inactive in covered areas during the day and out hunting at night. While native to the tropics of Asia, they are also found in Florida and Sri Lanka. They are widely known to be an invasive species outside their native region. Past high demands in aquaculture and aquarium trading have introduced the clown knifefish to new waters. They are usually exported as juveniles and raised by ornamental fish breeders that have accidentally and deliberately released the invasive species. Their ability to tolerate high salinity and polluted waters have led to the predation of several endemic and endangered native species.

These fish are primarily carnivorous, allowing them to widen their food spectrum in response to environmental changes In their native habitat, they have very few natural predators; they are at the top of the food chain in newly inhabited waters, often preying on smaller fish, crustaceans, and insects. Adults are known to be territorial and prefer to travel alone. Clown knifefish migrate locally, but are not migratory spawners like salmon. Spawning is observed from March to August, peaking from April to May, They produce larger eggs than species that do not care for their eggs, and the extent of care depends on the egg sizes. All Chitala species demonstrate the same parental care method. The nests are actively cared for by both parents, but the males guard the nest. When guarding, males become defensive and hostile towards potential predators. They exhibit a rolling motion that exposes their broad, silvery side. Fertilized eggs are hatched by fanning, which helps supply dissolved oxygen. The eggs are spherical in shape, transparent with a milky yellow tone, and adhesive surface with projections. Adults can reach up to 3.3 ft long in the wild, but their developmental timing is different between natural and laboratory-reared conditions. The adult mortality ratio is male biased because clown knifefish have few natural predators in their native habitat. They are at the top of their food chain, so sex-specific mortality in the guarding parent is lower than expected. Males are concentrated in nesting sites during incubation and early development stages where nests are constructed and eggs are constantly fanned. Males have smaller bodies because their body condition declines from the energy exerted in guarding the eggs and juveniles. Females have larger bodies for greater reproductive success. Size is assumed to be directly correlated with fecundity, so larger females have a higher chance of being courted.

The International Union for Conservation of Nature has listed the clown knifefish as "least concern", due to their wide native range and ability to withstand diverse, unfavorable conditions. Although the species has a large presence in Southeast Asian aquaculture, it is widely known as an invasive species to regions primarily in Asia and the United States. They are commonly consumed in Southeast Asia, primarily Thailand. Since they contain several small bones, they are typically minced for fish balls or deep fried. {| |- valign="top" |, Thailand]] | |}