Chitala ornata (Gray, 1831)
Common names: Knife Fish, Oscillated Feather Back, Clown Feather Back Fish, Clown Knife Fish, Spotted Knife Fish (English); Mannaya, Dot maluva (Sinhala);
Synonyms: Notopterus chitala (Hamilton, 1822) and Notopterus ornatus Gray, 1831
Identification characters: D 9-10; A+C 110-135; V 6
This species carries a unique morphological feature that distinguish it from all other Sri Lankan native freshwater fishes. This is its long anal fin which continues along as the caudal fin. Mature fish normally display five to ten (or even more) black spots ringed with white that usually decrease in size as the fish grows (Goonatilake, 2007). Juveniles, on the other hand, do not have spots but display an overall striped pattern. Their long anal fins are used to make graceful forward and backward movements.
Total length: Up to 100 cm. An adult fish may weight about 5 kg. A number of different colour morphs have been recorded in Sri Lanka.
Morphologically similar species:
Chitala ornata is mostly misidentified with Notopterus notopterus, C. borneensis, C. hypselonotus, C. lopis, and C. chitala in the aquarium trade (Roberts, 1992). These species are usually used in the aquarium trade but are not recorded in Sri Lanka.
History of introduction:
This fish has been accidentally introduced to the natural habitat from aquariums. The fish was recorded in lakes around Colombo after the major flood that took place in June 1992 (Goonatilake, 1994). Chitala ornata was first reported in “Diyawanna Oya” in 1994 (Amarasinghe et al., 2006).
Its native range is tropical Asia in the Mekong and Chao Phraya basins of Indochina, Thailand (Roberts, 1992) and Laos (Baird et al., 1999). It has also been introduced to regions outside its native range.
In Sri Lanka, it mainly inhabits freshwater bodies, particularly the larger rivers, lakes, and swamps, such as “Diyawanna Oya in Sri jayawardanapura Kotte, Weresganga in and Bolgoda lake in Bandaragama and Dodangoda-Matugama area (Amarasinghe et al., 2006; Goonatilake, 2007; Shirantha, and Amarasinghe, 2009).
Dispersal and reproduction:
Reproduction of this species usually occurs from March to July. Females of this genus lay eggs on a stake or stump of wood, while the males fan them with their tails, keeping them well aerated and silt-free. They also guard them against small catfish and keep a close eye against other predators (Davidson, 1975). Juvenile clown knife fish usually school near water logs and plants for security, whereas more mature specimens usually are more territorial and eventually become solitary.
Impact on native species and habitats:
The clown knife fish is a generalist predator and feeds only on live prey. They mainly feed on crustaceans, insects, and fishes. This is a nocturnal species. Clown knife fish can also breathe air directly and therefore can survive even in stagnant water with low oxygen levels such as urban polluted water bodies.
Direct exploitation/destruction of native species:
Studies suggest that this fish is linked to the decrease in the number of native species such as Aplochielus dayi, A. parvus, Horadandiya athukorali, Puntius vittatus, Puntius bimaculatus, Rasbora sp. and Amblypharyngodon melettinus (Gunawardena, 2002).
Current uses: Knife fish is not popular food fish in Sri Lanka. Juveniles are popular in the aquarium trade.
Natural threats (predators): Unknown. Otters (Luttra luttra) are probably the main predators.
Prevention and control: No control efforts are recorded in Sri Lanka to date. However, in native counties, it is popularly consumed as a food fish and, fished at a large and small scales, and used in aquaculture (IUCN, 2012). Juveniles are popular in the aquarium trade where large fish are popularly used in public aquaria. In Thailand, it is often used in food products. Therefore, due to the high consumption rate of this species as a food fish and use of juveniles for the aquarium trade the, population is kept under control.