Pterygoplichthys spp (Hancock, 1828)
Common names: Tank cleaner, Sail-fin catfish, Orinoco sail-fin catfish, Butterfly pleco, Janitor fish, many-rayed pleco, sailfin pleco, scavenger.
Identification characters: D 1.7-7; A 1.3-5; P I.6-6; V I.5-6
The body of a mature Pterygoplichthys multiradiatus is covered with flexible bony plates. The abdomen is covered with large white spots irregularly joined to form a vermiculate pattern. A ventral sucking mouth, pectoral fins with thick toothed spines and the presence of 9-14 dorsal fin rays with a single spine distinguish this species from other Pterygoplichthys species (Nico & Martin, 2001).
Total length: Regular length is about 35 cm (generally reached within the first two years (Hoover et al., 2004)), but it can grow up to 50 cm.
Morphologically similar species:
P. multiradiatus is commonly confused with other Pterygoplichthys species (West et al., 1999). Uncoalesced dark spots on a light body distinguish P. multiradiatus from P. anisitsi, which has light spots on a dark body, and from P. disjunctivus, which has coalesced dark spots on a light body. However within Sri Lanka P. multiradiatus is only in the aquarium trade.
History of introduction:
The fish was accidentally released or escaped from ornamental fish farms or aquariums. The first wild population was observed in 1992 in the Bellanwila-Attidiya sanctuary (Goonatilake, 1994).
The species inhabits freshwater streams and lakes (Nico & Martin, 2001). It thrives in weedy, mud-bottomed canals.
In Sri Lanka it is present in freshwater reservoirs and river estuaries in the North-Western and Western provinces (Silva & Kurukulasuriya, 2010), but has also been observed in the Eastern province (Jinadasa et al., 2014). It has been recorded from Bellanwila-Attidiya, Nedimala, Bolgoda (Western province), Kandy around Polgolla (Central Province), Mawil-Aru, Rambaken Oya, Maha Oya (Eastern province) and Minneriya Tank (North-central province) (Weerakoon and Goonatilake as per observation, 2015).
Dispersal and reproduction:
Female P. multiradiatus have a high fecundity rate. Approximately 472-1238 mature eggs can be produced. Eggs are laid in burrows, prepared by the male P. multiradiatus. Males also exhibit parental care (Hoover et al., 2004).
Impact on native species and habitats:
P. multiradiatus browses on substrate, mainly feeding on benthic algae and aquatic weeds, and thus may potentially displace native algae feeding fauna, but will also take worms, insect larvae and other bottom-dwelling invertebrates as food (Hoover et al., 2004).
Males excavate tunnels along banks, which lead to siltation problems and shoreline instability, feeding behaviour could re-suspend sediment or alter substrate size and may displace smaller, less aggressive native species. Large pectoral and dorsal spines pose choking hazards for predaceous birds and can damage fishing gear (Hoover et al., 2004).
Direct exploitation/destruction of native species:
No records available on this aspect.. But it may compete with native species for food and space.
Current uses: Use in the aquarium trade. Few feasibility studies have been done on using this fish as a food source.
P. multiradiatus can tolerate very low oxygen concentrations in water by breathing atmospheric oxygen (Armbruster, 2003; Nico & Martin, 2001). It can withstand poor water quality and survive up to 30 hours out of water (Nico & Martin, 2001) which makes it a superior species, and competitor, for survival.
Prevention and control: No control efforts are recorded in Sri Lanka to date.
This fish is not popular among fishermen. In the Philippines it is sold in bulk in an attempt to get rid of the invader. Being bottom dwellers they are readily exposed to contaminants and heavy metals which may bioacumulate in their body tissues (Jinadasa et al., 2014). Therefore consumption of this fish may pose hazardous effects to humans over time. However, it still can be processed for human consumption, fishery products, fish feed or fertilizer production (Jinadasa et al., 2014).