Clarias culture in Thailand commenced in the late 1950's, originally in the Bangkok area. Although there are five species of clariid in Thailand, where they are known locally as Pla Duk, only two, Clarias batrachus (Pla Duk Dan) and Clarias macrocephalus (Pla Duk Oui) are farmed. Both are highly esteemed, although Clarias macrocephalus, which is considered to have more tender meat, is the more valuable. This is unfortunate since C. batrachus grows faster, and is more readily available at the fry stage, but the market for both is generally high.
In the wild, clariids feed principally on small invertibrates such as worms, crustaceans and insects, but they are also major scavengers of dead vertebrates such as other fishes. In culture in Thailand they are fed principally on trash marine fish, supplemented with rice bran, boiled broken rice or manufactured pellets.
In Thailand the spawning season is during the period February to October- ie. the end of the cold weather and during, or immediately after the rainy season, although there is some evidence that they may spawn at any time if subjected to sudden freshwater flows or sudden temperature changes. C. batrachus spawns in deeper water and generally excavates a horizontal hole in an earth bank where the 2–5,000 yellowish-brown eggs are deposited, to hatch in approximately 20 hours. C. macrocephalus spawns in depressions on flat grassy bottoms of ponds, with the male guarding the eggs till they hatch. Paddy fields are the commonest nesting sites for C. macrocephalus.
