Tropical cyprinids from southeast Asia, region in which these fish are being widely cultured either in mono- or polyculture.

HABITS:

Tawes are herbivorous, which is not common among the fish fauna. Due to this characteristic, they are used in some countries as an alternative to grass carp for weed control.

SPAWNING:

Tawes, like most tropical cyprinids, are potentially year-round spawners, but hatchery operations are usually confined to the beginning of the rainy season, when there is adequate water to supply the strong current necessary. Tawes spawning ponds are 200 to 500 m² in area, 35 to 50 cm deep, and located no more than 700 m above sea level. During the 3 to 4 months between spawnings, broodstock are kept in special ponds and fed on rice bran and soft plant leaves. Broodstock may be used a maximum of five times. One pair of spawners/50 to 70 m² of surface area is a good stocking rate. Mating generally occurs at night and is accompanied by an audible humming noise. Sometimes the fish are reluctant to spawn, in which case the water is beaten with bamboo slats. When spawning is over, the current is shut off and the eggs spread evenly in the pond bottom. Hatching occurs within 2 to 3 days; after about 20 days the fry are strong enough that the flow of water through the pond may be restored. Average production of tawes fry is 10,000 to 20,000 25-day-old fish or 5,000 50-day-old fish/female.

GROWTH:

Depending on the fertility of the pond, the fry may be reared for 25 or 50 days. In fertile ponds they reach lengths of 2 to 3 cm in about 50 days. Common carp fry, about 10 cm long, may be stocked with the tawes fry, as the agitation of the bottom caused by common carp feeding is believed to be beneficial. Tawes are about 300 g in weight and 25 cm in length by the second year of the rearing cycle, when they have reached maturity and are used as spawners for the first time.

USES:

Even though considered by many as a second-rate fish, tawes are widely used in polyculture as well as weed control throughout southeast Asia. The interest in tawes as a means of biological control of weeds is increasing since the use of grass carp entails the risk that they may escape into natural waterways and destroy valuable plants.

CULTURE:

Cyprinid fishes are rarely farmed in monoculture in the Eastern Hemisphere, but tawes are one of the exceptions. Sometimes they are grown in floating cages in Japan and Cambodia. As to polyculture, tawes may be raised in combination with native Asian catfish (Pangasius spp.), milkfish (tawes usually constitute the main crop), Tilapia mossambica, Java tilapia, and even the freshwater prawn, Macrobrachium rosenbergi. Some farmers in Malaysia and Singapore use a combination of Sepat Siam (an anabantid fish), common carp, Java tilapia (or Tilapia mossambica) and tawes as an alternative to the usual Chinese carp complex.

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