Naturally distributed in eastern India and Southeast Asia and the Philippines; one species (Clarias batrachus) has been transplanted to southern Florida and many tropical and subtropical countries.

HABITS:

These catfishes are distinguished by the possession of an accessory air-breathing organ, which enables them to exist for hours at a time out of the water, or indefinitely in oxygen-poor waters and even moist mud. These catfish live in fresh and brackish water and can survive in temperatures as high as 90° F.

SPAWNING:

Collection of naturally produced fry, extensive though it is, cannot provide enough stock for commercial culture. Thai fishery officials have undertaken, with considerable success, to spawn Clarias spp. in captivity. As early as the mid-1950s it proved possible to spawn C. batrachus by methods similar to those used in spawning channel catfish in the United States. In place of the metal or wooden containers used to spawn channel catfish, horizontal holes, 20 to 35 cm in diameter, were dug in the bank a little over 1 m apart, and aquatic plants were provided nearby. About 80% of the pairs stocked near such holes spawned within 7 to 10 days, yielding 2000 to 5500 fry per spawning. C. macrocephalus was induced to spawn by means of pituitary injection. Spawning was produced within 14 to 16 hours in 60 to 80% of cases. Fertilized eggs are placed in shallow thoughs and jars, where hatching takes place within 20 hours at 26 to 33° C.

GROWTH:

Thai culturists grow three crops of C. batrachus annually to marketable size: about 26.5 cm and 145 g).

USES:

Walking catfish are very hardy and can live in muddy, low-oxygen water. They can be cultured at high densities, resulting in high production per unit water area. Ponds must be enclosed, since this species can move short distances over land: walking catfish have received considerable notoriety escaping from tropical fish dealers and becoming established in Florida, where it is believed they can compete successfully against local, less hardy species. Despite their rearing advantages, the aquaculture potential of walking catfish in the USA is somewhat limited due to legal problems associated with introducing an exotic species, the need for year-round warm water, the comparative toughness of the meat, and the lack of an established U.S. market.

CULTURE:

Ponds used in growing Clarias spp. for market are 100 to 1000 m² in area and 1 to 3 m deep. They are prepared for stocking by firming the banks to discourage climbing or burrowing, and by erecting a fence around each pond. Fry in production ponds are stocked at about 180/m² and fed on ground trash fish, mixed with rice bran at a ratio of about 9:1. Fertilization, with about 30 kg of farmyard manure per 100 m², is carried out only if growth is poor. Thai culturists achieve an average survival rate of 37%, a 5 to 6:1 FCR, and the tremendous annual yield of 97,000 kg/ha.

REFERENCES:

Areerat, S. 1987. Clarias culture in Thailand. Aquaculture 63:355-62.

Burgess, W. 1989. An atlas of freshwater and marine catfishes: a preliminary survey of the Siluriformes. T.F.H. Publications, Neptune City, NJ.

Diana, J. S., S. L. Kohler, and D. R. Ottey. 1988. A yield model for walking catfish production in aquaculture systems. Aquaculture 71:23-35.

Idyll, C. P. 1969. New Florida resident, the walking catfish. National Geographic 135:846-851.