Aquatic Animal Health Research Institute
Department of Fisheries
Kasetsart University Campus
Jatujak, Bangkok 10900, Thailand
Chinabut, S. 2002. A case study of isopod infestation in tilapia cage culture
in Thailand. p. 201-202. In: J.R. Arthur, M.J. Phillips, R.P. Subasinghe, M.B.
Reantaso and I.H. MacRae. (eds.) Primary Aquatic Animal Health Care in Rural,
Small-scale, Aquaculture Development. FAO Fish. Tech. Pap. No. 406.
Tilapia is one of the most economically important species of cultured fish and is more resistant to disease than are many other species. However, when raised in intensive culture systems, tilapia suffer from increased parasitic and other infectious disease problems. Recently, cage culture of red tilapia (Oreochromis niloticus) in small reservoirs and sandpits throughout Thailand has increased, with the normal culture period being four months. A severe isopod infestation of tilapia in these cage-culture systems in central Thailand was recorded between June 1998 and January 1999. The mortality rate was 50-100% within 2-7 d after initial infestation. Trichlorfon at a concentration of 0.5-0.75 ppm for 24 hr is being recommended for pond treatment. However, chemical treatment for cage culture is not practical. Therefore, biological control may be the method of choice for prevention. Since the immature form of the isopod is planktonic, stocking more plankton-feeding species or cleaner-fish into the reservoir is recommended. Economic losses due to isopod infestation based on 50-100% mortalities was estimated at between US$234-468/cage.
Tilapia is one of the most economically important species of cultured fish and is more resistant to disease are than many other fish species. However, intensive culture systems increase parasitic and other infectious disease problems. Recently, cage culture of red tilapia in small reservoirs and sandpits throughout Thailand has increased; the normal culture period is four months.
Salespersons for a feed company, who work closely with the farmers, reported a severe isopod infestation of tilapia in cage culture in central Thailand to the diagnostic laboratory at the Aquatic Animal Health Research Institute (AAHRI). The infestation occurred between June 1998 and January 1999. The number of cages in this area was 200-300, with a size of 3 x 3 x 2 m. The fish were stocked at a size of 50 gm at the rate of 1,000-1,250 fish/cage. Mortality was 50-100% within 2-7 d after infestation.
The parasitic isopod, Alitropus typus (Fig. 1), is a common crustacean parasite of fish in Southeast Asia which feeds by sucking blood. After feeding on the fish, they drop off the host and stay in the substratum while digesting their meal. After the digestive process is finished, they will again attack the fish. Under aquarium conditions, 15-20 of these isopods can kill a 2-3 inch tilapia within 5-6 hr. Peak infection by this parasite is in the rainy season.
Trichlorfon (Dipterex) at a concentration of 0.5-0.75 ppm for 24 hr is recommended for pond treatment; however, chemical treatment for cage culture is not practical. Therefore, biological control may be the method of choice for prevention. Since the immature form of the isopod is planktonic, stocking more plankton-feeding species or cleaner-fish into the reservoir is recommended.
Production of tilapia is 400-450 kg/cage after four months of culture. The
wholesale price is US$/1-1.2 kg. Therefore, the economic loss due to isopod
infestation based on 50-100% mortality is US$234-468/cage.
