A case study of isopod infestation in tilapia cage culture in Thailand.
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 days after initial infestation. Trichlorfon at a concentration of 0.5-0.75 ppm for 24 h 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.