The Second International Symposium on Tilapia in Aquaculture

Proceedings of the symposium held in 1987 in Bangkok, Thailand, by tilapia scientists to discuss strategies for future research and development in the tilapia industry worldwide. Contains 82 full papers, 17 poster abstracts and author and species indexes. The full papers were presented under 7 sessions: culture systems, management and production; pathology; genetics and reproduction; nutrition, physiology; biology and ecology; and economics and socioeconomics.Tilapia culture, Conferences

The use of chemicals in aquaculture in Thailand

In Thailand, many chemicals are used to treat diseases of cultured aquatic animals and to improve water quality in culture facilities. Along with the intensification of aquaculture practices that has occurred in recent years in Thailand, chemical use has also increased, particularly in marine shrimp culture. This paper summarizes information on the types of chemotherapeutants commonly used in Thailand, their sources and costs, the treatment regimes used, the adverse impacts that have resulted and the hazards posed. Also included is information on national regulations, a summary of on-going research, and recommendations to aquaculturists, producers and suppliers of chemicals, government agencies and scientists. It is concluded that although chemicals and drugs will continue to play an important role in the development of Thai aquaculture, they must be used with caution to avoid adverse effects such as environmental damage and the development of resistant strains of pathogens. To minimize chemical usage, additional emphasis needs to be placed on developing good management practices for aquaculture systems

Epizootic ulcerative syndrome of fishes: rhabdovirus infection and EUS induction experiments in snakehead fish

Rhabdoviral agents have long been found to be associated with Epizootic Ulcerative Syndrome (EUS) although the presence of granulomas caused by the fungus Aphanomyces invadans is currently used as the diagnostic criterium of EUS. In the past few years, rhabdoviruses have been readily isolated from EUS-infected fish during the early period of some outbreaks in Thailand, but the role of viruses in EUS remained unclear. Rhabdovirus infection and EUS induction experiments were therefore conducted in this study. The rhabdovirus strain T9412 from EUS-diseased snakehead fish was used to infect healthy snakehead. The frequency of virus re-isolation from juvenile fish infected by a number of routes decreased to 50-75% on day 7, 0-50% on day 14 and 0-25% on day 30. The virus was more virulent at 20°C than 29°C, and caused death in snakehead fry with a LD50 equal to 2.16 Log10 TCID50/ml. EUS induction in juvenile snakehead fish was experimentally achieved using both rhabdovirus and Aphanomyces invadans type species RF-6. All (20/20) juvenile snakehead developed multiple EUS lesions by day 30 at 20°C when fish were first injected intramuscularly (i/m) with virus followed by bath challenge with fungal spores. Fish which received L-15 medium by injection and were then bathed with fungal spores also developed EUS lesions although, fewer (7/20) were affected. The rhabdovirus injection alone induced only small haemorrhagic wounds at the i/m injection site in some fish held at 20(C, and most wounds healed by the end of the experiment. A similar induction experiment conducted at 29(C failed to induce the EUS disease. Results of this study indicate that the rhabdovirus is lethal to snakehead fish fry at low temperature. The virus persists for only a short period of time in the juvenile fish and induces minor skin damage. Low temperature was found to be an important factor in facilitating the host fish to succumb to rhabdovirus and A. invadans infection in the laboratory. Therefore, one possible combination of events leading to EUS in snakehead fish is low temperature and the presence of rhabdovirus and Aphanomyces pathogens