The two economically important species of marine fish cultured intensively in net cages in Thailand are the sea bass (Lates calcarifer) and malabar grouper (Epinephelus malabaricus). It is a fact that diseases always become one of the problems for intensive fish culture, because of various factors including environmental stress. A number of diseases have been reported in sea bass and grouper culture in Thailand, including parasites, bacteria, viruses, fungi, nutritional problems and environmental stress. The paper provides a summary of the problems.
Diseases of Cultured Sea Bass, Lates calcarifer
The parasites of sea bass had been documented as follow:
Protozoa: Cryptocaryon irritans, Trichodina sp., Epistylis sp. and Oodinium sp. (Amyloodinium sp.).
Sporozoa: Henneguya sp. and Opistonectus sp.
Monogenetic trematode: Diplectinum latesti, Pseudorhabdosynochus latesi, Dactylogyrus sp.
Digenetic trematode: Lectithochirium sp., Pseudometadena celebesensis, Bucephalus margaritae, Prosorhynchus pacificus, Rhipidocotyle sp., Ectenurus sp., Lecithocladium neopacificum, Sanguinicola occidentalis and Cardicola sp.
Nematode: Cucullanus sp., Raphidascaris sp. and Anisakis sp.
Cestode: Tetraphyllidea sp.
Acanthocephala: Acanthocephalus echigoensis
Crustacean: Caligus sp., Ergasilus sp., Aega sp., Gnathia sp., Lernanthropus latis, Aegathoa sp., Cymothoa sp.
Hirudinea: Pontobdella sp.
Saprolegnia sp. is a non-septate fungus found on the gill and skin of sea bass.
Most of the bacteria found in water are opportunistic bacteria, which can cause disease problems in fish when the fish are under stress. This stress factor can include pH, dissolved oxygen, temperature changes, and other factors. Bacteria found from cultured sea bass are as follow:
Not many viral diseases of sea bass have been reported. Lymphocystis has been reported as a viral disease of cultured sea bass in both marine and freshwater environments.
Kidney disease is one of the nutritional diseases of sea bass, with hyperphosphorus assumed to be the cause.
Swimbladder stress syndrome (SBSS) of sea bass fry is associated with a combination of handling, high ambient temperature, salinity and dense algal blooms. No particular cause of SBSS has been established.
Gas emboli can be spread in various tissues, especially around the fin.
Diseases of Cultured Malabar Grouper, Epinephelus malabaricus
Grouper culture in Thailand has been carried out for more than 10 years. Malabar grouper (Epinephelus malabaricus) is the most popular species of grouper cultured in floating cages. The main diseases found in cultured grouper are given below.
There are several parasitic organisms, which can cause various levels of mortality in grouper.
Protozoa: Cryptocaryon irritans, Trichodina sp., and Scyphidia sp.
Sporozoa: Sphaerospora epinepheli
Monogenea: Pseudorhabdosynochus epinepheli, Gyrodactylus sp., Benedenia sp., and Cycloplectanum epinephili
Digenea: Cardicola sp., Lecithochirium neopacificum, Prosorhynchus pacificus, Gonapodasmius sp., and Pseudopecoeloides sp.
Nematode: Raphidascaris sp.
Cestode: Tetraphyllidea sp.
Acanthocephala: Acanthocephalus sp.
Crustacean: Caligus sp., Thebius sp., and Gnathia sp.
Hirudinea: Unidentified species
Vibriosis seems to be the most serious bacterial disease of grouper and Vibrio parahaemolyticus comprises the majority of bacteria isolated from infected fish.
Viral nervous necrosis was first known as “paralytic syndrome” of fry and fingerling grouper. The virus found from infected fish is a picorna-like virus. Affected fish exhibit dark coloration of the head and tail, loss of equilibrium and cork-screw-like swimming.
 Aquatic Animal Health Research Institute, Department of Fisheries, Kasetsart University, Campus, Jatujak, Bangkok 10900, Thailand