However, seed production from grouper in hatcheries in Thailand is still inconsistent and fry and fingerlings are normally collected from the wild using small traps, push nets, shelter traps or by gill netting. Grouper are usually cultured in floating cages along the seashore and in rivers near the sea. Many kinds of pathogen have been identified in cultured grouper. Diseases caused by protozoa Parasitic protozoa cause severe losses in fry and juvenile grouper. Fish suffer from skin irritation and scrape their bodies on the site or bottom of the pond or net.
Diseased fish refuse food and gather near the surface of the water.
Tail rot and skin damage with loss of mucus and scales are typical clinical signs. Common parasites are Trichodina spp and Cryptocaryon irritans . Diseases caused by monogenea Monogenean trematode parasites often found on the body and gills of cage-cultured grouper. Fish with severe infections have small focal haemorrhages on the body, which often result in secondary bacterial infection. Disease caused by digenea Digenean trematode parasites are frequently observed in the intestinal tract of culture and wild grouper.