The recent growth of the aquaculture industry in the Mediterranean has been most noticeable in Greece and Turkey. However, production is still dominated largely by mollusc production of mussels (Spain and Italy) and oysters (France), which contribute around 80% of the total. In the last decade, there has been an increasing dominance of the sea bass/sea bream group (40, 000 t in 1995) over the more traditional mullets. This has been due to improvements in larval rearing techniques, the formulation of specialized feeds and the use of sea-cages. However, European Union (EU) financing of certain infrastructural aspects has also played an important part. New species, such as sheepshead bream, red sea bream and groupers are also beginning to be developed.The scale of increased production has naturally led to specific disease problems for the main cultured species of sea bass, sea bream, mullet and amberjack. Bacterial disease conditions are mainly due to vibriosis caused by various species of Vibrio and pasteurellosis caused by Photobacterium damsela. However, lesser problems can be related to Aeromonas sp., Pseudomonas sp., Streptococcus sp., Mycobacterium spp., Chlamydia-like spp., Nocardia sp. and Flexibacter spp. Viral problems have been caused by the recent occurrence of a nodavirus-like infection, lymphocystis, and an erythrocytic infection (VEI). Additional problems are caused by parasites that include ectoparasitic flagellates (Amyloodinium sp. and Ichthyobodo sp.), endoparasitic protozoans (Eimeria sp., Ceratomyxa spp., Kudoa sp. and Sphaerospora sp.), monogenean parasites (Diplectanum sp. and Furnestia sp.), crustacean parasites (Caligus sp. and Ergasilus sp.) and by fungus (Ichthyophonus sp.).