Myxosporean infection causing intestinal disease in farmed turbot, Scophthalmus maximus (L.), (Teleostei : Scophthalmidae)

The present report describes an intestinal disease which causes important l osses in farmed turbot. Mortality rates were higher in summer and reached 1 00% in all tanks where the disease was confirmed. Affected fish showed exte rnal signs consisting of anorexia, sunken eyes and a typical prominent bony ridge on the skull. These signs can be considered the pathognomonic signs of the disease, together with the gut lesions seen in the histological stud y. Pallor of the internal organs, intestinal haemorrhages and the presence of liquid in the intestine were also observed, with ascites in heavily infe cted fish. Histopathological damage was evident in the gut, with severe ent eritis, detachment of epithelium, haemorrhages and inflammation of the sube pithelial connective tissue. The myxosporean aetiology was demonstrated in all the fish showing the characteristic signs of disease. Myxosporean stage s, including scarce spores, were found in the affected epithelium or free i n the intestinal lumen together with epithelial debris. The present study d emonstrates the importance of this myxosporean disease which represents a s erious threat for turbot culture. This is also the first record of a member of the Myxosporea in turbot.