An unusual site of infection by a microsporean in the turbot Scophthalmus maximus

We report a microsporean infection which affected a population of juvenile turbot Scophthalmus rnaximus (Rafinesque, 1810) in a fish farm In the Ria de Vigo ( N W Spain), causing high mortality.The uninuclear spores (4 25 X 2.00 pm) contained a character~stic posterior vacuole with a large inclusion body; the xenomas, some displaying microvilh-type projections on their surface, were situated in the connective tissue between muscle fibres, leading to severe myodegeneration.The infection was also observed (though with less spectacular pathological effects) in the liver and the intestine, this being the first time that microsporidiosis has been recorded in these organs in the turbot.On the basis of morphological and pathological characteristics we consider that the aetiological agent of the infection might be Tetramicra brev~filum.In fish which survived the infection, all signs of the disease &sappeared.