Marteiliasis affecting cultured mussels Mytilus galloprovincialis of Galioa (NW Span). I. Etiology, chases of the infection, and temporal and spatial variability in prevalence

The histological location, morphological fedtures and ultrastructural characters of the sporulation of the parasite causing Marteiliasis affecting cultured mussels in Galicia fit the characteristics defined for the type species Marteilia relringens The early stages of the infection are confined to the host stomach epithelium. The spreading of the parasites through the host digestive diverticula involves a n exponential increase in the number of parasites as the infection progresses, suggesting the occurrence of merogony, in addition to the well known sporulation. The infection usually triggers a host hemocytic reaction that may slow down or even stop the infection at times. The study of 5 zones of culture disclosed great spatial variability in the prevalence of Marteiliasis on mussels throughout the bays of Galicia, including a n area in which no infection was detected. The culture zones located within the bays showed higher prevalences than those located outside. There was no significant difference in the intensity of the infections among the affected zones Sporulation occurred throughout the year Several peaks of both prevalence and occurrence of heavy ~nfections took place every year. Considering the areas affected by Marteiliasis, the higher the prevalence of the infect~on the higher the mortality. In some of the studied zones, mortality was significant for the mussel farming industry.