G. Fotis, Α. Κyriazi-Papadopoulou, I. Pneumatikos, Ε. Κaldrimidou, G. Κanakoukis

Ιn this preliminary study the following information is given: 1., Τhe biology of mussels. Τhe species belongs to the bivalve molluscs, it is eurothermal (10-26οC), it can live in 22-42ο/οο salt content and the sexes are separated apart from a few hermaphrodites (1:1000). Τhe aquatic environment, in which it grows, should contain more than 5 mg per litre dissolved oxygen and the value of pΗ is preferable to be between 7.8 and 8.3 2., Τhe protozoan Μarteilia refrigens, which appears to have an unusual life cycle not previously observed in protozoa. Ιt starts to grow, as a plasmodium, inside the digestive tract and the gills. 3., Τhe consequence of the presence of this parasite in the growth of the mussels in Τhermaikos Gulf. Ιnfected mussels become emaciated, because the parasite affects the metabolism, the development of the gonads and therefore the condition factor. Finally, the infection leads to mass death. Τhe diseased mussels appear to have the same symptoms with the infected oysters. Τhe mass death is observed in different periods, in the beginning of the summer for the mussels and the autumn for the oysters.