Effect of high temperatures on the ultrastructure of Leydig cells in Mytilus galloprovincialis

Individuals of the mussel Mytilus galloprovincialis (L), collected from the Black Sea, were subjected to relatively high temperatures (25°, 28° and 30°C) for 60 h Ultrastructural studies on Leydig cells of the mantle indicated progressive modifications in their structure. Mainly, we established that a continuous decrease of glycogen quantity in the cells took place as the temperature raised, while the lipid content increased, up to 28°C. Between 28° and 30°C the lipid content decreased as a result of a pronounced degradation process. An increase of membrane permeability and the disturbance in the synthesis of mucoproteic secretory granules were observed. It is concluded that for Mytilus galloprovincialis the thermal adaptation zone ranges between 25° and 28°C. 28°C is the upper tolerable limit temperature, while 30°C acts as a lethal temperature.