EXFOLIATION OF EPITHELIAL-CELLS BY THE SCALLOP PLACOPECTEN-MAGELLANICUS - SEASONAL-VARIATION AND THE EFFECTS OF ELEVATED WATER TEMPERATURES

Previous studies have shown that large numbers of ciliated and noncili ated epithelial cells (diam.: 6 to 15 mu m) are released by adult sea scallops, Placopecten magellanicus (Gmelin), during summer months in N ewfoundland when water temperatures are at a maximum and gonads are we ll developed. Such exfoliation of cells could be a response to stresse s associated with elevated water temperatures and/or spawning activity . In the present study an electronic particle counter/sizer was used t o further investigate the factors that influence exfoliation of epithe lial cells by juvenile and adult scallops throughout the year. We obse rved release of epithelial cells from juveniles, and from adults colle cted in months when gametogenic activity was minimal, indicating that exfoliation does not occur as a result of reproductive activity alone. SEM analysis revealed little difference in surface characteristics of the gills, mantle and gonad between scallops that had released cells and those that had not, suggesting that exfoliation of small numbers o f cells may be a consequence of cellular turnover and normal physiolog ical function. Adult scallops were monitored in a second experiment to determine the effects of raising water temperatures from 8.5 to 14.7 and to 21.0 degrees C on the frequency (proportion) and rate of cellul ar exfoliation. Only at the highest experimental temperature (21.0 deg rees C) were exfoliation rates significantly higher than rates recorde d at 8.5 or 14.7 degrees C. SEM analyses revealed some damage to gill, mantle and gonad tissues when scallops were exposed to 14.7 and then to 21.0 degrees C for a total of 8 d.