MANIFESTATION OF LYMPHOCYSTIS DISEASE IN AMERICAN PLAICE (HIPPOGLOSSOIDES-PLATESSOIDES) EXPOSED TO LOW SALINITIES

Lymphocystis disease virus (LDV), an iridovirus, is the aetiological a gent of benign skin tumors observed in a wide variety of teleosts. The disease appears ubiquitous, but its manifestation is poorly understoo d because of the difficulty in isolation and cultivation of the virus in vitro. American plaice (Hippoglossoides platessoides) were trawled in the Gulf of St. Lawrence and acclimatized for at least 6 wk in capt ivity. Fish were then exposed to lower water salinities and examined r egularly over a period of 6 wk. Lymphocystis tumors were recorded and samples prepared for electron microscopy. Statistical analysis reveale d a significant increase of the occurrence of tumors in relation to de creases in salinity to 7 g/L and increases of exposure time up to 42 d . Iridoviruses were regularly observed in fish tumors by electron micr oscopy. Although plaice survived well, low salinities may have caused physiological stress which reactivated a latent iridovirus.