Effect of temperature and salinity on in vitro zoosporulation of Perkinsus sp in Manila clams Ruditapes philippinarum

The effects of temperature and salinity on in vitro development of Perkinsus sp. prezoosporangia isolated from cultured Manila clams in Korea were investigated, and the difference in resistance to low temperature between prezoosporangia collected in winter and those collected in summer was compared. Temperature and salinity had significant effects on the development of prezoosporangia, and the developmental rates increased with increasing temperature and salinity. Prezoosporangia isolated in winter sporulated and released motile zoospores at 10degreesC, although the rates were significantly lower than those at 20 and 30degreesC. However, no prezoosporangia collected in summer sporulated at 10degreesC. Low salinities (less than or equal to10parts per thousand) had a significant negative effect on the development of prezoosporangia. A small number of prezoosporangia sampled in summer did sporulate at 5parts per thousand, but further developments including formation and release of zoospores were not observed. However, prezoosporangia sampled in winter and incubated at 5parts per thousand released motile zoospores, although the rates were significantly lower than those at higher salinities.