Survival characteristics of Cercaria chackai (Digenea: Transversotrematidae)

Abstract

AbstractThe survival characteristics of Cercaria chackai, the larval form of the curious ectoparasitic digenetic trematode Transversotrema chackai, in sea water, sea water diluted with deionized water in different proportions, deionized water, pond water and tap water were studied. Naturally shed, fresh cercariae had the maximum life span of 20 h 40 min in pond water at salinity 17·8‰, pH 6·45, O2 5·76ml/l and temperature 31·5°C. With increase in salinities beyond 17·8‰, survival time was drastically reduced and beyond 23·58‰,, was restricted to a few minutes. In sea water with a salinity of 38·3‰, the maximum survival time was only 8 min. Below 17·8‰ salinity, although the survival time was less, the difference was not very marked and even in tap water with no salinity, the cercariae lived up to 19 h 50 min. In deionized water the maximum survival time was only 3 h 15 min. Since pond water at pH 6·45 allowed maximum survival time, it is presumed that the cercariae preferred a slightly acidic medium. As temperature was maintained constant and oxygen was available, neither of these two factors, apparently, affected the survival pattern. It is concluded that C. chackai is a typical freshwater form showing considerable tolerance to fluctuations in salinity although the family Transversotrematidae is considered to have a marine origin.