Some Growth Characteristics of Tetrahymena sp., a Parasite of Guppy, Poecilia reticulata and the Effect of a Mixture of Two Commonly used Protozoacides on its Population Density

Various species and strains of Tetrahymena have a potential for being more virulent especially when the water is high in organic matter and fish are immunologically depressed causing "Tetrahymenosis". An outbreak of Tetrahymenosis was experienced by Sri Lankan guppy farmers in the recent past for which different treatments were employed indiscriminately. Present study investigated some growth characteristics of this fish parasite, which could be useful in import risk analysis and in screening female brooders of guppy. Tetrahymena sp. tested multiply rapidly in the presence of freshly killed guppy (as the substrate) and chloramphenicol 50 µg ml^-1 with a generation time of 2.6 hours at 28°C. Combined effect of methylene blue (2 mg l-1) and Zinc free malachite green (0.03 mg l^-1) completely inhibited in situ multiplication of Tetrahymena.