CHILODONELLA SPP AT 4 FISH FARMS IN NORTHERN FINLAND

A total of 4.1% infestation with Chilodonella spp. was found among fis h studied in 144 tanks in 1987-1989, representing 14.0% of the tanks i n which fish are reared at four salmonid farms in northern Finland. Tw o species were found, C. hexasticha and C. piscicola, and both occurre d on salmon (Salmo salar L.), sea trout [S. trutta m. trutta (L.)] and brown trout [S. t. m. lacustris (L.)]. Variability was observed in th e length and width of the C. piscicola specimens and the number of cil iary rows or kineties. Large specimens which had more kineties than av erage for C. piscicola were found mainly on the skin of salmon aged 1- 2 years. The number of kineties in the right ciliary band was found in stepwise logistic regression analysis to be of importance when typing C. piscicola specimens. Fingerlings were found to be more susceptible to Chilodonella infestation than older fish, and mortality varied in the range 2-10% in the course of the epizootics in the three fish spec ies. Most mortality cases were caused by C. hexasticha, occurring main ly on the gills of the fish. Chilodonella piscicola was most often fou nd in salmon and occurred at lower water temperatures than C. hexastic ha (mean water temperature when found for the first time being 13 degr ees C and 16 degrees C, respectively).