Occurrence of Ichthyophthirius multifiliis (White spot) infection in snow trout, Schizothorax richardsonii (Gray) and its treatment trial in control condition

High altitude raceways reared Schizothorax richardsonii stocks were monitored periodically for white spot infection at experimental coldwater fish farm, Chhirapani, Champawat, Uttarakhand. Total 1268 numbers of fishes with mean length (cm) ranging from 15.53 ± 0.20 to 16.86 ± 0.08, and mean weight (g) 24.70 ± 0.05 to 26.73 ± 0.06 were examined from January - December 2009. Presence of pinhead sized white spots (0.4 to 0.8 mm) was observed on dorsal body surface and caudal fins of sampled fishes during month of April. The causative agent was identified to be a ciliate parasite, Ichthyophthirius multifiliis. A temperature dependant infection pattern was noted with maximum prevalence (%) of 84.80 ± 1.83 in July followed by a decline in December (21.99 ± 2.13). Prevalence varied significantly (p< 0.05) between the months as water temperatures dropped with onset of winter. Trophont counts following dip treatment for five consecutive days under laboratory conditions with 2% common salt, 250 ppm formalin and a combination of the two, of samples of the snow trout, Schizothorax richardsonii, infected with Ichthyophthirius multifiliis, indicated that treatment with combination of salt and formalin was significantly (p< 0.05) effective than either salt or formalin alone in controlling the infection.