Keywords: Rainbow trout, cage culture, Phewa lake

Production potential and growth study of rainbow trout (Oncorhynchus mykiss) was carried out in floating cages in Lake Phewa of Pokhara valley for 137 days from 27 November 2002 to 13 April 2003. Five different stocking size 20 – 29 g (T₁); 30-39 g (T₂); 40-49 g (T₃); 50-59 g (T₄) and 60-69 g (T₅) of rainbow trout were stocked at density of 12 fish/m³ in 8m³ (2m × 2m × 2m ) sized cages. The experiment was laid out in a completely randomized design with three replicates in each treatment. Fish were fed twice daily with 37% CP content pellet feed at the rate of 3% body weight. Water temperature at fish stocking was 20° C which lowered down to minimum of 14.5° C and was increased to 23.5° C at harvest. There was no significant difference in daily weight gain, net fish yield and survival rate of rainbow trout among all treatments (P> 0.05). Stocking size of 60-69 g (T₅) produced the highest harvest size of about 140 g of rainbow trout within 137 days. The daily growth rate was 0.5 –0.6 g/fish. Food conversion ration (FCR) ranged from 2.8 to 6.9 and survival ranged from 52% to 76%. Growth rate of the rainbow trout decreased during the last 15 days of the experiment (after end of March). Dissolved oxygen of Lake Phewa ranged from 5.1 to 9.0 mg/L at surface and 5.1 – 8.6 mg/L at 2.0 m depths for four months from December to March. The study showed that rainbow trout could be successfully grown in cages in the Lake Phewa for about four months from the last week of November to end of March. However, it is suggested to stock 100 g size in order to harvest the trout of 200 g size.