The rainbow trout, Oncorhynchus mykiss (Walbaum) is a species of salmonid native to tributaries of the Pacific Ocean in Asia and North America. The species has been introduced for food or sport to at least 45 countries, and every continent except Antarctica. The introduction of trout in India was attempted simultaneously in Kashmir in the north and in the Nilgiris in the South in 1899 and in 1906 a well-established hatchery built in Harwan, Kashmir which started producing seed of this species.
The reproductive biology of Rainbow-trout (Onchorhynchus mykiss) were studied in Balkhela river (tributaries of river Alakhnanada) for the period from 2012-2014. Rainbow-trout breeds from December to February. The maturity stages of both the sexes were obtained in gradual development from stage III (September) to stage VII (December). Few male trout were observed in oozing stage during the month of November. Most of their female breeders showed maximum gonado-somatic indices (GSI during December to February while peak value were observed in the month of February. GSI in male trouts showed higher values during October to January while peck value was observed in November. The oocytes of Rainbow-trout (Onchorhynchus mykiss) ovary were observed in various phases. The oocyte development of this fish was divided into seven stages (I.,Immature, II. Early maturing, III. Maturing, IV. Late maturing. Mature or pre-spawning, VI. Spawning, VII. Spawning).