A study on the seasonal cyclicity of ovarian development in adult Himalayan snow trout, Schizothorax plagiostomus.

Schizothorax plagiostomus, commonly known as snow trout, is a popular food fish found in parts of Central Asia and the Indo-Himalayan region. Despite such a broad range of distribution and potential financial value, it is a highly neglected cold-water ichthyofauna. Furthermore, an alarming decline in Schizothoracine population has been reported in the recent past due to climate change and uncontrolled anthropogenic interference. In this study, the seasonal variations in ovarian architecture and development were examined in adult S. plagiostomus from Garhwal Himalayan region, Uttarakhand, India. Ovarian-somatic index ranged from 16.86 ± 0.29 to 0.31 ± 0.56, with a maximal value in September and a minimal value in April. Ovarian histology revealed the abundance of primary growth oocytes in resting and preparatory stages; primary/secondary vitellogenic oocytes with numerous cortical alveoli were predominant in the developing stage of pre-spawning ovaries; secondary/tertiary vitellogenic oocytes were conspicuous in actively spawning ovaries; and atretic follicles/oocytes were discernible during the regressing stage of spent ovaries. Scanning electron microscopy of mature ova (mean diameter 2.003 ± 0.01 mm) prominently showed the structure micropyle (mean diameter 12.93 ± 3.38 μm). Fecundity analyses suggested that September was the principal breeding season, whereas residual spawning occurred with fresh rain in late winter during February-March. Collectively, this is the first comprehensive qualitative and quantitative report of the seasonal variations in the ovarian development and function for S. plagiostomus. These data may provide valuable information towards the captive breeding programme as well as conservation and management for Schizothoracine fishes in normal and altered climatic conditions.