Evaluation of seasonal cyclicity of testicular development in adult Himalayan snow trout, Schizothorax plagiostomus

Schizothorax plagiostomus commonly known as snow-trout, is a popular game-food fish, found in the cold waters of the rivers, streams, tributaries and lakes of the Hindukush- Karakoram- Himalayan mountains/ foothills even at the elevation of 1180–3000 m above from the sea level and is considered to the be major source of animal protein. In recent past, there has been a severe decline in Schizothoracine population due to uncontrolled anthropogenic activities and climate change. Therefore, there is an urgent need for critical analysis of annual gonadal development in Schizothorax species. In this study, the seasonal variations of testicular architecture and development were examined in adult S. plagiostomus at Garhwal Himalaya, Uttarakhand, India. Testicular-somatic index were found to be ranged from 0.254 ± 0.06–7.104 ± 1.62 with maximal value recorded in September-October and minimal in April-May. Testicular histology revealed abundance of undifferentiated spermatogonia, meiotic spermatid and spermatozoa in pre-spawning and spawning capable phases respectively. The ultra-structure of spermatozoa showed 1.78 ± 0.27 µm long ovoid shaped head without any acrosome, 0.35 ± 0.05 µm long ellipsoidal mid-piece and 22.5 ± 0.65 µm long flagella. We further have evaluated the milt/semen volume, estimated the sperm density and motility in male brooders. Notably the spermatogenic capacity was found to be consistent in two breeding seasons i.e. spawning capable (September-October) and residual spawning (February-March) phases. In summary, this is the first comprehensive qualitative and quantitative report of the seasonal variations of the spermatogenic output in adult male S. plagiostomus. This data may provide valuable information for the conservation management and artificial breeding program of S. plagiostomus.