Morphology and reproductive biology of two hill stream Cyprinids, Balitora brucei and Psilorhynchus balitora, from the Ranganadi River (India), with a special note to their conservational threats

The current work represents the study on morphology and reproductive biology of two indigenous torrential fishes, Balitora brucei and Psilorhynchus balitora, for the first time. The Gray’s stone loach Balitora brucei and balitora minnow Psilorhynchus balitora abound in the torrential water bodies of South East Asia. The current paper redescribes morphology based on the fresh collection. Specific parameters of reproductive biology on both the fishes have been studied for the first time. Both the species were adapted to the same ecological conditions of the river Ranganadi. Fish specimens were collected at a fortnightly interval from the river in the Lakhimpur district of Assam, India. The detailed study includes morphological data analyzed with Mann–Whitney U-test and specific reproductive parameters such as condition factor (K), gonado-somatic index (GSI), modified gonado-somatic index (MGSI), and Dobriyal index (DI). Progressive development of the gonads was confirmed with dissection and histological study. Both the species are multiple breeders with prolonged reproductive seasons ranging from 4 to 5 months. Both the fishes are found to be migrants from upstream, and a good number of individuals were recorded during the monsoon season, reflecting the sampling site as a breeding ground. During winter, the local people use various chemicals, piscicidal plants, and electric instruments for fishing resulting in a steep decline in the number of individuals for both the species. Moreover, the effect of the North Eastern Electric Power Corporation Limited (NEEPCO) dam is evident on the decline of the ichthyofaunal diversity of the river. The results of present study will provide the baseline information on these two species of fishes for planning conservation measures in future.