Environmental stress due to acidic pH of water was found to be one of the major factors leading to toxic effects on the sperm of a hill-stream fish Devario aequipinnatus of Meghalaya, India. The Scanning Electron Microscopy of the transverse section of testes of the fish collected from its natural habitat with acidic pH (5.6-6.0) showed that the sperms were clumped together and their tails were either absent or were of extremely small length. The acrosome and midpiece were also not well differentiated. When the fingerlings from the natural habitat were reared to maturity in aquarium with water from natural habitat after changing the pH to alkaline range (8.0-8.2), the clumping of the sperm was not observed. The sperm tail was found to be well-developed along with well-differentiated acrosome and midpiece. Since the only change in the water quality parameters of the experimental aquarium as compared to those of the natural habitat was the pH, it is evident that the abnormal features of the sperm observed in fish from natural habitat is mainly because of environmental acid stress.

Epizootic ulcerative syndrome (EUS)-affected Puntius ticto exhibited a number of abnormalities in scale, gill, skin, and muscle at surface microstructural level. Lepidontal damage including breakage of individual lepidonts and complete loss of lepidontal assembly was evident in the scale. Disturbances in the gill included fusion of gill-lamella, distortion of lamellar surface, damage of primary and secondary gill lamella as well as breakage of gill racker. The skin of EUS-affected Puntius ticto showed breakage of epidermal cell boundary, distortion, and loss of alignment of cells including lesions at places. Loss of alignment of muscles along with breakage and distortion of individual fibers was also evident. The similarities of these abnormalities in EUS-affected Puntius ticto with those of pesticide and other pollutant toxicity reported in some fish is discussed with the help of relevant literature.

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Cyprinid fishes of Meghalaya were investigated from twin drainage basins Brahmaputra and Barak-Surma-Meghna. 27 cyprinid fishes under 14 genus and 7 sub families were recorded from rivers and reservoirs of four different gradient zones. The diversity of Cyprinid fishes was highest with 49% representation of Cyprinids at lower elevation Zone IV below 500 m above MSL and bio diversity indices estimated as H: 3.05, 1-D: 0.10. In contrary lowest diversity with 7% representation of fishes was observed at elevation 1501 to 2000 m above MSL in Zone I with bio diversity indices H: 0.25, 1-D: 0.57. Distribution of commercially important cyprinids under genus Labeo, Systomus and Cirrhinus were found to be restricted to rivers of Barak-Surma-Meghna drainage basin. Catch percentage of cyprinids indicates that 70% of fishes exhibit occasional occurrence and 30% as common occurrence. High percentage of occasional occurrence, low catch composition percentage and with restricted distribution of commercially important fishes to only certain rivers of Barak-Surma-Meghna drainage is an indication of depletion of cyprinid resources in the state and requires taking multi prong conservation measures to protect cyprinid fishes in Meghalaya.