Objective To explore the cataract development and its influence on the living status of BY-F swordtail fish.Methods To notice the development of opaque appearance in the eyes of swordtail fish and to examine the external appearance and behavior changes of the blind fish.The eyeballs were taken at different development stage of the disorder and examined by histopathology.Results The blind fish often became dark-colored.Varying opacities were seen in the fish eyes.Red hyperplastic lesions covering the cornea surface were found in some blind fishes.Most pathological changes were found in the lens.Conclusion The blind fish were suffering from cataract.The cataract can cause other eye complications in BY-F swordtail fish.The BY-F swordtail fish are susceptible to develop cataract.