Abstract.Blindness developed in Atlantic menhaden,Brevoortia tyrannus(L.), within 4 weeks of captivity in an indoor open culture system. Ophthalmoscopic changes indicative of retinal degeneration were substantiated by the absence of retinal electrical activity as measured by conventional electroretinography. Results of histological evaluation suggest that photo‐receptor degeneration, occurring initially in the rods of the central retina, was the primary abnormality. With chronicity, all retinal layers degenerated, and marked pigment proliferation developed. Other pathological changes included uveal vascular engorgement, vitreal and anterior chamber haemorrhage, and cataracts. With the exception of dermal hyperpigmentation, no systemic abnormalities were consistently observed. Phototoxicity is the suspected cause of this degenerative retinopath