Retinal degeneration in celestial goldfish. Developmental study.

The celestial goldfish were systematically reared from fertilization for life, revealing developmental processes of retinal degeneration. The eyes began to protrude laterally at the age of 90 days, rotated antero-dorsally at 120 days, and thus the 'celestial eye' was completed. The retina developed to normal mature structure by the age of 50 days. No degenerative findings were revealed before the start of eye extrusion. The first morphological change, irregular distribution of melanin granules in the pigment epithelial layer and disorientation of the outer segments of photoreceptors, was detected at the age of 90 days. At 120 days, the pigment epithelial layer lost melanin granules at places and was occupied by phagocytes. Photoreceptor cells were destroyed, and phagocytes, containing melanin granules, appeared in the inner retina and/or choroid. The retinal degeneration started simultaneously with eye protrusion. The regular telescopic-eye goldfish have large, extended eyes as those of celestial goldfish, but they develop no retinal degeneration. Celestial goldfish seems to be an interesting new type of hereditary retinal degeneration in vertebrates.