Melanoid tapeta lucida in teleost fishes

Abstract

Abstract In a limited survey of bony fishes of the superorder Ostariophysi, melanoid tapeta lucida were found in ten families of siluroids (catfishes), three families of characoids, and one family of gymnotoids (knife-fishes). The tapeta contained ‘catfish reflecting material’, which is a compound consisting of oligomers of 5,6-dihydroxindole-2-carboxylic acid combined with decarboxylated S-adenosylmethionine. The tapetum lies in the retinal pigment epithelium and the reflecting material is enclosed within tapetal spheres. They are 0.27 um in diameter (Corydoras) and are densely distributed through the cell processes. Chemical methods for recognizing and quantifying reflecting material (including both moities) are given. The content of catfish tapetal pigment was 1.1-18 mg/g wet eye; and of decarboxylated S-adenosylmethionine, 0.2-3.3 mg/g; the higher values were found in the smaller eyes. Among characins a red pigment was found in the pigment epithelium; it was apparently the same as New Zealand parrotfish red pigment. A method of extracting the pigment is described and a spectrum presented. Variations in the relative extent of the tapetum and red pigmented areas in some characoids are noted.