Elements of Iridophore Pigmentation in Green and Blue Phenotypes of the Siamese Fighting Fish, 'Betta Splendens'

Abstract

Metallic pigmentation in Betta splendens varies in color and also in densiity and/or distribution. Questions persist as to the mechanisms involved and the specific genetic controls. Metallic effects such aa this are usually produced by crystals (primarily guanine) in integumentary cells called iridocytes or iridophores. Betta phenotypes are identified as green (the wild type), blue, and steel blue. Generally green colors of this nature are thought to be caused by a yellow screeninq substance over a blue underlying color. This could be the case for Bettas but it has not been described. No physical or physiological explanation has been presented to explain the existence of two blue phenotypes. This study attempted to reveal differences in iridophore elements which might explain this difference. Variations were found in crystal elements as follows: (1) numbers of crystals in clusters, (2) distances between crystals, (3) sizes and thicknesses of crystals, and (4) the general patterns of orientation of crystals. Examination of electron-micrographs of 32 clusters or stacks of crystals from steel blue fish and 65 from blues revealed that in general crystals in steel b1ues tend to be larger, to have more space between each crystal, to have lower numbers of crystals per stack, and there was less variation in orientation of stacks. In addition, evidence was found for existence of "dermal chromatophore units."