Anemonefish Chromatophore Distribution and Organization Revealed by TEM Studies

Anemonefish have a characteristic vertical white barred color pattern on an orange background made by a specific distribution of three types of pigment cells: melanophores, xanthophores, and iridophores. This color pattern is an interesting alternative model to zebrafish to understand the cellular and molecular basis of complex color pattern formation. Using transmission electron microscopic observations, we have investigated the pigment cell composition in the skin of the anemonefish Amphiprion ocellaris and found that: 1) white skin comprises iridophores and isolated melanophores; 2) orange skin contains xanthophores and scattered melanophores; and 3) black skin encompasses melanophores only. All three pigment cells can be found in the dermis. Iridophores are also present in the hypodermis, but general cell morphology differs depending on the dermal layer, distinguishing them into S-type and L-type iridophores. While melanophores can mix with xanthophores and iridophores, xanthophores and iridophores are not in direct physical contact, always being separated by melanophores. Anemonefish with differing color patterns than A. ocellaris, either color mutants or other anemonefish species, possess different pigment cell distribution and organization reflecting their respective colors. Our analysis provides key data to inform on the mechanism generating the diversity of color patterns present in anemonefishes.