The skin structure in multiple color variants of barramundi (Lates calcarifer): A histological, immunohistochemical and ultrastructural overview

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Barramundi (Lates calcarifer), a popular aquaculture species, has silver to bronze skin coloration with rare golden, “panda” (golden and black spots), and black variants. Increased production of these rare color variants is commercially desirable; however, the differences in skin-cell morphologies have not been characterized. Microscopy, transmission electron microscopy, and immunohistochemistry were utilized to characterize morphological, ultrastructural, and cellular differences between barramundi color variants. Notably, melanophores, iridophores, and xanthophores were evident. Differences in the occurrence of melanin were visible, with a reduction in melanophores in the golden (average of 0.47 melanophores/cm2) versus the silver (average of 218.6 melanophores/cm2) or black (average of 462.9 melanophores/cm2) color phenotypes. Furthermore, a significant decrease in melanophores was observed in panda variant at the edge between golden and black patches: golden vs. edge (p < 0.001), golden vs. black (p < 0.001) and edge vs. black (p < 0.001). The TEM analysis revealed a distinct difference in melanophores and mature melanosomes, with stages 1, 2, 3, and 4 melanosomes present in silver variants and rare stage 1 (immature) melanosomes in golden variant. Furthermore, the immunohistochemical techniques provided independent and thorough documentation of the presence and maturity of melanophores and melanosomes across highly valued barramundi color variants. In conclusion, the color of barramundi appears to be driven by the presence/absence and number of melanophores in the skin layer.