Chromatophore distribution and inferior performance of albino Japanese flounder Paralichthys olivaceus with special reference to different chromatophore expression between albinism and pseudo-albinism.

Albinism with a large variation in body color was found in a hatchery population of Japanese flounder. In addition to albinism, ambicoloration and pseudo-albinism were simultaneously observed in some individuals. Albinos had a remarkably lower number of melanophores on the scales of ocular side than wild-type individuals did, although no significant difference was observed in the numbers of xanthophores and iridophores. The intensity of body color significantly correlated with the number of melanophores among the albinos. No significant differences were observed in the intensity of body color and the number of melanophores between the ocular side and the ambicoloration area. Pseudo-albinism was accompanied by the reductions of melanophores and xanthophores, indicating the different expression patterns of chromatophores between albinism and pseudo-albinism. The combined effects of albinism and pseudo-albinism caused the disappearances of melanophores and xanthophores in the pseudo-albinism area of albinos. In addition to chromatophores, the different characteristics of several phenotypic traits were observed between albinos and wild-type individuals. Growth-related traits of the albinos were inferior to those of the wild-type individuals. Furthermore, the albinos had a larger pseudo-albinism area and a higher vertebral deformed rate than the wild-type individuals did. Individual multilocus heterozygosity and inbreeding coefficient measured by microsatellite loci did not show any indication that the albinos had higher inbreeding coefficient than the wild-type individuals did. This study demonstrated the expression patterns of chromatophores in the body color abnormalities of a flatfish species and the potential pleiotropic effects of an albinism gene on some phenotypic traits.