Increased occurrence of the rare golden color morph of Pacific chub Kyphosus sandwicensis in a no-take marine reserve

Pacific chub, Kyphosus sandwicensis, are typically gray but some individuals display a golden color morph. We estimated that the frequency of occurrence of the golden morphs increased significantly from 2007 (1.9%) and 2012 (2.6%) to 2017 (5.0%) inside a no-take marine reserve around Nihoa Island in the Northwestern Hawaiian Islands. While sporadic observations of a golden color morph have been noted for several other marine fish species, we provide a quantitative estimate of changes in the frequency of occurrence of the morph within a wild marine population.

Quantification of the expression of a temperature-sensitive pigment allele in sailfin mollies (Poecilia latipinna) by image analysis

Image analysis was used to quantify the activity of a temperature-sensitive macromelanophore-determining allele in sailfin mollies as the percentage of the body surface area covered by macromelanophores. Fish heterozygous for the macromelanophore-determining allele produced very few macromelanophores when raised at either 25 or 28 degrees C, even after more than 200 days. In contrast, the mean percent coverage for genetically identical fish raised at 22 degrees C increased steadily throughout the course of the experiment. Production of macromelanophores was sex influenced, with greater expressivity seen in males. At 22 degrees C, the mean percent coverages had significantly diverged between males and females by the age of 201 days. From that point on, the percent macromelanophore coverage of the males was consistently significantly higher than that of the females. The tendency to produce greater melanization at cooler temperatures is not the result of a heat-sensitive tyrosinase enzyme, as is the case in mammals carrying the Himalayan allele. In mollies, the activity of tyrosinase increases between 22 and 29 degrees C. We hypothesize that production of macromelanophores is under the control of a proto-oncogene.

Pigments and ultrastructures of pigment cells in xanthic sailfin mollies (Poecilia latipinna)

Electron micrographs of skin from xanthic (gold) sailfin mollies revealed numerous xanthophores, as well as scattered melanophores. The melanophores were seen to contain premelanosomes in various stages of development. This is consistent with the fact that xanthic mollies have been shown to be tyrosinase positive. Melanosomes in xanthic mollies appear to develop by one of two pathways: 1) from an endoplasmic reticulum-derived vesicle which develops an internal lamellar framework, and 2) by fusion of multiple Golgi-derived vesicles which lack an internal lamellar framework. Analysis of the pigments in the skin of the xanthic mollies identified four colorless pteridine pigments (xanthopterin, isoxanthopterin, neopterin, and pterin) and a carotenoid with an absorbance spectrum similar to beta-carotene. It appears that, unlike some other poeciliid fishes, sailfin mollies do not use pteridine pigments for orange coloration. Rather, they appear to rely primarily on carotenoids.