Generation of a white-albino phenotype from cobalt blue and yellow-albino rainbow trout (Oncorhynchus mykiss): Inheritance pattern and chromatophores analysis

Abstract

Albinism is the most common color variation described in fish and is characterized by a white or yellow phenotype according to the species. In rainbow trout Oncorhynchus mykiss, aside from yellow-albino phenotypes, cobalt blue variants with autosomal, recessive inheritance have also been reported. In this study, we investigated the inheritance pattern and chromatophores distribution/abundance of cobalt blue trouts obtained from a local fish farm. Based on crosses with wild-type and dominant yellow-albino lines, we could infer that cobalt blue are dominant over wild-type and co-dominant in relation to yellow-albino phenotype, resulting in a fourth phenotype: the white-albino. Analysis of chromatophores revealed that cobalt blue trouts present melanophores, as the wild-type, and a reduced number of xanthophores. As regards to the white-albino phenotype, they were not only devoid of melanophores but also presented a reduced number of xanthophores. Cobalt blue and white-albino trouts also presented reduced body weight and a smaller pituitary gland compared to wild-type and yellowalbino phenotypes. The transcription levels of tshb and trh were up regulated in cobalt blue compared to wild type, suggesting the involvement of thyroid hormone in the expression of blue color. These phenotypes represent useful models for research on body pigmentation in salmonids and on the mechanisms behind endocrine control of color patterning.

Early warming stress on rainbow trout juveniles impairs male reproduction but contrastingly elicits intergenerational thermotolerance

“…Eggs were then hydrated with rearing water for 20 min. and incubated at 11 °C in UV-treated water under constant flow, following conditions described in a previous study 51 . The percentage of fertilization at eyed-egg stage, hatching rate, and abnormality in eleuteroembryos were quantified for each cross.…”

CRISPR knockouts of pmela and pmelb engineered a golden tilapia by regulating relative pigment cell abundance

“…Similar studies in cichlids also demonstrated the importance of cell interactions in pigment patterning, even though the specific mechanisms might be different [24,[27][28][29][30][31]. Additionally, studies on rainbow trout suggested that homozygous mutation of an albinism gene, led to not only reduced number of melanophores, but also significantly larger size of xanthophores, which finally led to yellow-albino fish with golden color [32]. However, it remains to be further proved whether the change of the number, morphology and pigment synthesis of one type of pigment cells will also cause the corresponding change of the number, morphology and pigment synthesis of other pigment cells.…”

Melanin‐concentrating hormone like and somatolactin. A teleost‐specific hypothalamic‐hypophyseal axis system linking physiological and morphological pigmentation

“…While not a scenario where SL expression is directly targeted, the “cobalt” variant of rainbow trout exhibits colour interference, which correlates with a degenerated pars intermedia pituitary, with few SL‐synthesizing cells and extremely low levels of SL in plasma (Kaneko, Kakizawa, & Yada, 1993). In these fish, the light blue colour (“cobalt like”) arises because of a decrease in xanthophores relative to a normal rainbow trout, while melanophore numbers remains unchanged (Hattori et al, 2020). These observations agree with those in the medaka SL knockout (Fukamachi et al., 2004), but while colour interference is the only phenotype observed in the SL knockout medaka, the cobalt variant shows obesity with an enlarged liver and fat accumulation (Yada et al, 2002).…”