The brown trout (Salmo trutta, Linnaeus 1758) is characterized by a pattern of black and red spots on the skin. The red spots are distributed mainly across the lateral line region along the flanks. Recently, in the region of red spots, a new type of erythrophores (type 2) has been described, that differs from the erythrophores type 1, which are, in addition to numerous melanophores, present in the black spots. The skin in the red spots region also has a very specific expression profile of many genes associated with pigmentation. This specific expression may be associated with the erythrophores type 2, which stain the skin red. To confirm this, it is necessary to determine the expression profile of only this cell type. Chromatophores from the skin need to be isolated from other cells in the skin. We optimized the process of isolation and removal of chromatophores from trout skin and were the first to present a protocol for the isolation of individual pigment cells from brown trout skin, without the need to sacrifice the animals. Using this protocol, we were able to isolate erythrophores type 1, erythrophores type 2, and melanophores from differently colored regions of the skin. The RNA was isolated from the sampled cells and the expression of ten genes with a confirmed role in pigmentation and three genes associated with the lateral line organ, was quantified by qPCR. Despite the small sample size and statistically unsupported results, we conclude that each type of chromatophores, including both types of erythrophores, has a specific gene expression profile. Based on the results and observations associated with red pigmentation, we hypothesize that red dots or erythrophores type 2 are involved in the detection of external stimuli.
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