Effects of background adaptation on the skin color of Malaysian red tilapia

The effects of changes in background color, between white and black, on the apparent body color, the skin L*, a* and b* values, the MSH levels in the serum and the melanin-concentrating hormone (mch), proopiomelanocortin (pomc), melanocortin 1 receptor (mc1r) and tyrosinase (tyr) gene mRNA expressions of Malaysia red tilapia were investigated. After rearing in black (B) or white (W) background tanks for 27 days, the rest fishes were transferred to the same (WW and BB) or opposite (WB and BW) background tanks for another 27 days. The apparent body color of fish was paler in white background and darker in black background, and the body color was reversibly variable in response to transfer to the opposite background color. Correspondingly, the L* and b* values were higher and a* values were lower in white background groups than that in black background groups in the skin of fish (P < .05). The expression of mch gene mRNA in the brain were higher in W fish than in B fish (P < .05). In contrast, the pomc mRNA levels were higher in B group than that in W group in the pituitary of fish (P < .05). However, the MSH levels in the serum of fish were not significantly different between W and B group (P > .05) and peaked in WW group (P < .05). Interestingly, the expressions of pomc in pituitary, mclr and tyr in dorsal skin of fish on day 27 were higher than that on day 54 (P < .05). The malt mRNA expressions in the skin of W and B fish were not significantly different (P > .05). However, BB fish showed significantly higher skin mclr mRNA expressions than WW and BW fish (P < .05). The tyr mRNA in the ventral skin of red tilapia was highest in B group. And the expression of tyr mRNA in BB group was higher than that in BW, WW and WB groups in the skin of fish (P < .05). Present results will facilitate understanding the mechanism of fish skin color determination.