Effects of temperature on body color of Malaysian red tilapia during overwintering period

In recent years, red tilapia has been gaining popularity due to its very fast growth, the absence of black peritoneum, salinity tolerance and adaptability to any culture system. However, the pigmentation differentiation in genetic breeding and skin color variation during the overwintering period are the main problems limiting the development of commercial red tilapia culture. The pigmentation differentiation is not reversible and skin color variation during overwintering period is reversible with the environmental temperature increasing. Coloration patterns including whole pink, pink with scattered black spots and pink with scattered red spots have been found in our breeding population. In order to further understand the genetic molecular mechanism of pigmentation differentiation and variation so as to solve the skin color variation during overwintering period, this research compared the effects of different temperatures (16, 20, 25 and 30 °C) on apparent color, tyrosinase (Tyr) activity and skin pigment cells of Malaysian red tilapia during overwintering period. After fifty days experiment, we found the body color of most fish in T16 group changed to pewter from pink at the beginning. Most of the abdominal skin color in T20 group fish also varied to pewter. But the fish body color in T25 group had only slight change and the body color of T30 group was still whole pink. The Tyr activity of fish back skin, abdominal skin and serum increased with increasing of temperature, and was the highest in 25 °C group fish. However, the Tyr activity decreased in 30 °C group fish. The blood tyr mRNA expression increased with increasing of temperature, and the muscle tyr mRNA expression in 25 and 30 °C group fish were higher than that in 16 and 20 °C group. The melanocytes of fish dorsal skin decreased in number with increasing of temperature by slice microstructure observation. The results suggest that the color variation during overwintering period of red tilapia may be related to the changes of skin melanocytes and Tyr activity. The further study of the regulatory mechanism would help to understand the genetic mechanism of fish body color and improve the body color features.