Light stress affected body color by tyrosinase-mediated melanin synthesis pathway in hybrid grouper

Light intensity is an important environment factor in fish culture. However, its effects on the growth and body color formation were still unknown in grouper. In this study, three light intensities (10 lx, 250 lx and 1250 lx) were designed to stress the hybrid grouper (Epinephelus fuscoguttatus (9) and Epinephelus lanceolatus (male)) for 21 days. The growth performance, body color, melanin content, tyrosinase activity and melanin-related genes' expression were analyzed to elaborate the effect of light stress on hybrid grouper. The results showed that both 10 lx and 1250 lx light didn't remarkably change the growth and survival, compared to the 250 lx, which was used as the control. However, 1250 lx light sharpened the color contrast between black spots and light background on skin of hybrid grouper. LC-MS/MS analysis showed that melanin content was significantly upregulated by 80.1% by 1250 lx light, but wasn't changed by 10 lx light, compared to 250 lx. The tyrosinase activity was dramatically enhanced up to 5.2 times by 1250 lx light, but wasn't changed by 10 lx light. The qRT-PCR showed that 10 lx light decreased the Creb2 and Tyr transcripts by 33.7% and 10.7%, while 1250 lx light significantly increased the transcripts of Mitf, Tyr and Tyrp1 by 97.6%, 27.4% and 150.2%, respectively. The resulted indicated that light stress influenced body color formation of hybrid grouper by tyrosinase-mediated melanin synthesis pathway, which had a classical Creb2-Mitf-Tyr-Tyrp1 axis.