Response of body color change rearing under different light intensity conditions in farmed red spotted grouper, Epinephelus akaara

Abstract

Background Fish body color is one of the major factors that determine the commercial value of farmed fish, to understand for coloration mechanisms. The expression of melanin-related genes is according to the developmental stage and light intensity in the red spotted grouper, Epinephelus akaara. Methods To investigate changes in melanin formation and melanin-related genes in the larval development stage, fish larvae were reared from fertilized egg stage to 50 days after hatching (DAH). Experiment of body color changes was performed under each different light intensity conditions. Melanin-related genes expression was analyzed by real-time qPCR, and body coloration difference was represented by RGB (red, green, blue) code value. Results Expression levels of melanin-concentrating hormone (MCH) mRNA, pro-opiomelanocortin (POMC) mRNA, and melanocortin 1 receptor (MC1R) mRNA were at their highest 5 DAH (days after hatching). Expression levels of agouti-signaling protein (ASIP) mRNA were at their highest 10 DAH. Results of body color changes according to changes in light intensity conditions showed that the expression level of MCH mRNA in the 2000 lx group was the highest at 6 weeks. The expression levels of POMC mRNA and MC1R mRNA in the 1000 lx group were at their lowest at 9 weeks. RGB color code value under different light intensities were the brightest under 1000 lx and the darkest under 0 lx. Conclusion Our research suggests that POMC mRNA and MC1R mRNA in the red spotted grouper are involved in melanin synthesis, and these genes are thought to be controlled by light intensity. To better understand the molecular mechanism of coloration in the red spotted grouper, further studies are needed to clarify the relationship between melanophore development and melanin-related genes.

Effects of monochromatic lights on the melanophores arrangement in the spotted snakehead fish Channa punctata (Bloch, 1793)

“…Because of these densely arranged melanophores, fish have colour and texture. Natural sunlight stimulates dark colour due to melanin synthesis (Choi et al, 2020;Vissio et al, 2021). Similar results were noted by Logan et al (2006), where white-light adapted fish have melanophores aggregated, forming spots that cover the small area, while black adapted fish have dispersed melanin covering a large area of fish dorsal with dark lateral strips.…”

“…Because of these densely arranged melanophores, fish have colour and texture. Natural sunlight stimulates dark colour due to melanin synthesis (Choi et al ., 2020; Vissio et al ., 2021). Similar results were noted by Logan et al .…”

“…Several genes, stress enzymes, growth hormones, reproductive hormones etc may influence skin colour and hue fixing. MCH (skin lightening), MSH (skin darkening), somatostatin, melanocortin, melanin, catecholamine (adrenaline and noradrenaline, dopamine cortisol) etc are some of the important regulators of the body pigmentation (Choi et al ., 2020; Kasukawa et al ., 1987; Logan et al ., 2006; Vissio et al ., 2021; Wang et al ., 2020; Yang et al ., 2021). A physiological colour change signifies a rapid alteration in skin colour and shade, manifested as pigment aggregation or dispersion within stellate‐shaped chromatophores (Fujii, 2000).…”

“…Similarly, if an animal is kept on white background coloured environment, α‐MSH secretion is inhibited and MCH release increased. This results in the aggregation of pigment granules in the dermal melanophores and thus decrease in skin colour (Choi et al ., 2020; Oshima et al ., 1986). Results in rainbow trout show that the sensitivity of the hypothalamus–pituitary–inter‐renal (HPI) stress response differs depending on whether the fish are maintained in black or white tanks, which has been taken as evidence for a role for α‐MSH in the regulation of the HPI axis (Gilham & Baker, 1985).…”

Annual changes in ovarian development stages of farmed female red‐spotted grouper, Epinephelus akaara, and inducing sexual maturity using photoperiod manipulation

“…Therefore, the need for resource management for red‐spotted groupers is recognized, and sustainable aquaculture technology development for resource recovery and the aquaculture industry is required. Recently, various studies have reported the cultivation of red‐spotted groupers (Choi et al, 2020; Hwang & Baek, 2021; Jeon et al, 2020; Lee et al, 2020); however, information on the basic reproduction and physiological mechanisms of farmed red‐spotted groupers is still lacking.…”