Cinnamon clownfish, Amphiprion melanopus, typically live as part of a mated adult pair or an adult pair and an immature individual and social ranking in the group controls the sexes of the fish. In general, the female is the larger and dominant individual. If a dominant female dies or is absent, the male partner undergoes a sex change to become a female. This special reproductive characteristic provides a good model for which to study the mechanism of sex change. Sexual development and gonadal maturation in fish are regulated by hormones of the hypothalamus-pituitary-gonad (HPG) axis including gonadotropin-releasing hormone (GnRH) and other neurohormones, gonadotropins, and gonadal steroid hormones and peptides. Specially, light is among the most important natural environmental factors that regulate reproduction in fish. Light-emitting diodes (LEDs), which is a new form of lighting technology can be designed to output specific wavelengths such as narrow bandwidth light which is important because it can be tuned to the environmental sensitivity of a target species. In the experiment, the white fluorescent bulb and different LED (red, peak at 630 nm; green, 530 nm) were used. The effects of different illuminations were assessed by measuring the mRNA and protein expressions of HPG axis genes and sex steroid hormone level. For green LED light, significantly higher levels of HPG axis genes expressions, GSI, and plasma sex steroid hormone were obtained, compared to the red LED light spectra. Histological analysis also revealed the presence of vitellogenic oocytes in fish exposed to green LED light. The results indicate that exposure to short wavelength lighting accelerates gonadal maturation and sex change, and is likely to facilitate development of more energy-efficient aquaculture procedures. Also, have investigated that light reaction in marine organism's mechanism using LED lights, and high potential of application of Bio-photonics for the aquaculture.

• Na Na Kim(Division of Marine BioScience, Korea Maritime and Ocean University)