Abstract
This study investigated whether irradiation of a specific light wavelength could affect the sex differentiation of fish. We first found that the photoreceptor genes responsible for receiving red, green, and ultraviolet light were expressed in the eyes of medaka during the sex differentiation period. Second, we revealed that testes developed in 15.9% of genotypic females reared under green light irradiation. These female-to-male sex-reversed fish (i.e. neo-males) showed male-specific secondary sexual characteristics and produced motile sperm. Finally, progeny tests using the sperm of neo-males (XX) and eggs of normal females (XX) revealed that all F1 offspring were female, indicating for the first time in animals that irradiation with light of a specific wavelength can trigger sex reversal.
Highlights
Light is one of the important environmental factors for aquatic habitats
The experimental fish showed a high survival rate in each light-emitting diodes (LED) irradiation treatment at 60 dph. In both white and green LED treatment groups, dmy and dmrt[1] genes were detected in all orange-red body colored individuals, while only the dmrt[1] gene was detected in white body colored individuals by genomic DNA PCR (Fig. 2A,B), indicating that the body color represented the genotypic sex even if the fish were reared under green LED irradiation
We found that irradiation with green LED light during the sex differentiation period induced female-to-male sex-reversal production of fertile sperm in genotypic female, indicating for the first time in animals that irradiation of a specific wavelength can be a trigger for sex reversal
Summary
Light is one of the important environmental factors for aquatic habitats. Whereas the physiological mechanism of the effects of light, i.e. photoperiod and intensity, in growth and reproduction has been studied in many animal taxa[1,2], the knowledge on the effects of the wavelength, i.e. the color of lights, to physiological states of animals is limited. Medaka (Oryzias latipes) is a small model fish with several desirable features, including a short generation time, small genome size, and the availability of an inbred strain, Hd-rRII1, showing genotypic sex-dependent body color[17,18]. Their sex determination system is male heterogametic (XY/XX). In the retinas of adult medaka, 8 cone opsin genes, such as ultraviolet (SWS1), blue (SWS2-A, SWS2-B), green (RH2-A, RH2-B, RH2-C), and red (LWS-A and LWS-B) are responsible for photoreception with retinal chromophores and have already been identified[30] It has not been revealed which opsin genes are expressed in the eyes of medaka during the sex differentiation stage
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