Matsumoto, Y., Fukamachi, S., Mitani, H. and Kawamura, S. (2006). Functional characterization of visual opsin repertoire in Medaka (Oryzias latipes). Gene, 371 (2): 268-278.

We found that medaka has two subtypes of blue (SWS2-A and SWS2-B), two subtypes of red (LWS-A and LWS-B) and three subtypes of green (RH2-A, RH2-B, and RH2-C) opsin genes in the genome. We also found that the two blue opsins and the three green opsins genes are spectrally differentiated.