Adult see-through medaka fish. The left (A) and right (B) sides of the body of a female. The dorsal (C) and ventral (D) views of a male. a, air bladder; b, brain; bv, blood vessels; c, conjunctiva; f, fat tissue; g, gill; gu, gut; h, heart; k, kidney; 1, lens; li, liver; o, ovary; oc, optic cup; s, spleen; sc, spinal cord. The dark color of the gut comes from ingested feed (the scale bar represents 4 mm.). Reproduced with permission from Y. Wakamatsu (38) and PNAS Copyright (2001) National Academy of Sciences, U.S.A..