Fig. 1

(a) Medaka spawning at night, captured using an infrared camera. The female was on the right, and the male was on the left. The male wrapped the female with his fins during egg and sperm release. See Supplementary Movie S1 for the video. (b) Following at night, captured by an infrared camera. The female was in the front right, and the male was behind her. The male was following the female. See Supplementary Movie S2 for the video. (c) Quick circling at night, captured by an infrared camera. The female was in the lower left, and the male was in front of her. The male was circling the female. See Supplementary Movie S2 for the video.