Nocturnal hatching timing of mouthbrooding male cardinalfish Apogon niger

We observed hatching behavior by mouthbrooding males of the cardinalfish, Apogon niger. Mouthbrooding males showed no feeding activities at night, in spite of their nocturnal feeding habit. On the day of hatching, they released newly hatched larvae from their mouths on average 81 min after sunset. Semilunar hatching periodicity was significant, but its diel pattern was independent of the tidal rhythm. Sunset hatching map be advantageous not only to offspring because of their low predation risk but also to parental males because they can resume feeding sooner, thereby reducing the energetic loss from fasting while mouthbrooding.