In one of the marvels of nature, males of a fish species called the plainfin midshipman that dwells in Pacific coastal waters from Alaska to Baja California court females during breeding season using a nocturnal "love song" with an otherworldly sound.

Scientists have wondered what makes these fish sing only at night. A study published on Thursday provides the answer.

Laboratory experiments showed that the fish's vocalization, a low-frequency hum like a foghorn, is controlled by a light-driven internal clock and the hormone melatonin, known to govern sleep and wake cycles, researchers said.