This video is about a Lusitanian toadfish and other fish.
From New Scientist:
Zoologger: Bagpiper fish keeps intruders away with song
15:52 01 April 2015 by Mary Bates
Species: The Lusitanian toadfish (Halobatrachus didactylus)
Habitat: Bottom-dwelling, in rock crevices or muddy sediments on the floor of the Atlantic ocean and Mediterranean sea
It whistles, grunts and croaks. The Lusitanian toadfish is quite musical for a fish. It makes at least five kinds of calls, and males even sing in choruses to attract mates with their boatwhistles – long, rhythmical, tonal sounds.
Now it seems the boatwhistle has another function: keeping intruding males away. Lusitanian toadfish can reach over half a metre in length and weigh over 2 kilograms. They have large, flat heads and wide mouths, giving them the toad-like appearance that they’re named after.
During the mating season, from May to July, males create nests under rocks and then sing to attract females. Males are territorial and they defend their nests from intruders. After mating, females leave their sticky eggs in the nest for the male to care for until the young are old enough to fend for themselves, at about three to four weeks.
Although boatwhistles were already thought to act as a keep-out signal to other males, there was no direct evidence of this. So Clara Amorim, from ISPA University Institute in Portugal and her colleagues decided to test this hypothesis by muting male toadfish and seeing what happened.
Shushing a noisy fish
Lusitanian toadfish call by contracting muscles on their swim bladders, which releases air. Different sounds result from different contraction rates. Think of it as an underwater bagpiper.
Amorim and her colleagues muted some toadfishes by cutting and deflating their swim bladders under anaesthesia. These fish could still contract their muscles, but couldn’t make any sound.
They found that the nests of muted males were more likely to be intruded upon, probably because they were unable to sing. Their results suggest that boatwhistles are effective keep-out signals, reducing the risk of territorial intrusions and therefore nest takeovers.
“Boatwhistles are a cheap way to exclude intruders without engaging in a fight,” says Amorim. “Seeing that a nest is occupied is not as effective as hearing that there is a male in the nest eager to defend its territory.”
Some aspects of toadfish boatwhistles, such as frequency and pulse interval, are associated with the size of the fish, meaning that others can use it to assess the quality of potential mates or the fighting ability of rivals.
The Lusitanian toadfish is not unique in making underwater noise. Herrings fart to find each other in the dark, clown fish chatter by clacking their jaws together to warn intruders to stay away and another species of toadfish cries like a baby.