Moon farts
   New Scientist has a 
brief recording of fish making choral noises.  NS compares it to birds.  Sounds more like a housefly at Taco Bell.
However!  It also sounds like the formerly famous Pascagoula River Hum.  This supposedly happened around midnight, mainly at a full moon.  Fish certainly respond to moon phases.
I don't think there's an actual recording of the Pascagoula, but good old 
Strange As It Seems gave us an orchestral imitation.  Definitely the same notes and harmonies.
