I used a lamellophone, pressed it on the glass of the aquarium and played.
The fish responded, but their response was equivocal.
I felt that a demonstration that fish could learn to categorize stimuli as complex as music, according to a criterion as unnatural as musical genre, not only would show that they extract meaningful signals, but also might suggest a capability for higher order auditory processing comparable with that of pigeons and people.
CHASE, AVA R.: Music discriminations by carp (Cyprinus carpio). Animal Learning & Behavior , 29 (4), 2001. p 337