Pretty easy to do with off the shelf stuff. Photo sensors all over the aquarium read the ambient light level drop as a fish swims by and covers it with it's shadow. As the light level goes down, a corresponding inverse voltage is sent out to open an audio gate which allows one of several tracks of symphony sounds to come through an audio system mounted by the aquarium.
A digital multi-track recording of a symphony would be playing a series of different tunes at all times, but the individual instrument sounds would be silent until a fish swam by that track's corresponding photocell.
So a fish swims by the photocell mounted on the castle, the violin track fades in and out as it goes by. Another fish swims by the one mounted on the treasure chest, the flute section fades in and out, all within the structure of chord changes, crescendos, pastorale or fortissimo movements of the music tracks playing at all times. Every performance, even for the same song, would be different.
You could even do it for big municipal aquariums as well.
Add echo to everything just to tie it all together.-- doctorremulac3, Sep 26 2007 Well I'll be darned http://kstp.com/art...ries/s3086381.shtmlShe says she started doing this in 2007. Inspired by my idea or thought up at the same time separately? You be the judge. [doctorremulac3, Aug 25 2013] here at the bakery, you don't want to add "echo" to anything. but i'll add a bun for this aquatastic idea.-- k_sra, Sep 26 2007 Back in the early 70's, my dad brought home a handheld doppler ultrasound sensor, which we tried out on the goldfish tank. It would make cool "whooshing" sounds as the fish moved about. Thanks for the memory trigger!-- csea, Sep 26 2007 I cna't help believe but that there is some kind of music to the movement of fish already. They are all surrounded by electrical currents, and the interactions of those must form some kind of harmony, if you had the pickups to listen.-- DrCurry, Sep 26 2007 Somebody actually did this. (See link.)-- doctorremulac3, Aug 25 2013 Better luck next time trigger!-- spidermother, Aug 26 2013 random, halfbakery