Just my humble opinion, but:
I would like to see a frequency change with vertical position of the fish and tempo change with amount of movement, if the sound signal pulses. I wouldn't bother with preset tracks, that seems too gimmicky. The aquarium should be the sole dictator of the music. If the fish hold still, it should be quiet. but still lit. This would likely work best with one fish only, right?
As for light, I would set up a full-spectrum system (three bulb?) whose sensor takes the length of the aquarium and equates it to a given range of visible light. So the tank looks red when the fish is on the left of the tank and violet when he swims to the right, fading through all colors as he goes across. At this point, a fishkeeper would know where the fish is in the tank by ambient light and change in pitch of sound. He would also know how active the fish is by speed of tone production. The only dimension left is width. I would assign that to a volume control so that the tone and light are brightest when fish is toward the front panel and quieter, dimmer when he is near the back panel.
Now we can watch as the fish learns to control the tank and ultimately chooses one corner as its favorite.