In my project, the next step would be to add more interactivity. How to implement a sensor that senses a fish poking it or swimming nearby? Ideas?
A beam of light shining on sensors triggered when the fish swims in front of 'm ?
Preferably on a wavelength/colour the fish can't see not to disturb day/night.
A camera with movement-detection would be nice, but I guess finding one with such low resolution that arduino can handle it will be difficult.
A piece of wire, attached to the ground, pulley on top, that lifts a very small metal weight resting on a metal plate ? Weight/plate could be used as switch when the wire's poked hard enough.
A similar idea would be a touch-probe which is often used in CNC-applications.http://www.indoor.flyer.co.uk/probe.htm
You should of course change it in such way you could use it in the bowl, but maybe it works...
Don't tell 'm I also said RFID, I wouldn't like to read the comments if they find out my IP-address. ;-)