An easy way to do time lapse photography is to adapt an old photo device by welding wires on its main button.
Here is an instructable showing how to do it :
Then to take picture at a certain period, it is very simple to use an arduino.
This instructable shows how to plug an arduino to the welded wire by using a simple NPN transistor in saturation mode.
To make this module you will need :
- a npn transistor BC546
- a 5KOhm resistor (or two of 10kOhms in parallel)
- a piece of protoboard
- 4 pins
Obviously you also need some tools like a welder, nippers, tin,...
All the detail to mount the module are shown on the picture.
Here is a time lapse video of my beta fish (1 picture every 30s)