Do you have an aquaponic system? Cannot be there the hours that your fish have to eat? Big automatic fish feeders are quite expensive. Have a look how I made mine with 25 euros.
Step 1: The Concept
Here is a scketch of how it works. I found it here. There is a drill that while rotating carries the food out. The drill rotates with a motor and the food is contained in a bottle.
Step 2: Parts List
You will need:
1. a plastic bottle (I recommend you to use a normal water plastic bottle, the one I used was quite some trouble and I had to adjust some cardboard pieces inside)
2. 12 volt DC motor (I used one with gears to adjust the speed)
3. Drill (I made my own drill with a piece of plastic, see next step)
4. 12 volt adaptor (according to the motor)
5. Timer (if you have a big aquaponic system and you need lots of food, a one minute timer will be fine. Otherwise you will need a seconds timer, which is more expensive)
7. Plumbing pipes
Step 3: Making a Plastic Drill
I use a heating device and a stripe of acrylic to make my own light plastic drill. After heating the acrylic up, you twist it. Don't make the stripe too thick because then it folds up around itself and doesn't twist.