I've been researching different ways of propelling my fish, all 4 of my electromagnet attempts have failed, and instead I'm going to use a servo.
I have therefore emptied my money box to buy this little guy from a local hobby shop:
HS-65HB Mighty Feather servo.
Came with 2 extra horns and 4 screws for mounting, a good $28 spent!
Haven't powered it up yet but apparently it can supply 2.2kg-cm @ 6v