Take out the fish & use a stun gun
Remove your filters/heaters first.. but this might be the smartest idea.. I've tazed myself.. not that bad.. prolly won't kill much... If you're grounded and feeling frisky, plug some severed wires into a grounded circuit breaker and put the + and - in either end of the tank. It should bubble and realease hydrogen and oxygen gas on either lead if I remember 7th grade science class correctly.
Don't tell game and parks.. electro-fishing is illegal.