the amps will kill you. if it goes straight through your heart. stray voltages in a fish take will be cause by a magnetic field from pumps and powerheads it will not be carrying a current aka amperage unless there is a path to ground, then the resistance in the water will cause a current flow, water has a low resistance so the current will be minimal.
if you separate a wire and touch one end with one hand and the other hand with the other, then your body will act like a conductor allowing the current to flow right through you, if the current is more then 50milliamps there is a very good chance you will die of cardiac arrest, but it all comes down to how good of shape a person is, how old they are, how much water you have in your system, how fat you are as fat is a good conductor of electricity.
600 volts is alot of voltage, can cause a big explosion, can hurt but it is still livable, getting hit with an amp through your heart will kill you right away