[MARMIR]

...Just to put a little bit of fog in your mind I would suggest to do the other way round of what has been said so far.......I would suggest you to do exactly as any target shooter does when shooting to a static target....just aim the target, all your concentration must be focused on keeping the gun on the target, meanwhile your finger pull the trigger with a costant pressure (if the weight of the trigger is high,
constantly increase the effort on pulling the trigger) but remember: your mind and your arm are doing anything to keep the gun on target. When the shaft is released you'll be suprised (you should NOT know when your gun will shoot).
I would suggest to practice a little bit whit any kind of weapon you have or borrowed....
If your mind says "now I pull the trigger" you'll miss.....
The above is a good way to be accurate with fish that swim slow or are static....
Yes, I'm sure you will not find many of them but it's a good point to start from....
After a good time of practice you'll be able to apply this procedure to swimming fishes as well....your misses will decrease drastically...

Pls let us know....