when you say stuck... do you mean the fish has been sucked on the water suction part of the pump and cant get out or.....
do you mean that the fish has somehow got itself stuck in between the tank glass and the pump or stuck in the chassis of the pump.
Normally if fish get stuck on the suction part, really means theyre unhealthy.... fish generally have enough strength to easily avoid getting stuck on the sucking part of the pump.
Although, back in the day, I had a foxface and a zebra moral eel.... the eel took it upon itself to rip apart the plastic grate around the sucking part of the pump and left a big hole and the foxface somehow got it's nose stuck in the hole and couldn't get out.... only realised this when I came from work and needless to say, he didn't survive.