get an eheim or take some time to setup the hoses etc with the guards that are supplied with them? I can't see how a fish could be able to get into a filter these days, all intakes have strainers on them and pretty much all filters have spray bars
I would imagine streams/rivers where these fish live in the wild would be alot deeper than a tank. You might have stirred them up with all the splashing and what not, also they were probably thinking wtf is going on wheres all my water going.