Power heads are just like filters without the media. The intake is more or less the same. So there's just the thing with the lines to help stop fish from getting it. Normally any fish can swim away from the suction of a filter or powerhead. But if its sick, is really small, or the filter is really, really big fish can still get caught up in. The best way to stop this is will a pre filter. What this normally is, is a sponge that slips over the intake of the filter/powerhead. You can make one your self with a sponge with a hole big enough for the filter/powerhead intake.