As a general rule, any fish that gets sucked into the filter is very sick or diseased and doesn't have enough strength to swim away. The intake on filters simply isn't strong enough to suck in a health fish that can swim away (except fry maybe). Sick fish will often get stuck to he intake as they simply don't have enough strength to swim away. People see that and panic that the fish was killed by the filter but that's no the case.
is that with or without strainers?
RDD was pointing out that most fish when unwell tend to lose their swimming ability, this is seen a lot when they almost float with the currant. I seen it with the dwarf gouramis they almost lose their balance.
I expect its a bit like us humans we lose our feet and fall almost unconscious. Fish lose their ability to swim and when fit and well seldom the filter currant etc is just what they cope with.
I had a neon when small get sucked up and was told to put a stockingnette/ tights / pantyhose on the end of the filter. I did not have any at the time and did not ask hubby to rush of to buy when I was ill not his done thing buying tights lol, and that was the only one I lost.
A bit of gauze or tights or the socks you get for the gravel filter will not do any harm but the gravel filter socks I found were £5 a time and to be honest there would have to be something wrong and the fish like fry very small and I have to say I lost very few fry if any that way most I think were eaten if not enjoyed swimming.
