Fish laying on side following trapping behind filter

[chaosepoch]

Hi there, first post here.
I've just been changing the filter in my large (30-50gal) tank containing several fish of varying size and species

After going to place the sponge back in (no more than 5 mins cleaning it), I noticed one of the fish had gotten in the back where the (just dislodged) wiring goes in.
I immediately removed the filter and he swam out, kind of. He's sinking and laying on his side. He attempts to swim when provoked, but spins as he swim and sinks.

All parameters are fine, other fish unaffected (including other goldfish). I've removed him from the primary tank space and put him into isolation for the moment

Anyone have any advice on this? No physical injury apparent. Possible exhaustion/swim bladder/strain?

edit:correction of typos

[Merrilyn]

Welcome to the forum.

Sounds like he's suffering from stress. You can support him by putting some salt in the water, at the rate of one heap teaspoon per 40 litres.

That will make it easier for him to breathe.

Just leave him in a quiet darkened tank till he improves. After a day or so he can go back into the main tank.

They usually recover fully from something like that.

[chaosepoch]

Thanks for the advice, he is seeming much improved today. Propped-up but still standing. There is a small protrusion to one side but that seems to be the way the fin is angled. At least limited mobility has been regained