fish look as if someone squeezed fish in middle with thumb and index finger

[Combo]

ok I seen it somewhere but I can't find it now someone said fish look as if someone took index finger and thumb and pinched fish in center of the body what does that mean if fish look that way

[CliffsDiscus]

I see them
They are easily seen on some solid color Discus like the Blue
Diamonds and solid yellows. Sometimes pinch in on one side and a small bump the other side. This is a genetic inbred problem at the mid spine. Discus with patterns are
more difficult to spot. These are fish that should have been
culled at an early age but difficult for the breeder to spot.

Cliff

[Combo]

this morning my look very dark almost black i give them food they all eat, Few hours latter I looked and 3 of the 5 where black the other 2 very dark in color so I did about 95% water change, then they all looked normal for a little while and now have turned dark again just wonder if I should do something more . I have checked everything and nothing looks any different poop is all black at one point i did see one of them bumping against air line to the sponge filter I don't know if he was trying to scratch his face on it or he was just attacking it for some reason but for all the fish to be dark I took some pictures but they not showing how dark they look I post the pictures of them on my 29 gallon LFS discus thread