I looks like an injury to the slime coat from netting the fish or being trapped behind something. Is it a recent purchase?
Add salt at 3tbsp/10gal for a few days or stress coat per manufacturer instruction. Keep the water clean and it should heal in its own
Great minds Liz
In the second pic there's a PVC upright visible. How close is it to the glass? Could the fish have been trapped/squeezed between the pipe & glass? If so, prob good to wedge a slice of foam in there to prevent it happening again...
This is not ich. The others could be right about an injury. Good, clean water and maybe 3 TBS salt per 10g should help if it is. But, keep a very close eye on it and report immediately if it changes for the worse...
Thank you very much for quick response.
@ LizStreihorst, it been a week earlier since I bought them but I noticed four days ago an I thought it an advanced case of ich so I treated it and whole tank with ich-x.
@danotylor about two inches the between the PVC and the glass, but I think the injury (if it the right case) from the seller it self.
Should I use a separate tank for salt bath?
Thank you for resounding.
@LizStreithorst, good to hear that I bought it ten days ago, but it was lay on it side, few days after I noticed that issue but I thought it is an advance stage of an ich, so I treated them with ich-x with the rest for three days.
I was was scared when I see this injury from a close.
@danotaylor it approximately two inches between the PVC and glass wall with same for this fish, but it most likely it was from the seller so the salt will be my next step as you all suggests but no need for isolation, am I right?