Is it a bite or burn???

Have just noticed my longfin is injured...
He is in a 3ft tank with some mollies, a couple of platties, a 3" red tail shark, 5" sailfin plec and an albino longfin of the same size (both juvies)
I have never seen anything in the tank act agressively to anything...
I have tanken him/her out and treated him with some melafix but dont know what else to do...
Any ideas???





He is in a bowl of water in the pic not just on the table lol!

It could be an injury caused by scraping on a sharpish object or a bacterial infection, whichever the Melafix should handle it.

Your Redtail shark is it Epalzeorhynchos bicolor (formerly Labeo bicolor) they can sometimes get aggresive with age, they tend to harass other fish but as you've not noticed, unless it's doing it at night, then it's not to blame.

I have had the shark since he was tiny and have always kept a close eye on him incase he turned funny but he is so placid that I cant really see it being him.
I do have a couple of pieces of that creamy yellow stone with the holes in (I think its called live rock??) in the tank that I dont have in any of my other tanks...
Could he have hurt himself on that do you think???

Youve taken him or her out and treated with melafix.. your already doing the best you can, keep treating untill it goes away, and my guess its a fighting injury,

What would it have been fighting with Curby???
They all seem so placid in there that its hard to imagine any of them fighting...
When/if he gets better will it be ok to put him back in???

I also forgot to mention that there is damage to his dorsal fin too (the one on his back???)... Quite bad damage but his other fins and tail are all good...
Really worried that it will happen again if I cant find out what has done this to him...
The albino in the tank hasnt a scratch on him...
Also, just noticed, I have a small phantom tetra in there that has some damage to its tail...