Loaches Online Forum

About two months ago I noticed one of my weather loaches was missing his entire right pectoral fin. There was a wound type mark near where the fin was and just a bit of bone sticking out.

I don't know how this happened, I can't imagine the other fish (odessa barbs, blood fin tetras, BN pleco, other weather loaches) in the tank doing this. His fin was quite a bit larger then the head of my barbs and tetras. I doubt the other weather loaches would get this violent and I can't imagine the Pleco doing it either.

Anyway I treated with Melafix for about 10 days until the wound looked to be healed. Since then I've been closely watching it and he's grown back about 1/3 of the total length of the fin but progress seems to have stopped or significantly slowed.

I don't know if I should expect him to regrow the rest of this fin very slowly over the next couple years or if he'll just have to do with what he has.

I think it is remarkable that they can regrow at all! Imagine if your arm was off at the elbow

A fin injury that does not get as far as the body of the fish usually regrows 100%, though there may be a little color difference.
An injury that is more severe, like you are describing is less likely to recover fully, and I think it is great that he has done as well as he has. I sure hope the healing and regrowth continues!

As for how it happened... Usually, when fish nip at each others' fins the damage starts at the outside edge, and, unless the nipping fish really means business, the nipping does not reach the body. I do not think the fish you list are the sort to do this, unless one is a lot more nippy than average for the species. You would also see other fish with nipped fins, not just one fin on one fish nipped this badly.

Perhaps something injured this fish? Maybe he got his fin stuck in something? Just taking some wild guesses here.