What happened to his fin?

[Peach02]

Mandarin fish that I have had for about 3 months has lost part of its left front pectoral fin. his swimming ability does not seem to be impaired at all. Photos below, does anyone know what caused it and how to treat

other fish are
1x coral beauty
1x bicolour blend
2x occelaras clown (small)
2x fire goby
1x mandarin fish (smaller female newly introduced)

Good fin

Bad fin

 

[BadFish619]

Somebody probably picking on him unfortunately

 

[Peach02]

Somebody probably picking on him unfortunately

any idea what, only fish I've seen any aggression from is coral beauty and bicolour and only to each other and this was only twice with no damage done

 

[BadFish619]

Hard to say, someone will have a better idea than me. Could be almost any on that list. Bi color good candidate.

 

[Peach02]

Hard to say, someone will have a better idea than me. Could be almost any on that list. Bi color good candidate.

any recommendations on what to do?

 

[BadFish619]

Whenever I add a new fish especially something similar to another species I put him in a critter cage in the tank for a few days so they can see each other first. They were all peaceful until you put the new fish in? Other than find out who is doing it and remove him, or remove the goby until fins grow back but that doesn't solve long term problems. Provided of course someone is nipping and its not fin rot but hard to tell from the pics

 

[Peach02]

Whenever I add a new fish especially something similar to another species I put him in a critter cage in the tank for a few days so they can see each other first. They were all peaceful until you put the new fish in? Other than find out who is doing it and remove him, or remove the goby until fins grow back but that doesn't solve long term problems. Provided of course someone is nipping and its not fin rot but hard to tell from the pics

the two mandarin fish where from the same tank but one could be caught thats why I started with one and when they where in the same tank previously they got along.

I only noticed the fin damage after the new fish came.

never seen any aggression towards mandarin so no clue who is doing it

from what I've seen on google it does not look like fin rot as its a smooth 'cut' apart from a small bit sticking off near the torso

 

[BadFish619]

I'd say because you don't know the culprit you could catch the goby and put in a qt. Let it grow back. Not to say it won't happen again. Might even stop on its own if the fish work it out.

 

[Peach02]

I'd say because you don't know the culprit you could catch the goby and put in a qt. Let it grow back. Not to say it won't happen again. Might even stop on its own if the fish work it out.

With the way my live rock is set up and the process we went through at LFS to catch him I won’t be able to isolate him, the fish all seem perfectly content with the pecking order but blenny and coral beauty I think are competing for #1 spot with eachother

 

[Nicholas Scelzi]

I use an acclimation box when adding a new tank mate. And not always for the new guy. Sometimes I put the most current aggressive fish in the acclimation box while the new guy gets used to his surroundings