Tiger Oscar suddenly missing fins

[snufaluph]

I came home from work and found poor Frank in terrible shape. Just look at the picture... He was fine 2 days ago.



On Saturday we added a jewel and a festivum. The owner of the LFS said the jewel would do fine as long as we only had one in the tank even though they're a terror in groups.

I just want to make sure this is the result of a fish fight, and he doesn't have some kind of super fast fin-rot or something...? I'm new to this. We've had a 55 gallon tank for about 2 months, and it's been fully cycled for about 2 weeks. I just tested the water a few minutes ago, and none of the other fish seem distressed.

pH: 7.0
Ammonia: 0
Nitrite: 0
Nitrate: 10-20 ppm

I just don't see how one fish could do this to another fish when they're the same size. Help?

 

[Wiggles24]

It looks like one of your other fish attacked it. Size doesn't matter much to be honest, all fish but especially cichlids have their own personalities and just because a certain type of fish usually acts a certain way doesn't mean they will. Keep a close eye on your tank to see who is doing it.

 

[snufaluph]

I came back to the tank a few hours later to see the jewel trying to attack again. I moved it to fish jail (a big tupperware with some gravel, stress coat, and an airstone) and will be returning it to the store whence it came today after work (swapping out the water in the tupperware with tank water this morning before work, and this afternoon on my lunch break).

 

[Wiggles24]

Glad you found the culprit! Hope your poor Oscar heals quickly.