Rainbow Shark isn’t growing

[Atwatem]

Hi all! I’m not sure of all the details you need, but I have a 55 gallon tank, it’s cycled and healthy. We’ve had it up for about a year now and we haven’t lost any fish. My concern is we have 2 rainbow sharks that we bought together. One of them have seriously out grown the other. And I mean seriously out grown, it’s the same size it was when we brought it home a year ago, but the other is about 5 inches long now. I’m going to post a few pics. I guess I’m just wondering if this is normal. The one by the rocks is the smaller one. The one by the Crayfish and Castle is the larger one.
Thanks!!

 

[Colin_T]

Rainbow sharks are territorial and if you have 2 males, the dominant one will bully the smaller one and prevent it from growing. Male rainbow sharks have a black edge to the anal (bottom) fin.