It sounds like the groups arent set up properly I had similar problems with a few figures I made recently. The necks tore away from the body when turning the head or neck. I fixed it by looking at posette and the way that groups are made up on her. You could try looking at the angel fish or the dolphin and how the groups are done in that and copy the setup to your fish. I made a poser figure of a killer whale using the dolphins bones and it worked well. You do know that when making your own bones that you have to name the parts properly and exactly e.g. rShldr not Rshldr or right shoulder? It is better to name the bones correctly so the figure can work with poses and bvh motion files etc