The volitan, once full grown will be plenty big for a 125. IMO, not too big, but others may disagree. It should be the only really large fish in the tank. The trigger will be fine, but the panther will eventually outgrow the tank - they get huge, from what I've read/heard, they can pass the 3' mark. An eel will be a good addition, depending on the species. Sounds like a similar tank to my 75. I've got a Russells lion (slightly smaller than the volitan) and a banded moray eel. I'm planning on a female bluejaw trigger, then a 3rd fish which I have decided on yet, perhaps an angel or butterfly.