I would not do a puffer (Arthron sp.) in anything less than a 125. Same with larger lions (ie Volitans and Russels are the two most common). A 55g is just to small to house predatory fish for life. If you wish to buy baby versions and plan on upgrading in a year or so that is okay. That is what I did/am still doing now. I currently have a 2" baby Clown Trigger and a 3" Arthron immaculata puffer in a 55 and when they get big enough they will go in the 209G or by then I hope to someday get another 200+ gallon tank. I have kept Triggers, Lions, Puffers and Eels together but generally triggers are a bit to aggressive for fish that are not active (ie Lions and Eels). Some caution must be used in these cases. If you really want an eel you can do a Snowflake in a 55 just make sure your tank is 100% covered because they will slither out if given the oppertunity. If you do want to get a baby trigger and grow it up I would stick with the smaller ones (Huma, Rectangular Huma, Sickle-True Bursa-, Black Belly Bursa, or Undulated but they need a system all to themselves). Hope this helps and sorry about the discouraging news but a 55 is not big enough for most of the marine predators.
