You are talking about macropodus opercularis right? Well the males of this species, once mature, are aggressive whether spawning or not. With them being the more colorful and having more impressive fins, I assume you were interested in this sex rather than a female. If so, you are best off avoiding them as (besides the fact that you should only get 1 as 2 or more males would fight), it would probably harass the rams and would almost deffinately end up harming the honeys - even killing them. A female might work but you are better off not risking it at all - particularly as the fish you have in there already mean your tank is fully stocked and soem of them - such as the ghost knife - also make your tank over-stocked and you'll soon need to upgrade. Basically, with rams and other gouramies and large-growing fish already in there, you are better off not adding any more gourami-type fish at all (perhaps nothing at all until the knife is moved for that matter).
edit: yes, 4" is about right if you include the long tail extensions of the male. The average is more like 3" and males are slightly larger over-all than the deeper-bodied females (without considering fins which are much longer in males).
