i am no expert but i have a thread where i am keeping a bowfin 15"-16"and Florida gar 15"-16" together. It has been about 4 days now and i have seen them sitting on top of one another with no problems. They both were caught in the same area; I went back fishing the area where i caught those two and caught & released another bowfin and another FL Gar. So you may want to take that in consideration. I have had no issue of aggression yet but if you want mine to be guinea pigs i will keep you posted. 