I have a 10" tiretrack eel in a 55 gallon aquarium, and from past experiences I have had they are very territorial and will bite at other eels. He has killed two other eels including a fire eel. When I got him I had a smaller yellow tail spiny eel in the tank, and the two lived peacefully together until he started growing larger. I came home one day and he had bitten the other eels tail causing some pretty bad damage. I isolated the smaller eel into a 12 gallon tank, but he still died. Then I ended up getting a fire eel (idiot me), and from the get go the tire track eel chased him all over the aquarium. Tire track eels seem to have a really pissy nature about them, so dont assume that they will get along as a rule of thumb. I did have a firemouth cichlid in the same tank and it would mess with the tire track eel. The tiretrack would chase that cichlid all over the tank but could never catch him, and he would only chase the cichlid if it happened to bother him........it was sort of amusing. I plan on getting at least 125 gallon tank when the tiretrack eel gets larger. They are fun to watch but I dont think they are to social with other eels. Hope this helps.......