It makes a lot of sense why many people have had more success keeping fangtooth morays with pebbletooth ones but thanks so much for the infoHere's the thing about eels, in the wild when mature they are solitary. Whille in captivity there can be cases of success, there are also many failures in the long term. Juveniles will many times be agreeable, many times only short lived. Tank size obviously plays a role, and maybe even sex. Unless in a very large aquarium, more than one male may be a no go from the start. If you have a male tessa coming into maturity, this could be a no go, especially if you introduce another male. I don't think there is a way to visually sex eels. People are going to have more success with some species, fang tooth eels are more risky, because they can do deadly damage easily.