I guess everypone missed the fact that you only have a 65 gallon tank. That alone is to small for a 13" endi. I cant belive people are recommending rays either for a 65 gallon tank...
The electric catfish can only be housed alone and will grow to 39" and need a tank of 135 or more.
Your going to need a much bigger tank for the endi.
Look at the false gars, they dont get that big and will be too quick for the endi
oh and get a bigger tank