thats what mine does lol: the smallest one does to the biggest one nipping at the head but does not leave a mark i call it an hangry jerk move!Well when I had three of them in a 125 at prob 10-15" or so they would bicker, basically just get next to each other and slap one another with their bodies, reminds me of giraffes slapping necks or something. Anyway in the larger tank/ this tank one of the smaller fire eels nips at the others around feeding time or when he or she is hungry. Nothing serious though, they do not bite hard or anything so I do not think he would be able to injure any of the other eels, at least not at his current size.
love the size tank they are in! Whatcha feeding yours?
and did they darken up the bigger they got?