Aggression in 55g

[Bhack91]

Honestly this problem came as a surprise to me as I did not consider any fish I have as even semi-aggressive. I have 2 blue neon gynmogeophagus, 1 keyhole(was 2 up until about 5min ago) which are about halfway grown, 2 silver hatchets whom seem to be nuetral in what ever brawl this is, a BGK who I know it is not the killer, a twig catfish, and a baby albino senegal about 3 inches in length. What surprises me is that one of the gymno completely bullys the tank. I always thought it odd that he was so persist at bullying, but I have yet to see him do any nipping just a lot of chasing. I don't think its the bichir I have yet to see him chase or be chased. The keyhole that died was missing one of his pectoral fins, and my main suspect is the gymno... does this not surprise anyone exprienced with these fish? I personally thought they would just be a mellow cichlid that wouldn't mess with anything that didnt fit in its mouth. I know it is not the ghost knife because the keyhole was alive and well about two hours ago and the knife is on a strict nocturnal schedule. I know that i seem to be rambling, but i notice a weird behavior while typing. This same gymno that is bullying started to "shake" for lack of a better word the front of his dorsal fin as he was chasing the other. I guess my question is does this surprise anyone? and what would you recomend doing with them, I have a 29g stocked with columbian tetras and corys if I need to split them up. To be honest Im not sure how to go about splitting up who to what tank.

 

[Sab_Fan]

I no longer keep gymnos - - well, I still have one left - - but I have never observed them to be anything but peaceful; I have never seen a gymno start trouble, and they also don't get attacked much

the gymno that was shaking may be trying to initiate mating with the other gymno . . . that would only increase the potential for hostility