A 135 should be fine for them, at least for a very long time. I have heard 16" max size but mine seemed to be stopped at about 13". I had a pair, wasn't vented so may have been same sex, but I though it was M and F. They were bonded like a true pair, and swam around together most of the time, though the larger one did occasionally bash the smaller one. I would keep an eye on them, maybe they will become friends, though I have also heard of extreme aggression, and this is one of the meanest pike species.