A bit of googling, and all sources agree - Red eyed puffers and red eyed-red tailed puffers are both fresh water. Brackish will probably not kill them, but keep it low end (1.005 or less.) I've seen conflicting information on aggressiveness levels - one thing that does seem to be consistent is that, as they age, they become more aggressive and territorial. I don't know as would keep more than one male in a tank. You would probably do all right with a male and a female in a 15 gallon tank. I think the ottos would be OK for a while, but sooner or later would get ripped all to heck. Also, ottos prefer softer, more acid water, and red eyed puffers prefer harder more alkaline water. As fraglie as I have found ottos to be, I don't think I would try to keep them with any but pygmy puffers.