So, I've had this one guppy fry, who has been alone for his whole life. For whatever reason he was the only guppy fry to be born/survive for 1 or 2 months, at which point I moved him into his own 2.5 gallon with a heater and filter. He was in that tank alone for 2 months and has always seemed happy.
So, one of my other guppies is finally big enough to go into the tank (it's going to be a male only tank, so far he is the only one developed enough to tell the gender) and he seems happy, but the other one isn't. His fins seem slightly cramped, and he keeps chasing the other one around. Is this just typical male aggression/territorial behavior? Or has he decided he rather enjoys being alone?