>>i have 2 eastern painted turtles and one red eared slider. i just rescently got the second painted turtle and for some reason my original turtle keeps attacking him whenever i put him in the tank. he doesn't attack the slider but is very aggressive with the other painted. can someone explain this to me?
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Male turtles are territorial animals. You put another male into the territory of an established male. That's going to cause fights because he views the new one as an interloper to his domain. He's going to aggressively defend his territory because that's what males do.
If he's lived with the RES for a long time then that turtle is an accepted member of his territory.
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PHRatz