Posted: Thu Aug 06, 2009 9:40 pm
The obvious reason why they are fighting is because your tank is two small for the two of them. There's a rule about having 10 gallons of water per inch of turtle and, from what you're saying, I'm guessing that your turtles sizes added are bigger than 5 inches. Two years ago they were probably satisfied with the 55 gallon tank but as they grew this is no longer enough for them. They feel like the other one is invading its personal space and so they become aggressive.
There's something else that could also be happening. How are you feeding your turtles? Do you give their food in the tank or in a separate container? Besides the territorial issue, turtles sometimes fight over food. To eliminate this problem feed them separately in different containers.
What I suggest is that you try feeding them separately first (if you aren't already doing so) and see if they continue to fight. If they don't, you should probably still upgrade to a bigger tank. But if they remain aggressive, the solution would be to separate them in different tanks.
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Tank #1:
~Charlie - 4 inch male RES
Tank #2:
~Charlotte - 6 inch female RES