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Turtles/Sudden Unprompted Slider Aggression


My Sister was given two red eared sliders from neighbors that were moving about three months ago.  The larger one "Vern" is about 5"-6"long and we believe it is male due to his tale and long claw length.  The other turtle "Speedy" is much smaller, about 4" and thought it is hard to tell but we thought it might be female due to the shorter tail but we really can't be sure yet.
As of so far the two turtles  have been in a small 10 gallon tank where she had been hand feeding them and they had seemed fine. Today we went and got a 30 gallon tank and put them in it.  They seemed happy to have a larger space to swim around in. While transferring the two turtles I noted that the smaller turtle had a chunk of skin that had either been bitten or rubbed off of his neck.  I mentioned it to my Sister and she said she hadn't noticed it before.  Anyway, she just called me frantic because she said the larger turtle has been "stalking" and snapping at the smaller turtle.  I have two red eared sliders of my own so I am aware of some of their mating rituals but I wasn't sure if they are just fighting or if this is a more aggressive mating ritual.  I told her to just put them in separate tanks for tonight because she was so worried about waking up to a dead turtle.  They supposedly have never had issues like this before.  We cooled the water a bit and fed them are there any other suggestions you have? Is this just a territorial phase? Can they live tougher? What would cause this sudden aggression?

Hi Heidi,

I'm not sure how you could even fit two turtles of that size in a 10 gallon tank, but 30 gallons is much too small as well.  They should be in at least a 100 gallon tank, with a filter sized for a 200 gallon tank.  Turtles need a lot of room, and if they don't have it, skin/shell infections and aggression problems often result.  In addition, keeping a male/female pair together in a too small tank (or often together at all) is unhealthy for the female, because males can be quite persistent and a constantly harassed female can become too stressed to eat or bask properly.

However, at 4" the smaller turtle may not be quite mature yet, and may turn out to be a male.  In another inch you should know for sure.  What I would do is either get a bigger tank, or separate them into individual tanks, but those should still be bigger than 30 gallons.  You can figure a gallon of tank for every inch of turtle (but more is always good), so the bigger turtle needs 60+ gallons and the smaller turtle 40+, and of course if they get bigger they need more room.  This is one reason why having an outdoor pond for sliders is ideal.

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Questions regarding husbandry of Russian tortoises and other Mediterranean species, sulcata, and redfoot tortoises; general tortoise and turtle care; box turtle care. If I can't answer a specific question, I can provide sources for further research. Disclaimer: My advice is not a substitute for vet care. If I think your tortoise/turtle has a specific medical condition or injury that warrants a vet visit, I'll tell you so, and if possible I'll help you locate a vet. It is neither legal nor ethical for me to provide veterinary advice.


I have kept and bred Russian tortoises for over ten years and have other Mediterranean species plus redfoots and box turtles. I've worked with other tortoise and turtle species while doing volunteer rescue work; mostly sulcata but some leopards, California desert tortoises, yellowfoots, all box turtle species, red-eared sliders, etc. I don't personally keep aquatic species, but have access to a wealth of information and research to help you with any questions you might have.

My knowledge is based on hands-on experience keeping, breeding, and working with tortoises and turtles.

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