I wonder if any one can help me. I have had my male two yellow bellied terrapins for a year and a half after rescuing them. They are between 7 and 9 years old. They have always lived together since they were hatchlings. In the last month or so one of them is beng particularly aggresive to the other. It doesn't happen every day . However when he does he chases the other one around the tank and will bite at the back of his neck and his feet.
We sought advice from a local pet shop who indicated that our tank was too warm at 24c and suggested that we took the heater out all together as is may be making the boys amorous. The tank now remains a steady 18c.
I really don't know what to do. It seems awful to separate them as when they're not fighting they bask together and sleep on the bottom of the tank together. It seems odd that they have suddenly started demonstrating this aggression.
I would be grateful for any advice that anyone can offer me?

are you sure they're both males?

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Yes pretty sure. They both have really long nails and I was told that means they are both male?

I don't know anything about turts but I just thought that they might be mating as its only happened recently. And the neck biting is what torts do before mating.

But like I said, I don't know anything about them so wait until someone else comes along.

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separate them...it's your choice, but i would break up that battle for dominance....

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not sure as i'm a tort girl but with torts when they reach a certain size and become sexually mature then will start showing their dominance to others...this can include what looks to be mating rituals. so thats a possibility?

Also might be worth saying what size (SCL - straight carapace length) the turts are and what size tank they're in.

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the turtles have already said what you need to do...one will be tormented and get some chunks removed from his hind end...if you had a big pond, the one could keep away from the bully....but in a tank, he has no escape...this happens with tropical fish all the time... sorry!

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How big are the turts and how big is the tank? Overcrowding is often a cause of aggression and a bigger tank can sometimes be the cure, it's not guaranteed though and sometimes separation is the only answer.
You could try them in a bigger tank and see if that helps, if it doesn't then put a divider down the middle to keep them apart. That way you don't need two complete setups, provided your filter is big enough to cope with the bigger tank, and you could put their basking spots in the middle so they share the same lighting.

One of the boys is 8 inches and the other is about 7 inches. It is the larger of the two that is being chased by the smaller. The tank is a corner tank and is 3.5 feet across each of the corners and 4.5 foot across the bow front. 88 gallons of water. They have the water filled up 3/4 of the tank as they love swimming and have two large turtle docks either side of the tank. They also have plant pots in the bottom to hide in.
I was worried that it might come to separating them. We have put a temporary partition in the tank and they both are just sitting on the bottom of the tank looking sorry for themselves.
These boys are much loved and I will do whatever it takes for them to be happy. The last thing I want to do is separate them as most of the time they snuggle up together! However if this proves to be the only way for them to be safe and happy then it will have to be so. It will sadly mean that I have to look for a new loving home for one of them as I am pregnant and will not have the room for a second large tank.

One of the boys is 8 inches and the other is about 7 inches. It is the larger of the two that is being chased by the smaller. The tank is a corner tank and is 3.5 feet across each of the corners and 4.5 foot across the bow front. 88 gallons of water. They have the water filled up 3/4 of the tank as they love swimming and have two large turtle docks either side of the tank. They also have plant pots in the bottom to hide in.
I was worried that it might come to separating them. We have put a temporary partition in the tank and they both are just sitting on the bottom of the tank looking sorry for themselves.
These boys are much loved and I will do whatever it takes for them to be happy. The last thing I want to do is separate them as most of the time they snuggle up together! However if this proves to be the only way for them to be safe and happy then it will have to be so. It will sadly mean that I have to look for a new loving home for one of them as I am pregnant and will not have the room for a second large tank.