Degus that fight

Question
QUESTION: I have two degus, siblings from the same litter.  They've lived together their whole lives, now about 3 years.  Usually they get along great.  Occassionally one attacks the other, sometimes very violently.  It's always the same one that is the aggressor.  When the one gets injured, I separate them until she? heals (we're not positive of their sexes), then work hard to reintroduce them.  Any idea why this happens and how to prevent it?

ANSWER: It could be a hormonal problem. If you don't know the sex of your degu, then it just might be that one is trying to mate and the other doesn't want it. I suggest that you take them both to an exotics' vet, have them checked, sexed, and then go from there. If they are male and female, then one may have to be neutered. Keep them apart until you find out.
Ann

---------- FOLLOW-UP ----------

QUESTION: Yeah, I live in NYC and she's been to the Animal Medical Center, which is one of the top vet places in the country.  The exotic vet there is the one that thinks she's a girl and the other's a boy, but he's not sure. It does look like he's a spurned lover, but in three years she's never gotten pregnant.  Would adding another degu to the mix help, do you think?  They would be miserable if permanently separated, and usually they're fine together but when they fight she gets seriously hurt.  She had to have her tail amputated 1 1/2 years ago after he hurt her and it got a really bad infection.  We spent 6 mos. trying to treat the infection, but eventually it looked like her life was in danger so the vet said the tail had to go.  This week he bit her foot so badly that she was dripping blood all over the cage.

Answer
I don't think that adding another degu would help. It may cause more fighting. He has to be neutered, or he may kill her. That's the only way that they can live together in safety. Go to another vet. An exotics' vet should be able to tell the difference between a male and female degu. Put their cages side by side until you can neuter him. I have an animal Board that has a degu owner on it. If you would like to join, this is the link:
http://annkaratinatara.proboards101.com/
Ann