GERBILS FIGHTING! - Male Gerbils Have Suddenly Started Fighting. ?

I have 7 male gerbils livign in a tank together, they are a little over a year old . they have lived together fine since they were born, they are all definately male. However last night they had a mive fight. Only one gerbil (snowy) was injured. we kept an eye on them today. and they all seem to be fighting with one another. About half are seriously injured the other half are fine. as I say they have never had so much as a scratch on any of them. Wondering if anyone has experianced anything similar or has any advice, because my other gl tank is currently occupied by my female gerbil so i dont really have anywhere to keep the injured ones or trouble making ones. They have enough food and water and space so I really dont know what they are fighting over. Any help?