I have a nearly 6 year old female, long-hair Calico and a 10 month old, male, long-hair, gray striped tabby. Both are indoor cats. The tabby was introduced to the household when he was about 3 months old and came from a large litter. He was very accustomed to being around other cats and was very friendly with strangers. Our female calico also came from a large litter on a farm; we brought her home when she was 9 weeks old and she lived alone until we introduced the male tabby. Personalities: The female has always been a bit wary or edgy while the male has always been extremely loving and not afraid of anything. The female will run and hide from some strangers while she'll stay put with other strangers (we can't figure this one out). She runs and hides when the vacuum is turned on and jumps out of her skin at every loud noise. The male, on the other hand, chases the vacuum and is not otherwise scared of loud noises. Introduction: We followed all the guidelines for introducing the new kitten, i.e. keeping him in a separate, closed room for 3 days, letting him roam one-half of the house with the other half closed off, etc. The resident female sniffed at the doors as expected and was obviously curious about the new presence. Once they met face to face, the female hissed and moaned when around the kitten and simply avoided him for a couple of months. After about 2-3 months, the two cats were hardly separate. Whereever one was lounging, the other was within 3-4 feet, seeming to live comfortably with one another. The Fighting. However, in the last 3 months, they have begun to engage in what looks like playful tussling that leads to hissing and possibly biting (although it's hard to tell if there is ever penetration of teeth; the female will sometimes make a loud yell and run off but there never appears to be any injuries). Both cats have been an aggressor at times. The pattern of fighting is often as follows: The female Calico will begin the tussle by rolling on her backside with her paws spread open and up. (She looks very submissive.) She'll gently swat the male in the face (no front claws), while the male sits over her and looks on for a few seconds before he gently swats her back (also no front claws). Then they will get into a hugging position with one another and go after the other one's neck with their jaws wide open. Finally, they usually end the tussle by chasing each other (usually the male is chasing the female) through the house until the male gives up the chase. There never appears to be a "winner". Friends Again. Within an hour or so, they're back together, comfortably lounging around within 3-4 feet of each other. The last couple of weeks, we've even observed the male tabby actually "cleaning" the female while the female lays patiently for a minute or so before running off. We viewed the tussling, at first, as providing them exercise. However, we're concerning that as the male kitten continues to grow (he is now bigger than the older female), he will not understand his strength and eventually hurt the female. They "tussle" daily. I read information about cat fighting in both perfectpaws.com and petplace.com, and the information there indicates that all fighting is aggression that should be stopped. Anyone with any advice on how to deal with our cats' behavior is greatly appreciated.