We love our dogs, and generally they get on well with each other too!
However, sometimes two individuals just don't get on, and this can show itself as everything from growling to fighting.
Why does it happen?
Guarding and competing for: food, beds, toys, human attention is very common, we call this a 'trigger event'.
This results in a behaviour change which can result in the dog attacking it's housemate.
Eye contact is often the first stage once the trigger event has started, and care must be taken as an owner that you do not get bitten while trying to intervene between your dogs.
Sometimes it can be due to dogs competing for their position in the 'pack', so the aggressor is often the dog which is the newer member of the family.
Male-male or female-female housemates often fight more than male-female pairings.
What can you do?
Remove trigger events if possible.
Separate during the trigger event: for example at meal times, put their bowls in separate rooms, or at opposite ends of a larger room.
Supervision during the trigger event: Stay with your dogs and intervene by moving them apart if you see the first signs of aggression.
If aggression is not food related, then muzzling during the trigger event is a possible solution.
Short and longer term drug and non-drug options are available and are very successful, you should discuss this in detail with your vet, as options available will depend on age, breed, and any pre-existing illnesses or medications.
Referral to a certified behaviourist.