Firstly, Don't Panic!

It is very common for degus to be involved in minor squabbles and disputes, remember that they rely on establishing a strict pecking order or 'hierarchy' between group members in order to leave peacefully together for most of the time. Maintaining this hierarchy leads to some squabbling and non-serious dominance fighting, which includes:

Mounting
Chasing
Agonistic vocalising
Boxing
Jump-kicking
Back-turning

All of the above are considered normal transient behaviours (i.e. they don't last for longer than a few weeks until the hierarchy becomes stable again), and even though they can look a little extreme they are mostly designed to solve the dispute without causing injury. If your degus are engaging in this sort of fighting it is strongly advised to leave them to it and not to intervene (i.e. do not separate them), as by doing so you could set back the process for them or even completely reset any hierarchy they have so far established. However, if the fighting escalates and physical injury occurs you should step in.

When should I step in and separate my degus? Serious fighting indicates neither of the degus is willing to back down and submit to the other, and this is when injuries can be inflicted and you need to take action. These behaviours include:

Physical biting/wounds
Tearing out tufts of fur
Rolling around together locked in a ball

If your degus have sustained injury you will need to separate them immediately, but be warned that by doing so you are very likely to completely reset their dominance hierarchy, meaning you will not be able to put them back together again for some time and often after a lengthy reintroduction process. However, it is by no means the end of the world if you do have to do so (see below). Remember that in the wild, two degus in this situation would be able to put space between each other and escape the situation, but in captivity they can't always do so, so it's up to you to decide when is the right time to act on their behalf.

Note that the most common time you'll see fighting is over food, especially if the degus all share a feed bowl. To reduce this, provide all your degus with their own dish spaced around the cage.

>IMPORTANT NOTE Regarding Time of Year and Fighting<

Please remember that you are most likely to see fighting between your degus during breeding season (early winter to mid spring each year).

The reason for this is that at this time of year, your degus' physiology changes and their sex hormone levels begin to fluctuate, whether they get to breed or not. These hormones make both male and female degus far less tolerant of each other than at other times of year, and make them engage in more territorial behaviours and dominance activities. If your degus have suddenly started fighting more, and it's between November-April, then the cause is going to be breeding season hormones.

Note that it is very common for degus to fight the worst during their first breeding season after puberty, and subsequent breeding seasons are usually much calmer! Please be patient with them, it will settle down after a few weeks. Most of us know what it's like to have PMT!

What happens if I have to separate my degus?
Try not to worry if you have no choice but to separate your degus, it's very likely you will be able to reintegrate them after a few weeks or months being apart. In these cases it is advised to split their cage (horizontally where possible as per the intro guide) and swap them regularly (daily or weekly), but don't attempt any physical introductions until they are ready. If this occurs during breeding season, it's likely to take several weeks or months, but you'll know when they're ready as they will be paying much less attention to each other through the divide. As soon as you notice this change in behaviour you can proceed with introductions on neutral territory as per the guide- www.Degutopia.co.uk/deguintros.htm

Will neutering help correct the problem?
We find that in these cases, neutering does not provide a quick-fix for the problem. This is because the problem is largely psychological rather than being purely hormone mediated, so once it has started you cannot remove the hormones through neutering and expect things to return to normal overnight. To prevent things getting out of hand the following season then neutering can help, but you're much better off doing this outside breeding season (i.e. in the summer/autumn) for best results. The same goes for female degus!

My males have been fighting but now one of them has been squeaking for hours, is something wrong?
It is quite common for males to engage in long periods of 'barking' after mating/mounting/engaging in dominance behaviours. This vocalisation is very common and is a territorial alarm, used to alert others in hearing range that this territory is claimed. It is perfectly normal and does not indicate any problem.

My degus have been fighting but now they're cuddled up sleeping together, what's up with that?
Disputes can be lengthy but degus don't hold grudges against each other; it's normal for two fighting degus to snuggle up and engage in grooming after fighting. In fact, this is a very good sign as grooming in particular helps degus strengthen the bonds between them, indicating all is forgiven and the hierachy is starting to stabilise.

My degus have been injured and I've separated them, is there anything I can do for their wounds?
Superficial injuries can be treated by bathing in saline solution twice daily until healed in order to prevent infection. Deeper wounds should be looked at by your vet in case they need stitching/flushing, and always seek veterinary advice if there is any change in an injured degu's behaviour, or wounds become swollen, inflamed or start weeping.