Generally, aggressiveness is not something associated with guppy fish. They’re known and marketed as peaceful, sociable fish that make a great addition to a community aquarium.
So, it comes as a surprise to many, and especially to aquarists that have no previous experience with guppies, that these fish can become territorial and can become aggressive.
What gives? Why would an otherwise peaceful fish like the guppy suddenly become aggressive and territorial? And are guppies aggressive with each other or just other fish? Is their behavior dangerous?
These are the questions I’m going to address in this article about guppy aggressivity. I’ll preface things by saying that guppy fish are indeed generally peaceful, but if certain conditions aren’t met, you can push these fish to the limit, and they will show signs of aggression.
Here are some scenarios in which you may notice this behavior in action:
Guppies Chasing Each Other
Seeing guppy fish chasing each other isn’t uncommon at all. In fact, it’s normal mating behavior. Usually, you’ll see males chasing female fish all the time as they’re trying to mate.
If you see slightly smaller and more colorful fish with larger tails chasing the slightly bigger, less colorful fish with smaller tails, you’re witnessing normal mating behavior and it’s generally nothing to worry about.
Except that this constant badgering can become stressful to female guppies, especially if they’re outnumbered by males, and stress is another can of worms that you may need to deal with.
But even in aquariums without female fish, you may notice male guppies chasing each other. This isn’t out of the ordinary either as they’re competing for mating privileges and trying to establish their dominance, a pecking order of sorts.
If chasing isn’t accompanied by fin nipping or fighting, it’s part of their normal behavior and you shouldn’t become too alarmed.
You can place a few larger plants in the aquarium to offer weaker males some hiding spaces and to make it more difficult for other males to spot each other.
You should also make sure there is plenty of space in the aquarium and that your tank isn’t overcrowded, which can help ease the tension between your fish.
So, while chasing is usually just for show and nothing as serious as fin-nipping or fighting, which can cause injuries, it’s a good idea to keep an eye on the tank to see if this behavior subsides or not.
When things get taken up a notch and you notice injuries and fighting, you should immediately make the necessary adjustments (separate bullies, add females, adjust female to male ratio).
Male Guppies Fighting
Male guppy fish are wired to mate and in a male-only guppy aquarium, males will start to become aggressive towards each other if there aren’t any females around.
Aggression may progress to the point where there will be fights between male guppies. Even then, these fights may not be dangerous, and most aquarists report they’re more for show.
Males are just simply trying to impose their dominance and power, resorting to bullying and territorial behaviors.
Whenever you notice this type of behavior in your male guppies, the first thing you should do is to check for injuries like injured fins, tails, etc.
If there aren’t any signs of injury, it’s likely just a harmless rough and tumble between your male guppies, however, if your guppy fish start injuring other male guppies or other similar fish, you should separate them or add females to the mix.
Guppy Male to Female Ratio
Whatever the reason for aggressive behaviors, you should do your best to curb these behavioral manifestations lest you want to have problems later on stemming from infections due to injury.
A great way to ensure a peaceful environment in your tank is to avoid keeping only male guppies in an aquarium and being aware of the right guppy male to female ratio.
Guppies should not be kept alone, but they also shouldn’t be kept in numbers where males outnumber females. It should be the other way around — female guppy fish should outnumber male guppies.
Therefore, the ideal guppy fish group has 1 male guppy for 2-3 female guppy fish. This ensures that there aren’t too many males competing for very few females, plus it also reduces the number of pregnancies and places a lot less stress on female guppies.
Overpopulation in a mixed-gender guppy aquarium can become a serious issue if there are too many males and if guppy fry aren’t dealt with appropriately.
You can leave unwanted fry in the aquarium with their parents if there aren’t too many as the adult fish will eat them. Alternatively, you can save the fry by separating them from the adults.
Can Male Guppies Kill Each Other?
Although I haven’t seen it happening in my aquariums, guppy males can kill each other and even other fish too, especially if these other fish are added later to the tank.
Therefore, guppy fish can inflict death-causing injuries on each other, and even when fish won’t die of the injury itself, they may die because of secondary infections caused by the injury.
What happens is that either one guppy will bully other guppies or that multiple guppies will gang up on a single guppy. In both scenarios, the bullied guppy can die of the injuries.
When guppy fish nip at the fins of your other guppy fish and opportunistic bacteria or parasites can get into the body or bloodstream of injured guppies and cause their death.
However, I should also mention that this is an extreme behavior in guppies, and it shouldn’t discourage you from keeping guppies.
If you do decide to keep guppies, make sure you observe certain keeping requirements such as:
- Keeping guppies in 1:3 male to female ratio (this will make them less competitive and will eliminate aggressive behavioral models);
- Avoiding keeping only males in an aquarium (see the Male Guppies Fighting section above);
- Offering enough space for all your guppies to avoid overcrowding and related stress;
- Keeping guppy fish with compatible tank mates;
- Feeding them enough food;
- Separating nuisance fish to eliminate the risk of injuries.
If you meet these requirements, other than the normal mating behavior shown by male guppies when chasing females, you shouldn’t encounter any problems.
Can You Keep Guppies with Other Fish Species?
Yes, you can keep guppies with other fish species in a community aquarium, but they should be compatible fish. Therefore, aggressive fish, slow-moving fish, fin-nippers and larger fish aren’t a match for guppies.
Even so, there are plenty of fish that guppies can get along with including platies, mollies, swordtails, honey gouramis, cory catfish, harlequin rasboras, cardinal tetras, bristlenose plecos, and otocinclus catfish.
Fish compatible with guppies enjoy similar water parameters, have similar dietary requirements and have a peaceful nature.
It’s important to create a stress-free and healthy environment when setting up a community aquarium and account for the specific requirements of all fish species that are going to be housed together.
Make sure you set up a spacious aquarium, that your water parameters are in the optimal range for these fish, and that you have all necessary equipment to keep the water at stable temperatures.
What to do with Bullied Guppies?
Depending on the severity of bullying in your aquarium, you may need to take various actions. If there’s no injury yet, but the fish that’s causing trouble is hell bent on attacking your other guppies, it’s best if you remove the nuisance fish for a couple of days and try to acclimate it back later.
If there are signs of injury, you’ll need to quarantine the injured fish and monitor its health. If it comes down with some disease, you will need to apply treatment too.
As for the nuisance fish, you’ll need to separate it from the other fish for a couple of days to see if it calms down and to prevent any further injuries in the aquarium.
If it continues to cause trouble even after being separated and re-acclimatized, you may need to part with your troublesome guppy. You can sell it with a caveat or gift it to friends.
There’s a good reason why you should always strive to create favorable conditions for your fish, to avoid stress, and to keep them in their normal social groups.
Guppies as social fish that require company and don’t do well if kept singly or if they’re kept in groups that aren’t natural for them.
As you’ve seen in this article or witnessed it yourself in your aquarium, guppy fish can have an aggressive side that will manifest itself whenever their keeping requirements aren’t met.
That said, aggressiveness is not typical of guppy fish and if you follow my advice on how to keep guppies, it’s unlikely that you’ll run into these types of issues.