Why Do Koi Fish Kiss Each Other?

Koi, short for Nishikigoi, are the colorful varieties of the Amur Carp, usually kept in outdoor or indoor ponds for aesthetic purposes and often entice the visitor to linger longer and relax. What often intrigues the viewer is that koi appear to kiss one another or lock lips and can sometimes do so quite enthusiastically. But why do koi fish kiss each other, and is it normal?

Koi fish can appear to kiss each other for numerous reasons, but they are most likely fighting if the kissing behavior is violent. Another time you may notice your koi kissing is when your koi are in the process of spawning, where males will prod females to encourage egg-laying.

It may seem rather endearing when koi “kiss”; however, these stunning creatures are not necessarily friendly to one another. There are a few reasons why koi and other fish “kiss,” and it is crucial that fish owners’ understand this behavior; to prevent their aquatic pets from harming one another. Let us dive deeper into this topic (pun intended).

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What Does It Mean When Koi Fish Kiss Each Other?

If you notice your koi passionately “kissing,” you may be inclined to think that they are behaving affectionately, but this is not the case. One reason fish lock lips is to show dominance, often around feeding time. This is especially true between two males, but females are also known to engage in this grappling behavior.

When fish fight, there is no gentleness or love intended. This little critter’s most dangerous weapon is its robust and muscular mouth, and although generally easygoing, koi – if threatened – can become unduly rapacious.

Like other animals within the animal kingdom, a shoal of koi also develops a “pecking order,” with the larger, more aggressive ones in charge. A koi’s lifespan can range from 25 – 35 years, and these fish can grow up to 36 inches in length and weigh 12 pounds.

Although larger koi are docile, they may nip at the fins of smaller fish to assert dominance, so problems can arise when bigger koi feel the need to maintain their position in the pecking order and therefore get aggressive with smaller koi.

However, this behavior is rare for koi since they are pretty friendly and gentle creatures. Like goldfish, koi enjoy swimming around their pond and investigating with their mouths, so if you see them touching lips, they may simply be greeting one another. Some koi even let their owners pet them and will nibble on their fingers.  

If you would like to learn more about Koi fish agression, you can read my blog post called Koi: are they aggressive

What Causes Koi Fish To Fight?

Koi fish fighting over food

Battling fish will often lock their mouths and roll each other around. Luckily koi’s teeth are located far back, so they can’t bite one another, although, since they have such powerful mouths, they can cause terrible damage to each other. If you notice two fish fighting, you should do your best to separate them immediately before they can cause further harm.

As with any other creature, if sick or injured, a koi fish will try to protect itself, and its mouth is its best form of defense. Are we not often guilty of the same behavior? When we feel “under the weather,” are we not often irritable and less than amenable?

Unsuitable companions or too many mates, a cluttered environment, or a compromised diet can also cause this aquatic creature to become cranky. Like humans, fish have their personalities and different temperaments and can also have their “off” moments.

The koi are particularly special because of their heritage and coloring, and since they can be expensive, we wouldn’t want them injuring each other. If you notice your koi fighting during feeding time, a simple solution would be to sprinkle food around the pond in different areas.

Several stressors (some already mentioned) must be considered when creating a calm haven for one’s koi. Suitable preventative measures should be implemented to stop predators such as dogs, cats, or herons from disturbing your koi. Idyllic waters should result in less fighting and greater bonding – it is also essential to have the correct amount of males and females in your pond.

If you would like to learn more about why Koi fish fight, you can check out my blog post called Do koi fish fight each other

The Difference Between Koi Fish Fighting And Spawning

Fish in a pond during spawning season

Another time you may see your koi kissing is when the water is warmer and daylight hours are longer – during spring when spawning occurs. This behavior can also be a prelude to mating and is observed between multiple males and one female.

As with most males in the animal kingdom, male koi can become incredibly hostile during spawning, leading to aggressive behavior between the males. When two males lock lips, they generally fight over alpha-male status, breeding rights, or to prove who owns a particular territory within the pond. This type of lip-locking is a lot more aggressive, and the loser ends up badly hurt and usually dies. 

Some people may get confused between aggressive lip locking and gentle kissing. When the males nudge the females, the aim is not to hurt the female but rather to entice her to lay her eggs to fertilize them. This type of kissing behavior can be related to courtship.

Female koi can still get hurt during spawning, and many koi owners separate their fish during this period. Others attempt to trick the fish by not allowing the ideal spawning conditions to be met. It is good to distinguish between the two behaviors as you wouldn’t want to break up a great partnership between a male and female.

If you are thinking about breeding koi fish for profit, be sure to read my post called A guide to breeding Koi and how to make a profit

How To Differentiate Between A Male And Female Koi

Amongst other reasons, knowing the gender of your koi is helpful for breeding, especially if you wish to separate your koi to protect the females. Identifying your koi’s gender

 is much easier when they’re mature and over 12 inches, but gender revealing can be done before.

The simplest method to differentiate between the two is by looking at their fins’ color and shape. Male koi’s fins are smaller, more pointed, and more colorful. On the other hand, female koi have more prominent, rounded fins that are partly or entirely translucent or transparent.

The second way to tell is by looking at the body shape. Males are relatively long and thin, whereas females are built wider to accommodate the eggs and grow bigger than males.

If you would like to learn more about the difference between male and female koi fish, you can check out my blog post called Is my koi fish male or female.


It is vital to understand fish behavior to decipher what is happening within your pond and prevent your koi from injuring each other. In general, koi fish are friendly and easygoing. Still, when provoked or agitated, they can become aggressive towards one another, and you will notice them locking lips and engaging in battle.

Koi also demonstrate this “kissing” behavior during mating season when the males will chase after and push against the females. Being able to differentiate between the genders of your koi will allow for the protection of the females.





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