The koi carp is a type of common carp that is usually kept for decorative purposes. This species is long-lived, reaching 25 – 35 years of age, and can grow up to an enormous 90 cm (3 ft) in length. Koi carp are unmistakable, being brightly colored with a variety of markings.
Koi carp were originally reared by farmers in Japan, initially to supplement their diet through the winter months, but when color mutations began to appear due to the limited gene pool, the focus shifted to developing these. The selective breeding employed by the people keeping these carp not only resulted in physical changes but also caused many behavioral changes.
For example, the domesticated carp became less wary of predators, less efficient at hunting, and less likely to occupy bottom habitats, distributing themselves higher in the water column. It is entirely possible, therefore, that koi carp have evolved to have different social relationships to the wild common carp.
The Social Life of Koi Carp
Wild common carp have been reported to have seasonally variable social relationships, which are affected by the prevalence of predators, changes in water temperature and visibility, and food availability. Groups of wild carp will also show greater cohesion in daylight hours than they do at nighttime.
With a strong evolutionary history of being a social species, it is no surprise that koi carp also seek contact with conspecifics. A study of koi carp that had been introduced into the wild in New Zealand found that individuals often form pairs, with male-female pairs being most common, but pairs of fish of the same sex were also discovered to remain in close proximity to one another. Mixed pairs are often seen around the time of breeding, with males remaining close to females prior to spawning taking place.
Anecdotal evidence suggests that koi carp school and play together, and will greet each other – but there does not appear to be any scientific research to back this up. However, there is research showing that individuals will seek out contact with humans, including eliciting tactile interactions, which would suggest that they may engage in similar behaviors with their conspecifics.
However, not every interaction between koi carp is harmonious. Studies have found that groups of koi carp display more aggression than groups of similar species such as goldfish, with behaviors such as chasing and nipping being used against conspecifics.
What Does This Mean for Keeping Koi Carp?
Ensuring that koi carp are kept with others of their kind is essential for their welfare and general well-being. Not only do they appear to enjoy the company of others, but they also rely on it at times to curate a sense of safety – there is, after all, safety in numbers. Studies have shown that carp can engage in social learning, determining where food is by watching other individuals, so allowing koi carp to live in groups will allow them to function as naturally as possible.
Due to the small risk of aggressive behavior occurring between individuals, the amount of space provided to groups of koi carp needs to be carefully considered. Overcrowding may cause increased aggression, and introducing new fish into a pond may result in a temporary rise in agonistic behavior as they seek to establish a dominance hierarchy.
In conclusion, koi carp are a social species that thrive when they have contact with others of their kind. However, it is important to avoid overcrowding in ponds and ensure that fish have adequate space to move away from each other if they need to.
Super interesting to read some actual studies on this. I noticed that some of my own koi have become bonded over the years (often in pairs), and although I’m not sure if this is a ‘”true” social connection, the fact that there is research in this area to indicate it could well be is fascinating!