Aquarium, I+R+D

How to enhance the beauty and size of your koi fishes through crossbreeding?

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By Milthon Lujan

The researchers evaluated two genotypes obtained in the experiment. (A) F2 population obtained from the cross between the Nishikigoi Kōhaku female with the Hungarian carp male and the F1 male backcrossed with the Kōhaku female. (B) The Nishikigoi population descended from the cross between Kōhaku and Taisho carp. Source: Santos and Furquim (2024); Aquaculture and Fisheries.
The researchers evaluated two genotypes obtained in the experiment. (A) F2 population was obtained from the cross between the Nishikigoi Kōhaku female with the Hungarian carp male and the F1 male backcrossed with the Kōhaku female. (B) The Nishikigoi population descended from the cross between Kōhaku and Taisho carp. Source: Santos and Furquim (2024); Aquaculture and Fisheries.

For centuries, the koi carp, a dazzling jewel in the world of fish, has captivated hearts and imagination. But beyond its impressive colors lies a fascinating realm of genetics and selective breeding, where the pursuit of perfection drives constant innovation; however, uncovering the secrets of its growth and body conformation remains a challenge.

A recent study published by scientists from the Fisheries Institute, Agência Paulista de Tecnologia dos Agronegócios (APTA), delves into the captivating world of koi fish genetics, specifically exploring how crossbreeding between Nishikigoi (the ornamental carp we all know and love) and the Hungarian carp (Cyprinus carpio) can unlock hidden potential for growth and body conformation.

The research aims to bridge the knowledge gap by exploring the scientific foundations of koi genetics, making it accessible to both enthusiasts and researchers. By delving into the complexities of crossbreeding and its impact on desired traits, this study enables individuals to actively participate in the world of koi breeding and appreciation.

From global demand to local innovation

Koi have their roots in the common carp, a domesticated fish with a lineage dating back millennia. Selective breeding in Japan played a crucial role, in shaping the fascinating colors and elegant forms of koi. However, linguistic and cultural barriers often obscure the scientific knowledge behind these captivating creatures.

As the international craze for koi intensifies, farms have sprung up worldwide to meet the growing demand. This has fostered the development of new markets, particularly in America and Southeast Asia. Interestingly, the cultural nuances of each region contribute to the creation of unique types and breeds of koi, adding a layer of diversity to this already vibrant tapestry.

Aquaculturists, particularly in South America, crave koi with faster growth rates and shorter cultivation periods. Improving stock through strategic breeding programs emerges as a key solution.

In Koi competitions, judges meticulously evaluate each fish, assigning up to 50% of the score to body shape and 20% to color. This underscores the importance of a balanced approach to koi breeding, focusing on both aesthetics and growth potential.

The quest for the perfect Koi

In South America, aquaculturists strive to cultivate Nishikigoi with the ideal combination of dazzling color, rapid growth, and a shorter breeding period. Improving stock through enhancement programs for faster growth is a key strategy in this pursuit. Crossbreeding emerges as a powerful tool that allows breeders to combine desirable traits from different strains.

Crossbreeding, a well-established technique in aquaculture, has immense potential to boost desired traits such as growth rate. Studies with rainbow trout, channel catfish, and even other carp species have successfully employed this method.

Not just about color

While color undoubtedly enhances the appeal of a koi, growth, and body conformation play a vital role in its value. Research on various fish species, including salmon and perch, has shed light on the genetic foundations of body shape. However, the polygenic nature of these traits requires comprehensive whole-genome association studies for effective improvement programs.

Research has been dedicated to understanding the genetic basis of body shape in various fish species, including koi. This knowledge is crucial for breeders aiming to create aesthetically pleasing and well-proportioned koi. However, growth and body shape are often influenced by multiple genes, making it necessary to employ sophisticated genetic tools, such as whole-genome association studies, for optimal results.

Intentional hybridization plays a vital role in koi breeding. Careful crossing and selection lead to the creation of new varieties and the improvement of existing ones. However, the expertise required for this delicate process is often concentrated in Japan. This research proposes an alternative strategy: crossing koi varieties with Hungarian carp. These hardy fish boast superior growth rates and distinct body shapes, potentially offering valuable genetic material to enhance koi breeds.

Hungarian carp enters the scene

Traditional enhancement programs often face limitations in achieving genetic goals. This is where crossbreeding emerges as a powerful tool. By strategically combining genes from different koi varieties, such as the vibrant Nishikigoi and the robust Hungarian carp known for its accelerated growth, breeders can unlock a hidden treasure of genetic potential.

Hungarian carp boasts superior body conformation, faster growth, and increased resilience compared to the classic Nishikigoi. By strategically crossing these two breeds, producers worldwide can potentially introduce desirable traits into their koi lines.

The quest for excellence in Koi carp

The study aimed to delve into the world of crossbreeding by examining the growth and body conformation of offspring created by purebred Nishikigoi and Hungarian carp, along with their backcrosses. Understanding how these traits are inherited will pave the way for informed breeding practices that will ultimately lead to even more magnificent koi creations.

Researchers carefully monitored the growth curves of different carp genotypes, starting with fry selected for their Nishikigoi patterns. These fry were then divided into two groups: purebred Nishikigoi and crosses with Hungarian carp. Both groups were raised in controlled conditions, ensuring identical feeding schedules and living spaces.

The results were remarkable. Crossbred koi consistently outperformed their purebred counterparts in terms of:

  • Survival: More hybrid koi thrived throughout the study, showing increased resilience.
  • Weight gain: At the end of the study, the crosses had an estimated final weight 38.45% higher than that of purebred ones.
  • Feed conversion: Crosses efficiently utilized their meals, converting food into growth.

These findings paint a clear picture: crossing with Hungarian carp injects a powerful growth serum into Nishikigoi, propelling them to reach larger sizes and potentially higher value.

Additionally, the study delved deeper and analyzed how body morphometry changed as the koi grew. Interestingly, hybrids and purebreds followed distinct paths in their transformation journeys.

Crossbred koi showed more balanced proportions, deeper bodies, and longer fins, features considered highly desirable in the world of koi.

These findings suggest that Hungarian carp genes not only influence growth but also contribute to shaping a more aesthetically pleasing koi.

Application in the ornamental industry

By understanding the genetics of growth, conformation, and color, breeders can create koi that not only captivate the eye but also command higher prices. Crossbreeding opens up a treasure trove of possibilities, allowing us to:

  • Create koi that reach market size faster, increasing farm profitability.
  • Develop koi lines with the most aesthetically pleasing body shapes, garnering higher value in exhibitions and the market.
  • Maintain the vibrant colors and patterns that make koi so beloved, without sacrificing other desirable traits.

This study paves the way for a new era in koi breeding, where crossbreeding becomes a powerful tool to unlock desirable traits. Leveraging the genetic potential of different carp varieties, breeders can create koi that are not only incredibly beautiful but also commercially viable.


“Based on these results, it can be concluded that crossing Nishikigoi with Hungarian carp may be a strategy to improve desirable traits in koi,” concluded the researchers.

This research transcends the mere pursuit of beauty and aims to empower koi producers with the knowledge and tools needed to optimize their production. Harnessing the power of crossbreeding and scientific understanding, the future of koi promises a kaleidoscope of even more spectacular specimens, delighting enthusiasts and adorning ponds with vibrant elegance.

The study was funded by Mundo Koi Farm and Fapesp.

Vander Bruno Santos
Instituto de Pesca, Agência Paulista de Tecnologia dos Agronegócios (APTA)
São Paulo, 04014-900, Brazil

Reference (open access)
Santos, V. B., & Furquim, L. R. (2024). Evaluation of growth performances of crossbreds and backcrossbreds with purebreds Nishikigoi and Hungarian carp (Cyprinus carpio). Aquaculture and Fisheries.