Veiled koi (butterfly koi): origin, how to choose one, where to find it, and how to protect its fins

When a butterfly koi glides beneath the surface, its elongated fins ripple like silk sails. The effect is striking, especially when viewed from above. Long shunned by purists, the veiled koi has become a fixture in many garden ponds for one simple reason: it offers a different kind of elegance while retaining the robustness and familiar character of koi. Here's what you need to know before welcoming one.

Where does the veiled koi come from?

The classic koi is a Japanese selection of common carp, developed since the 19th century for its colors and body shape. The long-finned koi is much more recent: it was developed in the 20th century by crossing koi with a long-finned carp strain originating in Southeast Asia. Its fins continue to grow longer throughout its life. Names vary: butterfly koi, veiled koi, butterfly koi in English, hirenaga in Japan.

Traditional koi competitions, which focus primarily on body shape and pattern quality, kept it out for a long time. Some competitions now have a dedicated category for it.

The most sought-after varieties

How to choose the right one

• Fins: long, symmetrical, with no tears, whitened areas, or fraying.
• Body: well proportioned, with no deformities or signs of being underweight.
• Behavior: a koi that swims normally, without rubbing itself or staying isolated at the bottom.
• Origin: a seller who knows where their fish come from and practices quarantine.

Where to find a veiltail koi?

Choose a specialized aquatic garden center or a reputable koi dealer, where you can see the fish swimming before choosing. A fish bought without seeing it, or from a batch that has not undergone quarantine, is the primary vector of disease in a pond. In Belgium, ask about new arrivals at Aquiflor, our aquatic garden center in Nodebais: we advise you on selection and acclimatization.

Acclimating a veiltail koi on arrival

Transport is the riskiest time for a long-finned koi: in a bag that is too small, the fins fold and rub against the sides. Ask for a bag large enough for the fish to remain lying flat, and travel without detours.

On arrival, let the sealed bag float on the surface of the pond for twenty to thirty minutes, in the shade, to equalize the temperatures. Then gradually add a little pond water to the bag, several times, before gently releasing the fish without pouring it out all at once. Ideally, a new koi should spend a few weeks in a quarantine pond before joining the group: this is the best safeguard for all your fish. During the first few days, observe it: a koi that hides a little is normal, but a koi that remains stuck to the bottom with folded fins should prompt you to check the water.

Protecting the fins every day

What makes the veiltail koi beautiful also makes it vulnerable. Its long fins are more exposed to injuries and bacterial infections that eat away at them.

1. No sharp decor: sharp-edged stones, unprotected edges around wall openings, damaged grilles.
2. Pristine water: damaged fins are often the first sign of deteriorating water quality.
3. No nippy neighbors: avoid aggressive or overly lively fish.
4. Gentle handling: never use a rough-mesh net to remove it from the water, but a bowl or a transport sock.
5. Healthy mucus: the first barrier against infections.

Food and colors

The veiltail koi eats exactly like a classic koi, with food adapted to the water temperature. High-quality food enriched with natural pigments intensifies the reds and orange tones, which take on a particular vibrancy on the translucent fins.

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Frequently asked questions

— Is a veiltail koi more fragile than a classic koi?

It is just as hardy otherwise, but its fins are more susceptible to injuries and infections. Good-quality water and a pond without sharp decorations are enough to protect them.

— Can it live with classic koi?

Yes, without any problems. The two mix very well and, in fact, reproduce with each other.

— Do the fins grow back after an injury?

Yes, generally, if the water is good and no infection develops. Regrowth may be slightly irregular.

— How large does a veiltail koi grow?

A size comparable to that of a classic koi, with fins that appear even longer in proportion.

— Can a veiltail koi spend the winter outdoors?

Yes, like a classic koi, in a pond deep enough to maintain a frost-free zone. Simply avoid handling it when the water is cold: its fins then heal much more slowly.

In summary

• Koi resulting from a cross with a long-finned carp, which appeared in the 20th century.
• The same needs as a classic koi, with particular attention to the fins.
• Purchase from a specialist who practices quarantine, and transport in a large bag.
• Pond without sharp decorations, pristine water, gentle handling.

Last updated: September 28, 2026.