Koi dogs are a semi-aquatic species capable of living on land or in the water. While they do have gills and can live fully underwater, they tend to prefer the edges of rivers and lakes where they can choose between the two environments at their leisure. Most koi dogs choose freshwater environments, but some have adapted to beaches and tide pools and have loads of fun splashing around in the waves. They’re most often found in small caves or in hollows formed by tree roots at the water’s edge, and like to decorate their dens with soft moss, shiny rocks, and small oddities found in the mud at the bottom of the water.


Koi Dogs live in family groups with up to 6 adults and a combined school of babies, called guppies. Guppies are born in litters averaging 3-5. Guppies in a single litter can show many different color patterns, including one or two with completely opposite colors from the rest! Guppies are sleepy and very cuddly during their first weeks, and can take up to a month to open their eyes for the first time. Once they do open their eyes they become intrepid explorers, fearlessly poking around their pond or stream and harassing local turtles to no end.

When they grow up, littermates tend to stay in the same general area and remain in contact. Koi dogs are extremely affectionate, and don’t like to be too isolated. In the winter, nearby families will often gather into one larger group for the season. The adults work together to break through the ice for fishing and they all cuddle up together at night. Their dense coats and chubby bodies make them extremely warm and soft, and a large group cuddled up together in a den is one of the coziest things you’ll ever see!


Koi dogs stand between 18 and 24 inches tall and weigh between 30 and 50 pounds. Their build is typically stocky, with short, thick legs and chubby, rounded bellies. Their heads have a characteristic egg shape with no stop, and their eyes are wide and round. They have short, dense fur like a seal intermingled with small, smooth scales that form their markings. Most koi dogs have either white or black fur with markings in black, white, red, orange, blue, or gold. There are rare examples with more exotic colorations. Adults have two visible gill slits on each side of the face, and guppies have only one visible gill on each side. The second set opens up as they mature. Their ears are large and mobile.

Koi dogs have two fins at the shoulder of each front leg plus a long dorsal fin down the back, and the fins vary in size and shape between groups. Those living in salt water have shorter, more pointed fins while some particularly flamboyant freshwater varieties have developed long, flowing, scallop-edged butterfly fins. They also have webbed toes and heart-shaped paw pads, making them strong swimmers with enormous endurance in the water even if they are a bit clumsy on land. They have  thin, flexible, doglike tails instead of tail fins.


Standard koi dog colorations are based on and named after real world koi varieties. Each variety describes a base color (black or white) and a marking color, though most don’t indicate how the markings might be laid out. Shusui and Kikokuryu call for a specific “ladder” pattern of patches running down the center of the back, while Asagi, Matsuba, and Kujaku are all distinguished by the contrasting “net” design overlaying their regular markings. An ideal Tancho koi dog should have one large patch of orange or red; the darker and more symmetrical that patch is, the better. Other colors and markings are possible, but these are fairly rare.

A koi dog’s eyes can be any shade of blue, green, amber, or black, with rare examples showing two different colored eyes. All koi dogs have eyespots in the brow area, usually matching the color of the rest of their markings.


Koi dogs are a closed species. You’re welcome to create a koi dog character based on a koi dog or guppy art doll, or even a koi dog Figment that you’ve purchased, but you may not make your own from scratch unless you commission that design as a custom art doll from me and you may not make a character based on an existing doll that you don’t own. If you’d like to commission a new koi dog, please look over my commission information sheet and contact me by email so we can discuss! I’m happy to work with you to create a koi dog, including unique individuals based on alternate dog breeds or with special markings and colors.