Koi Health – Understanding the Basic Anatomy and Make Up of a Koi Fish

Get to know your Koi fish better and keep your Koi fish healthy by understanding their basic anatomy. Read this useful and important summary of the koi’s anatomy and physiology.


Koi fish is simply a carp that has been selectively bred in order to develop stunning patterns, colors and body shape. Koi are a fairly hardy fish, demanding relatively low-oxygen conditions and an ability to adapt to still, silty water. They are good at being transported which partly explains their popularity as they can be shipped all around the world under quite basic conditions.


The Koi’s body is ‘fusiform’ meaning it tapers towards each end. Their shape and proportion does depend on the particular Koi variety but anatomically, they are not so different from their predecessors.


Scales Most Koi have scales over most of their bodies, except for the head. Some koi varieties only have scales along the lateral line and dorsal line (called Doitsu or German-scaled koi) Healthy koi generally have all their scales in-tact as holes in the skin may allow bacteria to enter.

Nostrils The nostrils are just in front of the eyes and are used primarily for scent.

Gills The gills of a fish serve a similar purpose to our lungs. They absorb the oxygen in the water and help to transport that to the body. Carbon dioxide is released into the water via the gills too.

Mouth The Koi’s mouth is slightly below the tip of the head.

Eyes The eyes of a Koi fish are just in front of the gills. They are positioned to let the Koi see in two directions at the same time.

Ears Like most fish, Koi do not have external ears. They have internal ears that respond to the vibrations in the water.

Barbel This is an organ that looks like a whisker which is found in the mouth of some fish and turtles. They contain sense receptors that help to find food.

Heart Koi has a two-chambered heart that pumps heart around the body.

Pectoral Fins The two pectoral fins are on each lower side. They move in opposing directions. The Koi uses them to rotate on the same axis and for braking. Sometimes they are used to stir up the bottom of the pond when the Koi is searching for food.

Liver The liver is a key part of the Koi and essential for good Koi health as it serves many important functions from cleaning up blood and cleansing away toxic substances to producing bile for digestion and cholesterol for healthy nerve and cell function.

Gall bladder The gall bladder stores bile which helps with digestion

Pelvic Fin The pelvic fins are on each of the lower sides, about midway down the body. They help the koi fish rise or descend in the water

Spleen The spleen produces lymph cells and stores red blood cells.

Kidney The kidney acts like a filter to help fight disease and also allows excess water to exit the body as urine.

Swim bladder The swim bladder has two different sized chambers that can be inflated or deflated to control the orientation and level at which the fish swims

Reproductive Organs Male koi have testes and females have ovaries. Eggs and sperm exit the body via gonopores which are just in front of the urinary opening.

Anal Pore This lies just in front of the anal fin for the release of waste products including urine

Urinary Bladder Another key part of the Koi and vital for their health. The Koi has a higher salt content than its environment and must release excess water to equalize the salt concentration in a process called osmosis.

Lateral Line The lateral line is a clearly visible line runs along the mid-body of the Koi and contains special pores that detect vibrations through the water. It is often called the koi fish’s sixth sense.

Dorsal Fin This is at the top of the fish and it used for stabilization, namely keeping the koi upright. The dorsal fin may be lowered for a more streamlined body form when moving quickly through the water.

Anal Fin Used for stability

Tail or Caudal The tail acts like a rudder and to increase speed.

Now you know the essential parts that make up a koi fish, you can start to understand the different between Koi and other types of pet fish such as goldfish and help keep your koi healthy.

Previous post St Croix, Invisible to the World, Thanks to the Media
Next post Pal Zileri – Top Fashion Brand