UNDERSTANDING KOI BEHAVIOUR

Many Koi-Keepers watch their Koi for long period and admire their colouration, form and movement. However, have you ever paused to consider why or how the Koi moves as it does, how it changes colour, or what the various parts of the body actually do. This walk will examine some of the structures and functions of the Koi's body and, in doing so, hopefully provide you with a better understanding of your fish.

Fins
Each fin is comprised of a number of fin rays which support a fine membrane. The fin rays are of two types. Spinous rays are used for protection in many fish (e.g. corydoras) and are often the first ray in any fin in order to provide added support e.g. Koi. Muscles are attached to each fin ray to allow the fin to be raised or lowered.

• Tail - used primarily for propulsion and as a rudder to change direction. The shape of the tail indicates how fast the fish can swim. Fish with forked tails (e.g. orfe) are fast swimming, whereas a rounded tail (e.g. tench) indicates a slow swirnining speed.
• Dorsal and Anal Fin - provide stabifity in a shriliar way to the keel of a boat.
• Pectoral and Pelvic Fins - used for fine movements, directional changes and stopping the fish.

Scales
The scales are thin bony plates which cover the body of the fish to provide a flexible protective coating. The scales first form when the fish are 7-10 days old and increase in size as the fish grows to maintain a complete covering. This growth is achieved by the addition of rings of dentine around the edge of the scale. During periods of rapid growth (e.g. Summer in the British Isles) the rings are widely spaced. In the winter, or dry season, growth is slow and the rings are dose together By counting the bands of closely spaced rings the numbeof winters (or dry seasons) the fish has survived and therefore its age is known.

Colouration
The colouration of a Koi is due to the reflective irridocytes and the chromatophores, which contain the colour pigment. If there are no chromatophores present, and the irridocytes are on the outside of the scales, the Koi will have a silvery appearance; if the irridocytes are under the scales the Koi will appear white.

The coloured pigments are melanin Elack), erythrin (red) and Xanthin (yellow) each of which occurs in different chromatophores. By combkdng different chromatophores and the irridocytes a range of colours can be produced. For example, orange is given by red and yellow chromatophores. Blue is caused by black chromatophores covered by irridocytes.

Colour pigments are not synthesised by the fish, but need to be ingested. Therefore to ensure good colouration it is important to feed with foods containing natural colour enhancers such as Tetra-Pond Koi Sticks.

Senses
The six senses of a fish are developed to different levels depending on the fish species and the environment in which it lives. The senses are:

• Sight - Compared to man, Koi are short-sighted, having a range of perfect vision of only 1-2 metres and blurred vision for approximately 10 metres. This is more than adequate underwater, where visibility is usually restricted by algae and sediment. Despite their" poor" vision, Koi can see in colour with their detection of yellow and green being most accurate.
• Smell - Koi have a very good sense of smell. The olfactory organs responsible for detecting smells are located all over the head and anterior part of the body, but are concentrated in the nares and barbels. It has been estimated that goldfish have a sense of smell that is fifty times better than in humans.
• Taste - Taste receptors are located both inside and outside the mouth, allowing the fish to taste its food before ingesting it. Outside the mouth they are mainly located on the lips and barbels.
• Touch - Touch and pressure receptors are present all over the body of the Koi, but are concentrated on the head and barbels.
• Hearing - Fish have an inner ear situated at the back of the head, which can detect vibrations, orientation and pressure changes. To increase its sensitivity the inner ear is connected to the swirnbladder(which acts as an amplilier) by means of a chain of small bones. If the swimbladder is punctured sound perception is reduced to 2% of its original level.
• Lateral Line - The sixth sense of a Koi is the lateral line. This organ can be seen by means of a row of scales, each with a hole in it, running along the side of the fish. Under the scales is a canal which runs from the head to the base of the tail. The canal is filled with a jelly-like substance and contains man pressure wave sensors called neuromasts. Any vibrations in the water cause the jelly-like substance and consequently the neuromasts to vibrate. Nerve endings in the neuromast detect the movement. Slight differences in both the intensity of the stimulus and the time when each neuromast detects it, allow the Koi not only to detect movement but also ascertain from where it originated.

As the Koi moves it too produces vibrations. These vibrations bounce back from the underwater objects and are detected by the lateral line allowing the fish to build up a "sonar" picture of its surroundings. Using this system a Koi can successfully manoeuvre in the dark or in cloudy water.

From the preceding paragraphs it is obvious that the Koi we keep are higly adapted to life in an aquatic environment. I hope that the information presented will give you an insight into exactly why your Koi behave as they do and help you to get more out of your hobby.