Breeding Koi

Line Bar

Sexing Koi
It is impossible to sex koi smaller than about 25cm(l0in) in length, because they are sexually immature. Once the koi exceed this size, the testes (in males) and ovaries in females) begin to develop. The ovaries are much larger organs than the testes. Females are usually easier to spot, as the belly of a mature female koi is generally plump, whereas males remain streamlined and more 'torpedo' shaped. When males are ready for spawning, they develop breeding tuberdes on the head and pectoral fins, principally along the bones of the fin rays. These breeding tuberdes appear as fine raised spots and could be mistaken for white spot (Ichthyophthirius. The tuberdes are most profuse on the pectoral fins, where they are quite rough to the touch and arranged in fairly regular rows. They are used during breeding, when the male nudges the female with his head and fins to induce her to spawn.

Koi will naturally spawn in the hobbyist pond in the early summer. A water temperature of 20C (68F) is ideal, although koi will occasionally spawn at a temperature of 17C (63F). As the water in the pond warms, the koi will try to spawn 'en masse'. This is known as flock spawning and, although it can produce very healthy offspring, the quality of the patterns and colour are generally poor.

The female koi deposits her eggs - approximately 100,000 per kilogram of her body weight - over the pond walls, floor and on any plants. Unfortunately, it is very difficult to collect eggs deposited in this random manner in order to incubate them in an environment where they will not be eaten by their parents or attacked by parasites. If left to their own devices, a few of the eggs will hatch and you can then collect the offspring and raise them in an aquarium.

You can, however, ensure the survival of a greater number of eggs by placing artificial spawning ropes in the pond. The koi will deposit their eggs on these in preference to using the hard pond wall. To make these spawning ropes, cut 10cm(4in) lengths of 10-l5mm (0.4-0.6in)thick nylon-fibre rope and thread these between the strands of a l20cm(4ft)- piece of the same sort of rope.

As the koi prepare to spawn, you will notice males chasing a female, nudging her side with their mouths. The female will occasionally stop and suck at the sides of the pond in an attempt to clean an area on which she can deposit her eggs. This is the time to gently lower the spawning ropes into the pond. Spread out the coils of rope into a fanlike shape and anchor them to the side of the pond.

Try to avoid disturbing the fish before and during spawning, but keep a careful eye on them, as the males may bully some females. If this happens, remove the female and place her in a separate pond. Koi may prefer to spawn around dawn but they may also spawn throughout the day, when they have finished spawning, the females hang head down, respiring heavily, and the other fish will become less excited. Gently remove the spawning ropes and carefully place them in a vat for incubation. Koi are not good parents and unless you remove the eggs from the pond quickly, they will begin to eat them. Immature koi may also eat the eggs, so if you want to rear them, you should separate the spawning koi from others in the pond.

Incubating koi eggs
The incubator should have a reasonable capacity - a household water storage tank (about 450 litres/100 gallons) is ideal - and should, of course, be made of non-toxic materials. It will need a valve-operated water inlet point, and an outlet with as large a surface area as possible, screened with a fine (0.3-0.5mm) stainless steel or plastic mesh. Fine nylon stockings may provide an adequate alternative, although they are less robust.

Lay the ropes out in the vat with 0.2mg/ litre malachite green solution to stop fungus (Saprolegnia) from attacking dead eggs and spreading infection to living eggs. Place three lengths of string across the vat to keep the ropes (2in) below water level. Do not add any more water at this stage, but place an airstone on the floor of the vat to gently and continuously aerate the water, as developing eggs need plenty of oxygen. When you begin to see the growing koi's eyes in the egg - after one or two days - run a fine trickle of water into the incubation vat. The day before the koi hatches, the eyes in the egg will have a shine to them. Soon afterwards, the young koi will begin to wriggle then, gradually, over the next few hours, it will break out of its 'shell'. It will take three to four days for the koi eggs to develop and the fry to hatch at temperatures of 20-22C(68-7lF). Koi fry can develop at temperatures as low as l7C(63F), in which case their incubation will take five or six days, or as high as 25C(77F), which will decrease their hatching time. However, there is a greater chance of the fry being deformed at such extreme temperatures.

The development of the koi egg and fry
When the fry have hatched, they will inH stinctively seek shelter and hide in any cover they can find. The spawning ropes are ideal for this. Using a special sticky pad on their heads, the fry attach themselves to the ropes' fronds, or to the vat wall. At this stage in their development, the young koi have no swimbladder, mouth or vent. They breathe by absorbing oxygen through the fine blood capilaries that surround the yolk sac, which is still attached to the gut. It is essential that there is plenty of oxygen entering the water at this stage, as a reduction in the quantity of dissolved oxygen in the incubator could lead to mass mortality.

The koi fry have only one fin, which encircles the posterior end of the body. Asthe koi grow, feeding on their yolk sac until all the yolk is utilized, they develope paired fins, a mouth and other organs. After two or three days, the young koi swim up to the surface and take two or three gulps of air, which they force into their swimbladder. They then start to swim freely in mid water, usually congregating around the airstones - a sign that they are ready to be fed.

First feeding
Koi fry at the 'swim up' stage do not have any developed taste buds and so must detect their food by sight. Therefore they need to have food all around them. Hard-boiled egg yolk is an ideal food for the first day or so - this has very little dietary value, but will increase the size of the stomach. Newly hatched brine shrimp (Artemia sauna) larvae are also a good food source for young koi fry. Start feeding the brineshrimp when the koi are about one week old. After another week or so, the koi will be ready for a mash diet (the powder dust that is left after the manufacturing process of fish food). From this time onwards, feed the koi food of a size that can be taken by the smallest fish in the vat.

You will need to remove accumulated debris and waste frequently during this first feeding stage. A siphon made from aeration tubing is ideal for removing settled and suspended waste from the incubator, and an old toothbrush is useful to clean the outlet screen. You should also add fresh water regularly to the vat to remove nitrates and ammonia. Tap water which contains high concentrations of chlorine, should be aerated before it is added to the vat, to allow the chlorine to evaporate. After three or four weeks, the fry will have grown to 5-l0mm(0.2-0.4in) in length and will be starting to take larger quantities of more generously sized foods.

Growing on
At this stage, move the koi to a growing-on facility, such as an aquarium, tank or pond. Watch the young koi carefully, as cannibalism is not uncommon. If you suspect this, remove any larger fry to another tank. You can heat this to 20- 25C(68-77F) to provide faster growth rates, but be careful; if koi grow too fast, they lose their colour. One-month-old koi need about five percent of their body weight in food and should be fed little and often. As they grow, koi need less food - about two percent of body weight (6in) or larger. The size of pelleted food is critical; not all fish grow at the same rate and it is too easy to look at the larger koi and select the pellet size to suit them, forgetting the smaller fish. Unfortunately, koi that are nearer to the common carp in appearance grow faster than the prettier koi. This is because nishikigoi are highly inbred - that is, they are mated with other koi to which they are closely related, such as either parents or siblings - and, as with any highly inbred animals, nishikigoi are not as hardy as their wild counterparts.

© Copyright 1996-1998 By 
Eduard Freeman