Feeding and growth rate
The feeding pattern, and thus the growth rate, of koi depends on
many factors, such as water temperature, water quality, stocking density
and genetic background Koi feed most actively at temperatures in excess
of 15c(59F), thus sexually immature fish can grow rapidly during the summer
months when the temperature is warmer. Once koi are mature, their growth
rate slows considerably; in sexually mature fish, most of the food eaten
is utilized in producing eggs or sperm in preparation for breeding. However,
unlike many other vertebrates, fish continue to grow throughout their lives
and it is easy for pampered koi to reproduce and continue to grow because
of their art.
Water quality affects the rate of growth because koi lose their appetites
and may even stop eating if their environment is poor. Poor water quality
can also affect the fish's metabolism, thus hindering digestion of food.
The stocking density of the pond can also have marked effects on koi
growth rate. In a lightly stocked pond, koi will become sexually mature
while still of a relatively small size (25-3Ocm/10-l2in) and once mature,
growth is retarded. Although koi in a densely stocked pond will mature
at a much larger size (50-60cm/20-24in), competition for food will slow
the growth rate, food will be more scarce and the 'battle' for it can stress
some koi. You will have to decide on optimum stocking levels for your own
koi pond bearing this in mind. In fact, these considerations are really
most important for koi farmers.
The genetic background, too, influences the size to which koi will grow;
as the children of tall parents tend to be tall, and short parents produce
small children, so the same is true of koi. This is obviously a simplified
view of gene action, however, because of the significant role the environment
plays in influencing size.
Water temperature affects fish more than any other single factor. Fish
are ectothermic - their body temperature fluctuates in accordance with
the temperature of their environment, usually remaining 10C higher. As
the temperature drops, the ability of the koi to digest and assimilate
food decreases. In the winter months, therefore, at temperatures below
10C(50F), it is a good idea to feed cereal diets that the koi can digest
quickly and easily and that do not stay in the gut too long. High-protein
diets linger in the gut and can cause severe problems; the bacteria found
in the fish's gut, which play a role in breaking down some less readily
digestible substances, such as cellulose, may become pathogenic if food
is retained in the gut too long. As the water temperature rises, however,
the koi need protein for growth, repair of damaged tissue and injuries,
and for reproduction. In the summer, koi will benefit from a high-protein
diet containing 35 to 40 percent of fishmeal-based protein.
Nutritional content of food
Food contains various elements, such as proteins, fats, carbohydrates,
vitamins and minerals, which are essential for all animals to maintain
healthy bodies, grow and reproduce. Here we explain what these elements
are and why they are important components of food.
Proteins are made up of amino acids. Thirteen essential amino acids
should be included in any fish diet, although there are about 20 found
in natural proteins. An adequate diet contains sufficient quantities of
both essential and nonessential amino acids to allow the koi to grow, repair
damaged tissue and produce either eggs or sperm. Deficiency of protein
or any of the essential amino acids causes koi to grow more slowly and,
if this dietary problem continues, can result in a deformation of the spine.(Spine
deformities may have a number of other causes, such as disease, however).
Fats provide a source of energy to koi; their important role is in providing
fattyacids, such as triglyceride and phospholipids; vital components of
membranes surrounding all cell walls. Koi can make almost all of the fatty
acids they need with the exceptions of linoleic and linolenic acids, which
are essential and must be provided in the food. Linolenic acids are required
All fats are made up in a similar way to proteins, but of fatty acids,
rather than amino acids, bonded together with glycerol. If essential fatty
acids are omitted from the diet, symptoms of fin erosion and heart and
liver problems may result. Fats have a low melting point and are thus more
easily digested by koi. They are found in fish, soya and corn oils and
in high concentrations of wheatgerm. Fatty acids become rancid on exposure
to air - a chemical process known as oxidation. In koi, the liver is the
chief organ for storing fats and if stale food is fed to them it can result
in disease and death. Unfortunately, rancid food has no outward appearance
of having 'gone bad'. It is, therefore, worth buying smaller packs of food,
rather than a large quantity which is utilized slowly, and never keep food
from one year to the next.
Carbohydrates also form a scource of energy for koi but fish metabolize
them lessx readily than omnivorous birds or mammals. Too much carbohydrate
is very bad for koi health, resulting in either degeneration of the liver
or an excessive storage of these substances as glycogen, leading ultimately
to heart failure.
Vitamins are essential for the normal metabolism and growth of koi,
and requirements of some are increased during spawning. Vitamins are complex-structured
substances, needed in only small amounts in the diet, but deficiencies
can cause clinical disorders.
Vitamins are divided into two categories: fat soluble and water soluble.
Fat-soluble vitamins are found in a variety of forms, all of which are
metabolized slowly and can be stored in the body fat. An excess of fat-soluble
vitamins can lead to a condition known as hypervitaminosis, which, depending
on the vitamin, can lead to clinical disorders. Water-soluble vitamins
are easily absorbed and are not usually excreted.
All essential vitamins are supplied in more than adequate quanities
in proprietary koi foods and it would be unusual for the hobbyist to meet
clinical symptoms associated with defieciency.
Minerals, too, aid basic metabolic functions, as well as performing
their own duties, which include building skeletal structures, osmoregulation,
building of nerves, and maintaining the efficiency of gaseous exchange
in the blood system. Little is known about mineral deficiencies in fish,
probably because most minerals are absorbed from the surrounding water.
Normally 12 percent of the diet is made up of minerals, being contained
in fish food in the form of ash.
Nutritional requirement of koi
The type of food you give your koi and the quantity you offer them
will vary according to their size. The majority ofproprietary koi foods
have a ceral base with different ingredients added either to enhance colour
or aid digestion. Choose a food size that is small enough to be eaten by
the smallest fish in the pond, otherwise they may die of starvation. If
you keep very small koi with larger ones, offer a mixture of large and
small foodstuffs, but always make sure that young fish are adequately fed.
Most koi food comes in two forms: floating and sinking. Koi are bottom-feeding
fish and are, therefore, better suited to sinking food. This is made by
compressing the meal through a die at high pressure. The meal is held together
with fats and, again, takes a long time to be dissolved by cold water.
The disadvantage with relying on this type of food is that you will be
deprived of seeing your koi feeding. Fortunately, koi will take food from
the surface - indeed, you can even tame your koi to feed from your hand
- and special expanded (hollow) foods have been formulated for this purpose.
These are steam cooked to create an outer shell, which protects the food
particle from saturation for a while.(Once the pond water has dissolved
the shell, the food will sink.) Another advantage with floating food is
that it is easy to see when the koi have eaten enough. Take care when feeding
sinking types - uneaten food can easily pass unobserved, particularly in
Provide just enough food so that after five minutes it has all been
eaten. On koi farms in summer, smaller koi (i.e. below 15-20 cm/6-8in in
length) are fed five percent of their body weight per day, where-as large
mature koi (i.e. over 20cm/8in long) are only fed two percent. The nutritional
value of koi food is calculated by weight and not by volume. Normally,
lkg(2.21b) of fish food will increase koi growth by 500gm or even 700gm
in favourable conditions. In the winter, provide wheatgerm based diets
on a maintenance basis, in order to keep the body functions ticking over,
since it is too cold for the koi to grow. Wheatgerm is also a good source
of Vitamin E.
Feeding to enhance colour Koi are highly valued for their colour and
certain additives can be included in the diet to maintain and enhance the
fish's natural coloration. Carotene affects the red pigmentation, but if
used at too high a concentration, even the white pigment on the koi will
turn pink. Spirulina platensis also enhances and fixes the red pigment,
but does not turn the white to pink to the same extent. It is a type of
algae found and cultured in Mexico and eaten by the people, since it contains
a high level of protein. Initially, it was fed to koi on account of its
nutritional value and not because of its colour-enhancing characteristics.
Now that these have been established, it is fed to koi for only one month
each year, usually during September, but can be given at any time, even
during colder periods, at temperatures of 10c, but no lower. Some koi farmers
feed it for the month before the fish go to market to bring out the best
colours in the koi.
Good coloration is not only enhanced by good feeding, however. Healthy
fish tend to have much brighter colours than diseased ones. To bring out
the colour in koi, particularly the white, you must provide good living
conditions. Strong red and yellow pigments develop well in waters rich
in green phytoplankton (single-celled plants). Because koi are difficult
to see in green water, it helps to feed a diet that will enhance the red
pigmentation. Black pigment is enriched in hard water with a pH level of
7.5-8.5. Remember, however, that changing the pH and hardness of the water
can affect the toxicity of ammonia and nitrite.
Koi will relish a variety of livefoods, including cockles, worms
and prawns. Earthworms can be fed to the fish all year round and, like
prawns and cockles, are high in protein and soon become a favourite treat
- a sure way to gain the affection of your koi. Tadpoles from frogs are
another great treat in spring and, in summer, silkworm pupae, imported
from Japan, are an excellent source of protein. Feed these pupae only as
an occasional treat, however, as they have be shown to cause a diabetes-like
disease in koi. Chironomid larva and mosquito larva are a popular diet
for small fish, though not easily available. Daphnia ('water fleas'), plentiful
in earth ponds, are one of the first foods for koi fry but tend to be too
small for adult koi. Maggots are not recommended as they can carry harmful
bacteria from the decaying flesh. Do not rely on livefoods to form the
staple diet for koi, however, but offer them as a supplement to the regular
diet. If koi are fed on these titbits alone, there is a risk that nutritional
diseases will set in as the result of a lack of vitamins or amino acids.
© Copyright 1996-1998 By
Koi will accept many foods thrown to them in their pond, but many
of these are of little or no nutritional value and may even harm the fish.
Brown bread is acceptable, but white bread contains a mild form of bleach,
which does the koi no good at all. Do not offer beans, peas or corn, since
koi are unable to digest the hard outer casing of these foods. Koi will
take lettuce leaves and may also eat duckweed and other plants around their
pond (with the exception of blanketweed, which is too coarse for them to
pull off the sides).