Feeding and growth rate
The feeding pattern and growth rate of Koi depends on many factors, such as
water quality, water temperature, stocking density and genetic background.
Koi feed most actively when temperatures are in excess of 15c(59F), allowing
sexually immature fish to grow rapidly during the summer months when the temperature is
warmer.
The growth rate slows considerably in mature Koi; in sexually mature fish, most
of the food they eat is utilized in producing eggs or sperm in preparation for breeding.
The fish do continue to grow throughout their lives and it is easy for pampered
Koi to reproduce and continue to grow because of their artificially high feeding rates.
Water quality affects the rate of growth as Koi lose their appetites and may
even stop eating. Poor water quality can also affect the fish's metabolism, thus hindering
digestion of food.
The stocking density of the pond can also have a marked effect on the growth
rate.
In a lightly stocked pond, Koi will become sexually mature while still a 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),
but competition for food will slow the growth rate as food will be more scarce and the
'battle' for it can stress some Koi.
Water temperature affects fish more than any other single factor. Their
body temperature fluctuates according to the temperature of their environment. As the
temperature drops, the ability of the Koi to digest and assimilate food decreases. In the
winter months, when temperatures drop below 10C(50F), it is best to feed
cereal diets that the they can digest quickly and easily and does 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, 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.
Other foods
Koi will accept many foods but many 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.
If you should give them beans, peas or corn, you must cook
them first, since Koi are unable to digest the hard outer casing of these foods. Koi will
take lettuce leaves and duckweed and other plants around their pond. For a special
treat throw in pieces of orange (seedless) and watch them play.
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Nutritional requirements of Koi
The type of food you give your Koi and the quantity you offer them
will vary according to their size. The majority of Koi foods have a cereal base with
different ingredients added either to enhance colour or aid digestion. Choose a food size
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, give them a mixture of large and
small foodstuffs or crumble larger pieces for the smaller fish, 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, better suited to sinking food. The disadvantage being
this type of food will deprived you of seeing your Koi feeding. Fortunately, Koi
will take food from the surface, you can even tame your Koi to feed from your hand.
Another advantage with floating food is that it is easy to see when
the Koi have eaten enough. Unlike when feeding sinking types, uneaten food can easily pass
unobserved, particularly in murky water.
Provide just enough food so that after five minutes it has all been eaten. In
the Fall, 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, it contains a high level of protein. 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, 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.
For info on the benefits of Koi Clay to enhance the colour of your Fish and help
provide a healthy clear pond see Microbe-Lift
Calcium Clay Montmorillonite Clay
Live foods
Koi relish a variety of live foods, including worms and shrimp. Earthworms
can be fed to the fish all year round and are high in protein and soon become a favorite
treat.
Tadpoles are another great treat in the spring. Maggots are not
recommended as they can carry harmful bacteria from the decaying flesh. Do not rely on
live foods to form the staple diet, but offer them as a supplement to the regular diet. If
Koi are fed on these tidbits alone, there is a risk that nutritional diseases will set in
as the result of a lack of vitamins or amino acids.
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