Good nutrition creates healthy Koi Why feed Koi at all? Fish in the wild can fend for themselves, however, most ponds are not large enough to attract sufficient natural nutrition to support fish, and so Koi living in captivity have to be fed. Koi pellets are an unnatural food although they provide adequate nutrients, and can be augmented with other foods in the warmer months. Those Koi-keepers who have experimented by producing their own homemade Koi food will know pellets are far less expensive than buying the numerous raw ingredients and then struggling to blend them, as that is not a straightforward process. Heat destroys vitamins and minerals and home Koi food recipes require baking. My advice is to leave pellet manufacture to the experts and concentrate on the rest of the Koi diet, after all variety is the spice of life. The Koi life cycle The novice can be confused by the conflicting advice that circulates about feeding Koi and this can lead to a either a bad diet or hungry fish. The nutritional needs in Koi differ with the seasons, and change with the various stages of their life cycle.  For example, newly hatched fry require only their own egg sac, and once that has been consumed, they inflate the swim bladder and from then one can feed on infusoria or brine shrimp. Using the appropriate food means fry are reared more successfully.  There are critical phases in the development of newly hatched Koi, and without the right diet, abnormalities can occur, and they are less likely to survive. Once koi are juveniles, nutrition must provide energy as well as stimulate growth.  Maturity takes place at around two years of age, and the reproductive organs then need nutrients as they prepare for breeding.  However, it is normal for Koi to eat less when they are actually ready to spawn.  Elderly Koi take life steadier and use less energy, utilising their nutrition more for body repair. During disease if the body does not have resources to draw on, recovery can be slow, or even impossible. Whilst it is unlikely, a Koi-keeper will find foods suited to each stage of the life cycle, variety in the daily diet, and a higher protein level in the younger fish is easier to provide. The breakdown process In Koi, the breakdown of food to extract the nutrients takes place in the gut, as they do not possess a stomach. Peristalsis is the process by which food passes through the digestive tract, and it is faster in Koi than in many animals and other fish species. Water temperature either increases or decreases the metabolic rate in Koi, and this in turn alters their capacity to digest food. Koi excrete more waste than other pond fish species and that is why their pond has to be well maintained.  Koi need a form of protein that contains all the essential amino acids that support growth as well as tissue repair, and keeps the metabolism functioning normally. Protein sources vary in type, and in the amount of amino acids, they contain.  This is one of the main reasons for giving Koi variety in their diet and not relying solely on pellets.  Although they are an ingredient in pelleted foods, Koi do not need carbohydrates in their diet. Their energy for swimming comes from the essential fatty acids that are also an ingredient in pellets.  Koi should not be fed saturated fats as they can cause damage to the liver and other major organs, and might cause intestinal blockages in colder weather. Vitamins and minerals are added to most pellets although the diet cannot supply all the minerals Koi need, some must be extracted direct from the pond water, and this is why water changes are important. Minerals The passage of time, pumps, sterilisers, pond biology, and the Koi themselves all deplete the water of minerals. Every pond is managed differently, although small frequent water changes should be routine in every pond.  This requires an amount of water, depending on the gallonage, to be pumped out of the pond and replaced at least once per week in the spring, summer, and autumn and all year in heated ponds. Just adding water on an occasional basis due to evaporation is not sufficient, and large volume water changes are stressful, due to rapid changes in water chemistry and temperature. Unless an emergency arises large water changes should be avoided.  Rainwater and roof run off is often stored in water butts for pond use and this is not advisable.  There is no mineral content in this type of water, and it can contain pollutants and debris.  Tap water that has been dechlorinated or is supplied via a purifier is the safe way to mineralise ponds. Vitamins Many vitamins, minerals, and trace elements cannot be stored in the body, and this can lead to deficiency diseases in seriously underfed Koi.  Whilst Koi can synthesize vitamins such as B1 and B12, vitamin C is unstable and with no reserves in the body, Koi must obtain it regularly in their diet. Some vitamins are water-soluble and may be lost if pellets float too long on the pond surface.  The advice to soak pellets to soften them is not a good idea as this can remove the water-soluble vitamins.  The pharyngeal teeth located opposite the carp stone in the pharynx are capable of grinding large crustaceans, so Koi can easily cope with pellets. It is very difficult to guarantee the level of vitamins and minerals in pelleted food despite preservation techniques. Storing food for too long reduces the nutrient content, and heat or damp conditions can create moulds and fungi, many of which are toxic to fish. Never feed pellets that are damp or have a film or fungal growth on them, and ensure that Koi food is not accessible by pests such as rats or insects. Are my Koi underfed The variable approach to pond management during the colder months means some Koi are unfed for too long a period.  When Koi are dormant in winter they do not need food, and will sit on the pond floor conserving body resources and energy. However, some days are milder, and many ponds are naturally warmer and the Koi will be active and seeking food.  If unfed yet active, they will exhaust their nutrient store, making them vulnerable.  There has been concern for years that food will putrefy in the gut during winter rather than excreted. However, stasis, the term applied when the muscles that process digestion have stopped working, is misunderstood in Koi. It is a myth that Koi should not be fed from autumn until spring.  On all mild days during the colder months of the year, Koi will be looking for food and a wheat germ based food, or all season pellets should be fed.  If Koi are unfed for many months when the water is warm and their metabolic rate is higher, they can suffer anaemia, skeletal abnormalities, skin conditions, and infertility. Underfeeding predisposes Koi to disease, and such fish will have a shorter life span. Can Koi be overfed Koi know by instinct when they are full and will swim away from the feeding area to digest, so overfeeding is not a common problem in Koi.  None the less, there are other possibilities if Koi lose their body shape.  A rounded appearance in every koi in the same pond may be due to feeding pellets too high in carbohydrate, or another inappropriate food.  It is possible for fat to accrue internally putting the liver and other major organs at risk. When fed properly if Koi get little exercise due to the shape or size of their pond, girth can become an issue.  Koi fed continuously on high protein foods, with little variety in their diet, may not achieve the desired growth level.  Any form of intensive rearing has inherent dangers that vary with the age of the Koi.  In fry and fingerlings, excess protein can result in abnormal development, and a change of diet may be too late to rectify the problem. In older Koi, a high a protein diet over several months causes listlessness and digestive problems, and changing the diet to pure wheat germ for a month may aid recovery. The use of antibiotics lowers the normal intestinal flora and interferes with digestion, and their use should be restricted to genuine bacterial disease. Some ingredients in pond treatments can upset the gut and Koi may not want to feed. It is an unpleasant thought but Koi have been known to eat their dying companions, as it is raw protein, although this can spread disease.  Koi will also eat the flesh of small birds if there are branches overhanging the pond and this too has health implications.  Neither of these events is result of greed, it is simply nature in action.  The waste created by overfeeding can create health problems if it gives rise to ammonia, nitrite, or pond hygiene issues and that is why water testing is so important. Inappropriate diet Koi enjoy pellets and most brands deliver well-balanced nutrition. Although Koi stick foods are also popular being lighter, they naturally provide fewer nutrients compared with the same weight of pellets. They are best given as a treat rather than fed at every meal. Despite the advice about looking for the word “Koi” on fish food labels Koi are still fed pellets intended for other species. Trout pellets, for example, increase the size of Koi fast due to their high fat content. They are mainly fed to fish for human consumption, so health issues are less relevant. Some hobbyists feed such pellets inadvertently, as they are inexpensive and sold loose by weight not in a bag. Sturgeon grow to great lengths and are graceful fish, however, their needs differ to those of Koi.  When both species live in the same pond, one may suffer at the expense of the other when it comes to diet. It is impossible to control which species gets the pellet suited to their needs and metabolism.  I am aware of a few hobbyists who have fed soybeans to their Koi and Sturgeon this is not advisable and can interfere with their normal growth rate, it is best to check out new foods before introducing them to the diet. Additives and supplements There is a trend towards more additives in Koi food and this can be a good thing.  However, there are some unusual additives in certain foods that have had not had any long-term research carried out, and are unnecessary in the Koi diet.  Time will tell if Koi derive any benefits from such ingredients. Hobbyists are not averse to mixing vitamin supplements in with pellets although most brands need no enhancing. If this is carried out at every feed the Koi may be receiving too much of a particular vitamin. Although an uncommon condition, accidental vitamin overdoses do happen.  It is important to look at all ingredients in the chosen food and what the supplement will add in advance of its inclusion in the diet, and how often it will be fed is yet another factor. It is a well balanced diet that supports the normal function of the organs and systems of the body, and that means variety rather than more of ingredients already in the food. Natural foods It is worth bearing in mind that the price of Koi food is not an accurate indicator of its quality as apart from the food itself, packaging, advertising, and shipping, are cost factors.  It is better to use a trusted brand manufactured by a company that specialise in fish food, irrespective of cost or origins.  I am a great believer that Koi should have as natural and varied a diet as possible. Wheat germ is used extensively in Japan and can be mixed with other more expensive foods.  In the warmer months and in heated ponds nutrition can be as similar as possible to that of wild Carp and include cockles, prawns , and worms. In addition, shredded lettuce, oranges and a little wheat germ bread as a treat but not every day will be beneficial, and silkworm larvae are a summer luxury. Koi like sweet corn but it is important to keep to foods the gut is able to cope with and this is not properly digested.  Feeding table scraps is also a bad idea as the human diet is too high in fat, salt, sugar, and additives.  Some foods such as eggs can interfere with the absorption of vitamins and minerals in Koi.  Many foods the human body needs cannot be assimilated by or be of any benefit to Koi. Food for healing Diet plays a significant role in skin healing although not always directly.  In humans, skin is mainly a protective covering but in Koi, it has a larger role.  The scales are an outer barrier and also a store for minerals, while the skin is part of the osmoregulatory system. Life in water makes great demands on fish, although mother nature came up with a solution. If scales are lost and skin damaged by an injury within hours Koi are able to utilise minerals stored in their scales to help heal the breach, and this happens even when Koi are unfed.  The immune response triggers the release of cells to defend the body from infection at the site of an injury.  In addition, calcium, phosphorus, and other substances that will ultimately form the missing scales are delivered to the site.  A pond is a difficult environment for fish survival when injured, and a good diet is the best support. Body resources Koi mainly obtain phosphorus and calcium from their diet, and also extract calcium from their pond water.  It is essential to maintain the bony cartilaginous material that forms the skeleton.  Calcium also has a role in muscle function, and supports the nervous system.  This transfer of calcium and phosphorus takes place faster when it comes from the stores in the body, rather than direct from the diet.  The body needs minerals for numerous functions, and their level has to be in balance at all times, even when an injury is making additional demands to support the healing process.  This does not mean starving your Koi is a good way of aiding faster scale regeneration, as minerals have to be stored by the body to be accessible. However, it does mean that Koi in an unheated pond in winter can still heal and replace lost scales, although the process will be slower.  Skin regeneration begins at the outer edge of a wound or injury.  This outer area gradually becomes white in colour and this then extends towards the centre of the injury when it has a glossy appearance. Scale regrowth begins almost immediately after its loss, as long as the scale pocket is intact.  The capacity for healing and regrowth depends on the degree of damage into the deeper layers of skin, the water temperature, and if there is localised infection. Greed not hunger We cannot compare the feeding patterns of wild Carp with Koi, as rivers are colder than ponds. Even in very large Koi ponds, the water temperature is rarely high enough in spring for the same level of food consumption that will be taking place in smaller ponds.  Koi are cultured Carp bred for captivity, and need observing to see if they are active, and need feeding during the colder months.  Most Koi ponds are unheated, or a heater and thermostat are used, to prevent the dangerous low temperatures of winter. In such ponds, Koi will need feeding on mild days. Whilst life in a pond that is heated might shorten the koi life span a little, this is balanced out by the quality of life they enjoy, and they can feed all year.  Koi living at higher water temperatures naturally consume more food.  All these variables remind us there is no such thing as an average Koi pond, and feeding routines will differ considerably. In summer or at higher temperatures Koi should be fed several small feeds throughout the day rather than one large meal. If pellets are still on the surface, ten minutes after feeding cut back on the amount per feed, but not the number of meals.  Koi take some time to grind and then digest their food, and often excrete during this process. This can cause them to flick, and this should not be mistaken for a parasitic infection. Koi keepers are often concerned their Koi are never ravenous, yet they observe a mad dash for food in other ponds. Hunger is not the issue, it is the level of competition for food, that creates the rush to the pond side. When several large Koi all want to dominate the pond, they strive to be first in the queue at meal times, a tendency that can make them seem almost human.