Composition of natural food for Koi
The Koi carp belongs to the group of omnivores, with its diet consisting mainly of tiny aquatic organisms [1] .
The main components of Koi food
Based on intestinal examinations of two-year-old carp, the food components found can be divided into three categories:
- Crustaceans (Daphnia) [2]
- Insects (Chironomidae) [2]
- Food components (algae, plants, particles, etc.) [2]
Frequency and choice of food
The most important representatives of crustaceans are water fleas, while the insects are primarily chironomid larvae. The intestinal contents of a fish and their composition vary depending on the abundance of food. Food that is easy to ingest and is abundant is preferred. Over the course of the year, these can be, for example, insect larvae, water fleas, plant substances, snails and similar small animals [3] .
The nutritional composition of Koi food
The natural food has a high water content with only a low concentration of nutrients. Therefore, the carp must eat a large amount of food. The natural food has a high protein and fat content of up to 60% protein and 28% fat in the dry matter (without water content) [4] . The average protein content in the natural food is given as 55% [3] .
The debate about the right protein/fat ratio
A frequently discussed topic in the area of Koi nutrition is the correct protein/fat ratio of the food. This should always be based on the natural food intake of the Koi carp. Last but not least, Koi farms and pond farms still use natural food to raise their baby koi and young fish, as this is the optimal diet.
Conclusion: What is the most important thing in Koi nutrition?
In summary, it can be said that it is not the percentage of protein and fat that is crucial for nutrition, but the absolute amount of protein and fat consumed from food. The ratio of protein to fat is also relevant. Carbohydrates play a minor role in Koi nutrition. From a nutritional point of view, Koi only need small amounts of carbohydrates for growth.
Scientific sources:
[1] Geldhauser, F. & Gerstner, P. (2011): The pond farmer. Carp and minor fish . 9th revised edition. Ulmer Stuttgart, pp. 76 – 93.
[2] Barthelmes, D. (1967): Estimation of natural food conditions in carp ponds as a basis for improving the condition of carp and increasing yields . Dt. Fischerei-Ztg 14 (11), 330 – 343.
[3] Schäperclaus, W. & Lukowicz, MV (1998): Textbook of pond farming . 4th revised edition. Parey. Berlin, pp. 51 – 209.
[4] Schreckenbach, K. (2015): Nutrition of carp in ponds: Koi hobby . Institute for Inland Fisheries e. V. Potsdam-Sacrow.
Analytical composition
Protein
Growing fish require a sufficient supply of protein in their feed. Of the macronutrients (protein, fat, carbohydrates), protein is the most important in feeding. In addition to the absolute amount of protein, the ratio between protein and energy content of the feed is also crucial for the optimal growth of a fish. For each percent of crude protein, approximately 0.4 – 0.5 MJ of digestible energy is required [1, 2, 3, 5] . Failure to meet the required energy intake poses risks and leads to increased protein breakdown. This means that the protein consumed is used as an energy source and metabolized. It is therefore no longer available for fish growth.
As a serious consequence, this poor feed utilization also leads to increased water pollution due to increased excretion of nitrogen compounds through the gills (more under Relationship between feed composition and fish health) . If the energy intake is consistently exceeded, there is a risk of obesity and this puts the Koi under stress. The following section discusses the importance of fat in connection with protein. It is possible to replace part of the protein content in a feed with fat. This effect is called the protein-saving effect. Some experiments have shown that, while the total energy content remains constant, 5 – 12 % protein can be replaced with fat without any loss of growth. It is therefore conceivable to partially replace proteins with fats [2] . This means that a feed does not have to have a protein content of 50 % to be similar to natural food.
From a nutritional point of view, a feed with a high fat content and 40% protein is just as usable as a feed with a low fat content and a protein content of over 50%. One advantage of this higher fat content is the lower total protein excretion. This means that the pond water is less contaminated with nutrients (algae) such as nitrite/nitrate, ammonia/ammonium. In addition, the total amount of feed can be reduced. Fat is therefore extremely important for energy assessment. In this context, fat is the most important energy source for the protein/energy ratio.
To enable good growth of the fish, the protein content of a feed should not be less than 30% [4] . The quality of a protein is defined by its digestibility. This is largely determined by its origin. Animal proteins such as fish meal have a very good digestibility of 95%. Plant protein sources such as wheat protein, isolated soy protein or soy extraction meal have a slightly lower digestibility of 60 – 85% [3, 4] . This not only leads to increased water pollution, but also to a higher feed requirement. More on the subject of protein digestibility can be found in the article Amino acids.
Scientific sources:
[1] Schäperclaus, W. & Lukowicz, MV (1998): Textbook of pond farming . 4th revised edition. Parey. Berlin, pp. 51 – 209.
[2] Otto, D. (2016): Investigations into the composition of commercially available feed for koi and other carp species. Bachelor thesis. Faculty of Agricultural and Environmental Sciences, University of Rostock
[3] Spannhof, L. & Steffens, W. (1995): Introduction to fish physiology . Dr. Kovac̆, Hamburg.
Amino acids
Proteins in sufficient quantity and quality are of particular importance for the animal. The structure of a protein is determined by the composition of its amino acids. In animal nutrition, the amino acid profile is a crucial quality parameter.
Amino acids are divided into essential and non-essential amino acids. Koi cannot synthesize essential amino acids, so they must be ingested through food. In contrast, Koi can produce non-essential amino acids themselves from essential amino acids.
Only the content of essential amino acids can be used to assess protein quality. According to the principle of Liebig’s barrel (Liebig’s law of the minimum), a lack of intake of essential amino acids can lead to a reduction in growth [1] . This means that the koi can only use the individual amino acids for growth until the requirement for an essential amino acid is exceeded. It does not matter how high the amount of the other essential amino acids is, growth only takes place up to this one limited essential amino acid.
One of the essential amino acids is the sulfur-containing amino acid methionine. If the feed contains insufficient animal protein, this amino acid limits overall growth [1] . One of the most important tasks of methionine in protein metabolism is its involvement in muscle protein synthesis. Many commercially available koi feeds have an unfavorable amino acid profile that does not meet the needs of Koi and leads to poorer feed utilization [2] .
Amino acids are closely interrelated. The fish organism is capable to a certain extent of synthesizing non-essential amino acids itself and thereby substituting other amino acids. For example, cysteine can be used to substitute methionine, tyrosine and phenylalanine to a certain extent [3] .
The need for essential amino acids in protein is determined by the fish’s own amino acid composition. The more similar the amino acid profile of the feed is, the more usable the protein appears to be for the animal [1] . Fish meal has a very similar amino acid profile. For this reason, a high proportion of fish meal in the feed is beneficial for koi and serves as a sign of high-quality koi feed [2]
Scientific sources:
[1] Geldhauser, F. & Gerstner, P. (2011): The pond farmer. Carp and minor fish . 9th revised edition. Ulmer Stuttgart, pp. 76 – 93.
[2] Schreckenbach, K. (2015): Feeding carp in ponds: Koi hobby . Institute for Inland Fisheries e. V. Potsdam-Sacrow.
[3] Schäperclaus, W. & Lukowicz, MV (1998): Textbook of pond farming . 4th revised edition. Parey. Berlin, pp. 51 – 209.
[4] Steffens, W. & Arlinghaus, R. (2008): The carp. Cyprinus carpio L.; [with 47 tables]. 6th revised and expanded edition. Westarp-Wiss. Hohenwarsleben, p. 61.
Carbohydrates
Short-chain carbohydrates are rarely found in the natural diet of a carp, as the carbohydrate content in natural food is low. If animal food sources are available to the carp, crustaceans, insect larvae or mollusks serve as the main food source. Otherwise, the carp also uses available plant food sources such as algae and other plant components.
The proportion of carbohydrates in the plant and animal food sources mentioned is comparatively low. Based on this knowledge, carp are not dependent on carbohydrates and get their energy mainly from fat and proteins. This statement was proven in a study in which the carp were kept exclusively on a carbohydrate-free diet without showing any signs of deficiency [1] . Carbohydrates can be metabolized in the koi organism in two ways during digestion. Firstly, carbohydrates are used primarily for energy because they are broken down quickly. Secondly, if there is an excess supply of short-chain sugar-containing compounds, the energy can be stored. This happens in the form of glycogen in the liver or in the muscle tissue or in the adipocytes as fatty tissue.
If there is an excess of carbohydrates combined with too little protein, this fat storage occurs more frequently. The result is poor growth and reduced feed utilization [1] . For example, a low-protein but high-carbohydrate feed leads to fattening of the Koi, which cannot grow due to a lack of protein.
The carbohydrate content in feedstuffs comes mostly from grain starch (especially wheat). Grain starch is highly digestible and can be digested by carp up to 85 – 90% [2] . The carbohydrate content in a high-quality Koi feed should be less than 20%. From a production point of view, it is not possible to completely avoid carbohydrates in an extruded Koi feed.
Scientific sources:
[1] Wilson, RP (1991): Handbook of Nutrient Requirements of Finfish . CRC press. Boston, p. 35.
[2] Schäperclaus, W. & Lukowicz, MV (1998): Textbook of Pond Management . 4th revised edition. Parey. Berlin, pp. 51 – 209.
Fat
In the natural occurrences of natural food, the dry matter, in addition to protein, is almost exclusively fat. In contrast to carbohydrates and proteins, fat contains a significantly higher energy density.
As a result, it plays a crucial role in the metabolism of a koi. Fats not only serve as an energy supplier in the organism, they are also involved in the construction of cell walls and serve as a carrier substance for fat-soluble vitamins. Since the koi gets most of its energy from fat molecules, an increased fat supply can lead to better protein utilization. Proteins are thus protected and are not broken down to produce energy [1] .
Some experiments have shown that, with a constant total energy content, it is possible to replace 5 – 12% protein with fat without loss of growth. It is therefore conceivable to partially replace proteins with fats [2] . This effect is called the protein-saving effect. This means that a feed does not have to contain more than 50% protein to be similar to natural food. In nutritional terms, a feed with a high fat content and 40% protein is similarly usable as a feed with a low fat content and a high protein content of more than 50%. One advantage of this higher fat content is the lower total protein excretion. In addition, the total amount of feed can be reduced.
Consequently, fat is given immense importance in energy assessment. In this context, fat is the most important energy source for the protein/energy ratio. High-quality feeds use polyunsaturated fatty acids, mainly from marine animals (fish oil), and only small amounts from plant sources.
Feedstuffs that have a high content of unsaturated fatty acids (such as fish oil) become rancid after a certain time (oxidative processes). To prevent this reaction, antioxidants (e.g. BHT) are added to the feedstuff to prevent the progressive oxidation process. At 88 – 95%, fish and vegetable oils are highly digestible and represent a good source of energy for feeding [2] .
Scientific sources:
[1] Steffens, W. & Arlinghaus, R. (2008): The carp. Cyprinus carpio L.; [with 47 tables]. 6th revised and expanded edition. Westarp-Wiss. Hohenwarsleben, p. 61.
[2] Schäperclaus, W. & Lukowicz, MV (1998): Textbook of pond farming . 4th revised edition. Parey. Berlin, pp. 51 – 209.
Crude fiber
Crude fiber is not very important in feeding Koi. From an animal nutrition perspective, crude fiber components take on the function of dietary fiber. In general, crude fiber is the structural substance of plants and insects that gives them structure and shape. Crude fiber is mainly made up of cellulose, hemicellulose, lignin, pectin and chitin.
The use of components rich in crude fiber is kept to a minimum, as Koi carp are unable to digest these structures. Crude fiber only promotes the passage of chyme (the movement of food pulp in the intestinal tract), but can hardly be used for energy supply. The percentage of crude fiber required for this is too low. The bacterial breakdown in the digestive tract is also considered to be marginal and does not show any significant improvement in digestibility [1] . A high crude fiber content is also disadvantageous because the crude fiber content significantly reduces the digestibility of nutrients.
Some studies have shown that nutrient digestibility decreases with increasing cellulose content. An increase in the crude fiber content significantly reduces the percentage of protein and fat utilization. Based on this knowledge, the crude fiber content of a mixed feed should be less than 5% [2] . Studies have shown that the crude fiber content in many commercially available koi feeds is higher than stated [3] .
Scientific sources:
[1] Bergot, F. & Breque, J. (1981): Study of the digestive use of purified cellulose in arctic truite (Salmo gairdneri) and common carp (Cyprinus carpio). In: Reprod. Nutr. Dévelop. 21 (1), pp. 83 – 93.
[2] Steffens, W. & Arlinghaus, R. (2008): The carp. Cyprinus carpio L.; [with 47 tables]. 6th revised and expanded edition. Westarp-Wiss. Hohenwarsleben, p. 61.
[3] Otto, D. (2016): Investigations into the composition of commercial feed for koi and other carp species. Bachelor’s thesis. Faculty of Agricultural and Environmental Sciences, University of Rostock
Minerals and vitamins
Vitamins include organic substances that are necessary for the metabolism of organisms. Fish can synthesize some substances themselves, but others must be taken in externally. The feed industry adds vitamin and mineral mixtures to complete feed that are based on the needs of carp and are added by most manufacturers in almost identical concentrations.
Fish are able to absorb a wide variety of minerals through their skin and gills. Minerals such as sodium chloride (NaCl), potassium (K), iron (Fe), zinc (Zn), magnesium (Mg), calcium (Ca), copper (Cu) and iodine (I) are macro and trace elements.
A substance that is often used by feed manufacturers is montmorillonite. Montmorillonite is a clay mineral that is supposed to imitate the minerals found in Japanese mud ponds. It is hoped that this clay mineral will produce healthier fish with more expressive colors. Little is known about how it works.
The two most important theories speak of an improved supply of minerals and the elimination of toxins, which relieves the strain on the organism. This allows the fish to invest more energy in developing its color. There are currently several studies on this, but they do not yet show any reliable results.
Scientific sources:
No reliable results have been published yet.
Alternative health promoters
Alternative performance enhancers are intended to have a positive effect on the organism in terms of performance and health. Performance enhancers include probiotics, prebiotics, enzymes, organic acids/salts and essential herbs. They can be found under the additional categories of sensory and zootechnical additives (REGULATION (EC) No. 1831/2003) [1] .
Scientific sources:
[1] REGULATION (EC) No 1831/2003 OF THE EUROPEAN PARLIAMENT AND OF THE COUNCIL on additives for use in animal nutrition, dated September 22nd, 2003
Probiotics
Probiotics are defined as living microorganisms that reach the intestines in sufficient quantities in an active form and thereby have positive health effects [1] . One difficulty in using probiotics is their survival. Many do not survive the extrusion process (which is intended to preserve the food) and must be administered afterwards. It is difficult for the consumer to judge whether the probiotics reach the koi in a sufficiently living form.
Thus, the feed does not contain microbial metabolites, as is the case with antibiotics, but rather the microorganisms themselves. The mechanisms of action are diverse and cannot be examined in detail. They are based, among other things, on the displacement of the undesirable microorganisms, on competition for available nutrients or on the inhibition of the undesirable microorganisms by metabolic metabolites. For the most part, microorganisms are responsible for immune stimulation and the direct activation of immune cells [2] .
In animal nutrition, microorganism genera such as Saccharomyces, Enterococcus faecium, Streptococcus infantarius, Bacillus subtilis, B. licheniformis, B. cereus var. toyoi, Lactobacillus rhamno-sus, L. casei, L. plantarum, L. farciminis, Paediococcus acidilactici and yeasts of the genus Saccharomyces cerevisiae are most commonly used [2, 3] .
The metabolic products released by the probiotic bacteria are mainly organic acids, lactate, volatile fatty acids and enzymes. Some metabolic metabolites have been shown to have an antimicrobial effect. For example, lactobacilli produce bacteriocins and plasmid-encoded proteins that can inhibit the growth of other bacteria [2] . In a scientific study on trout, consumption of Lactobacillus rhamnosus after 30 days of testing resulted in a significantly increased activity of phagocytosis (absorbing dead microorganisms) and leukocytes (fighting incompatible substances such as pathogens) [4] .
Scientific sources:
[1] Federal Institute for Health Protection of Consumers and Veterinary Medicine (1999): Final report of the working group “Probiotic microorganism cultures in food”: Urban & Vogel Medien, Munich – available online at: https://www.bfr.bund.de/cm/343/probiot.pdf.
[2] Zentek J. (2011): Prebiotics, Probiotics , Institute of Animal Nutrition: Free University of Berlin, Berlin – available online at: http://geb.uni-giessen.de/geb/volltexte/2011/8235/pdf/ Zentek_Praebiotika_2011.pdf.
[3] Renard, B. (2005): Rare earths as performance enhancers in fish farming – studies on rainbow trout and carp . Dissertation: Ludwig Maximilian University, Institute of Physiology, Physiological Chemistry and Animal Nutrition, Munich – Available online at: https://edoc.ub.uni-muenchen.de/4354/1/Renard _Bernd.pdf.
[4] Panigrahi, A.; Kiron, V.; Kobayashi, T.; Puangkaew, J.; Satoh, S.; Sugita, H. (2014): Immune responses in rainbow trout Oncorhynchus mykiss induced by a potential probiotic bacteria Lactobacillus rhamnosus JCM 1136 . In: Vet Immunology Immu-nopathol 102 (4), pp. 88 – 379.
Prebiotics
According to the Federal Institute for Consumer Health Protection and Veterinary Medicine, prebiotics are “specific indigestible substances that promote the growth of selective bifidobacteria and possibly other microorganisms in the intestine and thereby achieve positive health effects” [1] .
Prebiotic additives such as carbohydrates, polysaccharides, oligosaccharides, disaccharides, short-chain sugar alcohols (β-glucans, mannanoligosaccharides from the yeast cell wall) are used in the feed industry [2] .
The principle of prebiotic products is not the body’s own digestion to provide energy, but rather the substances are selectively metabolized undigested in the intestine by microorganisms and used as their own energy source. Intestinal microbes break down ingested carbohydrates into the short-chain fatty acids acetate, butyrate and propionate. These short-chain fatty acids theoretically lead to a reduction in the pH in the intestine, which inhibits negative microorganisms [3] .
In addition to promoting desirable microorganisms, some undesirable microorganisms can also metabolize prebiotics. As a result, the desired theoretical effect is not always achieved. Studies on salmonids have shown a reduction in mortality when β-glucans were fed [4] .
Scientific sources:
[1] Wilson, RP (1991): Handbook of Nutrient Requirements of Finfish. CRC press. Boston, p. 35.
[2] Schäperclaus, W. & Lukowicz, MV (1998): Textbook of Pond Management. 4th revised edition. Parey. Berlin, pp. 51 – 209.
Organic acids and their salts
For centuries, companies in the food industry have used organic acids to preserve food and feed (silage, yoghurt, sauerkraut, etc.). Organic acids and essential oils are considered to be beneficial to health and have antimicrobial properties [1] .
Organic acids were once used for preservation to protect feed from spoilage. Now they are used in animal nutrition to lower the pH value in the digestive tract. The most common acids include propionic acid, butyric acid, sorbic acid, acetic acid, succinic acid, benzene acid, lactic acid, formic acid, citric acid and fumaric acid [1] .
The use of organic acids in cases of diarrhea is mainly used in young monogastric animals, i.e. piglets. Since gastric acid production is not yet fully developed and the number of microbes in the digestive tract is still relatively low, the use of acids can lower the pH value and protect the intestine from bacterial infection (E. coli bacteria). Improved protein digestion can also be ensured [2] .
Humic acids (peat) have always been used in aquaristics and pond farming to improve the health of fish. They can stimulate the body’s own cellular defenses in fish [3, 4] . It has been proven that feeding humic acids can reduce the residence time of toxic lead and cadmium in the organism [5] .
Scientific sources:
[1] Weber, G. (2012): Significance/benefits and efficiency of additives in feed: 24 Hülsenberger Gespräche , Lübeck – Available online at: https://www.schaumann-stiftung.de/cps/schaumann-stiftung/ds_doc/1_1_lf_weber.pdf.
[2] Freitag, M.; Hensche, HU; Schulte-Sienbeck, H.; Reichelt, B. (1999): Biological effects of conventional and alternative performance enhancers . In: KRAFTFUTTER/FEED MAGAZIN 2, pp. 49 – 57 – Available online at: https://www4.fh-swf.de/media/downloads/ fbaw_1/download_1/professoren_1/freitag/publikationen_pdf/Biologische_Effekte_konventioneller_und_alternativer_Leistungsfoerde-rer.pdf.
[3] Schreckenback, K.; Meinelt, T.; Spangenberg, R.; Staaks, G.; Kalettka, T.; Spangenberg, M. (1991): Investigations into the effect of the synthetic humic substance RHS 1500 on freshwater fish in aquaculture . Institute for Inland Fisheries, Berlin.
[4] Schreckenback, K.; Kühnert, M.; Haase, A.; Höke, H. (1996): Report on the effect of the pharmaceutical base substance HS 1500 on commercial and ornamental fish in aquaculture and aquariums . Institute for Inland Fisheries e. V., Potsdam-Sacrow.
[5] Rochus, W. (1983): The influence of peat humic acids on the absorption, excretion and distribution of lead and cadmium in the rat organism . In: Phys. Med. Rehab Kuror 35 (1) pp. 25 – 30.
Enzymes
Enzymes are used in animal nutrition to utilize food components that the organism itself is not capable of.
Not all animals are fully capable of independently synthesizing the enzymes required to process certain nutrients. By adding the necessary enzymes, the energy and nutrient supply for growth can be significantly improved. Amylases, for example, are used to break down starch and phytases are used to utilize phosphorus from plant sources.
Secondary plant ingredients
Secondary plant ingredients use the health-promoting, anti-parasitic, anti-inflammatory or antibacterial properties of medicinal plants to combat health problems. According to Regulation (EC) No. 1831/2003, these are classified in the categories of sensory and/or zootechnical additives. The legal differentiation between phytotherapeutic agents and feed additives (phytoadditives) is difficult to consider.
Phytotherapeutics are medicinal products that are made from whole plants or plant extracts [1] . Since phytotherapeutics consist of the same components as a phytoadditive (subject only to Regulation (EC) 1831/2003), the problem here is that they are subject to the Medicines Act.
One approach to getting around this problem is to divide the substances according to the amount used. This involves taking in phytoadditives in nutritionally significant quantities. The most common secondary plant substances include the groups of bitter substances, pungent substances, essential oils, phenolic oils, saponins, alkaloids, glycosinolates, mucilaginosa and tannins [2] . In terms of their chemical structure alone, secondary plant ingredients have an inhomogeneous structure, to which a variety of effects and mechanisms of action can be attributed. Unlike conventional medicines, the effect is not only due to a single active ingredient, but to the interactions of several substances involved [1] . Secondary plant ingredients have different effects on the organism, which can be described as anti-inflammatory, antiseptic, antiviral, immune system stabilizing, appetite stimulating, antiparasitic [3, 4, 5] .
In a 13-week feeding trial of Nile tilapia (Oreochromis niloticus) with oregano (Origanum vulgare), an oregano concentration of 1% resulted in a significant improvement in daily gain, relative and specific growth rate, and feed utilization [6] .
Scientific sources:
[1] Striezel, A. (2005): Guide to livestock health: holistic prophylaxis and therapy . 1st ed., MVS Medizinverlag, Stuttgart, p. 30.
[2] Wenk, C. (2003): Growth promoter alternatives after the ban on antibiotics . In: Pig News and Information 24 (1), pp. 11 – 16.
[3] Wetscherek W. (2002): Phytogenic feed additives for pigs and poultry. Conference proceedings : 1st BOKU – Symposium on Animal Nutrition, December 5, 2002, Vienna. P. 18 – 23.
[4] Jones, G. (2001): High-performing livestock and consumer protection are not contradictory, impact of a phytogenic additive . In: Feed Magazine 12, pp. 468 – 473.
[5] Schlicher H. (1986): Pharmacology and toxicology of essential oils . In: Therapiewoche 36, pp. 1100 – 1112.
[6] Seden, ME A; Abbass, FE; Ahmed, MH (2014): Effect of origanum vulgare as a feed additive on growth performance, feed utilization and whole body composition of nile tilapia, Oreochromls niloticus. fingerlinges challenged with pathogenic Aeromonas hydrophila . In: AGRIS Science 34, pp. 1683 – 1695.
Carotenoids
In order to influence the color of a fish, one group of micronutrients deserves special attention: carotenoids. In addition to the color aspect, carotenoids also serve as a precursor for vitamin A [1] .
Fish must obtain the necessary nutrients for color development from their food, as the organism is not able to synthesize them independently [2] .
Especially in today’s aquaculture and in the artificial keeping of koi ponds, the supply of carotenoids in sufficient concentrations is more crucial than ever. What is absorbed under natural conditions via algae and microorganisms, must be secured in the pond as needed through the feed.
For the owner, the color of the fish is one of the most important quality characteristics. In the skin of a fish there are chromatophoric cells that are responsible for the respective color characteristics when combining different pigment deposits. Chromatophoric cells can be divided into different cell types: erythoracic cells (red-yellow), xanthophoric cells (yellow) and melanophore cells (brown-black) [6] .
Astaxanthin, which is stored in the erythoracic cells, is considered the main carotenoid for red pigmentation and must be supplied through the diet [1] . With the help of β-carotene, lutein, zeaxanthin, iso-cryptotoxanthin, echinenone and canthaxanthin, which can be taken in through the diet, the fish is able to synthesize astaxanthin itself [1] .
The myth that color improvement is possible beyond genetic potential must be refuted. Even when fed with food containing colorants, fish with few chromatophoric cells do not achieve the color brilliance of genetically better equipped animals. It is possible to help the existing cells to achieve more color intensity with optimal care (within a certain framework). However, high-quality food cannot produce a “color miracle” if the fish has a poor disposition.
According to the latest findings and studies, the optimal astaxanthin content for koi food is around 40 – 80 ppm [4, 5] . Inexpensive feeds usually contain only small amounts of astaxanthin, if at all. To suggest a high color content, red dyes are often added to the food, but these cannot be used by the koi. Astaxanthin is very expensive and costs a four-digit Euro amount per kilogram.
Scientific sources:
[1] Tan Phaik Shiang (2006): Skin colour changes in ornamental koi (cyprinus carpio) fed different dietary carotenoid sources . Dissertation. Universiti Sains Malaysia.
[2] Steffens, W. & Arlinghaus, R. (2008): The carp. Cyprinus carpio L.; [with 47 tables]. 6th revised and expanded edition. Westarp-Wiss. Hohenwarsleben, p. 61.
[3] Naguib YMA (2000): Antioxidant activities of astaxanthin and related carotenoids . Agric.Food Chem. 48,1150 – 1154.
[4] Nguyen, NV; Khanh, TV; Hai, PD (2014): Study on Development of Formulated Feed for Improving Growth and Pigmentation of Koi Carp (Cyprinus carpio L. 1758) Juveniles , Research Institute for Aquaculture No. 2. Journal of Life Science. Ho Chi Minh City, Vietnam
[5] Kim, YO; Jo, JY; Oh, SY (2008): Effects of Dietary Spirulina, Chlorella, and Astaxanthin on the Body Color of Red- and White-colored Carp, Cyprinus carpio . Journal of the Korean Fisheries Society 41 (3), 193 – 200.
[6] Becher, H. (1929): Über die Entwicklung der Xanthophoren in der Haut der Knochenfische , Verlag von Julius Springer, Anatomisches Institut der Universität Gießen
Quality Characteristics of Koi Food: How to choose the best food for your Koi
Every Koi owner probably asks himself this question sooner or later: “How much money do I have to spend on food that will keep my Koi healthy?”
The price as the first indicator
The first indicator is the price. If the complete feed is very cheap, it is unlikely that high-priced raw materials were invested in during production. The use of high-quality raw materials means higher costs for producing the feed. Therefore, these additional costs must inevitably be reflected in the price.
High-quality raw materials are easier for Koi to digest and at the same time put less strain on the pond water. Easily digestible animal proteins and fats are many times more expensive than their plant-based alternatives. The price per kilo of high-quality fish meal is currently more than three times that of soy protein and even more than ten times that of grain. The situation is similar with fish oil and vegetable oil. Special additives such as spirulina or essential herbal oils are particularly expensive. The latter often cost a three-digit amount per liter.
Although the price is a first guide, it is not that easy to determine good food. Cheap food is not automatically bad and the most expensive food is not automatically the best.
Labels: The ingredients matter
The next guide is the nutrition information label. This lists the ingredients of a food in descending order of quantity. Look specifically for high-quality, expensive raw materials. Do they appear at the top? Are there any derivatives in the list?
What is in high quality koi food?
High-quality koi foods use expensive, high-quality components such as quality fish meal, algae, plant extracts, wheat germ, fish oil, carotenoids, immune stimulants and additives for nutrient optimization.
What to avoid: Derivatives and fillers
Cheap feeds use substitute raw materials, so-called derivatives. These substitutes should not be used at all or only in small quantities. A first indicator of a feed of insufficient quality is the listing of plant components such as grain, soy or plant by-products at the top of the label. An animal protein source should be in the first spot (largest percentage). Ideally fish meal, because its amino acid profile is very easily usable by Koi.
So-called fillers should also be avoided. Fillers are added to feed to increase its volume without having a positive effect on the nutritional value or properties of the feed.
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