In naturally occurring foods, the dry matter consists almost exclusively of fats, in addition to protein. Unlike carbohydrates and proteins, fat has a significantly higher energy density.
This gives it a crucial role in the metabolism of a koi. Fats not only serve as an energy source in the organism, but are also involved in the formation of cell walls and act as carriers for fat-soluble vitamins. Since the koi obtains most of its energy from fat molecules, an increased fat supply can lead to better protein utilization. Proteins are thus protected and not broken down for energy production [1] .
Several studies have shown that, with a constant total energy content, 5–12% of protein can be replaced by fat without impairing growth. Therefore, it is conceivable to partially replace proteins with fats [2] . This effect is called the protein-saving effect. Thus, a feed does not need to contain more than 50% protein to resemble natural food. From a nutritional standpoint, a feed with an increased fat content and 40% protein is just as digestible as a feed with a low fat content and a high protein content of over 50%. One advantage of this higher fat content is the lower total protein excretion. Furthermore, the total feed quantity can be reduced.
Consequently, fat is considered immensely important in energy assessment. In this context, fat plays the role of the most important energy source in the protein-to-energy ratio. High-quality feeds use polyunsaturated fatty acids primarily from marine animals (fish oil) and only small amounts from plant sources.
Feedstuffs with a high content of unsaturated fatty acids (such as fish oil) become rancid after a certain period of time (oxidative processes). To prevent this reaction, antioxidants (e.g., BHT) are added to the feedstuff to inhibit the progressive oxidation process. With a digestibility of 88–95%, fish and vegetable oils have a high digestibility and represent a good energy source 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 Management . 4th revised edition. Parey. Berlin, pp. 51–209.
