Crude fiber is not highly relevant in koi feeding. From an animal nutrition perspective, crude fiber components function as dietary fiber. Generally, crude fiber represents the structural substances of plants and insects, giving them structure and shape. Crude fiber consists primarily of cellulose, hemicellulose, lignin, pectin, and chitin.
The use of high-fiber components is kept to a minimum, as koi carp are unable to digest these structures. While crude fiber promotes chyme passage (the movement of food through the intestinal tract), it is hardly usable for energy. The percentage of crude fiber required for this purpose is too low. Bacterial breakdown in the digestive tract is also considered marginal and does not significantly improve digestibility [1] . Furthermore, a high crude fiber content is also disadvantageous because it significantly reduces the digestibility of nutrients.
Some studies have shown that nutrient digestibility decreases with increasing cellulose content. An increase in crude fiber content significantly reduces the percentage of protein and fat utilization. Based on this finding, the crude fiber content of a compound feed should be below 5% [2] . Studies have analyzed that the crude fiber content in many commercially available koi feeds is higher than stated [3] .
Scientific sources:
[1] Bergot, F. & Breque, J. (1981): Etude de l'utilisation digestive d'une cellulose purifiée chez la truite arc-en-ciel (Salmo gairdneri) et la carpe commune (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 commercially available feed for koi and other carp-like fish. Bachelor thesis. Faculty of Agricultural and Environmental Sciences, University of Rostock
