The African glass catfish is an omnivorous fish native to the freshwaters of the eastern part of the continent. With the increase in agricultural production and the development of new aquaculture farms for the production of fish, the numbers of the fish are rapidly increasing. The population is now about 12 million with a growth rate of about 2% per year and the production is about 300 tons per year. The African catfish is mainly caught for the production of fishmeal for fishmeal and pet food.
It is a bottom-feeding fish and the main feeding period is from October to March, when the water temperature is about 10° C. During this period, the African catfish lives mostly on aquatic insects and algae. The African catfish spends a large amount of energy on food transportation to the gills. As a consequence, the catfish has a high concentration of fat, about 25% of its body weight. The amount of carbohydrate and protein in the feed is usually about 1%.
With the improvement of the quality of live in Africa, the demand for large-scale fish culture is also increasing. Therefore, a large amount of catfish needs to be produced in the future. In order to achieve this purpose, high production, high survival rate, large growth rate and a more efficient feed system are essential. Currently, the main feed of catfish is live feed (e.g., insects and algae), but the use of artificial feed is attracting more attention. Artificial feed has the advantages of uniform nutrition, rapid growth, no pollution, small-scale operation, and so on. Among the artificial feeds, fish meal (FM) is widely used as a protein ingredient in animal feed, but there are lots of environmental pollution problems, such as fish meal being not easily digested by ruminants and nitrogen pollution in the body of fish. In view of this, the production of fish meal has a certain limitation, and the use of fish oil is of great significance.
Fish oil, also called liquid fat of fish, has been considered as one of the most valuable nutritional elements in the world. Fish oil is the only source of polyunsaturated fatty acids (PUFA) that can be metabolized by the body of animals. The main characteristics of fish oil are relatively high unsaturated fatty acids, especially docosahexaenoic acid (DHA) and arachidonic acid (AA) with anti-atherosclerosis, anti-cancer, anti-inflammation, anti-fatty liver, cholesterol-lowering, anti-cardiovascular disease, etc. In addition, the fish oil has a relatively high level of the long-chain n-3 polyunsaturated fatty acids, such as eicosapentaenoic acid (EPA), DHA and AA, and some other special nutritional components. Fish oil is commonly extracted from fish by the industrial processing method, such as solvent extraction and enzymatic extraction, and the process is energy.