The application of different kinds of fat in fish feed

As we all know, fat not only provides energy in fish feed, but also provides essential fatty acids for fish growth. Choosing the right fat source and fat level can save protein, reduce feed costs, and reduce environmental pollution. Due to resource constraints, the price of fish oil has been increasing in recent years, so feed manufacturers and fish nutrition experts are working hard to study the nutritional requirements of fat for fish. Under the premise of not affecting growth, the feasibility of using other animal oil and plant oil instead of fish oil was explored.

1.?Commonly used fat sources in aquatic animal feed

Commonly used fat sources in aquatic feed include fish oil, tallow, lard, coconut oil, palm oil, corn oil, soybean oil, rapeseed oil, sunflower oil,and linseed oil. Fish oil mainly contains n-3 fatty acid, such as DHA and EPA. Coconut oil contains 89% saturated fatty acids, including 48% lauric acid, 17.5% myristic acid. Palm oil is a oil extracted from palm fruit, the color ranges from dark yellow to dark red, and contains 40% palmitic acid, 41% palmitoleic acid. Plant oils are high in linoleic acid such as soybean, corn, peanut, and sunflower oils

2.?The ability of fish to utilize fat sources in the feed

Different kinds of fat are mainly composed of different fatty acids, because the ability of fish to utilize different fat in the feed is actually the ability to utilize fatty acids in the feed. At the same time, the fat in the feed in turn affects a series of reactions such as the physiological and biochemical reactions of fish. In general, fish tend to use saturated and unsaturated fatty acids for energy, while PUFAs are generally used as functional substances and are retained in the body. For example, rainbow trout use most of the 16:0 fatty acid as energy.

2.1. Effects of fatty acid composition on fat metabolism in fish

The fatty acid composition in the feed will affect the activity of lipase. Excessive highly unsaturated fatty acids in the feed will inhibit the activity of △6-desaturase, resulting in the inhibition of the conversion of 18:2n-6 to 20:4n-6. And feed with low unsaturated fatty acids feed, increased △5 and △6-desaturase activity。

2.2. Effect of different fat on the digestion of nutrients

Different kinds of fat have different fatty acid compositions, and fish has different capacity of digestion and absorption . With the rise of fat levels in the feed, the digestion of the atlantic salmon to fat increases, and the protein digestive rate increases with the increase in the content of plant oil in the feed.

2.3. Effect of different kinds of fat on fish growth performance and fat composition

For fish, the utilization rate of fish oil is high, and the utilization rate of lard and plant oil is low.

2.4 Effect of different kinds of fat on the composition of fish body

Different kinds of fat in the feed will significantly affect the HSI and fat of the fish, which will affect the composition of the fish body. The fat source of the feed has the greatest effect on the content of body fat and water, and following is the content of protein and ash, such as rainbow trout, atlantic salmon and so on.

2.5 Effects of different kinds of fat on fish muscles, internal organs, and fatty acids of internal organs

Fatty acids in fish muscles, liver, and adipose tissue are directly affected by composition of fatty acids in the feed, to some extent, it reflects the composition of fatty acids in the feed. Generally speaking, replacing fish oil with plant oil will reduce the content of EPA and DHA in the body, and the content of linoleic acid and linolenic acid increases.

In conclusion, the replacement of fish oil with plant oil will be a hot topic in the future. Rational use of plant oil will be helpful for the sustainable development of the world's aquaculture.