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Nucleotide-enhanced shrimp resistance to disease
The biggest problem currently facing shrimp aquaculture production is shrimp disease. Since the appearance of White Spot Syndrome Virus in Northeast Asia in 1992, this type of shrimp disease has swept across Asia (including India, Bangladesh, Sri Lanka, China, Japan, Thailand, Malaysia and Indonesia) and spread across the Pacific Ocean. American countries (such as Panama, Nicaragua, Guatemala, and Honduras). According to reports, due to the spread of shrimp disease, the shrimp farming industry in South America, especially Ecuador’s shrimp farming industry, has been hit hard by the economy. With regard to the prevention and control of viral diseases in shrimp, there is currently a lack of appropriate vaccines and medicines. People try to prevent these disasters by strengthening management. Some shrimp farms use folk remedies such as garlic, lemon and ginger for treatment, but the effect is not satisfactory. In response to this situation, research has turned to strengthening the animal's body's immune system by enhancing nutrition. Much research has been conducted on immunization, and encouraging results have been achieved with the use of glucose and other compounds in laboratories; however, few applications have been successful in production. Therefore, it is speculated that re-stimulation of the immune system in shrimp that has been infected by pathogens is not a good idea. The application of nutrients that enhance and promote the function of the immune system has consistently yielded consistent results. Yeast and fish hydrolysates have been used as feed ingredients and are known as "unknown growth factor (UGF)" for their good efficacy. It has been shown that many feeds (such as animal protein hydrolysates, yeast extracts, and single-celled organisms, etc.) have a production promoting effect on animals because they contain a large number of nucleotides and natural polynucleotides. Just as Amino Acids are structural units of the protein chain, nucleotides are structural units of RNA and DNA; nucleotides are also an important part of enzymes and cofactors such as ATP, NAD, and FAD. Since most organisms can self-synthesize nucleotides, they have been considered as an unnecessary nutrient. Recent studies have suggested that nucleotides are essential nutrients for mammals (including humans), poultry, fish, etc., especially when animals are under stress (such as diseases, injuries) or in their young and vigorous growth period. The lack of nucleotides is detrimental to growth and health. In shrimp rearing, are there any nucleotide deficiencies in the general shrimp diet? Aquaculture nutrition expert Devresse believes that “In terms of the nutrition of livestock and other laboratory animals and humans, nucleotides in foods have an effect on the growth and physiological functions of cells that are metabolically active in vivo (such as lymphocytes, macrophages, and intestinal cells). ". He also pointed out: "Aquatic Animal Nutrition research is still in its infancy, and shrimps need to accumulate information on their nutritional status during stress and illness. Can shrimps synthesize nucleotides themselves? It is very limited. And in their natural food contains a large number of nucleotides, which can be extracted from them." Through the analysis of some important components in shrimp feed formulation, the content of nucleotides in feed can be seen. To simplify the analysis, the sample is completely hydrolyzed into basic units and only purine bases and pyrimidine bases are determined. Multiplying the number of bases obtained by 2.4 is the number of nucleoside monophosphates. Nitrogen-containing purines and pyrimidines are very low in plant seeds (such as soybeans, wheat, and corn), but rich in marine products and microorganisms. Protein synthesis requires a certain ratio of various amino acids during animal growth. An appropriate ratio is also required for glycosides or their precursors (purine bases and pyrimidine bases). This demand for bases depends on the amount of RNA and DNA in the cells and also on the overall synthesis efficiency and metabolic compensation pathways in shrimp tissues. In general, a more complete mixed feed can meet the nutritional needs of shrimp. The following interesting facts can be found from the content of nucleotides in some feeds. 1. The content of guanine in the hydrolysates of squid and sardines is high; however, the guanine content in squid, cod and squid is very low. Marine products also contain large amounts of xanthines (precursors of IMP). GMP and IMP are the attractants for shrimps and certain fish. The role of GMP and IMP nucleotides in increasing food palatability is confirmed, and both biological and nutritional aspects are of great significance. 2. There is abundant thymidine in DNA, and thymidine only exists in a large amount in the protein of single cell organism (SCP), and the content in other tissues is higher than DNA. However, the formation of lymphocytes or blood cells in the immune system is related to the production of DNA. Therefore, thymine is also an important nutrient component. The availability of protein or yeast nucleotides of unicellular organisms is a matter of concern. Crustacean stomachs have a low rate of protein use in unicellular organisms. The proteolytic properties of these organisms suggest that they have low digestibility due to their well-established cell membranes. Yeast extracts are better than normal yeast feed ingredients; while fish digestibles are also digestible, but their disadvantage is that they dissolve completely in water for a few minutes, making it difficult to determine the actual utilization of shrimp. The demand for nucleotides in shrimps has not been reported. Studies in mammals show that if the level of nucleotides in food reaches 0.25%, the daily requirement for purines and pyrimidines is estimated to be about 500 mg, but the daily intake is not more than 4g as the maximum safety limit, which can prevent and treat Uric acid and gout. The addition of 10% of hydrolyzed yeast or 4% of yeast extract in the shrimp feed corresponds to a 0.25% addition level of nucleotides. The addition of nucleotides to feeds, and the total amount of shrimps needed for nucleotides, should be speeded up to perform the necessary research.