Application of cholesterol in aquatic animals
Cholesterol is a type of animal sterol, which is widely present in animal cells and blood in a free state or in the form of chemical bonds and fatty acids. In aquatic animals, it is the precursor of a variety of physiologically active substances such as ecdysteroids, sex hormones, corticoids and vitamin D. However, many studies have found that crustaceans and crabs cannot synthesize cholesterol in their bodies. Therefore, adding cholesterol to aquatic animal feed has gradually become a research hotspot.
1 cholesterol synthesis and metabolism
Cholesterol, also known as cholesterol, is a sterol compound with cyclopentane polyhydrophenanthrene as the core. It was first isolated in animal gallstones. In most tissues, the main raw material for cholesterol synthesis is acetyl CoA, which is excreted in the form of cholesterol and bile salts in bile. Cholesterol is an important component of animal cell membranes. It plays an important role in reducing cell membrane fluidity, protons, and Na + permeability to cell membranes, and can also form bile acids in the liver. Under ultraviolet light, The body transforms into VD3, and the vertebrate synthesis of cholesterol can be divided into three stages: the synthesis of mevalonate, the synthesis of squalene, and the synthesis of cholesterol.
2 Regulation of the synthetic cholesterol pathway
In the body, too much or lack of cholesterol can have an adverse effect, so its synthesis is strictly regulated. Zou Sixiang research shows that β-hydroxy-βmethylglutaric acid CoA reductase (HMG-CoAr) is the rate-limiting enzyme for cholesterol synthesis, and its half-life in the liver is only about 4 hours, so the activity of this enzyme is inhibited Enzyme activity in the liver decreases rapidly, thereby limiting cholesterol synthesis; low-density lipoprotein (LDL), on the one hand, inhibits the synthesis of HMG-CoAr reductase through cholesterol feedback to reduce intracellular cholesterol synthesis; When the content is too high, it prevents the synthesis of new LDL receptors, thereby preventing cells from continuously taking cholesterol from plasma; in addition, cholesterol regulation is also related to hunger and energy intake.
3 cholesterol application in aquatic animals
Fish meal is an important protein feed ingredient, not only rich in protein and essential amino acids, but also contains essential fatty acids, vitamins, minerals, cholesterol and so on. However, the current price of fishmeal is increasing, and the price of imported fishmeal is higher, which has led to the selection of plant protein in the feed, and the plant protein lacks some unknown growth factors. Therefore, a single feed ingredient needs to be added to the formula. Cholesterol is One.
3.1 Application of Cholesterol in Crustaceans
Adding cholesterol to the feed is necessary for the growth of crustaceans. Smith believes that cholesterol is one of the most expensive ingredients in shrimp recipes, and adding 2g to a ton of recipe means a 10% increase in cost. Crustacean cholesterol has been studied since the 1970s. At present, the research on the amount of cholesterol in shrimp is relatively complete. The results of Thongrod and other studies show that the cholesterol requirement in crustacean feed is generally 0.2% -1.0%, and excessively high levels will inhibit growth. Excessive cholesterol in the feed can adversely affect the growth of Homarusamericanus, P. monodon and P. vannamei. Gong et al. Studied the interaction of cholesterol and phospholipids in the growth of P. vannamei in feeds and found that there was a very obvious interaction between cholesterol and phospholipids, and the growth of P. vannamei increased with the increase in the amount of cholesterol in the feed. Significantly increased. When Chen studied the interaction of cholesterol and PC on juvenile prawns, he found that by adding 0.5% cholesterol, prawns can achieve good growth, and 1% cholesterol has no harmful effect on growth. Thongrod and other studies found that 0.5% and 1% cholesterol were added to the diet of juvenile shrimp (FenneropenaeusmeiguiensisDeMan) (primary weight 0.11g), respectively, and there was no significant difference between the weight gain rate and the control group (without cholesterol). Research by Briggs et al. Showed that freshwater macrobrachium rosenbergii (Macrobrachiumrosenbergii) do not need to add cholesterol to their feed.
3.2 Application of cholesterol in shellfish
In recent years, it has been found through isotopic tracer tests that shellfish can synthesize cholesterol from acetyl CoA. However, it cannot fully satisfy its growth and development. Trider et al. Reported that oysters require 0.1-0.2% cholesterol. The research by Zhang et al. Used purified diet as the basic formula and used a polyline model to evaluate the relative weight gain as an index. The results showed that the cholesterol requirement of Abalone wrinkled disc was 0.23%. Based on whether adding cholesterol to the artificial diet of abalone will affect muscle cholesterol The authors tested their muscles and found that the cholesterol content in the muscle was 93.6-99.8mg / 100g wet weight, which was higher than that in wild abalone (H. laevigata) muscle (72mg / 100g wet weight). , But its cholesterol content in muscle is lower than eggs (490mg / 100g wet weight) and scallops (400mg / 100g wet weight).
3.3 Application of cholesterol in fish
Studies by Sealey et al. Showed that adding 1.0% cholesterol to fat-striped fish meal diets fed hybrid striped bass, and the results showed that cholesterol did not promote growth. Twibell et al. Studied the supplementation of 1.0% cholesterol in soybean meal-based feeds. The results showed that the feeding rate and growth performance of Ictalurus punctatus were significantly improved, but the mechanism of promoting food intake and growth was not clear. Studies by Chen Qiang and others showed that under the nutritional background of peeled soybean meal, white fish meal, and casein as protein sources, the appropriate cholesterol (mass fraction 0.566%) in feed can improve the survival rate of cobia juveniles. Cholesterol has a saturation effect on the growth of cobia juveniles. Adding too much cholesterol to the feed will inhibit the growth of the body and cause liver disease. Adding an appropriate amount of cholesterol can increase the body's fat deposition, but excessive addition will cause the fat content of whole fish, liver, and muscles to decrease, affecting body fat metabolism. Chen Jinghua significantly reduced the activity of intestinal aminopeptidase, liver lipase, and intestinal alkaline phosphatase after replacing 45% fishmeal protein with soybean meal; the activities of these enzymes were significantly increased, and 0.0% and 0.5 were added to the replacement group feed. %, 1.0% and 1.5% cholesterol were fed to juvenile flounder, and it was found that the replacement of fish meal with soybean meal resulted in a significant decrease in plasma cholesterol content, growth, food intake and digestibility, and there was no significant difference with the fish meal group feed, but the 1.0% Cholesterol significantly promotes fish growth, feeding and digestion, while excessive cholesterol can inhibit the growth of flounder.