The feed additives have the major role to improve feed efficiency and more important to make low Feed Conversion Ratio (FCR) in aquaculture production. Feed additives may be both nutritive and non-nutritive ingredients and work by either direct or indirect methods on the aquatic animal’s system. The feed additives are supplemented in small amounts (alone or in combination) for a specific purpose to improve the quality of shrimp as a final product. Also, it preserves the physical and chemical quality of the diet or to maintain the quality of the aquatic environment.
The feed additives have been characterized to stimulate the speed of growth or the ability to reach the maximum sizes of the species. The feed additives have been necessity of the aquaculture productions to promote for an optimal growth development, the weight gain and the survival in certain stipulated period.
Roles of Feed Additives in Shrimp/Fish Nutrition
The range of feed additives used in aquatic feeds is very diverse. Additives are used in aqua feed to preserve the nutritional characteristics of a diet or feed ingredients prior to feeding. The feed additives have the functional properties as antioxidant and mold inhibitors, emulsifiers, stabilizers, binders, feed stimulants, attractants, growth promoters, molting inducer, Immunomodulator, antibiotics, probiotics, prebiotic, mycotoxin, antioxidants, color/pigmentation agents, antimicrobial compounds, disease preventer, organic acids, bile acids, hormones, herbal extracts etc. Enzymes also used to improve the availability of certain nutrients (e.g. proteases, amylases) or to eliminate the presence of certain anti-nutrients (e.g. phytase).
The feed additives promote the growth and better health performances of cultivated organisms. Also, feed additives improve their immune systems and induce physiological activities beyond traditional feeds.
Bile Acids as Feed Additive
Bile acids are the major constituents of bile and they are produced in the liver. Bile acids are secreted into the intestine where they play crucial biological roles such as promoting fat utilization as a natural emulsifier, activating lipase to improve fat digestibility and protecting animal liver.
Fats and oils constitute the main energy source of animals and possess the highest caloric value of all nutrients with almost 3 times higher apparent metabolisable energy than other feedstuffs. Hence, fats are widely added to animal diets to meet energy requirements. Digestion and absorption of dietary fat are poorly developed in young animals due to limited bile secretion.
Bile acids are important physiological agents for intestinal nutrient absorption. Bile acids are the end products of cholesterol catabolism. Bile acid synthesis generates bile flow and biliary secretion of bile acids, phospholipids, cholesterol, drugs, and toxic metabolites.
Mechanism of Bile Acids in Aquatic Animals Body
Bile Acids are the main active component of bile and it is a series of sterols produced in the process of cholesterol metabolism in animals. Also, bile acid is a mixture of complex components and has multiple biological activities. The major functions of bile acids are to assist the solubilization, emulsification and utilization of fat and fat-soluble vitamins. It protects the health of liver, hepatopancreas and gallbladder of fish and shrimps..
Bile acids have detergent action on particles of dietary fat which causes fat globules to break down or be emulsified into minute, microscopic droplets. Emulsification is not digestion but it greatly increases the surface area of fat for making it available for digestion by lipases.
Bile acids are lipid carriers and they are able to solubilize many lipids by forming micelles aggregates of lipids such as fatty acids, cholesterol and monoglycerides. Bile acids are also critical for transport and absorption of the fat-soluble vitamins.
Nutrients Transportation and Metabolism
Bile acids can regulate liver hepatic triglyceride metabolism through FXR binding to response element binding protein (SREBP-1C) to reduce hepatic steatosis (fatty liver). Bile acids can also reduce plasma cholesterol and triglyceride levels by enhancing the synthesis and transport of LDL (low density lipoproteins) and VLDL (very low density lipoproteins).
Solve Fatty Liver Disease in Fishes
As hormones or nutrient signaling molecules, bile acids help to regulate glucose, lipid, lipoprotein, energy metabolism and inflammatory responses. Fish has a delocalization in hepatocyte nuclear and there are a lot of fat droplets in the liver cells. After addition of bile acids, the hepatocytes of fish arrange closely with intact nucleus, obvious membrane boundary and healthy hepatocyte.
Function of Bile Acids in Shrimps
In shrimp and other crustaceans, lipids are the organic reserves and are usually the second largest biochemical fractions following protein. Among lipid, cholesterol is a major sterol in shrimp which occurs in all cells and in haemolymph either in free form or in combination with fatty acids.
Shrimp and other crustaceans are couldn’t secret bile acids and cholesterol by themselves. They require cholesterol which will convert into a molting hormone and allow rapid passage through their different larval growth phases. The health of hepatopancreas is vital for shrimp which will affect the survival rate directly.
Effects of Liver/Hepatopancreas in Shrimp Health
The liver/ hepatopancreas is an important metabolic organ and detoxification organ of shrimp. The hepatopancreas digests and absorbs the nutrients as store energy. Also fight against external invasion and expels toxins from the body.
The disorders or damage of liver / hepatopancreas are affecting on various functions of metabolic activities as well as health performances on shrimp like less absorption of nutrients, low metabolism activities, slow growth rate, weakened body, less immunity, , hemorrhage, rotten gills, enteritis, anti-stress ability, bad molting, more and more soft shell phenomenon, more diseases and infections, less production, digestive ability decline, wastage of feed nutrition, high FCR etc.
The hepatopancreas affected by environmental stress, pathogens invade, overload digestion and nutritional deficiency. So the protection of hepatopancreas should go throughout the whole culture process and relatively reduce the diseases incidences naturally in shrimps.
Importance of Bile Acids on Shrimp Feeding
The severe deterioration of pond environment, residue of petroleum products, heavy metal, ammonia nitrogen, disinfector residual etc are making harm to the health of hepatopancreas. Besides, high protein and fat content also bring heavy burden to enterohepatic system. Diseases happen on shrimp by poor environment conditions, bacterial infections and reduction of immunity ability.
The bile salt acts as strong protective agent for hepatopancreas to help various functions in litopenaeus vannamei. For enhancing better growth and for improving current management strategies toward sustainable shrimp farming, the application of bile acid as feed additive is so essential to solve the various problems.
Fat Digestion and Absorption: Bile acids promote digestion and absorption of fat and cholesterol by emulsifying fat, activating the activation of the lipase enzyme and forming mixed chylomicrons with enzymatic hydrolysate.
Lipid Metabolism: Bile acid plays an important role in regulating lipid, glucose and energy metabolism. Bile acid as a signaling molecule to regulate lipid metabolism. Bile acid activates many nuclear receptors in the liver and gastrointestinal tract. Bile acid synthesis is the major pathway for catabolism of cholesterol.
Enhances the Immunity: Bile acids can increase the disease resistance of shrimp with continuous feeding. Bile acids help to create an environment that kills and digests certain bacteria and viruses in the gastrointestinal tract. Feeding with the bile acid can enhance the better hepatopancreas function of the shrimp and it improves the immune system of the shrimp.
Prevents Toxin Compounds: The bile acids can reduce the toxic substances on hepatopancreas and make combine or break down intestinal endotoxin. It prevents endotoxin through the intestinal mucosal barrier and reduces intestinal absorption of endotoxin. Bile acids can break down the endotoxins into harmless substances or bind to endotoxins. Bile acids eliminate the toxin substances through excretion system from the body. The bile acids help to promote the secretion of a large number of thinner cells in hepatopancreas & liver. The bile acids reduce the damage of hepatopancreas caused by mycotoxins, heavy metals and other harmful substances.
Inhabitant of Pathogenic Organisms
The bile acid has a strong inhibitory effect on acute and chronic inflammation. Also bile acid has a significant antibacterial effect on gram-positive bacteria and gram-negative bacteria in intestinal tract. The large amounts of endotoxins are produced after bacteria killed in gut tract. The endotoxin can cause severe damage to hepatopancreas of shrimp.
The bile acids act as an effective fungicide and inhibit intestinal bacterial over-proliferation. It helps for maintenance of intestinal micro-ecological environment due to the bile acids surface activity. The deoxycholic acid (bile acid) can destroy the bacterial cell membrane and damage the entire cell. It inhibits the growth of bacteria and even causes bacterial cell death with inhibiting intestinal bacterial overgrowth
Prevents Soft Shell & Abnormality Moulting Phase
During abnormal molting phase, shrimps will have weak conditions such as soft shells and slow growth. These phenomenon have happened mainly due to lack of nutrition, lack of calcium source or some bacterial infections. The soft shell by bacterial infection is usually accompanied by abnormal body color, muscle turbidity, red body, etc.
Shrimps need a well balanced diet to accumulate considerable energy before molting. Each molting is the weakest period of the shrimp body. It is easy to infect on shell by the pathogen. The application of bile acids as a feed additive in regular intervals, the bile acid starts synthesis of nutrition rapidly and prevents the soft shell, abnormal molting, shell problems etc in shrimp’s body.
Growth Phase & Frequency of Molting: Shrimp’s molting activities are affected by endogenous and exogenous factors. The tissue growth of shrimp is conducted after molting and each absorbent enlargement after molting process. This is a major process of volume increase, followed by is a process of organizational growth.
The main endogenous factors mainly molting hormone (MIH) level effect of molting times on shrimp. Shrimp can use cholesterol from feed to synthesize molt ketone. The shrimp is capable of synthesizing cholesterol which can only be obtained from feed.
Therefore, in order to accelerate the speed of growth and metamorphosis, the use of bile acids has become an important tool to improve the molt frequency on shrimp. The bile acids can significantly promote the growth of shrimp.
Improve the Survival Rate: The bile acids improve the survival rate in shrimp due to proper development of immunity systems in body, utilization of nutrition, lower mortality rate etc. The bile acid also has strong anti-stress ability and it improves the level of SOD, GSH-Px and GR.
Control of WFS by Using Bile Acids: White fecal Syndromes (WFS) & White Gut disease in shrimp causes due to infection to hepatopancreas by pathogens in different sources. The long-term addition of bile acids in shrimp diet, the bile acids protect the hepatopancreas from the fundamental prevention of shrimp affected on WFS.
Prevents Hepatopancreas Necrosis (EMS/HPNS): The Vibrio parahaemolyticus, harmful physicochemical factors of pond and toxic algae are the direct cause of shrimp hepatopancreas necrosis. Also, the following factors are responsible for this disease like disorders of ecological farming system, low stress resistance, high load of harmful pathogens and toxic algae. The regular feeding with bile acid to shrimp, the hepatopancreas can be protected and prevented from the infections.
Sustainable Shrimp Culture Practice with Bile Acids
The feed is the biggest source of nutrient loading in aquaculture production and its impact is essential for sustainable development, either intensive or semi-intensive. This will help reduce negative impacts and improve predictability of environmental effects.
Nutrition and feeding will play an essential role in the sustained development of shrimp culture practice. Growth, health and reproduction of shrimp and other aquatic animals are primarily dependent upon an adequate supply of nutrient, both in terms of quantity and quality, irrespective of the culture system in which they are grown. Supply of inputs (feeds, feed additives etc.) has to be ensured so that the nutrients and energy requirements of the species under cultivation are met and the production goals of the system are achieved.
The dietary supplementation of exogenous bile acids as a feed additive in shrimp diets can effectively improve the utilization and digestibility of fat, provide fat with more energy. Bile acids help to improve growth performance, lower feed costs, sustain feed quality, reduce fat deposit in the liver, prevent fatty liver, bind to endotoxins, eliminate endotoxins out of the body and protect the intestine and liver health.
Feed additives “bile acid” contribute to sustainable aquaculture by supporting profitability, feed efficiency, water/pond quality, pellet quality and support health performances. Bile acids lead to many of the factors involved in sustainable culture practice such as improved feed efficiency, lowers feed costs and reduced environmental discharges. Also, bile acid feed additives make mycotoxin risk management solutions for profitable and sustainable aquaculture.
Without Bile Acids: Cell nucleus deviation, cell nucleus is not clear; a large number of fat drops in the cell. With Bile Acids: hepatopancreas cell are densely arranged, cell nucleus is intact, cell membrane boundaries are clear, and hepatopancreas cells are healthy).