Commercial fish feeds usually contain high fish meal as the major protein source, ranging from 30-50 per cent (Hardy, 1995). But now-a-days, fish meal is generally avoided in the feed due to its scarcity and high cost. Hence, aquaculture nutrition have been trying to improve the nutritional value of fish feed by enzyme supplementation, to find suitable alternatives to fish meal, since last decades, stated Prakash Chandra Behera, Technical Manager of AQUA, PVS Group, India.
Feeding enzymes to shrimps and fishes is one of the major nutritional advances in the aquaculture sector since last few years. Exogenous enzymes are now extensively used throughout the world as additives in animal diets. Also, supplementation with enzymes can help to eliminate the effects of antinutritional factors and improve the utilization of dietary energy and amino acids, resulting in improved performance of fish/shrimps (Farhangi and Carter, 2007; Lin et al., 2007; Soltan, 2009).
The primary purpose of enzyme application in feeds is to improve digestion. The digestive processes will work better and result shown in improved feed efficiency by providing an extra dose of enzymes. Further, aquatic animals are lack certain digestive enzymes during early development or throughout their life. In the case of fishes / shrimps lacking certain enzymes even in adulthood, application of these enzymes results in better utilization of nutrient fractions that are digested by the enzymes.
Enzymes are one of the many types of protein in biological systems. Their primary characteristic is to catalyze the rate of a reaction but is not themselves altered by it. They are involved in all types of anabolic and catabolic pathways of digestion and metabolism. Enzymes tend to be very specific catalysts that act on one or ,at most a limited group of compounds known as substrates. Enzymes provide additional powerful tools that can inactivate anti-nutritional factors and enhance the nutritional value of plant-based protein in feeds. They provide a natural way to transform complex feed components into absorbable nutrients.
The addition of enzymes in feed can improve nutrient utilization , reducing feed cost and the excretion of nutrients into the environment.
Sources of Enzymes:
Enzymes are produced in every living organisms from the higher animals and plants to the simplest unicellular forms of life as they are essential for metabolic process. Microorganisms that generally involved in production of various enzymes are:
Bacteria: Bacillus subtilis, Bacillus lentus, Bacillus amyloliquifaciens and Bacillus stearothermophils.
Fungus: Triochoderma longibrachiatum, Asperigillus oryzae , Asperigillus niger and yeast
In animals, digestion of food is carried out by the animal’s digestive system and by microorganisms that inhabit the intestinal tract. The bacteria present in the gastrointestinal tract of fish/shrimp are potent producers of proteolytic enzymes. They may also produce cellulase moderately. The adding of live microorganisms to diets to produce enzymes is possible in specialty feed applications. Large scale commercial enzyme applications are rely on enzymes produced by microbial fermentation technology.
Anti Nutritional Factors in Aquafeed
Feed ingredients from plants sources contain some compounds that either the shrimp/fish cannot digest or which hinder its digestive system because they cannot produce the require enzymes to degrade .Though the palatability of many plant materials has demerits, anti-nutritional factors are the most serious concern in replacing the fishmeal completely in feed formulations. Anti-nutritional factors have an adverse impact on the digestion of feed and its efficiency. There are many kinds of anti-nutritional factors and they are associated with the most widely used plant materials like trypsin inhibitor proteins, glucosinolates and phytate.
Heat inactivation and water soaking are the two common detoxification methods used to overcome most of the anti-nutritional factors.
Factors contributing to use of Enzymes
- Increase need for quality food grain for fish/shrimp
- Increase need for quality animal products /by –products
- Search for alternate sources of food with better nutritive value
- Economic margins(reduced cost : benefit cost)
- Quick realization of profits
- Rise of environmental awareness
Types of Enzymes available for Fishes / shrimps
Many enzymes have been used in fish/shrimp nutrition over the past several years which includes cellulose, (β-glucanases), xylanases and associated enzymes like; phytase, proteases, lipases and galactosidases. Enzymes in the feed industry have mostly been used for culture animals to neutralize the effects of the viscous, nonstrach polysaccharides in cereals and other food grains.
Action & Benefits of Feed Enzymes:
- Reduces in digesta viscosity
- Enhances digestation and absorption of nutrients especially fat & protein.
- Improves Apparent Metabolizable Energy(AME) value of the diet
- Increases feed intake, weight gain and feed gain ratio
- Reduces ammonia production
- Improves nutrient Digestibility.
Endogenous enzymes found in the fish/shrimp digestive system which help to break down large organic molecules like starch, cellulose and protein into simpler substances.
The carbohydrate digestion improves by using microbial enzymes. Addition of exogenous carbohydrates enzymes to feed increase utilization of unavailable dietary carbohydrates .High levels of non-starch polysaccharides (NSP) such as cellulose, xylans and mannans reduce the nutritive value of many plant ingredients. Intestinal enzymes to digest these carbohydrates are not produced by most animals.
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