Fish as a source of animal protein has played an important role in the nutritional budgeting of many nations. Fish production is becoming a very important source of valuable protein food. Fishmeal is the major protein source in aquaculture feeds. However, the supply of fishmeal is not growing worldwide and the price is often high, so the replacement of fishmeal with cheaper protein sources is needed. Chicken viscera are among such protein sources replacing fishmeal. Viscera are the large organs inside the body: such as the heart, lungs and stomach. Research findings has revealed that certain chicken visceral organs such as heart contain over 80% protein of excellent quality while traditional fish meal normally contain 60 – 80% high quality protein.
Fish meal, or fishmeal, is the most important component in fish feed formulation. It is a commercial product made from fish and the bones and offal from processed fish. It is a brown powder or cake obtained by drying the fish or fish trimmings, often after cooking, and then grinding it. If it is a fatty fish it is also pressed to extract most of the fish oil. Fishmeal is a nutrient-rich and high protein supplement feed ingredient that stores well, and is used primarily in diets for domestic animals and sometimes as a high-quality organic fertilizer. Fish meal and fish oil replacement has been the focus of very significant research efforts and hundreds of scientific papers in recent years. Despite years of research, fish meal and fish oil remain very important, quasi essential, components of successful commercial feeds for most fish and crustacean species. This generally has an impact on the feed and production costs for many aquaculture products.
Over the past five decades, dozens of different protein and lipid sources have been evaluated in hundreds of “practical” feeding trials. Many of these trials focused on replacing fish meal, fish oil or other high quality protein and lipid sources by putatively more cost-effective protein and lipid sources. What is often overlooked in many trials is that fish meals and fish oils are complex ingredients that are known to vary greatly in chemical composition. The raw material sources and types, seasons, and processing equipment and conditions used in the manufacturing of these ingredients all have great impacts on the chemical composition and nutritive value of these ingredients. Incorporating "20% fish meal in the diet" or "replacing 50% of the fish meal or fish oil of the diet" may mean very different things depending on the type and chemical composition of the fish meal and fish oil used in the study and the fish meal and fish oil levels in the control diet for such a reason, the composition of the ingredients to be used for replacing fish meal must be determined.
PROTEIN AND AMINO ACIDS UTILIZATION
Protein is the principal constituent of the tissues and organs of fish body and therefore an essential nutrient for both maintenance and growth in fish. The requirement for proteins in fish are therefore very obvious since protein constitute above 45 -47% of the tissues dry matter. A continual supply of protein is needed throughout life for maintenance and growth. Catfish, like other animals, actually do not have a protein requirement, but they require a source of non specific nitrogen and indispensable amino acids. Usually the most economical source of these elements is a mixture of proteins in feed stuffs Ingested proteins are hydrolyzed to release amino acids that may be used for synthesis of tissue protein or if in excess, used for energy. Use of protein for energy is expensive, thus catfish feed should be balanced to assure that adequate levels of non specific nitrogen, amino acids and non-protein energy are supplied in proper proportion.
It is more precise to formulate fish feed based on amino acid requirements. Nutritionally, amino acids may be classified as either indispensable (essential) or dispensable (non-essentials). An indispensable amino acid is one that the animal cannot synthesize in quantities. Sufficient for body needs, thus they must be supplied in the diet. A dispensable amino acid is one that can be synthesized by the animal in quantities sufficient for maximal growth. Most simple - stomach animals, including catfish require the same 10 indispensable amino acids.
Table 1: Amino Acids Requirements of Catfish
JUSTIFICATION FOR CHICKEN VISCERA AS A REPLACEMENT FOR FISH MEAL
Fish meal is the most important component in fish feed making. Fish meal contains 60-80% protein of excellent quality, which is highly palatable to fish. Since fish meal is a good source of essential amino acids, it is often used to supplement feeds containing plant proteins. Fishmeal is also rich in energy, minerals and essential fatty acids. It is used at levels up to 50% in catfish fry feeds, up to 12% in catfish fingerling feeds and from 0-8% in grow-out fish feeds. Fishmeal remains the major dietary protein source in fish feed but escalating cost, uncertainty unavailability and lesser quantity has necessitated the use of other protein sources to reduce feed cost without compromising growth. Therefore, efforts have long been directed to find alternate protein sources of good quality which are less expensive and readily available as substitutes for fish meal component in practical diets. A chief and readily available source of high quality animal protein is chicken viscera which are considered as a waste in the poultry industry. In poultry processing industry, viscera accounts for nearly 30% of the byproducts. Fish meal is a major protein source in aqua feed especially for carnivorous species. Increasing demand, unstable supplies and high prices of fish meal with the expansion of aquaculture have made it necessary to search for alternative protein sources. Moreover, price of fishmeal is often high. It is neccesary to replace fish meal with cheaper protein sources Plant protein sources such as defatted soybean meal and corn gluten meal are good candidates as fish meal substitutes. However, those ingredients contain anti-nutritive substances such as phytic acid and also lack essential nutrients such as taurine. For such reasons, that is why the use of animal protein source is necessary and the cheapest and more reliable animal protein source that is readily available in most countries of the world is chicken viscera.
One of the greatest challenges in contemporary aquaculture especially in relation to fish nutrition is finding a desirable replacement for fish meal. Researchers from all over the world have been conducting researches in order to find replacement for fish meal from both animal and plant sources. However, there are certain disadvantages that are associated with the replacements from plant sources ranging from low nutritious value to lack of essential amino acids. On the other hand, an animal source gives better results. Researches on chicken viscera have revealed fascinating results and more work is being done by scientists from all over the world. My current research focuses on proximate analysis of chicken viscera as a potential replacement for fish meal in Pangasius culture. It is hoped that the ending results will reveal more clues that will justify chicken viscera as a potential replacement for fish meal.
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