Culture of aquatic animals especially fish culture has undergone a dramatic worldwide growth in the last few years. The aquaculture industry is the fastest growing food production industry in the world and approximately 50% of all fish consumed by humans is from aquaculture (Thorarinsdottir et. al., 2011). Nutrition plays a vital role in improving animal productivity (Jacob and Raj, 1987). Understanding about the nutritional requirements and production of fish feed is essential to the development and sustainability of aquaculture as the industry has matured.
Prepared or artificial diets may be either complete or supplemental. Complete diets supply all the ingredients, protein (18-50%), lipid (10-25%), carbohydrate (15-20%), ash (< 8.5%), phosphorus (< 1.5%), water (< 10%), and trace amounts of vitamins, and minerals necessary for the optimal growth and health of the fish (Craig and Helfrich, 2002). Nutritionally complete feeds should be used when fish are reared in high density indoor systems or confined in cages and cannot forage freely on natural foods or natural foods are absent or where natural foods only make a small contribution to nutrition. When substantial amounts of natural productivity are available, supplemental feeds (incomplete, partial) don’t need to contain all essential nutrients and are intended only to help fortify the natural foods with extra protein, carbohydrate and lipid in the culture systems.
Feeds can be farm-made single component feeds like rice bran or mastered oil cake to commercial feeds. Kitchen wastes may also be considered as one of the types of farm-made feeds produced economically for a small scale culture venture. Farm-made or on-farm feeds consist of one or more artificial and/or natural ingredients, produced for a particular farming activity and not for any commercial purpose. Mixtures of ingredients subjected to some form of processing (simple mixing, grinding and cooking) done on-farm or in small processing plants are generally regarded as farm-made feeds and are often used in small-scale semi-intensive aquaculture practices. Commercial feeds are formulated and manufactured from a homogenous mixer of several ingredients, in various proportions that ensure precise quality targets in terms of size and texture, stability and nutritional composition at a highly competitive price. Commercial complete feeds are used usually in intensive and semi-intensive practices.
Some feeds are formulated with antibiotics for treatment of Vibriosis, and other bacterial infections are sometimes called medicated feeds.
A. Feed Types:
Feeds can be produced either by steam processing, producing compacted, pressure-pelleted (sinking) feeds; or by extrusion, which produces expanded floating or buoyant feeds.
In general floating feeds offer numerous advantages over their sinking counterparts. Raw materials are propelled by screws along the barrel of the extruder machine to cook the materials at 120-175ºC for about 30 seconds. The homogenous cooked mixture is forced through a die at high pressure. The material expands because of the pressure difference. Floating feeds are more digestible as a result of cooking process and the heat and pressure deactivate destructive enzymes as well. Increased starch gelatinization helps the feed to be more stable in water by disintegrating less quickly that gives enough time to the fish to take the meal completely. Moreover, the farmer can directly observe the feeding intensity of his fish and adjust feeding rates accordingly determining whether feeding rates are too low or too high is important in maximizing fish growth and feed use efficiency. Another side effect is that farmers can visually monitor the health condition of the reared fish as they come to the surface to take feed.
In contrast, floating feed can be detrimental with respect to consumption by competitors and some fish species.
Sinking feeds are solid feed pellets that submerged during application. Bottom feeder shrimp, for example, prefer sinking pellets (density greater than that of water, 1 g/cm3) and will not accept a floating feed (Craig and Helfrich, 2002). The farmer cannot always estimate feeding rates properly in relation to the biomass present in his pond and feeding whether too low or too high than the actual requirement. It cause lower weight gain in a particular age and enlarge the culture period when feeding rate is low. In the other hand, overfeeding causes subsequent loss of feed supplied as well as deteriorating water quality that may results in a number of problems.
B. Feed Ingredients:
Wide ranges of ingredients are used in preparation of aquafeeds. They include aquatic and terrestrial plants (Duckweeds, Azolla, Water Hyacinth, etc.), aquatic animals (Snails, Clams, etc.) and terrestrial-based live feeds (Silkworm Larvae, Maggots, etc.), plant or grain processing products and byproducts (De-Oiled Cakes and Meals, Beans, Grains and Brans) and animal-processing by-products (Meat and Bone Meal, Bone Meal, Blood Meal, Feather Meal, etc.). There are more than 35 low price raw materials found locally in Bangladesh can be used in the preparation of supplementary feed of fish and shrimp (Ali and Hoq, 2010).
Table 1: Ingredients used commonly as sources of protein, carbohydrate and fat.
|Protein||Fish meal, Dry fish, Soybean meal, Meat and bone meal, Rape seed cake, Mustered oil cake, Soy protein concentrate, Blood meal, Krill meal, Maize gluten.|
|Carbohydrate||Rice polish, Maize, Flours, Wheat meal, Extruded gelatinized starch.|
|Fat||Fish oil, Vegetable oil, Crude oil, Full fat soybean.|
A wide variety of additives are used that would have positive effects on growth and feed conversion without causing bacterial resistance to fully utilize valuable raw materials in feed pellets.
C. Feed Production:
Production of feed includes two major steps as feed formulation and processing or preparation.
Feed formulation is the process of quantifying the proportion of ingredients to be put together, to form a single uniform mixture or pellet that will provide all the nutritional requirements of the target fish. It is a central operation in feed production, ensuring that feed ingredients are economically used for optimum growth of reared species. It requires a good expertise in fish biology and nutrition along with a deep knowledge about feed ingredients and their roles. Most large-scale fish farmers depend on commercial feed mills for their feeds, to obviate the need to do their own formulations or feed preparation. It is therefore essential that formulations are accurate, to ensure that cultured fish are not adversely affected. Feed formulation is a science and an art at a time, requiring knowledge of feed and fish in view of economic aspects when using formulae.
Feed formulation can be done in two major steps as,
- Ingredient selection and restrictions and
- Identification of nutritional specifications.
- Drying and
D. Feed Characteristics:
Flavor and taste
Flavor and taste of feed is especially important in the case of bottom feeding animals. Smell can be detected by the specific anatomical receptors in fish, but flavor has to be dissolved in water for the fish to locate it. Some fish have receptors in their mouths, or on the head or lips. Some even have taste receptors on their skin. These receptors carry messages to the brain and tell the fish to swim towards the food. Some kinds of food can strongly stimulate fish to feed by their flavor.
Color and Buoyancy
Some fish that are used to feeding on floating feed may not take to sinking feed that has sunk to the bottom. Similarly, bottom feeders rarely come to the top of the aquarium to eat food. A majority of the fish species in the tropical variety are however not very picky when it comes to the buoyancy of food.
A fish can “hear” sounds through the vibrations that take place in water. By picking up these vibrations in water, fish become aware of the feeding frenzies that cause many fish to conglomerate when the feeding begins. Also, there are fish that are so used to a routine in their feeding that they start grouping when they hear sounds that normally precede feeding.
Sizes of pellets
Feeds are produced in a variety of sizes on the basis of the die diameter and the cutter blade action. The pellet size ranges from fine powder for small fries or fingerlings to 1/2 inch or larger pellets. The pellet size must be limited to about 20-30% of the diameter of mouth opening of the fish species concerned. In case of feeding too small pellets than the appropriate size, more energy have to be used by the cultured animal during searching and eating more pellets that results in inefficient feeding. On the other hand, pellets that are too large will depress feeding and may cause choking in severe cases.
E. Maintaining feed quality:
A variety of factors govern the quality and wholesomeness of aquafeeds. Feedingstuffs origin, processing, handling and storage, as well as many other factors related to the market, can affect at different levels both quality and safety of feed (Pinotti and Dell’Orto, 2011). Feed quality can be ensured initially by using good quality ingredients. Purchase of raw materials must conform adequate quality, traceability, environmental sustainability and safety standards.
Feed manufactured in the factory is usually of desired quality, but that level of quality may have been fall by the time it reaches a farmer’s pond finally. Commercial fish feed is usually purchased by large farms as bulk feed in truckloads and stored in outside bins (Craig and Helfrich, 2002). Finished feeds undergo deteriorative changes during storage which not only lower their nutritive value below minimum specifications but also affect their palatability and appearance. Feeds should be stored in dry, well ventilated warehouses out of direct sunlight with a minimum temperature change to reduce micro-climatic variations and containment for control of pests. All feed should be used within two months of manufacture and inspected regularly. During long storage there may arise growth of mould, degradation of vitamin potency and fat rancidity. Unnecessary handling damage the feed bags and creates dusts that are not usually consumed by fish and wasted. Pests (i.e. mice, rats, roaches) must be controlled strictly in the storage, to avoid contamination. Proper storage is a simple, but an important part to keep the products at a high quality.
Nutritionists, industry, farmers, and overall the government authorities have to pay attention to animal feedstuff production processes, thereby acknowledging that animal feed safety is an essential prerequisite for human food safety (Pinotti and Dell’Orto, 2011).
- Ali, M. Z., and Hoq, M. E. 2010. Improved Fish Feed Management in Aquaculture. Extension Manual No. 38. Bangladesh Fisheries Research Institute, Mymensingh.
- T. Jacob and R. Paul Raj. 1987. Linear Programming Technique In Fish Feed Formulation, (In:Summer Institute In Recent Advances In Finfish And Shellfish Nutrition) Central Marine Fisheries Research Institute, Cochin, India.
- Steven Craig and Louis A. Helfrich, 2002. Understanding Fish Nutrition, Feeds, and Feeding, Virginia Cooperative Extension, Virginia Tech. pp 420-256.
- K. W. Chow, Quality Control in Fish Feed Manufacturing, Food and Agriculture Organization, Rome, Italy.
- Luciano Pinotti, Vittorio Dell’Orto. 2011. Feed safety in the feed supply chain. Biotechnol. Agron. Soc. Environ. 15 (S1), 9-14.
- Thorarinsdottir, R. I., Jokumsen, A., Björnsson, B. T., and Torrissen, O., 2011. Local raw materials for production of fish feed for aquaculture, Nordic Innovation Centre – Project no. 10102.