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Fish Feeds and Feeding the Fish |
Major Nutritive Factors in Fish Feed
Fish feed is to feed fishes including prawns and shrimps to produce the energy and essential nutrients they need for their maintenance, movement, normal metabolic functions and growth. And the fish feed can be natural food or/and supplied by fish farmers. The requirements of fish feed are different in quantity and quality according to their different sizes, reproductive states, feeding habits and digestive anatomy. And also the feed requirements are influenced by environmental variations such as temperature, the resources of natural food available.
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The major nutritive factors in fish feed are the macro-nutrients that are protein, amino acid, fat and carbohydrate; and the micro-nutrients that are vitamins and minerals.
1. Protein is the most important nutrient in fish feed, and fishes have a high demand for the amount of protein in their feed. The protein amount varies according to fish species and growing phases, that is carnivorous fishes > omnivorous fishes > herbivorous fishes, and young fishes > old fishes. The protein digestion and absorption differ from fish species, water temperature, feed ration, physical and chemical properties of fish feed.
2. Animo acid is the component of protein. Protein is digested and absorbed by being resolved into animo acid through the enzyme. There are 10 kinds of needful animo acids can not be synthesised in fishes, which should be kept balanced in amount of fish feed for fishes growing well.
3. Proper amount of fat improves the digestible energy in fish feed and reduces the feeding of protein feed. Feeding fishes with high-fat feed before winter can reduce fish death in low-temperature period. But excess
fat in feed will affect the quality and edibleness of fishes, so the fat amount in fish feed should be 4%-10%.
4. The fish has a great need for carbohydrate (saccharides, starch and cellulose), because the carbohydrate is the energy source for them. To make fishes have good protein digestion and grow in good condition, the carbohydrate of fish feed should be in a specified volume.
5. Vitamins are complex organic compounds required in small amount for normal growth, reproduction, health and general metabolism, and they are rich in all kinds of fresh food. Vitamins especially vitamin C and vitamin A are easily damaged by heat or light, so good feed machine, reasonable techniques and right storage are necessary.
6. Minerals include macro-elements and micro-elements. They are important for the development of fish bones, and they are the catalyzer of enzyme working system for improving fishes’ absorbing and utilizing nutrients. What have to be considered when adding minerals in fish feed is the content of minerals in the water where fishes live.
Reasonable Nutrition Requirements of Fishes
1. The need for protein
—herbivorous fishes: 22%-30%
—omnivorous fishes: 30%-40%
—carnivorous fishes: 38%-55%
Tips: the need for protein of the same kind of fish increase with water temp rise
2. The need for amico acid
Arginine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, valine
3. The need for carbohydrate
—temperate-water fishes: 30%
—cold-water fishes: 21%
—carp and grass carp, etc.: 30%-50%
4. The need for fat
Fishes have high digestion rate for the fat, especially for the low-melting-point fat and the digestion rate is above 90%. the major fat that fishes need is the The usual fat is minuent unsaturated fatty acid (n-3&n-6). Fat is an important-economical energy source for fishes, and the usual amount of fat in fish feed is 5%-6%, the maximum can be above 10%.
5. The need for vitamins
—the fish has short intestinal tract, so synthetic vitamin C is not available for it.
—some vitamins should be added in fish feed directly, because the fish has poor abilities of compounding them.
—the need for high-protein, low-energy feeds of fishes means the fish has a great demand of vitamin B that helps the amino acid metabolism.
How to Feed Fishes with Different Fish Feeds
1.Concentrated grain-cake feed: it should be cracked, soaked and ground into pulp for fingerlings, and macerated for medium-sized and large-sized fishes.
2.Raw cereal feed: big cereal grains like the corn need to be crushed before feeding fishes; small cereal grains like the millet can be sprouted before feeding fishes, because the fresh baby sprouts are rich in nutrients and easy to digest, which turns out to be good for fishes growth.
3.Green forage: direct feeding after removing the dirt from the green forage is for medium-sized and large-sized fishes; splashing feeding after cutting or pulping and combining with 0.2% salt is for small-sized fishes, and it is better if cut the green forage, then boil it and mix with bran.
4.Fermented bran feed: the fermented bran have to be macerated and ground to feed small-sized fishes; and for medium-sized and large-sized fishes, it need to be fermented till there is winy smell. The first-time feeding should be a small quantity, and increased gradually (can not be more than 30% of the daily ration).
5.Protein fodder: earthworms, larvae of flies, insects, etc. are the first-rate animal protein feed for fishes, and they can be fed to fishes directly or used with other feeds after dried and processed into powder. The block animal protein feeds must be ground and mixed with binder to make them into bulk to raise their utilization rate. And fishing by-catch or small fishes are suitable for marine fishes.
6.Manure feed: manure of chickens, pigs, cattle, etc. all can be fish feed. The manure is dried, then processed into powder and combined with other feeds at a certain proportion. The proportion is 40%-50% chicken manure, 50%-70% cattle manure, 30%-50% pig manure.
7.Pellet feed: fish feed pellet usually has a diameter of 2.5-8mm and a length of 5-10mm. Direct feeding is available, but if the fish pellet feed is moist, it should be dried first; it can not be used if it has gone bad.
Fish Pellet Feed Production Equipment
1. Fish pellet feed curing equipment: usually there is a steam curing device equipped on the hard feed pellet machine to enhance pellets’ cohesiveness, making them not disperse so fast in the water.
2. Puffed feed pellet equipment: it is a product of developing mew-type feed by puffing pig hair, feather, livestock feces to make them into feedstuff; puffing soybean meal, vegetable cake, cottonseed cake, etc. to remove the toxin from them.
3. Feed pellet coating machine: to prolong the qualitative time of feed pellet, the feed pellet machine can be equipped with a feed pellet coating machine. If the produced pellet has a high moisture content that more than 16%, it should be dried before coating.
4. Fresh-soft feed pellet production unit: grind the fresh-live feedstuff into paste and mix with other powder feed, then process the mixture into fresh-soft pellet feed to keep the active substances in the live feed.
5. Fish feed pellet production unit of one-step process: the production done by this production unit needs no steam added in the feed, so it is dry-in and dry-out. If the moisture content of raw materials is less than 12%, and the moisture content of the final product is less than 10.2%, there is no need for drying.
6. Sinking-floating fish feed pellet production unit: the product produced by this unit is recommended for prawn by the U.N., which do not disintegrate in the water and then rise to the water surface after a couple of hours, reducing water pollution and saving fish feed.
7. Normal temperature and normal pressure floating fish feed equipment: this fish feed equipment has no heating device. Under normal temperature and normal pressure, the produced feed pellet can float promptly and keep not disintegrate for hours.
8. Micro-capsule fish feed production unit: featured by natural coating and spray drying for micro fish feed pellets that have a diameter of 5-10 micrometer, and 0.8 million pellets per milligram.
9. Superfine grinding unit: to make fish feed easy to digest, usually the no-screen superfine grinding technology is applied to feed the biggish fingerlings or as the raw materials for pellet feed.
Qualified Fish Pellet Feed
The pellet feed for fishes should be of smooth surface by finely grinding the ingredients, high curing rate, balanced nutrition, good palatability and high water stability which should be at least 30 minutes. Sizes of fishes determine the diameter of fish feed pellet, and generally pellet length is 2 times of pellet diameter, which means a proper size for feeding fishes and a cost reduction.
About Water Stability
Water stability of fish feed pellets is important, especially for prawns, because the pellet should remain intact in water until it is ingested. The water stability of the feed pellet depends primarily on how well the individual ingredients bind together. And high water stability can be achieved by:
1. Using finely ground ingredients to fill up the small cavities on the surface of the pellets to reduce the rate of water penetrating into the pellet.
2. Using pelleting machine to increase the compaction of the ingredients mixture.
3. Cooking the ground ingredients or the moist pellets to increase the proportion of the gelatinised starch.
4. Avoiding high concentration of fat, water repellent or highly water-absorbing ingredients in the pellet production mixture.
5. Taking use of binders, such as starchy plant products that includes palm starch, cassava starch, potato starch, bread or wheat flour, rice and maize, and other aquaculture binders include alginates (seaweeds), carrageenan, plant gums (guar gum, locust gum, gum arabic), agar, high-gluten wheat flour, chitosan, propylene glycol alginate, gelatin, carboxymethylcellulose (CMC).
Estimating the Right Amount of Fish Feed Required Per Ration
Fishes’ feed intake and metabolism change with fishes’ ages and sizes, air temperature, water temperature and PH value. In order to avoid over or under feeding the fish, right amount of feed must be given each time. The amount of feed to be provided to the fish per day, the feeding rate, depends on the fishes’ body weight. Fish adjust their food consumption rates to meet their metabolic energy requirements. Therefore, the required ration varies with time during the production cycle depending on:
1. The fish size (i.e. its average weight)
2. The pond water quality (water temperature, dissolved oxygen and pollutant levels)
The amount of feed required per ration can be calculated as follows:
The amount of feed required per ration=average fish size (weight)×feed rate (%) ×total number of fish in the pond
Where, the feed rate is the feeding amount as a percentage of the fish’s average weight.
When the water temp rises to above 15 ℃ in spring, the feed ration can have a gradual increase, and the daily ration is about 1% of total fish weight, also a small amount of concentrated feed is needed. When the water temp rises to above 20 ℃, daily ration is about 2% of total fish weight; water temp is around 30 ℃, daily ration is 4%-5% of total fish weight, because fishes have a great appetite at this time for growing fast, but overfeeding is not allowed and what is necessary is to adjusting water quality to avoid pollution. The water temp starts to fall in autumn, large amount of feeding has to be kept, because autumn is still a growth season for fishes, and daily ration is 3% of fishes’ total weight. Water temp in winter has a sharp decline, daily ration should be 1%-2% of fishes’ total weight to keep their fatness.
How Many Times Fishes Should be Fed Per Day
The number of times the fishes are fed per day is the feeding frequency. To obtain high efficiency of feed utilization and optimal fish production, the following conditions should be taken into consideration:
1.For optimum growth and feed conversion, 4-5 times feeding per day is enough, but in grow-out ponds, feeding 2-3 times a day is adequate.
2.Juvenile fishes need to be fed more frequently that adult fishes, because they are higher in metabolic rates and their stomachs are too small to hold all the feed they require for one day.
3.It is better to give frequent feeds in small quantities.
4.Observe how fishes respond to frequent feeding and portion the feed appropriately.
5.Record the daily feed amount to detect any drop in consumption, it also helps the calculation of feeding cost and FCR (feed conversion rate).
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Well-storing Means Full Economic and Nutritional Value of Fish Feed
Fish feeds, like most food products, have a finite shelf life and special handling requirements. In order to realize full economic and nutritional value of these feeds, it is necessary to store and handle them properly. The feed ingredients also has to be kept well. Fish feeds and ingredients of them require special care during storage to prevent deterioration in quality. Because environmental factors, such as moisture, temperature, light and oxygen influence deterioration and losses in them.
1. Fish feed ingredients storage
Ingredients should be stored for as a short period of time as possible, especially in tropical conditions. The storage depends on the type of ingredient.
As mentioned above, since vitamins can be ruined easily and they are expensive ingredients, they need special care of being kept either in the manufacturers’ containers or in airtight lightproof containers under air conditioning or refrigeration. Vitamin stock should be turned over at least every six months.
Fat must be kept in sealed plastic containers which is preferable, in a cool and dark place.
Dry feed materials should be protected from rain in a building with good ventilation.
2. Fish feed storage
For reasons of cost and convenience, dry diets and low moisture feed are presently widely used feeds in aquaculture. These include extruded feeds, hard pellets, crumbs and flakes. The general rule for preservation of these feeds is to store them in a dry, well-ventilated area that affords some protection from rapid changes in temperature. Cooler temperature are best. A good storage facility should also provide adequate containment for control of pests.
High moisture trash and moist pellet feed can be kept about one week when stored at a low temperature of -20℃. Otherwise, they must be used immediately after purchased or manufactured.
