Most aquatic farming systems are intensive or semi-intensive, especially for fish and shrimp. Intensive fish farming requires extra food for stocked fish. As a result, the cost of such cultivation is high. The main purpose of fish feed preparation and formulation is to mix nutritional value and balanced ingredients which keep the growth, reproduction and health of the fish exact and also keep the cost within range. The food must be palatable to the fish and must contain no antioxidants. The food should be such that it maintains the quality of the fish meat and does not change the quality of the water too much.
Aim of Fish Diet Preparation
Proper nutrition is an important factor which affects the growth, reproduction and longevity of farmed fish. Fish nutrients vary from species to species and even from different stages of the life cycle of the same species. The main objective of food preparation is to prepare food with locally sufficient food ingredients within the sustainable and tolerable cost so that balanced nutrients are available and maximum production is ensured by taking the required amount. Nutritional quality, adequacy of food items, production cost etc. must be taken into consideration while preparing food. Notable among these considerations are the taste of the prepared food, the anti-nutrients and the acceptability of the food.
The food is prepared mainly-
- The food should be one that meets all the nutritional needs. Such food is used in intensive farming methods.
- Prepared foods help or nourish natural food sources, especially phytoplankton and zooplankton. This type of food is used in semi-intensive farming methods and it is not necessary to have all the necessary nutrients in such food. This type of food is called supplementary food.
- Refined and semi-refined foods are commonly used in research to determine the amount of nutrients needed.
Forms of Diets
The composition of the food that is fed to aquatic animals, especially fish and shrimp, varies. Potential food-
- Living food, usually in the larval stage, is needed by most aquatic animals.
- Grass type of vegetative foods are supplied or grown on fish farms.
- Prepared food that comes in different types or textures.
Feed Ingredients
The food ingredients of animals and fish are mostly by-products obtained from human food processing plants. Different types of food ingredients are used for fish and shrimp. New (1987) identified the following 10 types of food.
- Grasses
- Leguminous plants
- Different types of fodder plants
- Fruits and vegetables
- Root crops
- Cereals
- Oil producing seeds and husks
- Animal by products
- Different food ingredients and
- Additives
Grasses
Organisms feed on such food by grazing it directly or by supplying it in large or in pieces. Dry grass is also used as cattle feed and in small quantities as a source of carotenoids in fish and shrimp feed. It is used in small quantities in the diet of fish other than herbivores due to its high fiber content.
Legumes
In the case of mammals, the stems and leaves of the legume are used as grass. Some of these (Epil Epil, Alfalfa etc.) are used successfully in fish feed. Legumes contain proteins (20-50%) and minerals. The seeds of leguminous plants contain adequate quality nutrients for fish. Legumes suitable for fish diet are acacia, pea, nuts, epil epil, bean, soybean.
Soybean meal is the most widely used legume food which is used as fish and shrimp food. It contains high levels of protein. According to Lim and Akiyama (1992), plant proteins contain significant amino acids that make up for the lack of essential amino acids in fish and are a good source of linoleic, linolenic acid and phospholipids.
Miscellaneous Fodder Plants
The leaves and aerial parts of various plants that grow as fodder are called fodder plants. Parts of such plants are boiled in water or dried in the sun and used as leaf meals. Foods made from such plants have been shown to be beneficial for fish (New 1987) . According to Ng and Wee (1987), leaf meals made from cassava (Manihot esculentus) make up 20% of the protein deficiency in Nilotica fish. Leucaena leucocephala, which is made from epil-epil leaves, meets up to 25% of the protein requirement of nilotica fish. It has no mal-nutrient elements. In Thailand, the Ipomea sp is used at a significant rate as a substitute for the Puntius gonionotus.
Root Crops
High levels of sugars are present in root plants. Hence, it is a significant source of fodder for cattle. Although it has limited use as a food ingredient in fish. Some parts of such plants are used as high quality human food and most fish species are unable to digest the sugars present in them. With few exceptions, root plants are deficient in proteins, calcium, phosphorus and vitamins. A small amount of the material obtained from the root is used in compound food. Since it contains toxins, it has to be purified through heat. Fish food from certain root plants have special properties in their diet, which increases the time it takes to float the food. Potatoes and cassava starch are used as additives.
Cereals
Grains and cereals are used as an important ingredient in fish feed as it contains high levels of sugars. In addition, the presence of starch in it helps to increase the time when food is floating in the water. Toxins are released from such ingredients by applying heat during food preparation. Cereals contain proteins and lipids. Although it is deficient in some amino acids (lysine), it is used in food as a high level of protein.
Oil bearing seeds by products
There are many types of plants that produce seeds or fruit oils. Vegetable oil factories produce large quantities of plant by-products that are used as animal feed. It contains high levels of protein and low levels of sugar. Oilseeds contain 20-50% more protein than cereals. But oil seeds do not contain essential amino acids such as lysine and threonine. Notable among the products used as fish food are soybeans, nuts, and soybeans. Sunflower, cotton, palm, poppy, rubber etc.
Animal by Products
Animal by-products are a very important component of fish diet. Such elements are rich in amino acids and vitamins. Animal derivatives, especially fish, have an unmarked growth factor such as food made from blood, bird fins, fish meal, meat, raw fish, fish oil, fish silage, shrimp mill etc. Like plant foods, animal foods lack essential amino acids. Blood contains high levels of leucine but low levels of isolysine. Leucine and isoleucine interact. As a result, when high levels of blood meal are used in the diet, leucine and isoleucine interact, resulting isoleucine deficiency in fish.
Notable among the animal by-products is the fish meal. Fish meals are mainly made from marine fish. The quality of fish meal is affected by different types of influencers, such as different types of raw materials, nature of drying and temperature. Anti-oxygen such as ethoxyquin (400-600 ppm) is added to the fish. Foods derived from marine sources contain polyunsaturated fatty acids.
In addition to fish meals, researchers have discovered some methods or techniques to further improve the use of fish by-products. One such strategy is fish silage production.
Fish Silage
Fish silage is made by self-digestion through common acidic medium, especially formic acid. Such an acidic medium prevents multiplication of digestive bacteria. But it also increases the activity of protein-digesting enzymes. The big problem with fish silage is that it is in liquid form. As a result it is less used as a suitable fish feed as it wastes a considerable amount of time during use and at the same time it increases the oxygen demand (BOD) of the reservoir or water body. In Norway, it is used sparingly to make soft pellet feed.
In Asia, especially in China and India, animal products such as silkworms, pupa compounds or single foods are used. Silk pupa is used directly in carp farming. In the case of semi-intensive fish cultivation, silk pupa is used as an additional source of protein in the pelated diet (Nandeesha et al. 1990).
Table: Average main ingredients in selected animal by-products (%)
|
Animal by products |
Water |
Crude Protein |
Lipids |
Crude fibers |
Nitrogen free extracts materials |
Ash |
Calcium |
Phosphorus |
|---|---|---|---|---|---|---|---|---|
|
Hen Eggs |
4.0 |
46.5 |
41.6 |
0.0 |
4.3 |
3.6 |
0.20 |
0.74 |
|
Fish meal |
|
|
|
|
|
|
|
|
|
Anchovy (Engraulis ringens) |
8.2 |
65.3 |
7.1 |
1.0 |
3.4 |
15.0 |
4.03 |
2.61 |
|
Herring(Clupea harangus) |
7.9 |
72.7 |
8.5 |
0.8 |
– |
10.1 |
2.04 |
1.42 |
|
Tuna (Thunnas spp) |
7.0 |
59.0 |
6.9 |
0.8 |
4.4 |
21.9 |
7.86 |
4.21 |
|
Various freshwater Fish |
9.0 |
66.7 |
9.1 |
1.0 |
– |
14.9 |
5.40 |
2.90 |
|
Fish Silage |
|
|
|
|
|
|
|
|
|
Tilapia(Oreochromis mossambicus) |
71.9 |
15.6 |
4.2 |
– |
– |
5.0 |
– |
– |
|
Herring(Clupea harangus) |
77.7 |
15.5 |
3.4 |
– |
– |
2.1 |
– |
– |
|
Mackerel (Scomber scombrus) |
70.2 |
16.9 |
12.0 |
– |
– |
2.1 |
– |
– |
Miscellaneous feed stuffs
Various other food ingredients are used in fish food. But their value has not been fully determined even today. Some of these compound materials are called Non-conventional Feed Stuff. Sugarcane is used as a non-conventional ingredient in other animals. Such non-conventional feed stuffs are mainly marine weeds, sugarcane by products, microbial proteins, algae, fertilizers and cellulose.
Additives
Additives are those materials which are used as small quantity in the fish feed during feed preparation to increase feed attraction, palatable to the species under culture system and to prevent disease, and microbial activities and to enhance the horse power efficiency of feed.
Additives is being used in animal feedstuff including-
- Synthetic amino acids
- Vitamins
- Binders
- Antioxidants
- Preservatives
- Prophylactic medicines(antibiotics)
- Hormones
- Antimicrobial agents
- Feeding stimulants
Feed Formulation
Food formulation is not very easy. It is a method where food is selected and mixed with the right amount of essential nutrients. Different ingredients are selected in the right proportions and mixed in a certain proportion which is nutritiously balanced, pelletable, flavorful and easily preserved. The basic information required for feed formulation is-
- Essential nutrients for cultivated species
- The diet of the species
- Locally adequacy, cost and nutrients of food ingredients
- Ability to use nutrients from different food elements by cultivated species
- Expected food intake
- Accepted food additives
- The type of food processing desired etc.
Numerous influencers are considered when formulated food is used in aquatic organism farming. In intensive and semi-intensive fish farming, the cost of food formulation is particularly important. During food formulation, proper supply of nutrients for different types of cultivable species is ensured so that the required 40 nutrients are present and the quality of the food is maintained. To this end, food adaptability, taste, food preparation methods, preservation methods and chemical contamination can affect the quality of food and the production of cultivated species. Undoubtedly, food formulation method is adopted considering the nature of fish cultivation. Formulated food in intensive farming system provides only supplementary nutrition to farmed fish.
Lal (1991) made some general observations that are important and consistent with all other food formulations. Such observations extend the various considerations which are mentioned below:
It is necessary to ensure that the improved food formula is nutritionally and economically advanced. Under normal circumstances, food prepared considering an economic aspect helps in producing healthy and disease resistant fish at low cost.
Food ingredients and their adequacy, seasonal changes, etc. are considered when preparing food. At different times of the year, food companies take advantage of the availability of different types of food ingredients at low cost.
When protein levels are stated, it is expected that the protein will be of good quality, easily digestible and acceptable levels of amino acids will exist. It is believed that satisfactory energy exists in food. Getting the right amount of protein, vitamins and minerals depends on getting the right amount of energy. Thus the balance energy in supplying nutrients is more complex than the proper amount of specific nutrients.
High quality food can be made from high quality food ingredients. Freshly prepared food is more palatable and acceptable than old food. Many vitamins in food are lost due to lack of proper storage. Lack of nutritional value in food is observed when food is not mixed properly or fish is fed in bad weather.
Factors to be considered in diet preparation
The different types of influencers affect the food formulation as mentioned below:
Essential Nutrients Requirements: Species, strains, fermentation stages, health, temperature and various environmental influences are taken into special consideration in culture methods. All these influences affect the essential nutrients.
Composition of Ingredients: Variations in the composition of food ingredients are observed regionally, seasonally, on soil fertility, food processing and storage. The most varied components are proteins and essential amino acids. It is necessary to separate food ingredients from enzyme inhibitors, other toxins such as alphatoxins and microtoxins.
Digestibility and Nutrient Availability: If food formulation is to be done properly, then it is necessary to have knowledge about the digestibility of every nutrient in all the components of the food.
Other Dietary Components: Certain food components are mixed with food for physiological or economic reasons. These are binders, antioxidants, etc. Such ingredients are mixed in small quantities and have no nutritional value or provide any energy. Addition of such substances is required when proper food is prepared.
Dietary Interaction: There are four types of nutrient interactions in fish. These are micronutrient-macronutrient interaction, mineral-mineral interaction, mineral-vitamin interaction and vitamin-vitamin interaction. Such interactions are influenced by a variety of factors, such as food ingredients, food processing methods, cultivated species and their age, and a variety of environmental influences. Different types of interactions are described below:
Micronutrient-macronutrient Interaction: A variety of influences on the metabolism of most nutrients, such as the quality and quantity of proteins, energy sources, etc., are also observed.
Thiamine adequacy is affected by protein and lipids in foods with the same caloric value. Studies on Onchorhynchus mykiss have shown that when thiamine-deficient foods are consumed at 150 C temperatures than those with high levels of thiamin-deficient lipid, thiamine-deficient diseases occur in fish and fish die at a higher rate. This is indicative of the effect of thiomine deficiency in foods with high lipid content. Similarly, there is a relationship between the metabolism of pyridoxine and the metabolism of proteins or amino acids.
Mineral-mineral Interaction: It has become possible to know the interaction of many essential minerals. The required magnesium depends on the calcium and phosphorus in the diet. Copper and zinc, on the other hand, act as opposites. However, according to Knox et al. (1981) it was not possible to know the increase in magnesium when the amount of calcium and phosphorus in the diet increased. Selenium interacts with sulfur, zinc, mercury and calcium. Selenium is a component of the anti-oxidant enzyme glutathione peroxide. Selenium is able to change the toxicity of other heavy metals.
Vitamin-mineral Interaction: Numerous vitamin-mineral interactions have been reported in fish. Fish absorb calcium from its peripheral environment through the gills and it also enters the intestinal mucosa through food. Hamilton’s (1989) study observed the interaction of vitamin D and calcium. According to him, the chemistry of water interferes with the metabolism of vitamin D in fish. Namirton (1984) reviewed the interaction of ascorbic acid and minerals. The two main interaction in fish are ascorbic acid and iron; ascorbic acid and copper.
Ascorbic acid (vitamin C) is involved in iron deficiency in fish. Vitamin C deficiency lowers blood serum iron levels. Rainbow trout have low levels of hemoglobin and hematocrit in their blood.
Vitamin-vitamin Interaction: Vitamin-vitamin interaction is very common in fish. Labeo rohita has been shown to interact with vitamin B12 and folic acid. When these two types of vitamins are deficient, the symptoms of deficiency become more severe.
Flavor Quality
Sometimes marine fish have environmental effects on their organoleptic properties. Such effects depend not only on the components of the food chain and the solute, but also on various physical influences such as temperature, photoperiod and water cycle. At low temperature, the body of fish concentrates more unsaturated fatty acids in its body tissues and various organs. Since fatty acids are associated with odor and physique, they affect the organoleptic properties of fish during processing and storage. Therefore, in order to maintain the organoleptic properties of farmed fish, it is important to maintain the right level of environmental influences.
The organoleptic properties of fish depend on the type of fish farming and the type of reservoir. In the case of ponds, fish usually live in stagnant water, so the environmental impact on organoleptics is greater. Bad smell is a common problem in fish farming in ponds. This type of odor is known as geosmin. It is caused by a type of bluish green algae called Oscillatoria sp. This organism grows in clay soils rich in more organic compounds and it effects on oxygen in the mud-soil and water level.
Water also stinks from industrial waste. Important chemicals from industrial plants that make water stink are phenol, tar and mineral oil. Although very small amounts of these substances are present, it spreads bad odor. In common carp cultivation, the presence of 0.015 mg/l O-chlorophenol and 0.06 mg/L P-chlorophenol have found to cause bad odor.