NUTRIENTS IN FISH FEED

NUTRIENTS IN FISH FEED

1.0   PROTEIN
       As protein is the most expensive part of fish feed, it is important to accurately determine the protein requirements for each species and size of cultured fish.
       Of all amino acid profile, lysine and methionine are often the first limiting amino acids. Fish feeds prepared with plant (soyabean meal) protein are typically low in methionine; therefore, extra methionine must be added to soyabean-bean based diets in order to promote optimal growth and health.
         Protein levels in aquaculture feeds generally average 18-20% for marine shrimps, 28-45% for catfish, 32-38% for tilapia, 38-42% for striped hybrid bass. Protein requirement usually are lower in herbivorous fish (plant eating) fish and omnivorous fish (plant-animal eaters) than they are for carnivorous (flesh- eating) fish, and are higher for fish reared in high density (recirculating aquaculture) than low density  (pond aquaculture) systems.
      Examples of protein feedstuffs are fish meal, meat meal, chicken offal meal, feather meal, blood meal, soyabean meal or cake, groundnut cake, cotton seed cake, duckweed, maggot, maggot meal etc.

2.0  FAT AND OIL
   Fat and oils are high-energy nutrients that can be utilized to partially spare (substitute for) protein in fish feeds. Lipids typically comprise about 12-25% of fish diets, supply essential fatty acids (EFA) and serve as transporter for fat-soluble vitamins. Sources include animal fats (e.g. lard, fish oil, poultry oil talon) and plant oils (e.g. palm oil, soyabean oil, groundnut oil, sesame oil and palm kernel oil.
        Marine fish typically require n-3 HUFA for optimal growth and health, usually in quantities ranging from 0.5-2.0% of dry diet. The two major EFA of this group are eicosapentanoic acid (20:5n-3) and docosahexanoic (22:6n-3).
                
3.0     CARBOHYDRATE
   Carbohydrates are the most economical and inexpensive sources of energy for fish diets. Energy is not a nutrient. It is released during metabolic oxidation of carbohydrates, amino acids and fats.
        Carbohydrates are included in fish diets for energy, to reduce feed costs and for their binding activity during feed manufacture. Fish need energy to move about in the water and to consume the feed provided to them. Cooking starch makes it more biologically available to fish.          Sources include maize, maize bran, guinea corn, millet, wheat bran, rice bran, dried cassava peel meal.  Up to about 20% dietary carbohydrate can be used by fish.
    
4.0    VITAMINS
Vitamins are organic compounds necessary in the diet for normal fish growth and health. They are often not synthesized by fish, and must be supplied in the diet. The two groups of vitamins are water soluble and fat soluble.
        Water soluble vitamins include: choline, inositol, folic acid, pantothenic acid, biotin and ascorbic acid (vitamin c). Of these, vitamin c probably is the most important because it is a powerful antioxidant and helps the immune system of fish.
       The fat soluble vitamins include vitamin A(retinols; responsible for vision), vitamin D (cholecaciferol; bone integrity), vitamin E (tocopherol; antioxidants), and vitamin K (menadione; blood clotting, skin integrity). Of these vitamin E receives the most attention for its important role as an antioxidant. Deficiency of each vitamin has certain specific symptoms, but reduced growth is the most common symptom of any vitamin deficiency. Scoliosis (bent backbone symptom) and dark coloration may result from deficiency of vitamin C and folic acid respectively.
     Sources of vitamin include premix, duckweed, and other feed ingredients.

5.0     MINERALS
They are inorganic elements necessary in the diet for normal body functioning, skeletal development and normal body functioning. Major sources of minerals in the feed include bone meal, oyster shell, limestone, salt, and premixes. They can be divided into two groups (macro-minerals and micro minerals) based on the quantity required in the diet and the amount present in fish.
      Common macro-minerals are sodium, chloride, potassium, calcium, phosphorus. These minerals regulate osmotic balance and aid in bone formation and integrity. Micro-minerals are required in small amounts as components in enzyme and hormone systems. Common trace minerals are copper, chromium, iodine, zinc, and selenium.
       Fish can absorb many minerals directly from the water through their gills and skin, allowing them to compensate to some extent for mineral deficiency.

6.0   WATER
Water is an important nutrient in the body of fish. It serves as a transporter for other nutrients. We seem not to bother about it because is the medium which the fish lives. In this case the quality becomes very important.

    FEED ADDITIVES
Feed additives are not nutrients but are edible materials added to feed for the  purpose of performing specific functions which are capable of improving the texture, strength of pellets, taste, aroma, attraction, feed consumption, utilization, prevent stress from infection and disease, cure disease and promote growth and reproduction.
       They could be in form of drugs (antibiotics), antioxidants, flavor or attractants.       Antioxidants are used in feeds to prevent quality deterioration through the prevention of rancid oxidation of fat and nutrient deficiency.