FISH NUTRITION, FISH FEEDING AND FEED FORMULATION

Introduction

 Compared to terrestrial animals, fish have certain specific characteristics in terms of dietary requirements:

  • They have lower energy requirement
  • Require less lipids in feed (except for cold water species such as trout)
  • Can directly absorb certain mineral element from water medium

There are three types of food used in aquaculture:

  1. Natural food occurs naturally in fish ponds. This includes detritus, bacteria, plankton, worms, insects, snails, aquatic plants and fish. Their occurrence and abundance depends on the water quality and in particular
  2. Supplementary feeds usually consist of feed materials available locally such as terrestrial plants or agricultural by-products like wheat

Many kinds of feed materials may be used as supplementary feeds for your fish such as:

  • Terrestrial plants: grasses, leaves (e.g. cassava)and seeds of leguminous shrubs and trees vegetables;
  • Aquatic plants: water hyacinth, water lettuce, duckweed;
  • Small terrestrial animals: earthworms, termites, snails;
  • Aquatic animals: trash fish;
  • Rice: broken, bran, hulls;
  • Wheat: middling, bran;
  • Maize: gluten feed, gluten meal;
  • Oil/cakes after extraction of oil from seeds of mustard, coconut, groundnut, cotton, sunflower, soybean;
  • Cottonseeds;
  • Brewers wastes and yeast;
  • Slaughterhouse wastes: offal, blood, rumen contents;
  • Manure: chicken droppings, pig manure

Supplementary feeds are available in two forms

  • Dry feedstuffs such as cereals and cakes with about 10% moisture. These are easier to transport, store, and to distribute to the
  • Wet feedstuffs such as blood, rumen contents, molasses and brewery wastes with 30 to 50% moisture. Moist feeds do not keep well, and only small quantities should be prepared at a time. These feeds require special treatment, for example mixing with dry feedstuffs to absorb part of the moisture or drying to improve storage life before

 

  1. Complete feeds are made from a mixture of carefully selected ingredients to provide all the nutrients necessary for the fish to They are made in a form which the fish find easy to eat and digest. These feeds are difficult to make on the farm and are usually expensive to buy. Under intensive systems, feed provided to the fish must meet all their dietary requirements. The fish rely wholly on exogenous feeds. The feeds must be complete in terms of nutrients supply.

Fish Dietary Nutrient Requirements Protein

  • Important tissue building component
  • Also important in repairing worn out tissues
  • Important to juveniles for
  • Fish requires much more protein levels in feeds compared to most domestic animals

 

In semi-intensive production, protein comes from the algae (resulting from proper pond water fertilization) and exogenous feeding with supplemental feed. However in intensive production of tilapia, the diets should have 28-32% protein.

Carbohydrates:

Provides energy needed by the fish to carry out its physiological activities like respiration. Any excess is converted and stored as lipids

Fats

They are utilized to supply energy like the carbohydrates. They also provide structural support and act as precursors to physiological chemical processes. Excess of fats reduce the marketability of fish. Diets for adult fish should not have high amounts of lipids because it accumulates and reduce flesh quality. Trout is able to utilize fats much more effectively and can ingest considerable amounts with their diet.

Deficiency in essential fatty acids result in reduced growth, de-pigmentation, erosion of fins, fatty liver and even shock.

Vitamins

Vitamins are required in very small quantities but play a major role in the chemical processes within fish body. Deficiency results in poor health and deformities.

In artificially produced feeds, a balanced mix of vitamins and minerals (premixes) can be obtained from specialized feed manufacturers. They should be used in proportions that meet the nutritional needs of the fish under culture.

Minerals

These are inorganic elements needed for various metabolic functions. Fish can obtain some of them through the gill surfaces into their bodies. Some important minerals include calcium, potassium, sodium and magnesium.

Other feed additives

Some feed additives that could be used in fish feeds includes attractants, binders, dyes and medicinal agents like vaccines.

Feed Conversion Ratio (FCR)

  • Feed conversion ratio (FCR) is calculated from the kilos of feed that are used to produce one kilo of whole fish
  • It tell a farmer the amount of fish feed needed to produce one kilo of fish
  • It can be used to estimate the quantity of feed needed in a production season for a given crop of fish
  • For example, if the estimated FCR for a feed is 3:1, it means that a farmer needs 3kg of that feed to produce 1kg of

It is important to note that:

  • Small fish need more food than larger
  • Where there is plenty of natural food, less supplementary feed should be used
  • Where low stocking densities are used, less supplementary feeds are used
  • The better the quality of the feed (low FCR), the less the quantity needed to feed the fish
  • More food is required in warm water than in cooler
  • It is therefore recommended for producers to constantly adjust the feeding throughout the production cycle for better
  • FCR will be affected by Overfeeding, poor feeds, poor pond fertilisation for semi intensive production and poor fish

FISH FEEDING

It is normally not easy to estimate the amount of feed to provide to each pond. However, the following should be avoided:

  • Under feeding, will lead to loss in fish production;
  • Over feeding, uneconomical (higher production costs) and may also result in poor water quality

A producer must at all times know approximately how many fish and how big they are in each pond to be able to estimate the amount of feed to give.

How to feed:

For most fish, feeding twice a day is sufficient – at about 10 AM and 4 PM. Earlier than 10 am in the morning, the water is a bit cold and oxygen levels are low so this is not a good time t feed the fish.

If you feed at close to the same time and at the same place in the pond every day, the fish will learn to come for the feed.

Recommended feeding rates for tilapia or tilapia/clarias polyculture

Approx month after stocking

Assumed size of fish

Amount of wheat bran per day

Pelleted diet (26% protein)

1-2

5-20g

1 g/fish

1 g/fish

2-3

20-50g

1-3 g/fish

1-2 g/fish

3-5

50-100g

3 g/fish

2 g/fish

5-8

100-200g

4 g/fish

3 g/fish

8 or more

Over 200g

5 g/fish

3-4 g/fish

FEED FORMULATION

 The purpose of feed formulation is to ensure that the aquaculture diets meet the nutritional needs of the fish under culture during it various stages of growth.

Therefore, for one to be able to formulate a specific feed for a particular fish, they need to know the following nutritional needs as regards the fish:

  • Crude protein
  • Crude fibre
  • Energy
  • Specific amino acids and
  • Ash

The most common and simplest method of formulation fish feeds in Kenya is the square method.

For example, if the desired feed should contain 25% protein, and there are two ingredients to use (fish meal with 50% protein and rice bran with 8%)

 

  • The desired protein level is inserted at the centre
  • The two ingredients with their protein levels are place at each corner on the left hand side of the square
  • The differences between the centre and each feed ingredient are place at each corner on the right side diagonally opposite the ingredient (ignoring the plus or minus signs)
  • The upper right hand corner in this example indicate the proportion of fish meal needed and the lower one that of rice bran
  • This can be expressed as
    1. Ratio i.e. fish meal:rice bran 17:25
    2. Percentage 17/42 = 40.5% for fish meals and, 25/42 = 5% for rice bran.