Fish Feeding

Credits: Biovision-Infonet

Compared to terrestrial animals, fish have lower energy requirement (they are more efficient), they require less lipids in feed (except for cold water species such as trout), they have higher protein requirements and fish can absorb certain mineral element directly from the water.

There are three types of food used in aquaculture:

 In organic fish farming the natural feeds and supplemented feeds not treated with chemicals can be fed:

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 fertilization.

2. Supplementary feeds usually consist of cheap feed materials available locally such as terrestrial plants or agricultural by-products. Many kinds of feed materials may be used as supplementary feeds for your fish such as: 

• Terrestrial plants: grasses, legumes, leaves 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, polishing, bran, hulls
• Wheat: middling, maize bran: gluten feed, gluten meal
• (Oil/cakes after extraction of oil from seeds of mustard, coconut, groundnut, cotton, sunflower, soybean. This group of feeds contains chemicals and is not used in organic fish farming.)
• 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 fish. 
• 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 feeding.

3. On large scale intensive fish farms complete feeds are made from a mixture of carefully selected ingredients to provide all the nutrients necessary for the fish to grow. 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 growth.

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 fat.

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 fats because it accumulates and reduces flesh quality. However, 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 the fish body. Deficiency results in poor health and deformities. When fed with a variety of green plants, vitamin supply will be sufficient. 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  inorganic elements are needed in smaller or larger amounts 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. When fed with a variety of plant material, mineral supply will be sufficient.

Other feed additives

In intensive, non organic fish farms  feed additives  could be used in fish feeds includes attractants, binders, dyes and medicinal agents like vaccines. In ponds and other outdoor fish farms one should be very careful not to pollute and spoil the surrounding water and animal life in it.

FISH FEEDING 

i). Small fish need more food than larger ones. 
ii). Where there is plenty of natural food, less supplementary feed should be used
iii). Where low stocking densities are used, less supplementary feeds are used
iv). The better the quality of the feed (low FCR), the less the quantity needed to feed the fish
v). More food is required in warm water than in cooler water.
vi). It is therefore recommended for producers to constantly adjust the feeding throughout the production cycle for better results.
vii). FCR will be affected by overfeeding, poor feeds, poor pond fertilization for semi-intensive production and poor fish health.

Some practical guidelines in feeding fish to adjust the feeding throughout the production cycle.  

• Small fish need relatively more food than larger ones. The small ones are less efficient in using their feed.
  * When plenty of natural feed is available, less or no supplementary feed should be used. I general supplementary feed is more expensive.
  * Where stocking densities is low in a pond, less supplementary feeds are used. Fish can grow on the available material
  * More food is required in warm water than in cooler water, depending on the temperature zone of the species.
• In ponds it is not easy to estimate the amount of feed to provide. However, underfeeding should be avoided because it will lead to loss in fish production. Overfeeding should be avoided because it is uneconomical (it raises the production costs) and it may also result in poor water quality

A producer must at all times know approximately how many fish  there are in each pond to be able to estimate the amount of feed to apply. It therefore recommended that a producer conducts fish sampling in the ponds at least on monthly basis and keeps record of it.

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 to 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 in g per fish per day

Age in month	1-2	2-3	3-5	5-8	8 and more
Weight of fish (g)	5-20	21-50	51-100	101-200	Over 200
Wheatbran (g/day)	1	1-3	3	4	5
Pelleted diet (g/day)	1	1-2	2	3	3-4

FEED CONVERSION RATIO (FCR)

Feed Conversion (FCR) is the ratio of the quantity of food given to the fish (in kg) to the weight gain of fish (in kg), over a given period. 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 certain feed is 3:1, it means that a farmer needs 3kg of that feed to produce 1kg of fish.  The better the quality of the feed (low FCR), the less the quantity needed to feed the fish. It is a measure for intensive, industrialized farming were all feed is weighed (and processed). When fish is fed with alga, other plant material and droppings from animals etc. it is impossible and not sensible to account a feed conversion ratio. FCR will be affected by overfeeding, poor feeds, poor pond fertilization for semi-intensive production and poor fish health.

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 square method – How to formulate fish feeds: The square method
The most common and simplest method of formulation diets 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%) 

i). The desired protein level is inserted at the centre
ii).The two ingredients with their protein levels are placed at each corner on the left hand side of the square
iii). The differences between the centre and each feed ingredient are placed at each corner on the right side diagonally opposite the ingredient (ignoring the plus or minus signs)
iv). The upper right hand corner in this example indicates the proportion of fish meal needed and the lower one that of rice bran
v). This can be expressed as

• Ratio i.e. fish meal:rice bran 17:25
• Percentage 17/42 = 40.5% for fish meal and, 25/42 = 59.5% for rice bran.

Fertilization and manuring

Where the natural pond productivity is enhanced through water fertilization, reasonable production can be achieved without exogenous feeding. Although yields will be lower than those obtained with exogenous feeding, fertilization will reduce the quantity and expense of feeding. Application of an inorganic fertilizer high in phosphorus should be done prior to stocking fish to create an algal bloom. Tilapia productivity is stimulated mainly by an increase in phosphorus and to a lesser extent by an increase in nitrogen. The inorganic fertilizers used in Kenya are DAP (Diammonium phosphate) and CAN (Calcium ammonium nitrate) and are not allowed in organic fish farming, while animal manure is allowed. 

Animal manure is widely used in Kenya in fish production in earthen ponds. The quality of manure as a fertilizer varies depending on the source animal and the quality of feed fed to the animal. Pig, chicken and duck manures increase fish production more than cow and sheep manure. Animals fed high quality feeds (grains) produce manure that is better as a fertilizer than those fed diets high in crude fibre. Fine manures provide more surface area for the growth of microorganisms and produce better results than large clumps of manure. 

The manure should be composted before being used in the fish pond. It spreads easier and does not take oxygen from the water for the process of composting while minerals are kept in the material during composting

Manure should be distributed evenly over the pond surface area. Accumulations of manure on the pond bottom produce low oxygen conditions (during decomposition) in the sediment resulting to reduced microbial activity and sometimes result in the sudden release of toxic chemicals into the water.  

Methods of applying manure 

• Crib method: A compost crib constructed using wooden sticks at one or more sides of the pond. It helps fertilize the water gradually. The manure in the crib requires frequent turning to facilitate the release of nutrients.
• Bag method: A bag is filled with manure and tied to the corner of the pond. The bag is shaken weekly or daily to release nutrients.

Manure application rates for ponds 

Manure application rates depend on the size of the pond, which is expressed as surface area of the water in the pond. The recommended rate is 50 g of dry matter per m2 per week i.e. 5 kg/100 m²/week.

The maximum rate depends on the quality of the manure, the oxygen supply in the pond and water temperature. If early morning DO is less than 2 ppm, manuring should be reduced or stopped until DO increases. When water temperatures are less than 18deg C, manure application should be discontinued. At low temperatures the rate of decomposition decreases and manure may accumulate on the pond bottom. A subsequent increase in temperature could then result in oxygen depletion.

Agricultural Lime

• Used to improve soil quality, which helps the organic and chemical fertilizers to work better. It also helps to clear up muddy water.
• In red soils; about 20 kg per 100 m² can be applied. Black cotton soils may require a little more.

Some characteristics of organic and chemical fertilizers

Allowed in organic fish farming: Organic (farm manure)	Not allowed in organic fish farming: Chemical: DAP, Urea, MAP, TSP
Contains trace minerals and vitamins.	Contains only what the label says
Uses oxygen to decompose.	Does not use oxygen when dissolving
Is highly variable in composition depending on feeds given to the animals and bedding used	Varies little in composition from what is indicated on the label.
Can help reduce turbidity due to clay silt in the ponds	Does not reduce turbidity
Can help reduce seepage in ponds	Does not act on seepage
Some of the ingredients can be consumed directly by the fish	Not directly consumed by the fish

Manure application can be made easy by placing animal production units adjacent to or over the fish ponds so that fresh manure can easily be delivered to the pond on a continuous basis. This also allows the feed wasted by the animals to fall into the fish pond and utilised by the fish. Effective and safe manure loading rates are maintained by having the correct number of animals per pond surface area.