Feeding manegement in aquaculture.
Introduction
1. In Section 2.0 of this manual, you have learned that plants are able, through photosynthesis, to utilize sunlight and simple nutrients to produce new organic material. On the contrary, animals, including fish, cannot. Thus to survive, grow and reproduce, fish need to feed on organic materials such as plants, other animals, or prepared feeds containing plant and/or animal material. It is therefore most important for you to ensure that your fish get the food they require, both in quality and in quantity.
Selecting fish foods
2. There are three types of food used in fish ponds:
natural food;
supplementary feeds;
complete feeds.
3. Natural food is found naturally in the pond. It may include detritus*, bacteria*, plankton*, worms, insects, snails, aquatic plants and fish. Their abundance greatly depends on water quality. Liming (see Chapter 5) and fertilization (Chapter 6), in particular organic fertilization, can help you to provide a good supply of natural food to your fish.
4. Supplementary feeds are feeds regularly distributed to the fish in the pond. They usually consist of cheap materials locally available such as terrestrial plants, kitchen wastes or agricultural by-products.
5. Complete feeds may also be regularly distributed. They are made from a mixture of carefully selected ingredients to provide all the nutrients necessary for the fish to grow well. They must be made in a form which the fish find easy to eat and digest. These feeds are quite difficult to make on the farm and are usually quite expensive to buy.
6. The system of production can be defined according to the type of food given to the fish:
extensive: fish production depends entirely on natural food;
semi-intensive: fish production depends on both natural food and supplementary feed; more fish may be reared in the pond;
intensive: fish production depends entirely on complete feed, and the stocking rate no longer depends on food availability but on other factors such as water quality.
7. In the following sections, you will learn more about natural food (Section 10.1) and supplementary feeds (Sections 10.2 to 10.6). If you are interested in complete feeds, you should read another FAO manual entitled Feed and feeding of fish and shrimp: a manual on the preparation and presentation of compound feeds for shrimp and fish in aquaculture,
Natural foods for fish
There are several kinds of natural foods
1. Natural fish foods present in a fish pond are very diverse and usually consist of a complex mixture of plants and animals.
(a) They range from microscopic to relatively large size.
(b) They may be alive or dead (detritus) and available from bacterial decomposition.
(c) They are generally present in various parts of the pond:
near the shore such as rooted high plants;
floating in the water such as plankton;
on the surface of or within the bottom (benthic material or benthos*) such as worms, insect larvae and snails;
covering the surface of submerged objects (biological cover or autwuchs*);
swimming around such as aquatic insects, frogs and fish (nekton*).
2. To help you manage your pond through fertilization (see Chapter 6), you should learn to recognize the most important groups of natural fish foods. For this you will need a simple microscope (see also Section 15.3), which you might be able to find in a local health centre, school or in a fish-fry production centre. Ask your extension agent for advice. Look at the following pictures remember that some of these organisms can be very small and practically invisible to the naked eye.
Note: 1 micrometre (micron)= 1�m = 0.001 mm.
Which natural food do fish prefer
3. The food preferred by fish varies considerably, depending on species and development stage.
4. As you have already learned, fish larvae do not actively feed but survive on reserve food in their yolk sac (see Section 9.4). A short time before the yolk sac is absorbed, early fry start eating natural foods, which usually consist first of the smallest plankton such as microscopic algae and rotifers. As their mouth size increases, the fry eat increasingly larger plankton (cladoceres/copepods) and insect larvae/pupae. Little by little, as the fry grow older, food preferences change to resemble more and more those of adult fish.
5. Adult fish belong to different categories according to their feeding preferences, as illustrated in Table 27.
(a) Herbivores prefer plant materials such as:
phytoplankton*, for example the Chinese silver carp;
higher plants, for example Tilapia rendalli, grass carp, and the Asian cyprinid Puntius.
(b) Omnivores eat a mixture of various natural foods, although most of them have preferences for certain foods such as:
zooplankton*, for example the Chinese bighead carp;
bottom fauna, for example common carp;
bottom detritus for example mrigal, an Indian cyprinid;
phytoplankton, for example the Nile tilapia;
fruits and seeds, for example the South American Colossoma.
(c) Carnivores prefer animal food such as insects, tadpoles, frogs and smaller fish, for example trout and catfishes such as African Clarias and Asian Pangasius.
6. You should ensure that there is a good supply of the type of natural food your particular fish species prefers. Phytoplankton organisms are the easiest to produce using a good fertilization programme (see Chapter 6). Zooplankton will then develop rapidly in the presence of algae to graze upon.
7. If you want to encourage the growth of biological cover, a mixture of minute surface-attached plants and animals, in nursery ponds, you can fertilize the water and use bundles of dried grass or crop stems fixed underwater.
Checking on phytoplankton
8. If your fish are phytoplankton feeders, it is particularly important to control regularly both the quality and the quantity available.
9. To check on quality, slowly pull a phytoplankton net (see paragraphs 12 to 15) across the pond in one direction. Try to cover a large area of water. Determine which types of algae are present with the help of a simple microscope (see Section 15.3). There should not be too many filamentous algae.
10.To check on quantity, estimate water transparency either with a Secchi disk or with your arm (see Section 2.3). The abundance of plankton is good as long as the transparency is less than 60 cm (see Section 6.0).
Checking on zooplankton
11. Control quality and quantity of the zooplankton as follows:
(a) Check on quality by slowly pulling a zooplankton net (see paragraphs 12 to 15) across the pond in one direction. Try to cover a large area. Determine which are the predominant types of zooplankters present with the help of a simple microscope (see Section 15.3). Look especially for eggs and juveniles:
if there are many, adequate food is present for a healthy development of the zooplankton;
if there are only a few, food for zooplankters is lacking.
(b) Check on quantity by filtering through your zooplankton net a known volume of pond water taken at several sampling points throughout the pond. Proceed as follows:
using a 10-l bucket for example, take five water samples to obtain a total volume of 50 l;
filter them through your net to concentrate the zooplankton within its bottom container;
transfer this zooplankton into a graduated glass tube;
kill the zooplankters by adding a pinch of table salt or a few drops of formalin;
let them settle for about one hour at the bottom of the tube;
measure the settled volume of zooplankton;
if it is equivalent to at least 3 ml/100 I water, there is enough zooplankton available to feed your fish. If you have sampled, for example 50 l of water, you should then have a settled volume of at least 1.5 ml.
Supplementary feeds: qualitative aspects
Why use supplementary feeding
1. There are several reasons why you should supplement the natural foods available within the pond with artificial feedstuffs originating from outside the pond, for example:
when natural foods become insufficient to feed your fish well and ensure good growth; and
when you wish to raise more fish in your pond to produce a higher crop and still have good growth.
2. As you make more use of supplementary feeds, you change from an extensive system to a semi-intensive system of production.
Selecting supplementary feeds.
3. When deciding on the use of supplementary feeds on your farm and their selection, look for feedstuffs that are:
of good nutritional values: with high protein* and carbohydrate* content and low fibre content (see paragraphs 6 to 9);
well accepted by the fish you plan to feed;
cheap in price: for a given food quality, the lower the cost, the better;
available most of the fish-growing season;
of minimum additional cost for transport, handling and processing;
easy to handle and store.
Note: of particular importance for small rural farmers: if possible, it may be better to group together to buy bulk quantities and reduce selling price and transport and storage costs.
4. Many kinds of materials may be used as supplementary feeds for your fish such as:
terrestrial plants: grasses, legumes, leaves and seeds of leguminous shrubs and trees (see Section 4.1), fruits, vegetables;
aquatic plants: water hyacinth, water lettuce, duckweed;
small terrestrial animals: earthworms, termites, snails;
aquatic animals: worms, tadpoles, frogs, trash fish;
rice: broken, polishings, bran, hulls;
wheat: middlings, bran;
maize: gluten feed, gluten meal;
Oil/cakes after extraction of oil from seeds of mustard, coconut, groundnut, African palm, cotton, sunflower, soybean;
sugar cane: molasses, filter-press cake, bagasses;
coffee pulp;
cottonseeds;
brewery wastes and yeast;
kitchen wastes;
slaughterhouse wastes: offals, blood, rumen contents;
silkworm pupae;
manure: chicken droppings, pig manure (see Chapter 7).
5. Select the feedstuffs most useful to you according to the criteria given above.
6. Feedstuffs are classified according to their relative content of protein, carbohydrate and fibre
7. Proteins are primarily made of water, carbon and nitrogen. They are broken down during digestion by the fish into different amino-acids* used for growth, reproduction, repairs and secretion processes. Proteins are mostly found in animal by-products, oil-bearing seeds and their processed cakes. Juveniles and broodstock fish require more proteins than others.
8. Carbohydrates such as starches, sugars and cellulose are primarily made of water and carbon. They provide the energy required by fish for maintenance and living activities. Good carbohydrates are mostly found in cereals and molasses. Indigestible cellulose predominates in brans, hulls, coffee pulp, sugar cane bagasse and whole cottonseeds, where fibre content is also high.
9. To obtain best results, use simple mixtures of various feedstuffs to provide your fish with the additional proteins and good carbohydrates required. As far as possible, avoid using a high proportion of fibrous materials to feed your fish. Remember that such materials might instead be very useful for preparing compost (see Section 6.3).
Presenting supplementary feeds
10. Supplementary feedstuffs are available in two forms: dry and wet.
11. Dry feedstuffs such as cereals and cakes are easier to store, to transport and to distribute to the fish.
12. Wet feedstuffs such as blood, rumen contents, molasses and brewery wastes require special treatment before feeding, for example mixing with dry feedstuffs to absorb part of the moisture or drying to improve storage life (see Section 10.6).
13. As a result, supplementary feeds are usually presented to fish either dry (about 10 percent moisture) or moist (30 to 50 percent moisture). This last form is preferred by some species and may be more palatable and better digested, giving better results. The feed may also be better utilized by reducing losses. But moist feeds do not keep well, and only small quantities should be prepared at a time.
How fine should the feedstuffs be
14. It is important to adapt the size of the feedstuff particles to the mouth size of the fish to reduce feed losses and maximize feed utilization (see the chart below). Depending on the size of the fish, preparation may involve different processes, such as:
crushing or grinding dry feedstuffs for juvenile fish; and
chopping plant materials into small pieces for herbivorous fish.
15. Remember that feed particles should not be finer than necessary, because with fine particles:
nutrients are more easily dissolved into the water;
it becomes more difficult for the fish to feed properly;
more particles may be lost by the fish and will decompose in the water
Supplementary feeds: quantities to use
1. You should aim at providing all the feed the fish need to:
maintain body functions such as blood circulation and routine respiration; and
grow, increasing in size and producing eggs, for example.
2. If the quantity or quality of feed available is limited, fish may not grow, may lose weight, or may even die from food deficiency. Growth will occur only after maintenance needs are satisfied. These needs increase with water temperature, because the activity of the fish also increases. They are relatively greater in small fish compared with larger fish.
How often should you feed your fish during the day
13. Increasing the frequency of supplementary feeding during the day has several advantages, particularly if natural food does not form a major part of the daily food intake, namely:
reducing food wastage;
reducing dissolved oxygen consumption and improving water quality;
reducing nutrient losses attributable to leaching, thereby improving food quality;
improving uniformity of fish sizes, giving more possibility for the less aggressive fish to feed;
improving fish growth and feed utilization.
14. Before deciding on how frequently you should feed your fish, note the following points.
(a) The smaller the fish, the more frequently they should be fed.
(b) Dry feeds need to be distributed more often than moist feeds.
(c) In any one feeding, no more than 3 percent of the total fish weight should be distributed.
(d) The feeding frequency should be reduced as the water temperature cools down, or if it exceeds optimum levels.
(e) The frequency should be adapted to the fish species. Tilapias do much better with small but frequent meals. On the contrary, trout larger than 50 g do well on one meal a day.
(f) The feeding cost should be checked to make sure it is not excessive compared to the yields obtained.
15.After deciding on how often you will feed your fish each day, subdivide the daily ration accordingly. Adjust it frequently on the basis of feed utilization.
Example
You determine a daily ration of 2 kg. If you decide to feed your fish twice a day, each meal should be made of 2 kg � 2 = 1 kg of feedstuffs
Checking on feed utilization
16. You should regularly check on feed utilization to adjust feeding properly. This is usually done on several occasions.
(a) Before feeding, check it there is any feed left over from the previous meal. To do this you may need to use a light scoop made of fine-mesh metal netting mounted on a long handle. Adjust the feeding accordingly.
Example
Fingerling common carp are fed once a day in the presence of a good supply of natural food. Two to three hours after feeding, check the feeding place. If there is no feed left, increase the DFR slightly on the next day.If there is feed left over, check again five to six hours later. If there is little feed left over, use the same DFR on the next day. If there is more feed left over, decrease the DFR on the next day.
(b) During feeding, observe your fish carefully to see how actively they eat. A good appetite is a sign of good health and good water quality.
(c) Every 15 to 30 days, check on the new fish biomass present in the pond (see Section 16.4), and adjust the daily feeding ration accordingly. Check on feed utilization during the last 15- to 30-day period by calculating the food conversion ratio for this period (see paragraphs 17 to 19).
(d) At the end of the production cycle, check on feed utilization by calculating the food conversion ratio for this particular cycle (see paragraph 20). Base your calculation on accurate records (see Chapter 16).
Feed preparation and feed management with ng-source imo2 liquid.
Determining and using the food conversion ratio
17. The food conversion ratio (FCR) is the ratio of the quantity of food distributed (in kg) to the weight gain of fish (in kg), over the same period of time.
Example
Over a period of one month, the fish biomass has increased by 12 kg. The quantity of supplementary feed distributed has been 48 kg. FCR = 48 kg � 12 kg = 4.
18. The FCR can vary considerably, usually depending on the same factors affecting daily feeding rate, such as species, kind of feed, water quality and natural food availability. Remember that the lower the FCR, the better the feed is being utilized by your fish. Some typical FCR values are given in the chart below.
19. If you wish to be more precise, you should consider the fish production resulting from natural food separately. Deduct it from the total weight gain before determining the FCR for supplementary feeds only.
Example
In the earlier case, it is estimated that natural food supplies 25 percent of the fish growth, i.e. 12 kg x 0.25 = 3 kg. FCR of supplementary feeds is therefore 48 kg � (12 - 3) kg = 5.33.
20. To judge the efficiency of the feed utilization in a particular pond, determine the FCR for the period under consideration. Compare this observed FCR with the most reliable value known for the type of feed used, such as the FCR determined from past experience on your own farm or under similar conditions on other farms.
(a) if this observed FCR is much higher, there is a problem such as low dissolved oxygen, overfeeding, bad quality feed, lack of natural food or diseased fish. Determine and correct the problem.
(b) if this observed FCR is equal or lower, production conditions have been normal or even better than average.
21.Once you have established the FCR of a certain kind of supplementary feed, you can easily estimate how much of such feed (F in kg) you will require over a certain period of time to produce a certain fish yield (Y in kg) as: F = Y x FCR (see paragraph 5).
Stopping the feeding of your fish
22. There are several occasions on which it is advantageous or even compulsory to stop feeding your fish:
when the water temperature is too low or too high (see example);
when dissolved oxygen content is limited (see Section 2.5);
on the day you apply manure to the pond (see Section 6.2);
if ever a disease epidemic appears in the pond (see Chapter 15).
Example
When the water temperature is too extreme, fish stop feeding
23.Do not feed your fish for two or three days before stressing handling activities such as:
sorting or grading them (see Section 12.0);
transporting them alive (see Section 14.0);
their final harvest (see Section 11.0);
marketing them (see Section 16.8).
10.4 How to distribute supplementary feeds
1. In the two previous sections, you have learned which kind and what quantities of supplementary feeds can be used. Now you should learn when, where and how to apply these feeds in your ponds. One of the basic points is to adjust distribution according to the fish size and/or age.
Example
Feed your fish correctly according to their age.
When to feed your fish
2. Under normal rearing conditions, it is best to feed your fish at least once a day, usually for six days a week. Feed more often if possible, particularly for juvenile fish (see Section 10.3, paragraphs 13 and 14). In some conditions, such as limiting low temperatures, feed only every two to three days.
3. The best feeding time of the day is early morning, as water temperature and DO content start increasing (see Section 2.5). A second distribution may take place in late afternoon, a couple of hours before sunset.
4. In some cases, using demand feeders (see paragraphs 12 to 16), feeding time and amount are determined directly by the choice of the fish: feed is supplied when the fish are hungry.
Where to distribute feed
5. Depending on the type of feed, the size of the pond and the distribution method, feed may be applied in the following manner.
(a) On the entire pond area, for example when hand feeding finely ground dry feedstuffs in small ponds. It makes the food available over a wide area thus reducing competition among the fish.
(b) At selected feeding places, for example when feeding sinking feedstuffs in large ponds. It then becomes easier to check on food utilization. Proceed as follows:
select areas with a firm bottom, avoiding soft mud;
choose shallow water 0.6 to 1 m deep;
in large ponds, if you have no boat, keep the feeding places near the shores;
it is best to have several feeding places: in large ponds, 5 to 7 places/ha for juveniles, and 3 to 4 places/ha for older fish;
mark the selected areas well, with a vertical wooden pole emerging above the water surface;
change feed sites if spoiled food builds up on existing sites.
Overfeeding Fish.
Overfeeding is the number one cause of fish loss, and it’s not hard to see why. It is easy to forget how small our pet fish really are, and the fact that their appetites are not the same as ours. Also, because feeding our fish is the main way we interact with them, they certainly come to expect at least a little sprinkle of food each time we approach their tank—and it’s hard sometimes not to give in. However, hungry as they may seem to be, it is important to remember that overfeeding your fish can have serious consequences.
Contrary to popular belief, most fish who die of overfeeding do not actually suffer from any sort of gastrointestinal problem. In fact, the major issue is unrelated to the actual over-ingestion of food. Rather, problems occur when excess food is left uneaten and accumulates as waste in the aquarium. The products of decomposed fish food can be extremely toxic to fish and can also indirectly affect them by wreaking havoc in their aquarium environment. Common signs of overfeeding are easily observable in any fish tank; cloudy water, algae growth, mold/fungi, and clogged filters are some of the most obvious indicators.
Whether you are a new fish owner, or a long time fish lover who has noticed any of the above signs in your aquarium, there are some simple steps you can take to ensure that your fish are receiving an appropriate and safe amount of food.
A good first step is to arrange a feeding schedule. Fish owners who only feed their pets every other day are often surprised when their tanks show signs of overfeeding; actually, this is one of the most common ways people overfeed. Fish are naturally grazers or ‘nibblers’ of food, and are not really equipped to eat single large meals. When they are fed in this way, they will eat their fill and leave over the rest. This will not only lead to large amounts of food waste in the tank, but will also mean that fish are left malnourished in between feedings. Ideally then, schedules which include multiple small feedings will keep your fish healthy. Always make sure that everyone in your household is aware of the feeding schedule so that the fish aren’t accidentally fed again by different family members.
Next, making sure you feed the correct quantity during these meal times is critical. This will greatly depend on the specific needs of your fish. The best way to determine appropriate meal sizes is to carefully observe the eating habits of your fish. Begin by feeding very small quantities (as small as three or four flakes per fish). If this amount is consumed in a matter of minutes you may add more and observe again. In general, any food that is not eaten within five minutes will not be eaten at all. One of the most common feeding mistakes people make is feeding the tank rather than the fish; that is to say that people tend to feed more if the tank is large, regardless of the actual amount of fish inhabiting it. Make sure you consider this when sprinkling in your pets’ meals.
The quality of the food you choose is also important. A food which is low quality, stale, or simply inappropriate for your specific fish, will likely go uneaten and can cause some of the same problems discussed above. Different species of fish have different requirements and preferences (for example, whether their food is in flakes or pellets, whether it floats or sinks). It is therefore essential to learn all you can about the dietary needs of the various types of fish that inhabit your aquarium.
Finally, and because mistakes do happen, it is always a good idea to practice methods of removing excess food waste. This includes having a good quality filter, but can also involve regular siphoning or use of a net to skim the bottom of the tank. Including a ‘scavenger’ species in your aquarium (such as a catfish) can also help to clear any food that has fallen into otherwise inaccessible areas of the tank.
Perhaps the most unfortunate part about losing fish to overfeeding is the fact that it be can be prevented. As easy as it may be to over-feed our fish, it is also easy to avoid it. By being observant, educated, and just a little bit cautious, you can ensure that your fish are always happy and healthy, without being hungry.
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