One of the most important operational functions in shrimp culture is the provision of adequate food supply to ensure that the cultured animals attained the desired harvesting size within the targetted time frame. Feeds is among the largest operational cost of shrimp farming and every efforts should be made to ensure efficient utilization of feeds for growth. It is therefore necessary to have adequate knowledge on the feeding habits and behavior of the cultured organisms, their nutritional requirements and efficiency in dietary protein conversion for growth. Traditional shrimp farms in most Asian countries employ extensive culture operation in which the growth of shrimps fully depends on natural food organisms. In semi-intensive culture operation, supplementary feeds are given while natural food organisms remain the major food source. In intensive culture operation, shrimp growth is completely dependent on artificial diets.
In the natural habitat, shrimps feed on other small crustaceans, finfish, molluscs, polychaetes, ophiuroids and other slow-moving benthic organisms. They catch food with their pereiopods, take to their bucal cavity and nibble slowly. They are omnivorous but cannibalize if food is insufficient or of poor quality. They are also scavengers, feeding on any kind of decaying matter available in the habitat.
Natural food organisms are allowed to grow in well prepared pond fertilized with organic or inorganic fertilizers. These food organisms in the form of benthic blue-green algae, diatoms, green algae and various species of microscopic zooplankton and microbenthos serve as the natural food of the cultured shrimp. The nutrient composition of the major natural food organisms growing within ponds is shown in Table 5. The main types of natural food predominate in shrimp ponds are:
Lablab* - This is a kind of microbenthos composed of blue-green algae, diatoms and other microscopic plants and animals. In the Philippines, shallow brackishwater ponds below 40 cm are heavily fertilized to grow lablab for the culture of milkfish. However, lablab is also providing natural food for shrimps. Growth of lablab requires higher salinity which is not conducive for growth of the tiger shrimp. However, lablab is used as natural food for the post-larvae and juveniles in the first two months after stocking.
Lumut* - This is composed mostly of filamentous algae such as Chaetomorpha which are also growing in milkfish ponds. The lumut can be grown in low salinity compatible with the growing conditions for shrimps. Other living organisms attached to the lumut are also eaten by the shrimps. Herbivorous fish are often stocked to control the density of lumut in the pond.
Phytoplankton - Fertilization in pond promotes growth of microscopic plants known as phytoplankton, These primary producers serve as the main food of zooplankton and benthic organisms which in turn become the food of shrimps. The presence of yellowish-green color in pond water signifies good growth of desirable planktonic organisms organisms conducive for shrimp growth.
Other sources of food for the shrimps include macrophytes such as Najas graminen and Ruppia maritima which thrive at low salinities. These grow in abundance promoting also the growth of numerous benthic organisms attached to the plants. The shrimps grow well in pond with prolific growth of these plants since the shrimps feed on the benthic organisms as well as the decaying parts of the plants.
* in Filipino
Table 5. Nutrient composition of natural food commonly found with ponds.
|% Dry Matter
As the shrimp grow, consumption increase and the natural food in the pond becomes insufficient. Thus, many shrimp farmers provide supplemental feeds. The types of feed used are:
Moist/wet feeds - These are freshly prepared feeds using locally available ingredients. The feeds should be given fresh immediately after preparation. However, these could also be frozen and thawed when needed. The commonly used feeds include the following:
snails from the ponds with shells crushed
Dry pelleted feeds - Pelleted feeds are available commercially to be used as supplementary or full feeds of shrimps. These are also prepared using locally available ingredients. A good pellet feeds not only should meet all the nutritional requirements of shrimp but also stable in water for a certain period of time. The feeds should have also a longer shelf - life. Usually, commercial pellets are brought in bulk and should be properly stored in storage room with low humidity to minimize fungi occurence and insect infestation. It is advisable to ensure rapid turn over of feed supply.
Supplemental feeds may be given by broadcasting, through feeding tray or automatic machine feeder. Broadcasting method is carried out by spreading the feeds evenly into the pond surface. For bigger ponds, the use of flat-bottom boat is needed so that the mid-portion of the pond can be reached.
Feeding trays containing the apportioned feeds are placed strategically at different parts of the pond. The trays vary in size from 1–10 m2. The common materials used are woven bamboo strips or polyethelene screen (Fig. 22). The trays are usually tied at four corners and suspended into the water column. Normally, one tray per 10 to 100 m2 pond area is being practiced.
The use of feeding tray prevents feed wastage. At the same time, the size and condition of shrimp can be checked and their consumption rate estimated based on the left-over feed in the tray. The disadvantages however, are that when insufficient feeds are given or insufficient trays are used, the bigger and stronger shrimps might prevent the weaker and smaller ones from feeding. If there are many competitors (eg. tilapia) in the pond, they might consume the feeds before the shrimps can get hold of them. Hence, in order to minimize the above mentioned situation, a combination of broadcasting and feeding tray methods are usually employed.
Various automatic feeders designed primarily for fish were tried in shrimp ponds adopting intensive farming operation. Automatic feeders dispense a given amount of feed at certain interval during a 24-hour period. A timing device, usually electrically activated, is an essential component of such feeders. These can be set to deliver feed in small quantities several times daily allowing the culturists to feed without being physically present. Extensive comparisons between the efficiency of hand feeding in contrast to automatic feeder have not been made in developing countries. Although it cannot be stated with certainly that one method is more feed-efficient than the other, the savings in labor realized by utilizing automatic feeders is significant, assuming that each feeder does not have to be filled daily. Offsetting this advantage is the high cost of the feeding devices, a number of which may be needed in large ponds.
Fig. 22. A feeding tray
Optimal feeding rate and frequency are essential in maximizing conversion rate of feed to shrimp. The accuracy of determine the feeding rate is based mainly on the estimate of the density and size of the stock. The more common methods used to determine the feeding rate are:
Adjustment of feeding rate through visual observation of left-over feed - This is employed by the use of feeding tray. Five to ten percent of the feeding ration are placed at the feeding tray while the rest are broadcasted into the pond surface. Prior to feeding, the tray is lifted to observe whether the previously given feed is totally consumed. If so, the previously given amount of feed is considered insufficient. Hence, an additional 2–5% of the feeding ration is added. However, if the feed is not totally consumed, the previous feeding rate is reduced depending on the left-over feed. This method is very subjective depending on the experience and skill of the operator.
Periodic determination of the stock density for appropriate feed ration - This is done by the use of cast net. The stock density estimation is described in earlier section. The stocks are sampled at 15–30 days interval. The feed is given at 5–10% of the estimated shrimp biomass per day.
Feed ration based on assumed density - This method of computing feed ration is based on the estimated survival rate. Most culturists assume 100% survival for the first month of stocking, 90% for the second month and 80% for the third month. Feeds are given at fixed rate of 5–10% of the estimated shrimp biomass per day. Although the food requirement for maintenance and growth increases with increasing biomass, the relative food requirements per unit weight of animal decreases with increasing shrimp size. Hence, a sliding feed ration of 10% of the estimated shrimp biomass and 4% for the fourth month has been adopted.
The common feeding frequency adopted is 2–5 times a day. Most culturists feed their stock every morning and afternoon only. However, experiments have shown that apportioning daily feed ration several times a day improve feed conversion efficiency as it reduces feed wastage, ensures feed quality and more even distribution to the stock. If the stocks are to be fed 5 times a day, two should be given in daytime and 3 at night as the shrimps are more active when dark.