Perhaps shrimp farming has the most unprecedented phenomenon of rapid expansion worldwide, particularly with Penaeus monodon. This is mainly because P. monodon is a euryhaline species and it grows fast; hatchery techniques for seed production is also quite advanced compared to other tropical species of shrimps except the P. japonicus. Intensification of pond management techniques became popular.
The key factors to consider by shrimp farmers who intend to further intensify their management techniques are water exchange, feeds and feeding, and seeds supply which should be under the control of the operator. There are varying degrees of sophistication of techniques available to regulate these factors.
A vital factor influencing the high rate of productivity of intensive system is the capability to change water as often as possible within a short period of time. In Japan and Taiwan, it is necessary to effect a complete change of water in 2–3 hours. Sea-water and freshwater supply should, therefore, be available to provide the appropriate salinity level required by the shrimp at any stage of growth during the culture period. This capability requires an engineering design prepared by a knowledgeable and experienced aquaculture engineer. Figure 10 shows the relationship between productivity and water change in shrimp farming. The higher the rate of water change the higher the productivity. The reason for this is the removal of waste products in the culture facility and good aeration. Pumping of tidal water for this purpose has been found economical than relying on tidal inflow. Pump-fed ponds are more efficiently drained and also harvested completely; a 20 percent water change could be , effected daily in a .5–1.0 ha pond (Gedney, 1983). Tidal ponds could be renovated to provide better water exchange by constructing a pumping station that supplies water through a network of open canals on top of the pond dikes for water distribution in the various ponds. Water discharge is made through existing pond gates.
Figure 10. Relationship between productivity ' and rate of water change in shrimp culture ponds in Taiwan using black tiger conversion (B.T.C.) method Source: Hirasawa, 1985
|Size||Very large, > 2 ha||1.5–2.0 ha||1.0–1.5 ha||1 ha and smaller|
|Construction||Excavated, below sea level||Excavated/built up||Built up; above sea level||Built up; above sea level|
|Stocking density||Less than 1/m2||3–8/.m2||8–18/m2||18 above|
|Water exchange||Occasional||Regular||Often/very often||Very often|
Source: Young, 1987.
Supplementary feeds are essential production inputs for semi-intensive and intensive shrimp farming operations. The quality, quantity of feeds and frequency of feeding are important considerations in pond culture management.
Feed formulations contain 11 percent water compared to trash fish which has 75 percent water. Feed conversion efficiency of trash fish is 4–5 kg to 1 kg formulated feed. Snails and clams are used as substitutes for trash fish but 10–12 kg of this material is equivalent to 1 kg of formulated feed (Kuo, 1986).
Artificial feeds formulated in Taiwan used for the culture of P. monodon has an average conversion ratio of 1.8 to 3.3:1. At a density of 15–20/m2, a production level of 0.6 kg of shrimp per unit area (Liao, 1986) is obtained. The composition of this artificial feed is shown in Table 9.
The nutritional requirement of P. monodon is not fully known. There is no single formulation that is considered the best feed. Liao reported that P. monodon requires more animal protein in the early stages of growth but when it reaches a certain size, it gradually exhibits capability to consume plant proteins. This aspect requires thorough evaluation and study to develop appropriate feed formulations for use during the early and late stages of growth. Fish/shrimp nutrition scientists should look into this matter.
Feeds constitute a large percentage of production input. Therefore, feed conversion efficiency of formulated feeds and their costs are significant to shrimp farming. The quantity of feed increases when farming management system shift from semi-intensive to intensive management. Shrimp farmers have to use more feeds to compensate for the loss of natural productivity. This is exemplified in Taiwan as shown in Figure 11.
The frequency of feeding for PL stage is usually twice a day; for growers and finishers, 4–6 times a day. However, if the feed is not stable, the shrimps would feed more frequently. A feeding regime of 4–5 times a day should be enough provided this is done, from early morning staggered until midnight (Kuo, 1986). A generalized feeding schedule for marine shrimp larvae has been developed by AQUACOP (Figure 12).
Table 9. Composition of artificial feed used in Taiwan for grass prawn, P. monodon
|Stage or body weight of prawn||Shape of feeds||Size of feeds||Crude protein|
|P25 - 1g||Broken granules||< ø 2 m/m||> 40.0||3.3||< 18||< 3||< 1||< 12|
|1–10 g||Granules||ø 2.5m/mx2.5mm||> 38.0||3.0||< 18||< 3||< 1||< 12|
|10 g||Rods||ø h 3 m/m × 4 mm||> 35.0||2.8||< 21.5||< 3||<1||< 12|
Source: Liao, 1986
Figure 11. Relationship between food conversion ratio and productivity (B.T.C. method) in Taiwan
Source: Hirasawa, 1986
Intensive farms apply feeds at the rate 10–20 percent of shrimp biomass per day for shrimps less than 1 gram; for animals over 30 g, 2–4 percent of biomass is fed.
An example of feed application is shown below: (Stockwell and Williams, 1988).
Figure 12. Generalized feeding schedule for marine shrimp culture Source; Tacon, A. (1988)
Soybean levels greater than 10 percent can be used in feeds for shrimps and that the nutritional response to soybean meal in the diet of shrimps depends on the species of shrimp, size and the protein level in the feed, Research findings showed that soy-bean meal levels between 40 percent and 50 percent can be used to grow shrimp in the absence of natural food. It is possible that higher levels than 40–50 percent soy-bean in commercial feeds can be used for commercial shrimp production in ponds if micronutrients (vitamins and minerals) and semi-micronutrients are not limiting (Lawrence and Castillo, 1986). The ingredient composition of experimental diets used are summarized in Table 10.
|Day after stocking||Time of day|
Table 10. Ingredient composition of experimental feeds
containing 25 percent protein and 35 percent protein
levels used for tank studies
|Feedstuffs||Soybean content of experimental feeds|
|Experimental feeds containing 25 percent protein|
|Menhaden fish meal||15.8||9.6||3.3||0.0|
|Capelin fish oil||1.7||2.5||3.3||3.8|
|Experimental feeds containing 35 percent protein|
|Menhaden fish meal||18.7||12.4||6.1||0.0|
|Capelin fish oil||0.4||1.2||2.0||2.0|
All values are percent of feed on an as fed basis.
All feeds contained 1 percent lecithin, 0.5 percent cholesterol, 2 percent vitamin mix, 2 percent sodium alginate, 1 percent sodium hexametaphosphate and 2 percent fish solubles.
Calculated composition of experimental feeds containing 25 percent protein was: 25 percent protein, 8 percent lipid, 39 percent carbohydrate, 13 percent ash, 5 percent fiber and 10 percent water.
Calculated composition of experimental feeds containing 35 percent protein was: 35 percent protein, 8 percent lipid, 29 percent carbohydrate, 13 percent ash, 5 percent fiber and 10 percent water.
Source: Lawrence, Addison L., et. al., 1986
Formulated shrimp diets tested and proven under intensive rearing condition is summarized in Appendix 2. How to formulate feeds for shrimps is in Appendix 3.
There has been no comparative study conducted on the efficiency and cost of various commercial shrimp feeds used in the Philippines. The shrimp farmers simply go by previous experience in the use of certain feed brands they have tried in the course of farming operations. The cheapest feed may not be the best choice but often-times, the supply and availability of feeds at the time of need spells the difference in decision-making of farmers with respect to the use of feeds. Intensive shrimp farming requires a steady supply of feeds. Feed companies that are able to supply farmers at reasonable cost and terms of payment are able to obtain a bigger share of the commercial feed market.
Seeds supply is a critical factor in intensive shrimp farming operations. In the Philippines where supply of wild caught fry and hatchery seed production is still erratic, it is advantageous to have nursery ponds to keep adequate quantities of shrimp juveniles. The rearing of shrimp seeds is more complicated than the milkfish in the sense that shrimps molt and has different feed requirement during its larval stages of development. Keeping stunted juveniles may not have the same growth performance as the stunted milkfish fingerlings.
The cost of shrimp seeds is also high due to the unreliability of shrimp spawners. The full potential to produce shrimp juveniles is affected by several factors such as nutrition, diseases, water quality and skill of hatchery technicians. A shrimp hatchery has to have good facility and capability to hurdle all these limiting factors.
Regardless of size, hatcheries require two or more types of living food organisms for larvae rearing - such as unicellular algae or yeast for the protozeal stages; rotifers for the transitional stage from protozoea to mysis and postlarval stages of the shrimp fry. The manufacture of microencapsulated feeds using local feed ingredients should be made in order to simplify hatchery operations. This type of feed has been developed abroad and distributed in the Philippines and other ASEAN countries (FRIPAK). However, the high cost of this feed material does not encourage small hatchery operators to rely on this imported product although available in the commercial market.
Since the production and supply of shrimp juveniles is still highly fluctuating despite hatchery technology available in the Philippines, it is better to adjust the shrimp rearing management techniques according to prevailing conditions. Better use of rearing facilities such as the nursery and grow-out ponds would result to higher production.