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6.1 Outlook for Feed Resources
6.2 Outlook for Fertilizer Resources
6.3 Considerations and Limitations on Fertilization and Feeding Strategies
6.4 Economics of Fertilizer and Feed Use

6.1 Outlook for Feed Resources

It has not been possible to establish an official figure for the size of the entire feed manufacturing industry in the Philippines since only commercial operations are registered with the Government, and the registration of non-commercial feed milling is currently only voluntary. Although registration documents are used by the National Food Authority as the basis for corn import allocations during poor local harvests, this has only been an incentive for the larger and medium-scale non-commercial feedmillers who are not willing to take the risk on local supply or substitutes. Feed production by small-scale and backyard operations are consequently almost totally unaccounted for. Furthermore, concerning registered commercial and non-commercial production, it is also important to note that it is common practice for most feedmillers (as well as farmers and other business entities) to understate their actual production for various economical reasons.

The latest available registered national mixed feed production was 1.56 million mt in 1993 based on commercial and non-commercial operations (Animal Feeds Standard Division, 1995a). However, actual feed utilization is far greater and was estimated recently to be as high as 7.5 million mt (Villacorte, 1994). Using the 1994 import data for soybean oil meal of 655,066 mt (Table 33), a commodity which is specifically traded for use within animal feeds and has no competing local production (locally produced soybeans are used only for human consumption), an average soybean inclusion level of 10-15% in the feed would indicate a total feed volume of about 4.4-6.6 million mt. Furthermore, the importation of 111,147 mt of fish meal alone already represent 2.2-3.7 million mt of feeds at an average inclusion level of 3-5%. Considering the current availability of these and other major raw materials, it is reasonable to assume therefore that the actual compounded feed utilization in the country is at least 6 million mt annually. Requirements for the major feedstuffs based on this feed volume have been estimated and are shown in Table 75 (these figures do not include the largely unmonitored use of simple or single ingredient feeds, such as rice bran, corn bran, coconut meat, or cassava, by small backyard farmers).

The country’s MTADP for 1993-1998 aims to increase aquaculture production by 16.5% per year (including seaweeds), poultry and pig population by 5-6% per year, and cattle population by 12% per year (Section 2.8). In fact, the favourable economic climate in recent years has actually improved upon these targets. For example, the remarkable growth of finfish farming, particularly high-density milkfish culture and tilapia cage culture, is projected to expand annually the feed market for these species by at least 15%. The poultry and livestock sectors on the other hand have been registering annual growth rates of at least 6-8% with broiler chicken production expected to grow by as much as 10-15% in 1995. These developments and growth targets will therefore exert tremendous pressure on the country’s feed resources in the not so distant future.

From Table 75 it is evident that, with the exception of copra meal, the supply of all locally produced major feedstuffs is already critically low, if not already insufficient. This is especially the case for seasonal feed ingredients like rice bran and yellow corn (Figures 1 9a-c and 22a-c). Based on the MTADP, the Government aims to increase rice (paddy) production to 12.10 million mt and corn production to 7.0 million mt by 1998 from 1993 production figures of 9.43 million mt and 4.80 million mt, respectively. These targets represent annual yield increases of only 5.3% for rice and 4.4% for corn. Clearly, these modest growths will not be able to cope with expansion needs of the animal and fish feed manufacturing industries - inevitably leading to more severe seasonal fluctuations in the supply and price of rice bran and yellow corn. For example, the rice shortage that occurred during the third and fourth quarters of 1995 drove the price of rice bran up to an all time high of US$ 260-270/t from a price of normally less than US$ 155/t. This incident disrupted the operations of many fish feed manufacturers with some even having to cease production for several days. It is now believed by a growing number of feed millers that the country would soon have to import rice bran from neighbouring countries such as Thailand or Vietnam. Wheat pollard and wheat bran also have similar nutritional values to rice bran and are often used as substitutes. However, like rice bran, the supply of wheat bran and wheat pollard are also very limited, and will likely remain so as these feedstuffs are only by-products arising from the processing of bread flour.

Of all the major commercial feeds, fish and shrimp feeds require the highest protein level (Appendix 3). High protein feedstuffs such as fishmeal and soybean meal are thus most valuable in aquaculture. Compared to imported fishmeal, the quality of local fishmeal, including protein level, quality and freshness, is generally low and inconsistent. For example, within canneries, fish waste is often held for many hours at room temperature until a substantial volume is accumulated before this is brought to the processing plant. Furthermore, because of the rapid turnover of the local fish meal due to short supply, most manufacturers do not normally find it necessary to add antioxidants. Some fish meal manufacturers use spoiled fish obtained from fish landing sites or fish markets while village level fishmeal is produced from salted sun-dried fish. These quality aspects are generally not much of a concern for poultry and livestock feed which tend to utilize only 3-5% dietary fish meal. However, for aquafeeds which use between 12-35% fish meal, the risk of encountering dietary problems is high. Thus, local fishmeal are never used within shrimp feeds, and only local fish meal from tuna, when available, is utilized in commercial fish feeds.

The bulk of the tuna fishmeal produced within local fish canneries usually goes directly to a few large poultry and livestock feedmillers in Metro Manila and Cebu, and at least two large canneries and feedmills actually have related ownership. The situation therefore leaves little chance for small feed manufacturers to avail of the local tuna fishmeal supply. The stagnant local capture fisheries production (Figure 9) and the Government’s thrust in improving handling, processing, and utilization of fish for human consumption, will make the supply of fishmeal even more limited in the coming years. Aquaculture’s growing demand for fishmeal will therefore have to depend upon the imported supplies. In 1994, fishmeal imports reached 111,147 mt and was valued at US$ 38,264,630. With global concerns over the supply and availability of fishmeal in the future (Tacon, 1994), there is an urgent need to reduce and at least partially substitute fish meal with other sustainable and more cost-effective sources of protein.

Soybean, which has the highest protein level of all commercial plant feedstuffs, is increasingly being used as a fishmeal replacer (Tacon, 1 994) within Europe and the USA for such species as shrimp, salmon, and tilapia. In the Philippines the use of soybean oil meal within commercial feeds is only between 20-35% for milkfish and tilapia, and 10-20% for shrimp (Table 34). Moreover, there is little ongoing research effort to promote the greater use of soybeans, this being an imported feedstuff. Although the Philippines has vast tracts of land ideal for producing soybean (The Committee for Soybean, 1986), the local production of this legume for use in feedstuff is not currently economical for farmers. The largely small-scale and non-mechanized farming practices in the country, together with a multi-level marketing system (Figure 30) and the high cost of domestic transportation, makes local soybean more expensive than imported soybean.

The present trend of utilizing full fat soybeans within aquaculture feeds so as to benefit from its high lipid content (20%) and additional useful components such as lecithin (Wee, 1991; Lovell, 1990), should also be considered by the local aquafeed industry. In as much as the country imports soybean oil and lecithin for use in fish and shrimp feeds, the use of full fat soybean could significantly reduce the need for using imported soybean oil. Contract growing arrangements, such as those employed by some food companies, may perhaps be adopted by aqua feed millers directly with farming cooperatives so as to ensure the continuity and quality of supply, at a more stable cost.

Copra meal is the country’s largest local feedstuff resource with production probably in excess of 1.5 million mt annually. Unfortunately, the maximum level of copra that can be incorporated into feeds is only about 15-20% due to its low digestibility, low protein quality, and susceptibility to mycotoxin contamination. There has been little commercial interest in this regard to increase its utilization. Instead, copra meal is exported in large quantities, in particular to Europe for use as feed for cattle. In 1994, total copra meal exports amounted to 574,223 mt (Figure 24) valued at million US$ 53,015.9. Ironically, part of this product was imported back into the country in the form of milk and meat. It follows therefore that copra meal and other coconut related byproducts should be given greater attention by the government and the feed industry on how to increase their nutritional value and use in animal feeds. Coconut oil extraction, is not necessarily limited to producing copra as the by-product. Other processing methods that provide more nutritionally favourable means of improving the dietary value of coconut meat are available, although commercially attractive processing systems have yet to be developed. In a recent study by de Leon and co-workers (1995), it was demonstrated that fermentation of coconut flour can raise its protein level to 31.22% from around 17.24% (Gerpacio and Castillo, 1979). Total amino acid levels, including both essential non-essential amino acids, were also improved by 68.51%, 32.80%, and 21.49%, respectively. The nutritional as well as economic value of this high-protein by-product within poultry, livestock, and aquaculture feeds has not yet been tested. If its use proves to be favourable, the product may substantially reduce dependence upon fishmeal and other imported protein-rich feedstuffs.

Experience in the Philippines shows that shortages in the supply of major feedstuffs will tend to result in lower quality feeds. Many feed manufacturers, for example, tend to stock rice bran and corn during months when the supply is most abundant and at the least cost. However, this security in supply is attained at the expense of the freshness of the feedstuff. Rice bran in particular has a powerful enzyme system which is activated during the milling process and causes roughly 30% of its oil to hydrolyze into free fatty acids and glycerine within weeks depending on the temperature and ambient conditions (Enochian et al., 1981). Feed quality also suffers during these lean months as marginal quality ingredients or alternative feedstuffs are often used by force of circumstance. Unscrupulous traders take advantage of the frequent supply shortage by selling substandard or adulterated feed ingredients, particularly in the provinces where farmers have no access to feed laboratories. Adulteration complaints reaching BAI include the incorporation of rice hull with rice bran, low protein fishmeal with high quality fishmeal, starch with amino acids and vitamin-mineral premixes, among many others (Villacorte, 1994).

6.2 Outlook for Fertilizer Resources

In the use of fertilizers in aquaculture, Juliano (1985) reported that the average inorganic and organic fertilizer utilization for milkfish ponds was approximately 94.3 kg/ha/crop and 461.3 kg/ha/crop, respectively. Assuming an average of three crops per year and a total fishpond area of 200,000 ha, the annual fertilizer requirement of the aquaculture industry would be 56,580 mt of urea and phosphatic fertilizers (mainly 16-20-0), and 276,780 mt of chicken manure. These volumes represent 3.8% of the total chemical fertilizer sales for 1994, and 23.5% of the total chicken manure supply during the same year.

The supply and production of nitrogenous and phosphatic chemical fertilizers is a global resource phenomenon and is beyond the scope of this Atlas. As for chicken manure, its availability within the key brackishwater fishpond areas and chicken growing provinces are shown in Table 76. It can be seen that nearly half of the top 1 5 brackishwater farming provinces are deficit in the supply of chicken manure as far as fishpond requirements are concerned (not considering other competing uses). Of these provinces, Zamboanga del Sur and Panay island have the greatest shortages amounting to about 38,000 mt and 14,000 mt, respectively. Other provinces likely to have chicken manure supply problems include Masbate, Bataan, Lanao del Norte, and Western Samar. On the other hand, the neighbouring provinces of Batangas, Nueva Ecija, Bulacan, Pampanga, Rizal, Cavite, Tarlac, Quezon, and NCR exceed fishpond manure requirements by as much as 700,000 mt. Cebu, Negros Occidental, and Leyte are the only provinces in the Visayas and Mindanao with a substantial oversupply of chicken manure for fishpond use totalling to around 90,000 mt.

The prospect of transporting chicken manure to deficit areas is not economical unless the distances are short, such as between Cebu and Panay islands. The cost of shipping and/or trucking and handling these bulky fertilizers can easily double its cost to US$ 0.07-0.08/kg. At this price and with a milkfish farmgate price of US$ 2/kg, it is actually more profitable to feed the fish directly, and use the 3-5 week growing period for natural food as additional culture days instead.

6.3 Considerations and Limitations on Fertilization and Feeding Strategies

6.3.1 Manure loading in fishponds
6.3.2 Development of specific fertilization strategies
6.3.3 Maximization of pond carrying capacity
6.3.4 Use of low digestibility feedstuffs
6.3.5 Initiation of supplementary feeding
6.3.6 Production of farm-made feeds
6.3.7 Development of feeds for semi-intensive culture

6.3.1 Manure loading in fishponds

The regular application of manure over the culture period as a fertilizer and indirectly as a feed is well established in the pond culture of tilapias and carps in many parts of the world. Fish yield in properly designed and managed manure-loaded ponds can reach 5-10 t/ha/y without any supplemental feeding (Schroeder, 1978). In Luzon, weekly manuring is starting to be practised with stocking densities of 20,000-40,000/ha within freshwater tilapia ponds. The benefits of manuring milkfish ponds have yet to be properly quantified and established. The problem with manure loading in extensive milkfish culture is that the ponds are shallow, averaging 25-50 cm, capable of supporting only a maximum biomass load of 1,000-1,500 kg/ha. Beyond this, dissolved oxygen (DO) depletion, growth retardation, and fish kill becomes a serious problem; this is especially true during the summer months when salinity and temperature are high (resulting in low DO solubility) and when spring tides are relatively low. As manure adds up to the DO demand of a pond, even moderate levels of manure application can cause water quality to deteriorate in milkfish ponds. This in turn exposes the animals to stressful and sometimes lethally low early morning DO levels. For example, in the study conducted by Sumagaysay and Chiu-Chern (1991), production of milkfish within a pond fertilized with chicken manure broadcast daily at 3.5% fish biomass per day (computed on ash free-basis) was 27% lower than that of fish fed a diet of similar protein and energy load. Although primary productivity was highest within the manured pond, levels of nitrite, ammonia, as well as microbial activity, were also high.

Manuring within milkfish ponds will likely find valuable use only in relatively deep ponds. Experience of a farmer in Negros Occidental shows that a net biomass load approaching 2 t/ha in a 1 m deep water can be supported by daily cow manure application alone at 5-10% (moist weight) of the bodyweight provided that DO levels are maintained above 2 ppm. Manure application provides a practical means of reducing feed use and improving feed conversion; its application though should be made with consideration on the capacity to maintain the pond water quality, as well as on its possible effect on the flavour and market acceptability of the product. Compared to tilapia, the yield of milkfish ponds from manuring will probably be less since the latter species is more adapted to polluted environments, and to feeding on detritus.

6.3.2 Development of specific fertilization strategies

The combined use of inorganic and organic fertilizers for growing natural food organisms within pond culture operations is popular throughout the Philippines (Section 5.2). However, these practices tend to be generalized without specific reference to critical soil or water parameters. Many studies have already indicated that factors such as the soil organic matter, pH, nitrogen, phosphorus, micronutrients (e.g. Mg, Mn, Bo, etc.) have a profound effect on the primary productivity of fishponds, although information on the development of appropriate management strategies are still very much lacking. For example, in alkaline soils (typical within new ponds situated in calcareous areas such as parts of Cebu, Guimaras, Bohol, and General Santos), good growth of natural food is difficult to realize since high pH fixes phosphorus, making it unavailable. Alkaline soils are also a common problem within shrimp ponds recently converted to milkfish culture due to the build-up of agricultural lime. The regular fertilization practices will never produce luxuriant growth of natural food in these situations. However, use of higher levels of organic fertilizer and phosphorus during pond preparation, and higher and more frequent doses of phosphorus during culture, reportedly can produce good lab-lab growth. On the other hand, acid sulfate soils (which severely curtail natural food production and reduce fish growth) are a serious concern within many brackishwater areas around the archipelago. Under very low pH conditions, liming and fertilization, even frequently and in large quantities, have been shown to be of little benefit in increasing natural food production. The proper reclamation procedure and management of acid sulfate soils is therefore crucial in the efficacy of fertilization. This technology has in fact already been developed by the Brackishwater Aquaculture Center (University of the Philippines at the Visayas) in Leganes, Iloilo. At present fertilizer application rates are based largely on “generic” recommendations or experience. There is an urgent need to fine-tune fertilization strategies under different soil conditions, environments, and culture practices (much like that in agricultural crops), so as to improve the efficiency of fertilizer use in aquaculture.

6.3.3 Maximization of pond carrying capacity

Well managed extensive milkfish ponds usually attain a harvest biomass of 800-1,000 kg/ha/crop with natural food. It is quite obvious that there is little margin left for increasing production before the critical load of 1,000-1,500 kg/ha is exceeded. Moreover, even raising the biomass load near the pond’s carrying capacity will already have an effect on water quality and therefore fish growth and production. With the exception of a small number of extensive milkfish ponds which can hold water close to 100 cm, any sizeable increase in the yield in extensive culture would have to first deal with increasing the carrying capacity of the pond.

A constraint in the design of many extensive ponds which affects carrying capacity is the size of the pond gate. It has always been a tradition to make the gate opening only one metre wide even if the pond is large. Because of this the capacity to change water within most milkfish ponds is limited. This problem is further aggravated by the addition of bamboo slots to screen out exotic or nuisance fish. It is now known from experience in shrimp farming that the gate width can be readily increased 1.2-1.3 m without compromising its structural soundness. The installation of a separate drain gate on the opposite side of large ponds also helps to improve the efficiency of water change, especially in large or narrow ponds. As for screening out predators and competitors, a bag net or a semi-circular screen placed around the gate allows freer water flow. These management measures concerning the use of the pond gate can result to at least a 25% improvement in the capacity for tidal water change. This in effect could support a potential additional biomass load of 200-375 kg/ha over the standard carrying capacity of extensive ponds.

Cruz (1996) compared different methods for increasing the carrying capacity of milkfish ponds and concluded that the installation of a pump at a cost of US$ 750-1,000/ha (one 15,000-20,000 gpm pump unit per 10 ha water area) was a more cost-effective investment compared with deepening the pond (by 20-25 cm) which cost around US$ 1,900-2,300/ha. The use of a pump not only allows raising the pond water level but also permits more frequent water change even with relatively low tide water. Within semi-intensive milkfish ponds, pumping allows biomass loads to be increased to 3,000-4,000 kg/ha without the need of mechanical aerators.

6.3.4 Use of low digestibility feedstuffs

The use of feedstuffs with low digestibility and high fibre content results in a higher feed conversion and produces more faecal waste which can have a negative effect on the aquatic environment. Indeed, the recent spate of environmental problems encountered in intensive shrimp farming and in freshwater tilapia cage culture has been attributed to a large extent upon unconsumed and undigested feeds. As a result, many researchers are now questioning whether the economic benefits of utilizing these types of feedstuff justify the greater pollution they create. In one of the country’s leading fishery research centres, concerned nutritionists have already decided to abandon the use of copra meal. However, sustainable farming is not necessarily more attainable through the use of better quality ingredients. Equally important is the volume of feeds used in relation to the culture system and the surrounding watershed. Thus the environmental concerns associated with the use of low digestibility feedstuffs can perhaps be avoided if these feeds are only used in low density culture, or in “open” environments such as in brackishwater and marine cages or pens. The latter culture systems, as already mentioned, will be the largest growth area of aquaculture in food production.

Within earthen ponds, undigested feeds resulting from the use of high fibre ingredients become a substrate for the microbial growth and eventually contribute to the pond’s primary productivity via the detrital food web (Shroeder, 1978; Naiman and Sibert, 1979). Studies conducted at the Brackishwater Aquaculture Center in Iloilo with milkfish (Sumagaysay and Chiu-Chern, 1991) and tilapia (Fineman-Kalio, 1984) have demonstrated the economic potential of using high fibre feeds for producing moderate fish biomass levels. With limiting supply of most of the country’s conventional feed ingredients, these high fibre feedstuffs, which abound locally, should be given a second look as to how to improve their nutritional value (e.g. through bioaugmentation, fermentation, or enzyme treatment), application, and utilization within aquaculture feeds and environments.

6.3.5 Initiation of supplementary feeding

When growing milkfish, fish stocks are normally transferred to a series of two or three compartments of increasing sizes as natural food is consumed in each pond. Starting with fingerlings in transition ponds, these may be transferred to a formation pond (optional), and then finally to a rearing pond where they attain harvestable size. With the fish biomass increasing at each stage, stocking density is correspondingly reduced. A favourable bloom of lab-lab with proper fertilization is consumed within 30-60 days. Although the biomass load is highest in the rearing pond, in terms of net biomass productivity (NBP), this is similar in all compartments - typically around 400-500 kg/ha per crop for relatively productive ponds, with stocking size or stocking density having little effect (Cruz, 1996). This figure is essentially the natural food carrying capacity in brackishwater milkfish ponds. Beyond this biomass, natural food is overgrazed and any desired increase in productivity can only be realized through the introduction of supplemental food sources.

Extensive farmers usually start supplementary feeding when the bulk of the natural food has already disappeared. Visually estimating the available natural food, however, is difficult, and as a result the introduction of supplementary feed is often delayed. It is thus recommended that feeding be initiated before much of the natural food is consumed, that is, below a net biomass gain of 400-500 kg/ha. Such practices have the following important advantages: (a) fish growth is not disrupted as natural food starts to be limiting, (b) the presence of natural food improves the performance of supplementary feeds by complementing possible limiting nutrients in the formulation, and (c) the availability of other supplemental food sources prevents the excessive grazing on the natural food thereby allowing some degree of continued growth. Although natural food carrying capacity will vary from pond to pond this is relatively easy to establish after several crops.

6.3.6 Production of farm-made feeds

For many years now, various government institutions have been promoting the production of farm-made feeds for poultry, livestock, and fish. The prospect of producing farm-made feeds to reduce feed cost are attractive not only for large-scale farming operations but also for farms that are located in distant rural areas, where hauling cost is high, the supply of commercial feeds is irregular, and the freshness of feeds is generally lower. As far as aquaculture is concerned, however, on-farm feed manufacturing has failed to prosper in the country, and this can be explained by: (a) high cost and erratic supply of raw materials, (b) high capital requirement, and (c) lack of equipment designed for small-scale operation.

On-farm feed milling operations are disadvantaged by a higher cost of raw materials compared to large feed manufacturers who purchase at a bulk price; this difference is as much as 20-30%. On the open market, traders of feedstuff also tend to be more accommodating as far as credit is concerned to clients who purchase in large quantities whereas small purchases usually have to paid in cash. Furthermore, during lean months or shortage in raw material, it is almost always the large feedmiller that is prioritized by the trader. Many non-commercial poultry and livestock feed manufacturers for these reasons are already shifting back to the use of commercial feeds which is turning out to be more practical and economical.

In the case of NFA imported yellow corn, about 70% ends up with large livestock and poultry feedmillers. Although NFA also reserves yellow corn for small feedmillers, for one reason or another, many do not regularly avail of their allocation. Instead, they procure from dealers in the open market often at a higher cost. As a result, such irregular and unpredictable purchases of small feedmillers disqualify many of them from the usual 60-day credit term extended by the NFA (Villacorte, 1994).

The future of on-farm feed manufacturing in aquaculture will also depend greatly on the availability of simple and low-cost feed processing equipment. Those currently available, imported and locally fabricated, are designed more for the production of shrimp diets and are not practical for use in fish feeds.

6.3.7 Development of feeds for semi-intensive culture

Posadas (1988) identified semi-intensive culture, with its lower feed cost and inputs, as the most cost-efficient farming system in the country should shrimp market prices fall. During 1989 when world shrimp prices indeed collapsed, three feed companies produced special feeds for semi-intensive culture as farmers needed to lower production costs. However, although the feed cost 10-20% less than standard feeds, it failed to gain popular use by the industry and these feed lines were eventually abandoned by the manufacturers. The failure of semi-intensive shrimp feeds in the Philippines can be traced mainly to: (a) the insistence of the many farmers to use the feed for intensive densities, with obviously disastrous results, (b) the substitution of high quality ingredients, in part or fully, with untested ingredients (e.g. fishmeal, see Section 3.3.1), and (c) the lack of sufficient field trials of the formulation.

In fish culture, feed companies have yet to venture into the production of semi-intensive feeds. But with fish prices relatively favourable, there will probably be little commercial interest in such feeds since most farmers at present are more concerned on getting better growth than obtaining a lower feed cost. Also, the market for semi-intensive diets is seen to be limited to pond culture and the farming in eutrophic lakes where natural food supply to complement the feed is generally adequate. In marine cage and pen culture environments where natural food is easily overgrazed, semi-intensive feeds will find very limited use.

Experience in shrimp culture clearly indicates that much research still needs to be made in the development of low cost feeds for semi-intensive culture. The finfish industry should learn from this experience and prepare in the eventuality of lower farmgate prices. As in shrimp culture, feeds also account for the bulk of the production cost in fish culture.

6.4 Economics of Fertilizer and Feed Use

Contrary to the belief of many traditional farmers, the use of natural food (i.e. fertilization) in extensive culture is not always more profitable than the use of feeds. The economics between these two production strategies vary depending on several production and cost factors, primarily: the NBP of the pond, cost of growing natural food, cost of the feed, production cost, and farmgate price of the product. Cruz (1996) proposed the following approach for evaluating the economics of fertilizer and feed used in milkfish culture with consideration on the above variables (all prices quoted are in US$ based at a conversion rate of US$ 1 = P25.71):

Feed savings from the use of natural food = equivalent feed value of natural food - total cost of growing natural food
With knowledge from previous production data on the NBP of a specific milkfish pond, it is possible to estimate the equivalent feed value of natural food using the following formula:
Equivalent feed value of natural food = NBP/ha × FCR × feed cost/kg
It is important to note that although NBP is typically around 400-500 kg/ha for relatively productive ponds, it can still be higher or substantially lower. NBP can differ greatly between (and within) farms depending on factors such as the quantity and quality of inputs, soil type (e.g. OM level, acidity), intensity of sunlight, etc. As for the FCR value to be used, this should consider factors such as feed quality and feeding management, stocking size and harvest (or transfer) size, culture system (i.e. stocking density) - all of which have a profound effect on feed conversion. Additionally, FCR should be based on an environment where there is very little natural food available. Thus, given the sample data below based on an extensive culture operation, the natural food utilized during culture in terms of feed value is equivalent to around US$ 352.8/ha.

NBP = 450 kg/ha
FCR = 1.6
feed cost = US$ 0.49/kg (commercial)

Equivalent feed value of natural food

= 450 kg/ha x 1.6 x US$ 0.49/kg

= US$ 352.8/ha

Computing for the cost of growing natural food is quite complicated and involves more than the cost of organic and inorganic fertilizers, lime, molluscicide, piscicide, and labour. Not many milkish farmers realize that in the propagation of lab-lab which normally takes 3-4 weeks, time is sacrificed; this is actually opportunity loss in terms of crop cycles per year and should therefore be accounted in the total expense of growing natural food.

The concept of opportunity loss assumes that with feeding, the propagation period for natural food could instead be utilized to extend the culture period and grow the stock to a bigger and more valuable size (since 3-4 week of extra growing period is added at the end of the culture, the assumptions for biomass growth and profit data should be based on the projected harvest size and not as an average of the crop). Computation for the opportunity loss essentially involves the potential loss in profit based on the expected additional gain in biomass during the period sacrificed.

Total cost of growing natural food = (organic fertilizer + inorganic fertilizer + lime + molluscicide + piscicide + labour) + [total stock x growth/day x days required for growing natural food x (farmgate price/kg - production cost/kg)]
Given the following figures below for extensive pond culture at a prevailing farmgate price of US$ 1.95 kg for 300-400 g fish, the total cost of growing natural food is approximately US$ 320.3/ha.

1 ton chicken manure

= US$ 38.9

2 bags urea + 1 bag 16-20-0

= US$ 40.1

0.25 ton agri. lime (based on 7 ton/ha/y at 4 crops/y)

= US$ 5.8

molluscicide + piscicide

= US$ 27.2


= US$ 11.7

total stock/ha

= 3 000 pieces


= 4 g or 0.004 kg

days required for growing natural food

= 21 days

farmgate price/kg

= US$ 1.95 (at 300-400 g size)

production cost/kg

= US$ 1.17

Finally, the savings obtained on a per hectare basis from the use of natural food as compared to that of commercial feeds can be derived as:

Feed savings from the = US$ 352.8 - US$ 320.3 = US$ 32.5 use of natural food
It is apparent from the assumptions and computations made that the cost savings from using natural food is not really that large since the opportunity loss alone (total stock/ha x growth/day x (farmgate price/kg - production cost/kg)) already amounts to US$ 196.6 as compared to US$ 123.7 for the cost of inputs. Moreover, in the Philippines, the cost of chicken manure, molluscicide, and piscicide are probably among the highest in the region. It is worthwhile noting that the cost of controlling snails and nuisance fish used to be only around US$ 10/ha prior to the FPA’s banning of triphenyl tin compounds as molluscicides and organophosphates as piscicides in the early 1990s (these chemicals were found to have high residual toxicity, but since no effective pesticides have been found to date this has created a thriving market for costly and unproven substitutes, as well as smuggled triphenyl tins which are being sold at no less than US$ 200/kg or ten times its original price when it was still legal).

The cost savings of US$ 32.5/ha from natural food is based on data and practices in Region VI. The actual economic advantage of using either fertilizers or commercial feeds will differ between each area and will largely be governed by the farm’s proximity to Metro Manila and other urban centres (i.e. higher farmgate prices and generally lower cost of feeds and fertilizers), the season of the year, and the farm’s level of technology.

A number of important points can be inferred on what has been discussed and in relation to the equations given above. In areas where farmgate prices are high (Table 1 6b) or during seasons when prices are expected to peak (e.g. low fish supply, Easter, Christmas), growing natural food actually becomes disadvantageous in extensive culture and more so in semi-intensive and intensive culture since the opportunity loss from its propagation becomes correspondingly large. Fish supply in the country is normally lowest during the last 3-4 months of the year when heavy rains, monsoon winds, and typhoons restrict fishing as well as reduce fishpond yield due to poor natural food availability. During this time of the year, it follows therefore that profitability can be maximized with feeding by stocking higher. Ironically, farmers depending on fertilization are forced to stock less because of the lack of natural food.

In conditions where milkfish prices are low such as in production areas far from the demand centres, or when fish supply is abundant, fertilization will tend to be a more economical production strategy in extensive culture. When fertilization is employed, its advantage over feeding can be increased if the pond can be made more productive (i.e. higher NBP) and the cost of inputs and opportunity loss can be reduced. Realistically, it is probably only with the NBP and the growing period for natural food that significant changes can be made. With a productive pond soil and good management practice, for example, NBP with lab-lab as the natural food can be further increased to a maximum of 500-600 kg/ha/crop (it will be interesting to know to what extent manuring in deep ponds can raise the NBP; see Section 6.3.1). On the other hand, there are claims by some processed organic fertilizer manufacturers that the use of their product can cut down growing periods for natural food to around two weeks or less during the summer months. As far as the other cost and production factors are concerned, however, the farmer has little influence.

At present, with farmgate prices for milkfish normally above US$ 2/kg in major demand centres, the use of feeds is economically attractive both in semi-intensive and intensive farming systems where production costs are generally below US$ 1.2/kg and US$ 1.5/kg, respectively. The favourable market conditions and the increasingly credit- oriented marketing of feeds will likely encourage greater use of commercial diets even in extensive milkfish pond culture.

As for other pond reared species, the current approach for evaluating the economics of fertilization and feeding will probably also apply, provided that the NBP and other expense and production parameters are first established.

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