The high productivity of the waters of Laguna Lake has been studied and established by Dendy, Parsons and Rabanal. The native fish species of the lake were classified by Parsons as of poor quality and this has been confirmed in the course of this study and by Delmendo and Shimura. A pilot scale experiment to exploit lake productivity in producing fish was made by the Laguna Lake Development Authority in its Looc fish corral project. This experiment is still in progress.
There are various ways of rearing fish in impounded waters for intensive production. One is in fish ponds, another is through aquaculture utilizing enclosures, cages, etc. The high cost of land around the lake and the unsuitability of pond construction in the places surveyed in the marginal lands around the lake, necessitate aquaculture experimentation in order to determine economical and feasible methods of fish production.
The basic strategy is to use the lake as the medium for fish culture. On this
basis, relatively inexpensive fish rearing facilities could be provided in the form of
pens, corrals or even diking of moderate size bays of the lake. For example, the Looc
fish corral cost between 
2 000 and 3 000 per ha. This bamboo corral, although of
limited life expectancy, seems to compare favourably with the cost of 15000 per ha for
the unlined (no bank protection) Lumban fish pond.
The next step in the lake development is to provide fingerlings of the desired species to stock the pens. This will require establishing fish hatchery and nursery ponds equal to about 2 to 3 percent of the aquaculture areas. This percentage assumes that the species combination will include about 50 percent of stocking material which will be available from other fingerling sources, outside the lake area, i.e. milkfish or mullet.
The species to be used should be selected according to the following criteria:
The species combinations should utilize to the maximum all the components of the aquatic biota in the lake.
The fishery harvest should yield the highest net income per unit of pen area or water volume.
Use of selected species, such as tilapia and Chinese carp, for reduction of lake algae, clearing of vegetation or control of undesired species.
Before substantial capital investments are made in aquaculture facilities, adequate pilot and experimental programmes must be undertaken. These programmes would be carried out in limited size fish pens and experimental ponds. In addition to work on fish species, experimental programmes on utilization of low cost, locally available materials for supplemental feeding will be required.
The LLDA is negotiating for the use of the Bay Fishery Station of the Philippine Fisheries Commission. The station has a total area of 8 ha, of which 6 are already developed. Appendix 3 outlines a suggested development plan. The work programme herein proposed for the station is as follows:
Begin immediate work on hatching and rearing fingerlings of common carp, Chinese carp, tilapia and various native species, as further described in paragraph 3.3.
In small size fish ponds at the station and in small pens on the lakeshore, undertake experimental work on using various species combinations and various feed supplements.
Undertake experimental work to determine low cost and durable fish pen construction methods and operational procedures.
In formulating species combinations to be used in fish culture based primarily on natural food utilization, the criteria are given in paragraph 3.1. Basically, the species combinations have to be based on the relative abundance of the various components of the natural food. The quantitative analyses of Laguna Lake productivity show the following possible utilization of the natural food components by species:
| Benthic larvae | - | common carp |
| Benthic algae | - | milkfish/mullet |
| Plankton | - | silver carp, bighead, Tilapia nilotica |
| Detritus | - | T. nilotica, common carp |
| Higher plants | - | grass carp |
| Shrimps, young fish of low quality - snakehead and catfish species | ||
All except the predatory snakehead and the catfish (Clarias) are to be obtained from outside sources. A model starting combination derived from a combination used in Taiwan but substituting milkfish for grey mullet is as follows:
| Common carp | - | 30% |
| Silver carp | - | 20% |
| Bighead carp | - | 3% |
| Milkfish | - | 40% |
| Grass carp | - | 2% |
| Predatory native species | - | 5% |
The native species in the foregoing list are substitutes for sea perch in the Taiwan combination. In a modified combination for Laguna de Bay, snakehead and Manila catfish might be suitable substitutes.
Following are shown the current market prices of fish as at July 1971:
MARKETPRICES OF FISH
(/kg)
| Common carp | - | 1.50 | - | 2.00 |
| Chinese carps | - | 2.50 | - | 3.00 |
| Milkfish | - | 3.00 | - | 3.50 |
| Snakehead | - | 3.50 | - | 4.00 |
| Manila catfish | - | 10.00 | - | 12.00 |
| Clarias | - | 6.00 | - | 6.50 |
| T. mossambica | - | 1.50 | - | 2.00 (100–150 g) |
(T. nilotica, which grows to 250 g or more would perhaps command prices of 3.00 to 3.50)
Various species, which might be utilized to maximize net returns from the lake fishery and to improve the efficiency of natural food utilization, are discussed below.
Carp - Several species of Chinese carp have been introduced into the Philippines over the past five years and have found acceptability in the market but the production of fingerlings for the species is as yet a low stage. In addition to the Chinese carp, rearing and experimentation with Indian carp is also considered desirable. Thus the experimental station should be concerned with production of the following types of carp:
Catla (Indian)
Tilapia - The starting combination includes a large percentage of carp, which are among the low-priced market species. A substitution for part of the carp group, utilizing Tilapia nilotica or T. aurea, would provide a species with similar feeding habits to those of carp but with a higher market value. The T. nilotica or T. aurea has a high rate of growth, it can reach 250 g, which is the preferred size in the local market, within six months; is an efficient utilizer of natural food, plankton and detritus; fits in the multiple fish culture, with or without supplemental feeding; and the origin of T. nilotica is Lake George, Uganda, which has similarities in environment to that of Laguna de Bay. No adverse environmental or fish culture impact is anticipated by the proposed tilapia introductions, as Tilapia mossambica of the same genera has been resident in the Philippines for more than five years. The relatively small size and low market value of the T. mossambica warrant its augmentation by an improved variety.
Native Species - As noted in paragraph 2.2.3, the grey mullet, milkfish and Manila catfish (kanduli), Arius sp., were formerly fished in Laguna de Bay. The milkfish is the only species for which fry and fingerlings can now be obtained on a sustained basis. The other two species are very highly priced, but their fingerlings are not available for fish farming purposes. It is proposed that the experimental station undertakes work to locate sources of grey mullet fingerlings along the shores of rivers and estuaries of the nearby coastline and that experimental work be undertaken on the propagation of native species, including the kanduli and snakehead.
The use of fertilizers, particularly inorganic compounds, probably will not be desirable for pen culture because of the multi-purpose usage of the lake for municipal and industrial water supply. Such fertilizers could contribute to the eutrophication process by unduly nourishing algae growth. On the other hand, some limited and carefully controlled experiments in utilizing fertilizers at locations remote from the proposed water supply plant should be tried.
A more desirable method may utilize the pen area on a dual purpose basis with duck raising, in which pens are maintained over the water area. The ducks would feed on natural foods, such as shrimp and snail. The duck manure would be readily consumed by fish species such as carp and tilapia. About 100 to 150 ducks per ha could be reared in a fish pen according to Dr. F. Woynarovich (personal communication). Fingerlings for stocking would have to be of 20 to 30 g size to avoid consumption by the ducks.
If feed grains such as sorghum or maize can be utilized, a fish yield beyond that
available from natural foods can be realized. Such grains are, as yet, basically imported.
The conversion ratio of the grain feeds is at best 1:3 and could be less. With respect to
the fish species noted in paragraph 3.3, the common carp would be the main beneficiary.
However, the cost of grain locally is about 0.50 per kg and the sale price of carp is
1.50 to 2.00 per kg, thus the economics of feeding become very questionable. Locally
available feeds are principally rice bran and copra cake, about which there is little
available information with respect to utilization by fish species. This should be an
important area of experimentation by the Authority.
The design of suitable fish pens is basic to the proposed plan of aquaculture development. Because this is primarily an engineering design problem it is outside the scope of this report to make other than general suggestions. The present bamboo fish corral at Looc is estimated to have a life of about three years before rotting and deterioration render it ineffective. A severe southerly typhoon, such as occurred in November 1970, could cause major damage at any time.
There is very little known oriteria on which to base such design. However, the
engineering staff of the LLDA is quite confident that an improved structure with a longer
life can be designed at reasonable cost. The margin of cost between the 2 000 to 3 000
per ha of the Looc corral and the more than 15 000 of the earth-diked Lumban project show
a large margin for improvement of the fish corral within the range of profitability, if
the fish corral can be given a longer life at reasonable cost.
One specific suggestion is made with respect to the desirability of protecting fish pens from damage caused by wave action generated by typhoon winds. It is considered very doubtful that fish pens in deep water, i.e. 2 to 3 m, can be designed to withstand such wave action. However, by judicious use of breakwaters at cove entrances to provide a semi-sheltered area, it may be possible to control wave action over a large area. The entrance to Looc Cove is a particular case in point, where limited breakwater construction could eliminate wave hazard over 80 to 100 ha, where only 40 ha are now developed.
Plastic coated small mesh type of metal fencing will be a more durable screening material but will have to be imported. Perforated, reinforced polyethylene sheeting material of great strength can also be used for this purpose.
The United Nations report proposes reclamation of a 3 700 ha portion of the East
Bay of Laguna de Bay by construction of lake dikes in a complex system of inner ponds.
The overall cost of the project is 75.5 million, seven years would be required for
construction and feasibility is based on intensive production of 5 t/ha. At this point,
there are no data on Laguna de Bay production that would justify or support this yield.
An alternative project, proposed herewith, is shown in Fig. 3. It would utilize the same area of the East Bay as in the United Nations report but only through construction of the lake dike. That dike would be constructed with suitable openings so that there could be free flow of water and boat passage from the East Bay headwaters into Laguna de Bay but only through screened openings that would prevent fish passage. There would not be any interior dikes and thus the effective area would be increased from 3 700 to 4 200 ha. The resulting pond or pen would be stocked and operated in accordance with the procedures that would be established in the experimental work programme. A cooperative effort would be necessary with respect to the fishermen presently operating in this portion of the lake.
The best information currently available indicates that the yield from this portion of the lake is less than 0.3 t/ha. If the proposed development could reasonably assure a yield of 2 t/ha, a computation made by the Regional Economist of the LLDA, but not included here, shows the construction cost of the proposed project would only be one third of the United Nations report plan and the internal rate of return would be in excess of 50 percent, as compared to less than 7 percent for the United Nations plan. The foregoing is an approximation and therefore details are not included here.
An assessment has been made of what the fishery programme proposed herein could
generate in investment. If the experimental work proposed yields satisfactory results
within two to three years, it is reasonable to assume that 5 000 ha of the lake area
could be developed into pen fish culture within ten years. A harvest yield of 2 t/ha
appears reasonable. Assuming a unit price of 2.50 kg, gross revenues would be
5 000/ha.
If fish pen construction at 3 000 per ha has a three-year life and at 10 000 per ha
a ten year life, then, excluding interest, the cost per hectare would be 1 000.
Operating costs could be:
| /ha | ||
| Stocking at rate of 6 000 fingerlings per ha | 500 | |
| Rearing, feeds and fertilizers | 500 | |
| Cropping and contingencies | 500 | |
| Subtotal | 1 500 | |
| Construction | 1 000 | |
| Subtotal | 2 500 | |
| Overhead and miscellaneous (50% × 1 500) | 750 | |
| Total cost | 3 250 | |
| Net profit/ha = 5 000 - 3 250 = 1 750 or Total return from 5 000 ha = 8.8 million |
This return compares very favourably with present returns from lake fishing with a
yield of 0.4 t/ha, an average price of 1.25 per kg, and a harvest cost of 200/ha.
| Return | = | 0.4 × 1 000 × 1.25 - 200 = 300/ha or |
| Total return | = | 300 × 5 000 = 1.5 million |
The net increase would be 7.3 million per year.
Fishing on Laguna de Bay as a livelihood is a marginal economic existence. The 90 000 ha lake has some 10 000 fishermen or about one for every 9 ha. The 40 ha Looc fish corral of the LLDA has four full time employees and up to eight at harvest time to avoid net displacement. If the greater yields and larger returns projected in the preceding paragraph are realized the results would be very beneficial for the population around the lake. As a matter of interest, the employees of the LLDA at Looc are lake fishermen. There is tremendous interest in the fish corral development by the local fishermen. If the experimental work and development programme proposed is successful, a follow-up or organization and know-how through extension work will be essential. There is already heavy pressure on the LLDA from fishermen, local entrepreneurs and municipalities for guidance and assistance in fish pen culture projects.
The proposed development programme recommends introduction of new species, which will have to be obtained by import from other countries. Precautionary measures will be essential to assure that the new species fingerlings imported are healthy and have satisfactory characteristics. The first step in importing new species will be to obtain necessary licences and permits from the Philippine Fisheries Commission to permit the desired imports. A determination must be made that the species selected for import are of good basic stock, that there is no incidence of disease among the stock and that the exporting country so certifies. After the imported fingerlings are received in the Philippines, a suitable period of quarantine should be enforced to determine that the imported fish are free of diseases and have satisfactory characteristics for development of the strain in the Philippines. If new genera are considered for introduction, careful studies should be made of possible implications with respect to disease, predation and effects on ecological balances.
