Results of the information-seeking activities indicated the existence of indigenous technologies on fishpen and cage culture. The former has matured through years of experience without necessarily benefiting from results of formal research. On the latter culture system, although some operators have ventured in it on their own, there have been considerable formal research done and findings are quite sufficient to warrant its inclusion in the LBFDP.
The technology and practical experiences gained in these two culture systems are briefly discussed in the following sections.
The main factors being considered in selecting a site for fishpen or cage are as follows:
It must be within the fishpen belt prescribed by the LLDA;
A place where there is sufficient or moderate water current;
Deep but firm mud. Hard and sandy or gravelly bottom is avoided;
Water depth should not be less than 1.5 m during the peak of dry season;
Should preferably be located in a place that is sheltered from the destructive effect of big waves and strong winds.
The size of existing pens varies from less than one ha to 100 ha. The present trends have shown however an increase in pen size up to 400 ha by large corporations.
Various shapes of fishpen exist and those found to be technically feasible are the square, rectangular, and circular. The two latter shapes along with proper wind orientation during construction deflect added load caused by drifting water hyacinths and other flotsams and increased height of waves during stormy weather.
The usual components of a fishpen unit are:
These components are held together in place by a structural framework, nets and other materials.
Framework. The barrier is an outside enclosure provided with strong framework and large-meshed netting materials. The net does not extend to the bottom mud but only at mid-depth of the water column. This is a design innovation which has been adopted to protect the inner main fishpen enclosure against waves and flotsams. Although an added expense, the operators have recognized the significance of this structure.
The main pen enclosure impounds the fine-meshed fry/fingerling nursery and grow-out compartments. The bottom of netting enclosures for nursery and grow-out is embedded at least one meter into the mud with appropriate anchoring materials. The upper side is provided with a line of floats at about 800 g each to keep the net upright in case of accidental detachment of the net from the posts and walings.
The framework for the barrier and pen enclosure consists of vertical posts supported with horizontal walings, and transverse and longitudinal bracings. The most common material for the framework is bamboo. However, among the many species of bamboo available, the one with thorns, Bambusa spinosa, when matured is the most preferred because of its durability and longer life in water. A piece of mature bamboo measures 10 to 13 cm in diameter at the base and 2.5 cm or more in diameter at the end with a length of about 12 m.
Wooden posts and trunks of the palm tree, “anahaw”, (Livistonia rotundifolia) are also used either purely or in combination with bamboo. A matured “anahaw” measures 20 to 25 cm at the base and 15 to 18 cm at the end with a length ranging from 12 to 13.5 m. The palm tree was claimed to last for up to 10 years or more in water. Although it is more expensive than bamboo, much lesser number is required in construction due to its larger size and longer durability, thus making it cheaper to use. It also saves time in construction. However, the number of persons needed to erect an “anahaw” is 10 or twice as much as in bamboo. In erecting anahaw, the smaller end is the one being driven into the mud. Hence, the base extends upward and beyond the water surface.
The BRI Report (1980) recommends in their design that the spacing of bamboo post for barrier and pen enclosure are 2 and 5 m, respectively. Other fishpens, however, use closer spacings (as close as 30 cm) especially in deeper waters and open areas.
The length of horizontal walings effectively cover four posts. Each span of four posts has three walings (Fig. 2). The pen enclosure has no walings, but instead the posts are erected in a tripod form.
The span for longitudinal cross bracing covers four meters. There is a pair of transverse supports every posts of the barrier.
A variation in the connection between the barrier and main pen enclosure was presented in the workshop. The proposed design by the BRI for LLDA has the barrier and pen enclosure constructed independently with one another (Fig. 2). A design presented by the participants during the workshop had the barrier and pen enclosure stakes or posts interconnected by bamboo above the horizontal waling which is just above the water line. This consists of horizontal connections in a zigzag arrangement called “cadena” or chain (Fig. 5).
Netting materials. The usual netting material for the pen enclosures and barrier are nylon, polyethylene, Kuralon and polyester. Polyethylene and polyester are used such that the former is used in portions submerged in water, while the latter is usually located in parts exposed to the sun.
An example of mesh size as recommended in the BRI consultants' design for barrier net is 152 mm (stretched) or 3" x 3" (3 knots/6"); for pen enclosure 22 mm (stretched) or 1/2" x 1/2" (14 knots/6"); and for nursery 10 mm (stretched) or 3/16" x 3/16".
Anchoring net enclosure. Some variations in the kind of anchoring materials were also brought out during the workshop.
The BRI consultants recommend in their design a molded concrete cement which is circular but elongated and provided with central longitudinal hole from one end up to the pointed tip. Each weighs 10 and 2 kg for the grow-out compartment and nursery, respectively and is buried in the mud at least 1 m together with the net.
Bamboo pegs (“talasuk”) 0.5 m long or more with longitudinal hole. When properly driven with the net at spacing of 0.5 to 1 m into the mud, it has been claimed by some fishermen participants to have withstood against the strongest typhoon that hit their area. It is readily available and cheap. Its main disadvantage, however, is the possibility of being uprooted. Once uprooted, the other pegs will follow and mass escape of the impounded fish usually occurs.
Stones provided with hole for tying the net rope. This weighs 1–2 kg and is buried into the bottom mud every 1.5 m. It is also readily available and cheap. The main advantage over the bamboo peg is it still sinks and pulls down the net if accidentally uprooted. Thus, fish escape is minimized.
Other contractors simply tie the bottom end of the nets to the bamboo posts prior to staking.
Ropes, twines and ties. The size of rope (polyethylene or polyrope) for ribbing the surrounding edge of nets, including joints is 6 mm. For the float line, the usual size is 10 mm. For stitching, 1 mm polyester twine is used.
For tying the bamboo together, rubber strips, polyethylene or polyrope and high density polypropylene are used.
Construction usually begins in February or during the prevalence of calm and gentle winds. It is also timed such that the enclosure is ready for stocking and culture by March to June. Sequencing of construction of fishpen components is also given consideration. One contractor begins and completes the nursery enclosure ahead of the barrier and main pen enclosure. Stocking the nursery with fry/fingerling immediately follows while construction continues for the remaining portion of the work. With this if the work is completed in two months or so, there is already available stock of the right size that can be released to the grow-out pen compartment.
Erecting posts vertically and in straight line especially during windy or rainy days. There are only few skilled persons who can do this kind of work.
Skill in stitching the corners and seams of nets, hanging and tying the nets and bamboo together, under the water. When done carelessly fish escape through the holes in corners and seams.
The milkfish (Chanos chanos Forsskol) is the main species for culture in the lake. Characteristics of milkfish which makes it suitable as a cultured species are:
plankton feeder, although it takes other kind of food such as shrimps, filamentous algae and organic detritus;
can easily be acclimatized to freshwater environment;
grows fast in the lake, even without artificial feeding it grows from fingerlings to harvestable-size of 300–500 g in 4 to 5 months; and
it has good demand and price as a food fish in the Philippines.
Milkfish fry are collected along the coasts and reared in ponds for 21 to 30 days up to a fingerling size of 6 to 8 cm. There are now several nursery pond operators of supply pond-reared fingerlings to the pen operators of Laguna lake. About 300 million fry are needed every year to stock the fishpens of Laguna de Bay (Mane, 1981). The common source of fingerlings are Dampalit, Malabon and some towns of Bulacan such as Hagonoy, Obando and Paombong. Other sources are already quite far from the lake. The season for the production of milkfish seeds is from March to September reaching a production peak in May and June.
Nursery pond operators usually own a “pituya” (livefish boat) which delivers the stock to the grow-out farmers. To minimize stress, the industry has already developed a system for the counting of fingerlings. An example is counting the actual number of sampled fingerlings in one scoop or container. Counting is then expedited by just counting the number of scoop and multiplying it with the counted number per scoop.
Delivery of fish seeds by pituya is usually done during calm days as another precaution in minimizing stress. High mortality of 50 to 60 percent could occur after stocking when transport is done during rough weather.
In preparation to the loading of fry and fingerlings to “pituya”, the boat is partially or half-filled with clean saline water obtained near the source of milkfish supply.
Depending on the source of stock and location of fishpen, travel time of a live-fish boat typically takes about 4 hours or so. Hence, aerators are provided in the boat for oxygenation. As the water changes from saline to fresh conditions, gradual acclimatization of the fish seeds during travel time also takes place. This is done by pumping out partially at interval the original saline water from the source of seeds. Simultaneous with this is the removal of a hole plug in the boat to allow freshwater from the lake to come in.
As soon as the site of fishpen is reached, the fish seeds are seined out and transferred carefully into the pen nursery.
Another method of transporting fingerlings is through the use of oxygenated plastic containers that are placed inside buri bags. These buri bags are transported by land transport from the source up to the point closest to the fishpen site. The buri bags are then transferred to a waiting boat which will take them to the site.
(a) Nursery of fingerlings in pen. The delivered stock temporarily stays in the prepared nursery compartment. A pen nursery varies from 200–1 000 sq m in which the fry will be raised until they are large enough to be released into the grow-out compartment.
While in the pen nursery the fingerlings are being supplementally fed with fine rice bran given at about 5 percent dry weight of the extrapolated fish biomass. The stocks stay in the nursery for one to two months depending on the desired grow-out stocking size or until such time that it is no longer possible for them to pass through the grow-out net enclosure.
(b) Stocking fingerlings in grow-out compartment. Prior to stocking the grow-out compartment with fingerlings, elimination of predators is done. Control of predators is also done in the nursery compartment. Predators such as mudfish, gobies, Therapon sp, Arius sp, water snakes, etc. are ridden through peated netting and even with the use of electro-shocking device (Niclos and Librero, 1977).
Fingerlings are released to the grow-out compartment by lowering one side of the nursery net. The best months for culture begins from March to June.
The prevailing stocking density ranges from 30 000 to 40 000 per hectare. This stocking density is used if supplemental feed is not used. However, during low plankton productivity periods supplemental feeding of fine rice bran, old bread and cream cones can be given. Most often, the quantity of feed given is just a rough estimate. An example is giving one sack (roughly 35 to 45 kg) of cone or bread in three to five hectares per day is found adequate.
The culture period usually lasts for four to six months during summer and 6–8 months during cold months.
(c) Additional management measures. Assessment of survival and mortality is also being done by conscientious operators. Floating dead milkfish fingerlings after stocking in the nursery are counted and multiplied by two to account for the mortality at the lake bottom. With a record on mortality, including the reduction of fish during harvest, this provides a good feel to the operator on the remaining fish stocks as well as data on recovery.
Throughout the culture period, daily inspections of the framework perimeters and nursery nets are required. This routine takes notes of net damage, uprooting of net bottom, broken bamboo posts, and most important, poaching.
Vigilance and security against poaching have become a day and night activity. Large fishpens have strategically located guardhouses and well-coordinated night patrols composed of caretakers that rove in motorized boats around the fishpen in shifts. One corporation uses teams of night patrols that watch the inside and outside of the pen enclosure. The inside patrol drags a hook for the purpose of entangling gill nets or other gear that are usually used by poachers. These teams are provided with communication system for coordination and identification of position at any time. Their respective locations are being relayed to a central monitoring office which determines on a map if there is a gap left unguarded (Estrella personal communication, 1981).
(d) Harvesting. When the milkfish stock is already of a suitable market size, the operators prepare to harvest and simultaneously monitor fluctuations in market price to enable them to market their product at the best time and realize big profit. In the event of an impending typhoon, however, most owners opt to harvest their crop prematurely even at low price. The common method of harvest is by using the purse seine and gill net.
The quantity of fish per harvest is also regulated by operators of fish to prevent oversupply in the market. Hence, harvest for one season crop may last for several months; as harvest spread and the number of fish in the pen decreases, more natural food becomes available, thus resulting to larger fish recovered. some operators practice multiple stocking. As they harvest their crop, the number removed is immediately replaced by the fingerlings left in the nursery pen.
Proper handling and quality control during harvesting and marketing are being observed. If the fish are stressed during harvest, they turn reddish. This is avoided by preventing the catch from overcrowding inside the bag seine: (1) releasing back part of the harvest to the fishpen; (2) transferring part of the harvest to a much bigger bag seine; (3) haul part of the catch immediately; and (4) haul in the contents of the bag seine section by section and avoid compressing it.
The milkfish with “earthy-muddy” taste is common. However, this is minimized by feeding the fish daily for two weeks with ice cream cone rejects and old bread. To make feeding effective sectioning of the fishpen compartment by net dividers is done. Then the fish in the area scheduled for harvesting is fed. Feeding of fine rice bran is also being done.
The off-flavour taste of the milkfish in Laguna lake usually occurs during the end of summer and at the onset of the rainy season, notably June and July.
(e) Marketing. In marketing, the fish harvested are transported in the same live-fish boat “pituya” and other similar types. The boats contain 20–25 cm deep of water with crushed ice to chill the fish to death. Two to three blocks of ice per ton of fish is sufficient to maintain good quality fish. Rigor mortis sets in as soon as the fish are chilled.
When travel time is long as in the case of going to the Navotas Fishing Port, the melted ice with fish blood is pumped out at the same time adding more crushed ice.
Upon arrival at the fishing port, the milkfish is unloaded in tin trays or “banyera” and classified according to size or weight. Fish of uniform sizes are placed in the tin trays properly iced for wholesale disposal. Larger sizes command a much higher price than the smaller sizes on a unit weight basis.
Years of experience in fishpen business in Laguna lake has taught the operators to recognize the problems and complexities involved. At present, factors giving rise to risks to the industry are:
(a) Typhoons and strong winds. Yearly typhoons as well as flood with strong winds of 50 to 100 km/hr or more occur during July and November. Gusty winds also occur from November to January. This occurrence delays the construction as well as destroys the fishpen as a result of increased wave height and drifting flotsams.
(b) Periodic fishkill. This phenomenon occurs periodically in Laguna Bay with the most serious occurrence in July 1975 which drew serious government concern. Barica (1976) listed contradicting theories and observations about this phenomenon. The earliest occurrence of mass fishkill prior to 1975 were primarily attributed to excess bloom and die-offs of Microcystis. It was supposed that the algal toxins produced by the blooms or emitted by the bacteria associated with the algae, or clogging of the gills caused milkfish mortality. There were also some theories on the liberation of hydrogen sulphide, a phenomenon of “black water” patches moving through the lake and killing the fish; choking of fish stocks by water hyacinths, or by extremely high water temperatures and resulting in low oxygen levels. There were also some speculations about the possible effect of salt water intrusions, affecting the algae and causing them to die off; or the effect of a heavy rainfall which is believed to be very acidic and lowers the pH value of the lake water to levels intolerable to algae. In 1972, mass mortality of fish (90 percent in the affected areas) inside the fishpens (with no mortality reported in the open water area) was attributed or hinted to be caused by:
(i) The possibility of pesticides in lake water contributing to fish mortality.
(ii) Clogging of fishpen netting by water hyacinths and drifting debris which resulted in poor water circulation and oxygenation. A precipitation of CaCO3 on the fishpen bottom creating a solid white crust was also reported. Overstocking, 60 000 fish/ha and greater was suspected in some cases.
(iii) Limited durability of bamboo framing and netting materials.
(iv) Poaching continues to be a problem although heavy guarding is being practiced.
(v) Proliferation and lack of control in the construction of illegal fishpens.
(vi) Predation as a problem can only be minimized but not eliminated.
The design of a fishcage for use in an area depends to a large extent upon the depth of water in the body of water. Generally, floating cage and fixed cage (touching the bottom) designs are used in deep and shallow lakes and reservoirs, respectively. A cage may have a separate rigid frame with the netting materials sewn or attached to the skeletal frame.
A fishcage varies in size and the number deployed depends on the production goal and the available capital. The following data provide an understanding of the prevailing size of fishcage used in the country:
| Cage size | Width | Length | Depth | ||
|---|---|---|---|---|---|
| (m) | (m) | (m) | |||
| 1. | Small/experimental | a) | 1 | 1 | 1–1.5 |
| b) | 2 | 2–3 | 1.5–2 | ||
| 2. | Medium/semi- | a) | 3 | 3–4 | 2–3 |
| commercial | b) | 5 | 5–10 | 2–3 | |
| 3. | Large/commercial | a) | 25 | 50 | 5 |
| b) | 10 | 30 | 3 | ||
Materials for the construction of fishcages are essentially the same used for fishpen. Bamboo, oil drums, and styrofoams are commonly used as floats.
Extensive research using Tilapia nilotica as the main species for cage culture in lakes and reservoir has been conducted at the CLSU since 1975. There are also some recent reports on the trials of cage culture of acclimatized Penaeus monodon in Laguna de Bay. Cage culture of the common carp is just beginning.
The desirable characteristics of Tilapia nilotica as a cage culture species are:
It is a plankton feeder.
It grows fast in cage attaining 120–150 gm from a fingerling size in 3–4 months.
Unlike the milkfish, seed production is fast and simple to learn.
It is much hardier than the milkfish.
It is widely accepted in the market at a price comparable with that of the milkfish.
Land-based hatchery (ponds, ricefields and pools) and water-based hatchery (net enclosures in bodies of water) are common methods of producing tilapia needs. The BRI consultants projected that a 2 000–m2 pond of 0.5 to 1.6 m depth of water, stocked with 1 000 (750 females and 250 males) Tilapia nilotica breeders of 100–200 g each, could produce 160 000 fry per month or 1.28 million fry/year of eight breeding cycles. These fry when transferred to 1 000–m2 nursery ponds at densities of 200 per m2 with supplemental feeding of fine rice bran will grow to 5–10 g in two months. At 90 percent survival, each nursery pond will yield about 180 000 during the period or 720 000 fingerlings in a year of four 2-month cycles.
The water-based hatchery of LLDA at Looc, Cardona has produced at one time 200 000 fry from 12 breeding net enclosures in 2 spawning cycles or 3 months. Each breeding net enclosure is composed of a set of outer and inner enclosures measuring 4 × 12 × 2.5 m and × -10 × 1.5 m, respectively. The stocking density is 4 breeders/ m2 or 80 breeders per breeding enclosure stocked at 1:3 male to female sex ratio. The percentage survival up to fingerling size is at least 75 percent.
Four T. nilotica breeders (three females and one male) stocked in single enclosure measuring 1.5 x 1. x 1 m made of fine-meshed nylon netting materials yielded 500 fry in two weeks (Technology, 1980).
A circular plastic pool of 2.5 m diameter x 0.50 m deep had daily production of 6 000–7 000 fry when stocked with 35 females and 5 males of T. nilotica. The fry were grown to fingerling size in water-based nursery enclosure and at least 60 percent of the fry reached fingerling size with feeding of 65 percent fine rice bran and 35 percent fish meal.
Stocking density of tilapia fingerlings in cage also varies. A cage stocked with 50 to 75 Tilapia nilotica without any supplemental feeding had a harvest of 140 to 200 g per fish after four months culture period (Mercene, 1981. Personal communication).
Experimental results using 1 × 1 × 1 m cage at the Central Luzon State University indicated the feasibility of stocking 250 Tilapia nilotica per cu m with feeding of 75 percent fine rice bran and 25 percent fish meal yielding an average conversion of 2.5 kg of feed per kg of fish produced. Feeding is given daily at 5 percent of fish biomass. One-day ration is divided into two rations with the first administered in the morning and the other given in the afternoon.
Results of field verification of the CLSU data with trials conducted in selected lake and reservoir, however, indicated that the stocking density has to be reduced.
Considering all these and to have a conservative projection of production in cages, the BRI consultant has adjusted the stocking density of T. nilotica to 20 fish/m2 with no feeding while 40/m2 is with feeding of fine rice bran given at 5 percent of the fish biomass.
Culture period usually lasts four to five months. This may, however, extend up to six months for 150–200 g size during warm months and 6 to 8 during cold months. Recovery is usually higher than 80 percent.
Harvesting of fish in cages is much simpler than in fishpen. During harvest, the bottom net is lifted gradually from one side and the fish are scooped out from the other side. For large cages four to five persons are required to remove the fish out of the net.
Unlike the milkfish, live tilapia is preferred in the market. Harvest are brought to the market in tubs (“banyera”) and sold at a price about the same as for the milkfish.
Because of its small size cages are vulnerable to poaching if left unguarded. It is also risky to install cages in rivers due to great chance of pesticide contamination.
The design and modular arrangements of enclosure culture systems for the milkfish and tilapia as prepared by the BRI consultants for LLDA appear to be generally accepted by the fishermen participants during the workshop. Briefly, the proposal consists of a target total fishpen area of 2 500 ha for development. This area is divided into 50 clusters. Each cluster contains 11 modules of six 2.5-ha pen enclosure units for the milkfish, three 5-ha units, and two 10-ha units (Fig. 1). Each cluster is enclosed with a common rigid barrier made of bamboo framework and large-meshed net (152 mm (stretched). Inside the barrier are the inner fishpen enclosures which impound the nursery and grow-out compartments of the module. The schematic diagrams for the common barrier and pen enclosure are shown in Figs. 2 and 3.
In addition, each fishpen module/unit of 2.5, 5 and 10 ha has 2, 3, and 5 units of cages for tilapia, respectively. Each cage measures 10 m × 30 m × 3 m (Fig. 4).
In 1980, it was estimated that about 25 000–30 000
tons of milkfish was produced from 7 000 ha of fishpen in
Laguna de Bay valued at approximately 
200–250
million (Mane, 1981). This indicates that the average
production in fishpen is about 3 500 to 4 300 kg/ha.
The average annual production of brackishwater
milkfish ponds in the Philippines is only 600 kg/ha (as
determined during the early 1970's). A few progressive
milkfish farmers in the Philippines however, produce in
excess of 2 000 kg/ha per year. Assuming that the
national average had increased to 1000 kg/ha per year as
a result of the introduction of better technology. The
yield is still 3.5 to 4.3 times more than the production in
ponds.
Shown in Table 1 are figures obtained from the BRI consultants report which indicate the estimated profitability of three sizes of fishpen modules. These figures, however, include the incomes derived from the accompanying cage. The breakdown of these estimates is shown in Tables 3 and 4.
A cage of size 10 m × 30 m × 3 m as proposed by the BRI consultants can be stocked with tilapia at the rate of 40 fish/m2 with supplemental feeding of fine rice bran, and 20 fish/m2 without supplemental feeding. These stocking densities correspond to 12 000 and 6 000 fish per cage. This suggests that it would only need about 2 to 4 such cages to have comparable production with a hectare of tilapia fishpond stocked at 20 000 per ha.
With the view of providing an alternative culture system under the bank-financed project, the FAO team has determined the profitability of pure cage culture of Tilapia nilotica. The estimates were done following closely the assumptions used by the BRI consultants in order to make the results comparable. Furthermore, the concept in this pure cage culture follows the idea of providing a common net barrier that will enclose the cage lots. A lot consisting several cages is to be assigned to each family sub-borrowers. Thus, a number of families would be assigned inside the cage culture site, which is protected by common barriers. Small-sized common barriers have also been considered in the computation, namely: 2.5, 5, 10 and 25 ha. The number of cages to be enclosed per barrier has been limited to cover only 60 percent of the total area in order to provide space for water circulation.
The estimated profitability of the cage culture module
is presented in Table 2. The net income per cage varies
from 9 495 to 9 800. It increases slightly with an
increase in the size of the common barrier. This is due to
the reduced investment cost for the common barrier as
its enclosed area increases which correspondingly
accommodates a greater number of cages.
The estimated net income per cage suggests that a
family just needs to operate four 10 × 30 × 3 m cages inside
the 2.5 ha barrier to exceed the combined estimated
income from a 2.5 ha fishpen and 2 cages owned by two
families; and eight cages instead of 10-ha fishpen and five
cages with multiple ownership. Under this scheme, four
to eight cages would approximately need investment and
operational expense of 51 104 to 102 208 and for the
25-ha barrier, the amount is 47 640 to 95 280.
The assumptions used and detailed estimates, including yearly amortization of the above system are presented in Appendix 3. The profitability of a cage culture module with supplemental feeding of fine rice bran is also included. However, it is not discussed because of its reduced net income as compared to no feeding system.
