3. PEN AND CAGE CULTURE

In the Philippines the technical feasibility of this type of aqua-culture had been successfully demonstrated. For pen culture, milkfish is commonly used while tilapia is mainly used for cage culture production.

Inland water areas with at least 3.0 m depth of water and highly fertile are suitable for fishpen culture as well as cage culture. The latter may be used in deeper waters. Modification of cage design to suit the water areas under consideration is necessary. Pen and cage culture together is feasible. Cages for rearing of fingerlings are often used in fishpens.

3.1 Cage culture of tilapia in Laguna de Bay

For family fish cage culture operations an area of 500 m² to 1 000 m² water surface area is feasible. The number of cage units depends on the skill and capabilities of the fish farmer. Cage size found to be efficiently managed is 9 × 6 × 3.0 m. Recently, however, larger cage unit size of 200 sq m are being used as these have been found to be less prone to being stolen. Small cage units have been easily towed away by poachers.

Experience gained in cage culture in Laguna de Bay showed that a 13-cage unit facility using tilapia species gave a profit of 217.3 percent net income to capital investment in a 19.5 months of operation or an average of 72.4 percent a year; the ratio of net income to production cost was 37.0 percent or an average of 12.3 percent annually; and 27.0 percent to gross income or an average of 9.0 percent a year. The breakdown of costs and income based on actual operations are shown below:

			Total	% of Total
A.	Capital costs (1979–1981)1		25 050.95
	Construction of cages, perimeter fence, rafts, guard house and labour	21 699.95
	Equipment	3 351.00
B.	Operating costs		145 151.05
	Salaries and wages of three full-time workers	46 575.00		31.62
	Initial seed stock	2 904.00		3.02
	Feeds	34 006.70		23.59
	Transport	2 505.00		1.73
	Hired labour	3 127.00		2.17
	Fuel	12 518.05		8.68
	Depreciation of facilities and equipment at 30 percent	7 515.30		5.21
	Management and contingency costs	36 000.00		24.98
C.	Gross income		201 403.10
	Sale of 1 645 kg at 6/kg	9 916.10
	Sale of 3 667 kg at 7.79/kg	28 582.00
	Sale of 9 946 kg at 8.82/kg	87 756.50
	Sale of 9 028 kg at 8.36/kg	75 489.00
D.	Net income		54 447.60
	Annual average net income		18 149.20
E.	Profitability
	Ratio of net income to capital cost			217.3%
	Ratio of net income to production cost			37.0%
	Ratio of net income to gross income			27.0%

¹ Exchange rate: US$1 = Pesos 7.50.

The total net income generated by the facility during the period was 54 447.60 or an average of 18 149.20 which is higher than the national per capita income of 13 200.00 (1986). At current market price of tilapia in the market, the level of income could increase by 50 percent. The cost of production may be increased by about 20 percent based on current prices.

The water surface area utilized by this cage culture operation was 536 m² ; the average stock density was 92 fingerlings/m² and average production was 6 140 kg/crop or a unit productivity of 10.98 kg/m² .

A recent survey of tilapia cage culture production in Laguna de Bay showed production levels ranging from 26.0 to 51.0 mt/ha/year (Table 6).

Cage culture of tilapia is no doubt an economically viable activity which provide reliable source of family income. A family of five active members including the parents could operate at least 10 cage units of 6 m × 9 m × 3 m; family labour available will be gainfully employed and family income is more than enough to cover basic needs.

A summary of cage culture production based on a case study is shown in Table 4. Table 5 summarizes tilapia cage culture production levels in different parts of the country. It will be noted that cage sizes used vary widely; stock density per unit area also differ which indicates various preferences of cage culture operators or differences in skills. At present larger cages of 10 m × 20 m × 3 m with top cover and submerged under water are used. It is less prone to poaching. One cage unit would cost at present from 30,000 to 40,000 pesos including fish stocks at the rate of 20,000 fingerlings/unit.

3.2 Cage culture of marble goby in Nakhon Sawan, Thailand

The practice of culturing fish in cages is not limited to netcages. Cages made of wooden boards are also used. In some places, their more sturdy construction and rigid bodies make them more practicable than netcages. This is particularly true in bodies of water where the water flow is too strong for the netcage.

Table 4. Summary of fish production in cages

Farming cycle	Total area (m2)	Total stock density	Stock per m2	Total harvest (kg)	Yield per m2 (kg)	Ave wt/fish	Ave income/ m ()	Ave unit price/kg	Total sales
First crop	180	24 600	147	1 647	9.13	62.3	55.08	6.00	9 916.10
Second crop	306	27 830	91	3 761(3 667)	12.29	135.0	93.37	7.79	28 582.00
Third crop	911	86 130	95	10 129(9 946)	11.90	125.0	101.03	8.82	87 756.50
Fourth crop	747	58 700	78	9 028	10.62	153.8	95.80	8.63	75 481.00
Average	536	49 315	92	6 140.75	10.98	119.1	86.32	7.81	50 433.90

( ) Figures in bracket are kilograms of fish sold

Table 5. Summary of tilapia cage culture production levels in the Philippines

Table 6. Recent survey data on production of cage culture in Laguna de Bay

¹ Delmendo, 1966

² ADB, 1984

( ) Figures in bracket denotes area in ha

Cage culture operations in Laguna de Bay

This is the case with the wooden cages in the relatively swift-flowing Nan River in Nakhon Sawan, Thailand. The river is generally turbid with a relatively strong downstream flow. It has an average depth of 4 m and is relatively free of pollution.

The species being cultured here is a good example of the exploitation of a hitherto unused natural resources. The fish is the marbled goby, Oxyleotris marmoratus, a fish that is being cultured not for local consumption since very few Thais, if any, eat it. The whole production is bought by middlemen from Bangkok from whence it is exported live, to Hong Kong, Malaysia and Singapore. It is considered a delicacy by the end-users, mostly Chinese.

The cage of rough wooden boards much like a box measures 2.5 m × 6 m × 2 m deep. Twenty-five large diameter bamboos are attached to each of the long sides of the cage to serve as additional floats. The top part of the cage is covered with narrow wooden boards in the middle of which is a rectangular feeding slot, 40 cm × 60 cm. A cage usually has a roof and walls for protection against sun and rain. Another may have a complete house over it where the owner and his family lives. The wooden cage can last 6–8 years but the bamboos have to be replaced every 2–3 years. Each bamboo costs Baht 18. Each complete roofed cage, including labour, costs 15 000 (US$1.00 = 22.9).

Fingerlings averaging 100 g each bought from gatherers in Suphan Buri for 150/k are stocked in the cage at 80/m² all year round. These are fed every other day with ground trash fish, placed in a tray below the feeding slot, at the rate of 5 percent of the crop's body weight. The trash fish is bought at 15/k from suppliers who bring it all the way from the Gulf of Siam, 300 km to the south.

The crop is harvested partially after 10 months of growth and totally after 13 months. Harvesting during this period takes place any time the buyer arrives. Only gobies of 500 g or more are harvested, The price at the cage site is 200/k. With an average survival rate of 80 percent, each cage pro-duces 480–550 k of marketable gobies valued at an average of 95 000.

As much as possible, the goby culturist operates his cage himself with his wife and children helping with the work. Even those with multiple cages do not hire labour for the day-to-day operations. Only when he constructs a new cage or makes major repairs on his old one does he use hired labour. Though poaching is not a real danger, the operator does not leave his cage unmanned for any extended period.

Some of the culturists go into private trading. They buy marketable gobies at 200/k, transport these in oxygenated plastic bags, 5 fishes/bag, to Bangkok and sell these for #210 or more per kilo, Mortality in transit averages 1–2 k/trip.

The gobies in the cages mature after about a year as evidenced by the goby eggs floating inside. The culturists, however, do not use these eggs. They would rather buy 100 g fingerlings than raise goby fry to fingerlings. The fishery authorities are still studying the artificial breeding of O. marmoratus.

An idea of the popularity as well as profitability of wooden cage culture of 0. marmoratus may be gained from the more or less 1 000 cages being operated by 500 families along the 39 km length of the Nan River. An operator who furnished some of the information in this report owns seven fully-stocked cages, a 40-Hp long-tailed boat, a comfortable home on land nearby, uses hired labour and has his children in college.

For those who have the necessary capital, culture of O. marmoratus in wooden cages could be a lucrative enterprise, so long as the following factors are present: available fish seeds, trash fish and customers willing to pay the price.

Generally, wooden cages would be entirely applicable in fast flowing rivers that are not at present being fully utilized. The species to be cultured need not be O. marmoratus or other high-priced fishes. Moderately priced ones, preferably non-predators and indigenous to the region, could do.

Estimate Costs of a One-Cage Goby Project
(US$1.00 - Baht 25.6)

A.	Capital cost
	1 roofed cage (2.5m × 5 m × 2 m)		15 000
	1 small boat		3 000
	Miscellaneous equipment (weighing machine, scoop net, basins, tray, knife, etc.)		3 000
		Total capital cost		21 000
B.	Operating expenses
	120 k of fingerlings (100 g each) 150/k		18 000
	Trash fish for 10–13 mos.		12,000
		Total operating expenses		30 000
		Total capital cost and operating expenses		51 000
		Contingency - 10% of operating expenditures to cover mainly inflationary cost		5 000
		Total operating outlay		56 100
C.	Estimate gross sales
	(80% recovery, 500 g average weight/fish at an average wholesale price of 200/kg) .8 × 1 200 × .5 × 200			96 000
D.	Estimate net income			39 900/yr*

* Capital cost is recovered within a year of operation. In subsequent years the annual net income could increase to about 60 000 unless the operator increases the number of cages.

Cage culture of marble goby in Nakhon Sawan, Thailand

3.3 Cage culture of Pangasius in Uthai Thani, Thailand

Another fish being cultured in wooden cages is the giant freshwater catfish, Pangasius sutchi, locally known as “pla sawai” It is being cultured for local consumption in the Sakra Krang River, in Uthai Thani, about 180 km north of Bangkok.

The fish is cultured in wooden cages much like those in the Nan River in Nakhon Sawan. The usual cage size is 3 m × 6 m × 1,5 m deep. A cage made of thick boards costs J$12 000–1(14 000; that of thin boards 7 000–8 000. However, the former lasts 6–7 years while the latter only 3–4 years.

Cage culture of Pangasius sutchi in Uthai Thani, Thailand

A cage is stocked a maximum of 2 000 fingerlings each measuring 8–13 cm. Some culturists buy small-sized post fry and grow these in small nets to fingerling size. Others buy fingerlings ready for stocking in the cage. Still others have their own hatcheries. These latter ones have learned the technology of artificially spawning the Pangasius. They buy their own hormones and inject the fishes themselves.

The fingerlings are fed rice bran, chopped Ipomea, Lemna, cow dung and a pelletized commercial feed, Aquafac, The latter is mixed in the ratio of 5 percent of the total feed mix for the day. As the fishes grow, they are fed more and more with Lemna since this plant can be gathered from the river. In times of abundance, Lemna is used to the exclusion of the other feeds. In time, the fishes are also fed leftover leaves from the vegetable stalls in the markets nearby. In preparation for the market, the fishes are fed a mixture of 10 percent soft-boiled rice and 90 percent rice bran. These are mixed into a moist dough the size of a coconut, from which small chunks are pinched off and thrown into the fish cage.

Due mainly to the abundance of the daily feed, the fishes do not fight and compete for food, rarely succumb to disease and grow fast. There is practically no mortality.

The fishes grow to 1–1.2 k in 10 months and are ready for the market. Since the harvesting is done on a selective basis, the period may extend to the 12th month. The fishes are sold for an average of 16/k. The fish heads are also bought by the fishery authorities for 10/k. The pituitary glands of the same are removed and processed into hormones.

Along a 5 km stretch of the Sakra Krang River are about 280 wooden cages engaged in the culture of Pangasius. These are individually owned by about 120 families who have grouped themselves into an association for mutual help, protection and exchange of ideas.

Pangasius can also be cultured in freshwater ponds. However, due to poor water quality in the stagnant ponds and the peculiar smell of the mud in the pond bottom, the fish produced therein encounters very strong consumer resistance.

3.4 Cage culture of seabass in Songkhla, Thailand

The culture of fish in netcages is not limited to freshwater species. Marine fishes are also cultured in cages as it is being cultured in Songkhla Lagoon, Southern Thailand. The species being used is the seabass, Lates calcarifer.

There are about 70 families engaged in growing seabass seeds to marketable size in netcages spread out along the shores of the lagoon. A family may own a couple or more cages. Some of them learned the practical aspects of culturing seabass in netcages at a 1-month training course conducted by the National Institute of Coastal Aquaculture (NICA).

Some of the netcages are of the stationary type. The cage is attached to posts sunk in the bottom of the lagoon at 3–5 m distance. About 1 m of the cage netting is always kept above the highest tidewater mark. Even at lowest low tide the cage bottom does not touch the lagoon bottom. A 5 m long 12 cm dia post costs 70 and may last for 3 years depending on the barnacles that have attached to it. A 10 m × 10 m × 2.5 m deep cage together with the posts costs 4 000-5 000.

Other netcages in the lagoon are the floating type. The netcage materials are also of polyethylene but are attached to floats of either styrofoam, steel drums or plastic jerry cans. Wooden boards serve to connect the floats to each other and as catwalks used by the fish farmer.

Both cage types are stocked with 5 cm fingerlings at the rate of 800/cage or 8/m² (100 m² cage). There is no shortage of fingerlings. The Thai Government, through the NICA in Songkhla, has successfully spawned the seabass in captivity and is producing about 7 million fry annually with a survival rate of 30 percent. The fry are sold to privately-owned nurseries who raise these to 5 cm sized fingerlings. These 1.5 month old fingerlings are sold to netcage operators for 1.50-2.00 each.

Cage culture of seabass

The fingerlings in the grow-out netcages are fed minced/chopped trash fish at the rate of 10–20 k/daily. Trash fish are bought from the trawlers in the lagoon for 1/k. This is way below the cost of feed for the goby in Nakhon Sawan.

The growing period is 8–12 months. At the end of this period, the fish has grown to .8–1 k and is ready for the market. At 90 percent survival, a single cage usually produces a minimum of 570 k. Seabass fetches a price of 75–80/k wholesale. At the Songkhla market, it is sold for up to 100/k retail. Filleted seabass, used for sashimi, costs 120/k. Marketing poses no problem to the netcage operator. Most of the harvest is bought by local regular customers while the surplus is exported to Malaysia,

Lates calcarifer may possibly be raised in freshwater, according to fishery biologists of the NICA and the netcage culturists in Ban Hua Kao, a village in the Songkhla Lagoon. They point to the fact that from February to May, the salinity of the Lagoon's water is 15–30 ppt, From November to January, however, the Lagoon experiences a prolonged period of zero or near zero salinity. They say that this is caused by the high influx of freshwater from the creeks, rivers, streams, etc, that flow into the lagoon and the high volume of rain water in the region. During this latter period, the seabasses in the netcages do not suffer any marked increase in mortality. The 5–1 percent mortality is practically constant all year round. Despite the great change in their environment, the seabasses also continue to grow. Be that as it may, the possibility of culturing seabass in freshwater needs further studies.

Seabass can also be cultured in netcages in the coastal waters of countries not visited by destructive typhoons. In the Philippines, it would be possible in the southern part of the country - the Mindanao region which is relatively free of typhoons; in Bangladesh, the regions not visited by cyclones. In addition, institutional and organizational arrangements between government and private sectors have to be established to insure a steady supply of seeds. This situation already exist in Thailand.

Estimate Cost of a One-Cage Seabass Project
(US$1 = 25.6)

A.	Capital cost
	Netcage (10 m × 10 m × 2.5 m deep)			4 000
	Posts			500
	Small boat			2 000
	Miscellaneous equipment (basins, needles, scoop net, extra rope, twine, etc.)			1 000
	Total capital cost			7 500
B.	Operating expenses
	800 fingerlings, 51.75 each			01 400
	Trash fish:
	i) 20 k (l/k) × 300 days	6 000
	ii) 5 k (l/k) × 65 days	325
	Depreciation cost	2 497		8 822
	Contingency (10% of operating cost to cover mainly inflationary cost)			1 022
	Total operating cost			11 244
C.	Estimate gross sales
	(90% recovery, 0.8 kg/fish at 75/kg) .9 × 800 × 75			43 200
D.	Estimate net income			31 956

3.5 Cage culture of grouper in Phang Nga Bay, Thailand

Another marine fish that is now being cultured in netcages is the grouper, Epinephelus tauvina/salmoides. The fish is cultured in Phang Nga Bay, Southern Thailand. For purposes of this report, a specific netcage project in Ban Ko Mai Pai, a village in the Bay, is described here.

The project is owned and operated by an ordinary fisherman, assisted by a teenage son. He has had no training in the netcage culture of the grouper. He put up his project by copying one that had been put up by a neighbour after the latter had undergone a period of training conducted by the fishery authorities.

The project is a module constructed by the owner himself, consisting of 4 netcages, each measuring 3 m × 3 m × 2m deep with a mesh size of 3 cm stretched and costing a total of 3 600. The module uses 9 pieces of styrofoam, 1 m × 1.5 m × .35 m thick, costing a total of 350, as floats. Thirty-four mangrove trunks attached to each other in a trellis-like arrangement connect the floats together and serve as catwalks. The trellis also prevents the fish from jumping out of the cage. The mangrove trunks were gathered by the owner and his son from a nearby swamp.

The netcage can last 2–3 years, the styrofoam, a maximum of 8 months and the mangrove trunks 1 year.

The project is situated 25 m from the shore and is moored to the land by a 3 cm diameter rope and anchored to the bottom of the tidal creek with two heavy stone weights. The tidal depth of the water ranges from 2.5–5 m. Water salinity range is 29–33 ppt.

The owner also has 17 traps (bubo) which is constructed himself from split mangrove trunks and netting with a mesh size of 2 cm stretched. Each trap measures 35 cm × 80 cm × 35 cm deep. These are baited and sank to the bottom to catch small groupers to be used as seeds.

The four cages of the project are stocked with 1 000 groupers of varying sizes. These are fed trash fish at the rate of 30 k/day. Feeding is done twice daily if there are enough trash fish, otherwise only once. The owner buys the trash fish at l/k but relies more on the catch of his set bag net placed in a tidal creek a distance away from the village.

Due to the wide weight range of the seeds stocked, 100–400 g, some of the fishes would already reach sizes of 800 g or more by the fifth month in the netcage. These are ready for the market. A buyer from Singapore comes regularly to purchase all the marketable-sized fishes in the area. The process of harvesting and marketing is simple enough. The owner raises the net, the buyer points out his choices and the owner scoops out the chosen fishes. The rest are left in the cage to grow further. The buyer thus, by experience, knows when to return for the next batch of marketable-sized groupers. The groupers are sold for 80/k cash and transported live to Singapore.

The stock of the four cages are continuously replenished by the owner with seed-groupers newly caught by the traps. As a rule of thumb, however, he tries not to exceed a stocking rate of 300 seeds/cage.

The owner could not give a definite production figure for each and all of his four cages for any particular period. Lacking any records, he could only remember that he receives 3 000–4 000 per sale day which occurs 2–3 times a month. Neither could he remember the exact weight of the trash fish he bought and those he caught for any particular period.

The foregoing is classic example of small-scale aquaculture using methods only a few steps better than the absolutely primitive. However, the owner was aware of his limitations and knew that he was not exploiting his project's full potential. He was very receptive to suggestions to improve his project, especially the keeping of records. Despite all these, however, he was happy in the thought that he had created employment for himself and was appreciably augmenting the income from his traditional subsistence fishing.

In Ban Ko Mai Pai, an island village 10 km from Phang Nga, there are 20 families that own 68 netcages culturing E. tauvina/salmoides. Twenty of the operators underwent a government-sponsored 5-day training-study tour at the government netcage culture demonstration farm in nearby Ban Ko Panji. Immediately afterwards, they put up their netcages and organized themselves into a loose association for mutual help. They used their own funds while the fishing authorities provided technical aid. Extension workers visit the projects once a month regularly,

In the whole Phang Nga bay area, there are 3 000 (Somying, 1985) privately owned cages. The operators are fishermen engaged in subsistence or artisanal capture fishing. The fishing gears used are gillnets and boat-powered push nets. The main catch are tiny shrimps. These are dried in the sun, finely ground, salted and made into a shrimp paste locally known as “kapi”.

The introduction of netcage culture has a very salutary effect on the lives of the area's fishermen. The majority are very receptive to the new idea of culturing and raising fish to marketable size, as opposed to the traditional capture fishing. The high price of E. tauvina is a very strong incentive. As a consequence, government extension workers are being asked to provide more information and help, especially in providing the culturists with a steady supply of fish seeds.

Cage culture of grouper

The Government has been conducting experiments in the spawning of groupers in captivity, to provide the seeds so necessary to the development of the new industry. However, though preliminary results show some promise, so far no results similar to the production of L. calcarifer seeds have been achieved.

Estimate Costs of a 4-Cage Module Grouper Project
(US$1 = 25.6)

A.	Capital cost
	4 netcages (3 m × 3 m × 2 m)		3 600
	9 pcs styrofoam		350
	34 mangrove trunks - 10 each		340
	16 traps (bubo) - 30 each		510
	1 skiff		2 000
	1 set - bag net		2 000
	Miscellaneous equipment (scoop net, basin, weighing machine, needles, etc.)		2 000
		Total capital cost	10 800
B.	Operating expenses
	1 200 fish seeds - 5 each		6 000
	Trash fish (30 k/day, l/k, 240 days)		7 200
		Total operating expenses	13 200
	Total capital cost and operating expenses		24 000
	Contingency -(10% of operating cost to cover mainly inflationary cost)		2 400
		Total budgetary outlay	26 400
C.	Estimate gross sales
	(80% recovery, average fish weight - 800 g/fish, sale - 80/k) .8 × 1 200 × .8 × 80		61 440
D.	Estimate net income		35 000

This level of income is obviously higher than the prevailing per capita income of artisanal fishermen in the area which is about 6 855 (Somying, 1985). In this particular case, father and son earn about 15 500 each a year.

3.6 Pen culture of milkfish in Laguna de Bay

The development of fishpens in Laguna de Bay started from a pilot project established by the Laguna Lake Development Authority in 1971. The project was developed to demonstrate the economic and technical feasibility of aquaculture on the lake using enclosures. It was intended to provide small fishermen with alternative source of income or occupation to improve their economic conditions.

The success of fishpen operations on the lake triggered a tremendous private interest to such an extent that there are now more than 30 000 ha of Laguna Lake in fishpens. This is over and beyond the maximum area of 20 000 ha originally planned by the LLDA. Open water fishing activities were hampered by the haphazard construction of fishpens. Social conflict between small fishermen and fishpen operators occurred as a result of the lack of control of fishpen development.

During the last 10 years of fishpen development on the lake, the total investment generated from private sector is about 2.25 billion. The average production is 4–6 tons/ha/year. This level of fish output produces a total of about 120 000 tons a year. This type of aquaculture production surpasses that of the conventional brackishwater or freshwater pond culture operations.

Where the fishpen used to be a less capital intensive aquaculture venture, the current capital investments for fishpen construction increased tremendously. Small-scale fishpen projects (1–50 ha) would cost an average of 60 000/ha to construct; medium scale fishpens (51–100 ha), 50 000/ha; and large scale projects (over 100 ha), 40 000/ha. Although this is an arbitrary classification, it will be noted that the increase in size of fishpens decreases the. cost of development at the rate of 20 percent from small to medium scale, and about 30 percent from medium to large scale (Rabanal and Santos, 1985). Materials used are locally produced such as bamboo and Livistonia palm trunks as posts and main support. Polyethylene nettings or plastic materials are used as the main enclosures to keep fish stocks inside the fishpen. The fouling of these materials occurs fast which necessitates the structures to be depreciated at about 35 percent annually.

The cost of operation of fishpens is estimated at 10 000/ha to 25 000/ha. A 100-ha fishpen project would therefore need 92.5 million for operational capital annually. Based on these estimates, a small-scale fishpen project should be at least 25 ha to be economically viable.

Regarding the profitability of fishpen operations, an operator can obtain a profit of 20 percent annually and recover the capital and operating costs. The total production of fishpens in Laguna de Bay surpasses that of the open water fish catches (Table 7).

As a business, the risks are high. Typhoons and flood damages including mass mortalities caused by pests and diseases could cause partial or total loss. However, experiences have shown that these risks could be offset by even only one full year of good weather conditions; profits could reach very high levels.

Table 7. Total fishery production of Laguna de Bay (in metric tons)

¹ Delmendo, 1966
² Shimura and Delmendo, 1968
³ Delmendo and Gedney, 1974
⁴ ADB. 1984
* BFAR
( ) Ares in hectares

Fishpen in Laguna de Bay