Hu Baotong and Min Kwanhung
Changjiang River Fisheries Research Institute
Wuxi, China
INTRODUCTION
The development of reservoir fisheries in China can be divided into four stages: (i) before 1949 - fishing without stocking; (ii) during the period 1949–57 -the embryonic stage of reservoir culture; (iii) during the period 1958–66 - the bloom stage, and (iv) from 1967 onward - the new phase of development. The techniques of cage culture are a new approach to developing reservoir fisheries.
In China most reservoirs are deep, formed by damming valleys with sandy bottoms. Their morphometry limits the growth of aquatic macrophytes, with phytoplankton becoming the main primary producer. As a result, reservoir culture in China is characterized by artificially stocking silver carp (Hypophthalmichthys molitrix) and bighead (Aristichthys nobilis) feeding on plankton. Chinese carp fingerling production has not been able to keep pace with the rapid expansion of reservoirs. Thus a large quantity of the natural food (plankton) cannot be fully utilized, which results in poor yields. The current average production in China is only 90 kg/ha of reservoirs. In Longtou Reservoir, however, a maximum production for silver carp and bighead was 915 kg/ha, mean production for 1968–78 was 430.5 kg/ha (Zhang Lai Fa et al. (1981)).
REARING OF FINGERLINGS IN NET CAGES
Rearing large-sized silver carp and bighead fingerlings in net cages on natural feeds was successful in Xueyie Reservoir (Shandong Province), Xinanjiang Reservoir (Zhejiang Province) and Bailianhe Reservoir (Hubei Province). The following stocking rates are given: Bailianhe Reservoir cages were stocked with about 6 000 000/ha large-sized fingerlings of silver carp and bighead; Fujiaohe Reservoir with 390 000/ha; Datong Reservoir with 3 267 000/ha and Jinsahe Reservoir with 2 992 500/ha. The 666.7 m2 cages could rear 200 000–300 000 large fingerlings. A 3 333.3-ha reservoir with an average stocking rate of large fingerlings at 750 individuals/ha, will require 0.55–0.83 ha of cages to rear the fingerlings needed for stocking. However, if traditional fingerling ponds are used, 20.8 ha are needed at the present production level of 120 000 individuals/ha. In addition a great quantity of manure and feeds is required including 3 750–6 000 kg/ha as base manure. After the stocking of summerlings, 3 750–4 500 kg/ha of grass, 1 500–2 250 kg/ha of mixed compost or flushed nightsoil must be applied every 10–15 days. From September onward, with the gradual decrease in temperature, manure application can be reduced, but 2–3 kg of bean cake, wheat bran, etc., per 10 000 fingerlings is still needed as a daily supplement.
Large fingerlings of silver and bighead carps cage cultured on the natural planktonic feed would be sufficient for reservoir culture and at rational density great amounts of feed and manure would be also saved. In 1978, 1 570 000 fish 11 cm long each were produced from 0.4 ha of cages in Fijiaohe Reservoir, Hubei Province, and more large fingerlings were produced in cages in other reservoirs in Hubei, Shadong, Anhui and Zhejiang Provinces. In 1978 and 1979, 96 percent of silver and bighead carps originated from cage culture in Fijiaohe Reservoir. Cage culture is now prevailing from Helongjiang Province in the north to Kwangdong Province in the south.
Silver and bighead carps take plankton as their main food. Stocking rates are based on the type and biomass of plankton (Table 1). In Bailianhe Reservoir, with phytoplankton densities of 3 921 000/l and zooplankton density 3 000/l, over a 56-day experimental period caged fingerlings grew to 4–9 cm with 573 individuals/m3. In Xueyie Reservoir with phytoplankton densities of 1 884 000/l and zooplankton density 1 913/l, fingerlings grew from 4 to 9 cm over 66 days. Average density of fingerlings in cages was 300 individuals/m3. Recent practice in different regions shows that good production in cage culture can be achieved with phytoplankton densities of 2 000 000/l with zooplankton density 2 000/l during the main period of fish growth.
Hu Baotong et al. (1982) reported the results of research on silver carp fingerlings reared in cages with plankton as natural feed. The relationship between the density of fish and the survival rate is in inverse proportions (r = -0.2054). The density of fish and total yield of each cage are in direct proportion (r = 0.9203), however, density and the individual weight of fingerlings are inversely related (r = 0.7639). The optimum density for rearing silver carp fingerlings in cages was found to be 484 individuals/m3 under the conditions prevailing in Bailianhe.
The stocking ratio of silver carp to bighead carp in cages depends on the species and quantity of zooplankton and of the larger individuals of phytoplankton. During the period of intensive fish growth in Bailianhe Reservoir in 1977 and 1978, blue algae accounted for 70 percent of the phytoplankton. Anabaena spp. and Microcystis spp., which are dominant and digested by both silver carp and bighead are also the dietary base for their fingerlings in Bailianhe Reservoir. Further research is needed on the relationship between the composition of phyto- and zooplankton, the optimal proportion of silver carp to bighead fingerlings, and the stocking density so as to identify the potential of different water bodies for the production of silver carp and bighead seed.
TABLEFISH CULTURE IN CAGES
With the success of fingerlings rearing in cages in 1966, culture was continued in Bailianhe Reservoir in 1977, where there were three experimental cages. The surface temperature of the water where the cages were placed rose to 15°C in early April, 20°C in early May, 25°C in early June, 30°C in between July and mid August. The water temperature began to fall to 22°C from late August to late September, when the fish were netted from the cages. DO was 8.3–18.0 mg/l and pH 8.5–9.1. The transparency ranged from 15 to 95 cm, being much reduced during the flood season. Phytoplankton concentration averaged 4 600 275 individuals/l from June to September of which 59.9 percent can be digested by silver carp and bighead. Zooplankton varied from 7 090 to 13 759 individuals/l. The total volume of the three cages was 176 m3, the quantity stocked was 5 359 individuals weighing 1 146.1 kg. In 138–181 days, the total survival rate was 95.1 percent. The final number was 5 125 individuals weighing 4 684.7 kg, with an average 26.125 kg/m3 and a net yield of 20.125 kg/m3.
Ten other cages were used for further experiments from December 1977 to February 1979. The volume of each cage was 56 m3 (7 × 4 × 2 m). The available water volume was 46.15 m3. Water temperature and transparency were measured every day and the hydrochemistry and plankton analysed every month. The plankton analysis indicates that during June and August the dominant species of phytoplankton were Ceratium hirundinella, Anabaena and Microcystis. In about 400 days the total net yield from the ten cages was 11 325.65 kg, averaging 24.54 kg/m3. The size of fingerlings, density of stocking, proportion of silver carp to bighead and other parameters of production show that the production is enhanced with an increase in number of fingerlings. The regression equation between the fingerling biomass (Wo, kg/m3) and the yield (We kg/m3) is:
We = 6.5997 Wo + 17.646
However, the stocking density influences the individual growth rate of silver carp and bighead: the highest density in cage No. 1 resulted in the smallest body size, silver carp averaging 505 g/individual, bighead 280 g/individual. High density results in crowding, in lower food supply per individual and in other environmental parameters becoming thus unfavourable, affecting negatively the individual growth rate.
When stocked in cages, bighead carp was initially 53.8–110.9 percent heavier than the silver carp. When harvested, however, with one exception where the two species weighed the same (550 g), silver carp were bigger than bighead with silver carp weighing as much as 57.1 percent more. The average growth rate of bighead was less than that of silver carp, net individual growth of silver carp and bighead being 1 122–1 913 g and 400–883 g, respectively. Stocking with small fingerlings resulted in a high net growth rate, whereas the low net growth rate was attained with big fingerlings. The relationship between the net growth rate of standing crop and the stocking density was inversely proportioned (r = -0.9551).
Other experiments also proved that reservoir cage culture can achieve high yield. In 1978, in Hubei Province, a 0.3-ha cage area yielded on average 276 000 kg/ha. In 0.16 ha of cage water area in Bailianhe Reservoir, production reached a mean of 412 500 kg/ha, a figure 110 times higher than the pond production of 3 750 kg/ha.
The development of cage culture should be based on the water quality. Eutrophic water contains rich amounts of natural feeds and may be self-sufficient, whereas oligotrophic reservoirs could be adapted for intensive culture with supplementary feeding.
CAGE TECHNOLOGY
Rectangular cages employed in China are usually between 20 and 40 m2, with the recommended size being 7 × 4 × 2 m. The mesh size is 10–11 mm for summerlings of 4 cm average body length; 25–30 mm mesh size is selected for stocking fingerlings of 11.7 cm average body length for post-fingerling culture. Mesh sizes of nets used range from 0.7 cm for fingerlings of minimum size 2.7 cm, to 3 cm for fingerlings of 11.5 cm minimum length. Cages were made of PVC thread strung on bamboo, wooden or plastic frames.
Two types of cages are used. Standing cages are used in running water with 5–20 cm/sec flow rate, while floating cages are used in standing water. The cages slowly move about under the influence of wind assisting in water exchange and plankton input.
DISCUSSION AND CONCLUSIONS
Stocking in a reservoir should account for 10–15 percent of the total fish production. However, the shortage of large fingerlings of silver carp and bighead -the main species cultivated in cages in reservoirs - has restricted the development of reservoir fisheries for some years. The rearing of fingerlings in cages depending on natural feeds in the reservoir has many advantages, including the lack of competition with agriculture for land, no need for supplementary feeding and for manure application. It gives good quality fish and high economic returns. It is a reliable means of producing large size fingerlings in a greater, faster and more economical way. The Shandaoling Reservoir, Liaolin Province, has a cultivable area of 200 ha. It lacked 300 000 fingerlings for stocking in 1979. The development of cage culture provided 1 062 400 large fingerlings using part of the original pond area for rearing fingerlings, which not only provided 600 000 individuals for stocking the reservoir proper but also a large “surplus” (40 percent). Now cage culture for large fingerlings is a chief basis for the extension of reservoir fisheries in China. 53 333.3 ha of cultivated water in the Xinanjiang Reservoir, which connects Anhui and Zhejiang Provinces, is now a base for cage culture of large fingerlings destined both for other large water bodies and cage rearing within the reservoir itself. Different types of net cages for fry, fingerlings and post-fingerlings are used and 20 ha of water has produced 550 000 kg of fingerlings.
Cage culture based on natural food or with supplemented feeds for post-fingerlings is thus a new approach to intensive fish culture in reservoirs. Reservoirs are large, open water bodies where predators are common and the many inlets and outlets and poor management result in low catchability. Cage culture will overcome this problem.
Cage culture of silver carp and bighead in reservoirs with natural plankton as their food gives a high economic return. For example, in 1978 in Bailianhe Reservoir, 1 049 800 12-cm silver carp and bighead fingerlings cost yuan 29 964.85 at an average cost of yuan 285.44 per thousand fingerlings and including cage materials, summer fingerlings and manpower. The production was 70 000 kg for an expenditure of yuan 19 976.56 representing an average cost of yuan 0.28 per kg of fish. In Fuzhilin Reservoir, Anhui Province, in 1980, production from cage culture was 82 597.5 kg at an average expenditure of yuan 0.52 per kg of fish.
This shows that cage culture can be used for rearing of fry and fingerlings, and for growing fish to consumable size and for brood rearing. On average, a cage culture farm on the open water surface can account for up to 1 percent of the total open water area. The new cage culture techniques provide a new approach to aquaculture in large water bodies and contribute much to the aquaculture modernization in China.
REFERENCES
Hu, Baotong et al., 1982 Effects of stocking density on the production of marketable sized silver carp and bighead cultivated in the net cages. Chinese J.Zool., 4:33–4 (in Chinese)
Table 1 Some parameters of silver carp and bighead fingerlings reared in cages in different types of water in reservoirs
| Type of reservoir water | Phytoplankton quantity wet weight | Zooplankton quantity wet weight | Plankton wet weight | Stocking density | Stocking size | Growout size | Remarks | ||
| (104/1) | (mg/l) | (ind/l) | (mg/l) | (mg/l) | (ind/m3) | (cm) | (cm) | ||
| Eutrophic | 100–400 | 5–20 | 2 000–3 000 | 3–45 | 8–24.5 | 150–500 | 5 | 13.3 | Best results |
| Mesotrophic | 30–100 | 2–5 | 1 000–2 000 | 1.5–3 | 3–8 | 100–150 | 5 | 11.7 | Better results if adding certain amount of feeds |
| Oligotrophic | 30 | 2 | 1 000 | 1.5 | 3 | Relying on supplemented feeds | |||
T. Petr
FAO, Fisheries Department
00100 Rome, Italy
INTRODUCTION
For some time, capture fisheries in inland waters of the islands of the Indo-Pacific have been based both on indigenous and introduced fish. In some lakes and reservoirs west of the Wallace Line introduced exotics considerably boosted fish production. More to the east and especially on the Pacific islands, where lacustrine fish are virtually absent, a capture fishery based on self-sustaining species of fish can be established only when exotic species are introduced. The island nations, together with Hawaii and Guam, are increasingly confronted with the need for more scientific management approaches to fisheries development of their new reservoirs, the number of which is steadily increasing. The present paper briefly reviews the situation and discusses some of the problems faced.
INTRODUCTION AND STOCKING OF RESERVOIRS AND NATURAL LAKES
It has been suggested that Southeast Asian inland waters frequently lack suitable fish species which would establish healthy and rich stocks in a lacustrine environment. Fernando and Holcik (1982) have stressed that the reason behind this is that these waters are inhabited by fishes of riverine origin not adapted to lacustrine conditions and therefore unable to occupy all ecological niches. Giving the example of Parakrama Samudra Reservoir in Sri Lanka, they pointed out that prior to introductions of exotic fish, the fish yield of this well stabilized 1 500 year-old reservoir was only 1.07 kg/ha/year.
The Wallace and Weber Lines serve as geographical/ecological boundries separating the fish of the Asian realm from those further east. While Sulawesi and Timor have fish of freshwater origin, all but one species of New Guinea are derived from marine ancestors (Berra et al., 1975). Many such fish find the new reservoir environment alien because of the need of many species to undertake longitudinal migrations into brackish or sea waters. Such fish, however, may form a basis for subsistence and commercial fisheries on natural lakes situated up a river, such as Lake Murray in Papua New Guinea. This lake is connected with the Gulf of Papua by the Strickland/Fly River system, which provides access for young Lates calcarifer to enter the lake and to leave it again when mature enough to migrate into the sea for spawning. Such routes are, however, invariably lost, with the damming of the rivers. Because of this, fisheries planners and developers considering new reservoirs of the Indo-Pacific islands for fish production purposes, have decided that to achieve high production, exotic fish species must be introduced. Tilapias feeding largely on the abundant source of planktonic algae and detritus have been introduced into the island reservoirs of the region since the fifties and their impact on fish production is indisputable; the fish production has risen considerably and in some water bodies new fish stocks have utilized vacant ecological niches for which there were no indigenous fish. Tilapias, together with a number of other exotic fish, have also been introduced to boost the poor production of many natural waters.
The desire to overcome the shortage of fish due to overfishing and, on a few occasions, to provide recreational fishing in new reservoirs, are among the many reasons for stocking.
Development of capture fisheries in lakes and reservoirs of the Indian Ocean and Pacific islands has had two goals: to increase the fish production as a food supply (Sri Lanka, Indonesia, Philippines and, to some extent, Malagassy and Papua New Guinea) or to establish a recreational fishery (Hawaii, Guam, New Caledonia). In some countries (Fiji) the direction of inland capture fishery development is still to be identified and in others, such as New Caledonia and Papua New Guinea, where introductions of fish into new reservoirs were loosely designed and the management of stocks poor or non-existent, the inland water fishery policy may have to be adjusted. At present, it appears that the less populated an island, the less care is taken of the inland capture fisheries development. The reason behind this appears to be the easier availability of fish from the not yet overexploited marine fish stock. In some countries, the keen interest in aquaculture development seems to make the need for improvement of inland capture fisheries secondary to aquaculture. Cage and pen culture is being added in overfished lakes and reservoirs, especially in the more productive lakes. The types and intensity of lake and reservoir fisheries, as presented in Table 1, are very crude indicators of the potential for further development of inland capture fisheries in the respective countries. The island countries can be divided into two groups: those more populous ones which are situated predominantly west of the Weber Line and those represented by the islands of Oceania and by Madagascar, with a lower population density. The first group is represented by Sri Lanka, Philippines and Indonesia, which have a medium to intensive inland capture fishery, while the islands of Oceania and Madagascar have occasional to medium fishing intensity. In both groups the introduced exotics such as cichlids and to a lesser extent cyprinids and some other fish have played a major role in boosting fish production.
Introductions into natural lakes
Among the best documented introductions into natural lakes are those for the Philippines where, with the exception of Lake Lanao, which has a stock of 29 species including some 20 carp species (Frey, 1969) (Table 2) the indigenous fish fauna is depauperate. The Table shows the wide range of fish yield, with the shallowest (Buluan) giving a yield of 2 693 kg/ha/year, which is equivalent to that of a very well managed fish pond. In this lake, where the fishery is completely dominated by the introduced species, common carp contributed 59 percent to the total fish catch, with tilapias (30 percent) being second (Baluyut, 1983). Of the 16 species introduced in Laguna de Bay, milkfish, common carp and tilapias have contributed 27 percent to the total capture fisheries, which were dominated by the native Therapon plumbens (48 percent of the total catch) (Baluyut, 1983). Since 1979, there has been a decline in capture fisheries mainly due to overfishing and pollution and part of this decline has been offset by considerable growth in fish-pen and fish-cage production for milkfish (Chanos chanos) and tilapia (Oreochromis niloticus). The socio-economic impact of these changes is discussed by Smith (1983). In Lake Lanao, common carp formed 12 percent of the total catch, which constituted 50 percent of exotic fish. In Lake Mainit, native gobies continue to dominate the catch with 68 percent of the total, the tilapias (9 percent) being second. The other species introduced - such as giant gourami, common carp, tawes and milkfish - represent the rest of the catch. From the point of view of increasing fish yields from capture fisheries the natural lakes seem to have greatly benefited, especially from the introduction of common carps and tilapias.
The Philippines have at least two documented examples of the negative impact of introduced fish species. Until the introduction of tilapia, O. mossambicus into the 1 800-ha Lake Buhi, a miniscule (12.5 mm average adult size) transparent goby Mistichthys luzonensis formed the basis of the commercial fishery. By 1979, the goby disappeared from this lake. The major factors accounting for this decline were: tilapia fingerlings feeding voraciously on the goby, damming of an outflowing river, introduction of motorized pushnets and an explosive increase in a highly predacious shrimp. The manipulation of Lake Buhi by man, including heavy overfishing and the consequent changes in aquatic environment as described by Gindelberger (1981) point out the vulnerability of the ecosystem. To compensate for the disappearance of the goby and the decline in capture fisheries, fish cages have been introduced and, by 1980, O. mossambicus × niloticus hybrids from cage production already contributed 26 percent of all the fish sold at the market (Gindelberger, 1982).
The second case is the accidental introduction of two gobies (Glossogobius giurus and Hypsilotrix agilis) into Lake Lanao. Between 1963–64 and 1979 there was a drastic decline in the Lake Lanao fishery, where the quantity of fish marketed dropped from 1 986 to 169 t. Cyprinids decreased from 49 to 28 percent, but the goby Hypsilotrix agilis increased from nil to 21 percent of the fish marketed. It is not clear whether the decline in cyprinids is directly related to the explosive increase in the goby or whether other factors, such as the regulation of Lake Lanao water level or a simple overfishing, have been involved.
Among the two major natural lakes of Papua New Guinea with commercial fisheries, the Chambri lakes on the Sepik River system, together with numerous backwaters of this river, support large concentrations of the exotic fish O. mossambicus. The fishery for this species is currently suppressed by the explosive development of the exotic water fern Salvinia molesta (Mitchell et al., 1980). No data are available but prior to this environmental catastrophy it was projected to harvest 30 000 t of O. mossambicus from these lakes and backwaters by the mid eighties. The current harvest is considerably less, probably less than 3 000 t, and if the Salvinia cover persists in its present extent, there is no chance for launching a large-scale commercial fishery there.
Introductions into reservoirs
In the major reservoirs of Indonesia and Sri Lanka stocking with exotic fish has often resulted in spectacular yields. In Sri Lanka, it is predicted that 50 000 t from inland reservoir capture fisheries can be achieved by 1990 (De Silva and Fernando, 1980) from a total of some 10 000 reservoirs. This yield should be based mainly on stocked tilapias. In Parakrama Samudra Reservoir in Sri Lanka the fish yield of 445 kg/ha/year in 1975–78 came mainly from O. mossambicus introduced in this lake in 1952. It has been observed, however, that the share of tilapia in the total yield changes from year to year, with the indigenous Labeo dussumieri and Puntius sarana contributing 25 to 46 percent of the total (in 1978 and 1976 respectively) (De Silva and Fernando, 1980). The present high component of native fish in the total yield indicates that O. mossambicus does not appear to compete with them but rather makes the environment favourable for their optimal production. De Silva and Fernando (1980) have suggested that the biological activities of O. mossambicus may have a positive effect on the food supply of Puntius.
In contrast with the natural lakes of the Philippines and the Malagassy reservoirs, the exotic common carp introduced into Sri Lanka reservoirs is considered a failure (Fernando, 1980).
The stocking of exotic fish into Indonesian reservoirs has faced a series of problems, the most important of which are a high predatory pressure on the released fingerlings, severe drawdown and lack of spawning areas (Baluyut, 1983). In spite of that, Cyprinus carpio, Puntius javanicus and O. mossambicus established themselves successfully in Selorejo Reservoir (400 ha surface area, yield 110 kg/ha/year) and O. niloticus in Jatiluhur Reservoir (8 300 ha, yield 22 kg/ha/year). Jatiluhur, as a large and deep reservoir (maximum depth 110 m), has been regularly stocked since 1965 and for the last ten years with O. niloticus only. To enhance the quality of spawning, an artificial spawning bed of 3 300 m2 has been constructed. In Jatiluhur, Darma, Karangkates and Rawa Pening Reservoirs floating cage culture for carp and tilapia has also been introduced to enhance fish production.
In Madagascar, three mountain reservoirs have their low-level fisheries based entirely on introduced exotic species. Fish production estimates are based on experimental fishing and they decline with increasing altitude and the richness of the waters. Lake Alaotra (715.5 m altitude) has an estimated fish production of 100 kg/ha/year, Itasy (1 221 m) 75.5 kg/ha/year and Mantasoa (1 381 m) 15.4 kg/ha/year (Moreau, 1979). In Alaotra, the fish population is dominated by O. macrochir, with C. carpio and Tilapia rendalli following. Itasy is highly dominated by tilapias (O. niloticus, 55 percent, hybrid tilapia, 38 percent). Mantasoa has T. rendalli (58 percent), Cyprinus carpio (28 percent), Micropterus salmoides (7 percent) and O. niloticus (7 percent) (Moreau, 1984). In Mantasoa the native fish disappeared soon after the reservoir was created in 1935. The reservoir is also the poorest in nutrients, while Alaotra, a shallow lake of a floodplain character, is rich in organic matter.
In Hawaii, Maciolek (1969) found fish lacking as a native component of the natural lakes. The Hawaii capture fishery is therefore entirely based on exotic fish species. Some 30 species were introduced into the fresh waters since the end of the last century. The most important recreational fishery is now on Waihiawa Reservoir on Oahu Island. An angler's creel census has shown a high predominance of tilapias (80.4 percent), followed by Cichla ocellaris and Lepomis macrochirus (each 6.1 percent), Carassius auratus (2.6 percent), Ictalurus punctatus (1.6 percent), Cyprinus carpio (1.5 percent) and five other species all less than 1 percent each. Today 11 species are well established, forming the basis of the recreational fishery.
In Papua New Guinea, New Caledonia and Guam, reservoir fisheries are undeveloped. In Yate Reservoir in New Caledonia, blackbass (Micropterus salmoides) is being caught by recreational fishermen and O. mossambicus is known to exist in the lake. The Sirinumu Reservoir of Papua New Guinea has three exotic species represented by O. mossambicus, Trichogaster pectoralis and Gambusia affinis, and four native species (Berra et al., 1975). There is no regular fishing on the reservoir and fishery research is still to be carried out. In Guam, O. mossambicus and Cichla ocellaris are established in Fena Reservoir, but exotic fish introduced into Masso Reservoir have been virtually eliminated by poaching using chemicals.
DISCUSSION
There is considerable potential for expansion of inland capture fisheries by introductions and stocking. Introductions and stocking of natural lakes and reservoirs on Indo-Pacific islands has often increased the yield spectacularly, with the introduced exotic fish quickly dominating the fishery. The reasons behind the success of introductions of exotic fish have been discussed by Fernando (1980) and Fernando and Holcik (1982). The examples of some Sri Lankan reservoirs suggest that native fish may benefit from introductions of exotic species but examples from elsewhere show that stocks of native fish may decline as a result of introductions, as is the case of Lake Lanao cyprinids and Lake Buhi gobies. Combination of factors is often responsible for the decline in the overall capture fishery yields, including those of introduced fish. Where there seems to be little hope of improving capture fisheries by further stocking or management of the environment, the fishery may be rehabilitated through the introduction of fish pen and fish cage culture. However, intensive culture of this type may further aggravate the capture fishery, as has been observed in Laguna de Bay in the Philippines.
Tilapias are the prime candidates for introductions (Table 3) because of qualities such as prolific breeding, fast growth, herbivory with the ability of utilizing blue-green algae, tolerance of poor water quality and good taste. Native fish stocks of Indo-Pacific islands suffer from their low species diversity and from being mostly riverine fish of marine origin. Thus, only rarely is there an endemic flock of species which has diverged into the ecological niches of the lacustrine environment. Mostly, vacant niches are available to be filled by introductions of exotics. While tilapias seem to do well in most lakes and reservoirs of the region, common carp has done well in some lakes and reservoirs of the Philippines and Malagassy. Both tilapias and common carp self-reproduce.
The large range between lake fishery yields (Table 3) shows that the upper level of capture fishery yield is largely determined by the morphometry and physico-chemical characteristics of each lake basin. Stocking such lakes may maximize the yield to a certain limit and it should be one of the tasks of fishery scientists to identify for each lake and reservoir the maximum yield which can be achieved by the combination of native fish production and that from introduction and stocking. The need for increasing the stocking rate above such limits should then be considered only for special socio-economic reasons.
In Hawaii, a reservoir sport fishery based entirely on a cocktail of exotic species is in the process of being analysed for the reasons of its relative success, with the outcome to serve as a guideline for an improved fishery management. Stocking of exotics into new reservoirs on Pacific islands which have no native fish should be carefully designed, as the introduced fish community may provide invaluable information if carefully monitored. Such reservoirs could serve as an important large-scale experiment providing new insights into the stocking strategies aimed at maximizing yields from inland waters either for food or for sport.
Statistical records need to be improved as well as monitoring of major biological and chemical parameters directly related to fish production. Under the impact of intensive capture fishery, indiscriminate use of fishing gears, and active interactions between the introduced and indigenous fish, resulting in an unstabilized ecological system, predictions of a sustained yield are very difficult. The interactions between the exotic and indigenous fish and among exotic fish have been largely neglected and this is one of the major tasks to be aproached in the new reservoir stocking.
REFERENCES
Baluyut, E., 1983 A review of inland water capture fisheries in Southeast Asia with special reference to fish stocking. FAO Fish.Rep., (288):13–57
Berra, T.M., R. Moore and L.F. Reynolds, 1975 The freshwater fishes of the Laloki River system of New Guinea. Copeia, 1975(2):316–26
De Silva, S.S., 1982 Impact of exotics on the inland fishery resources of Sri Lanka. Abstract of paper presented at the Regional Workshop on Limnology and water resources management in the developing countries of Asia and the Pacific, 29 November–5 December 1982. Kuala Lumpur, University of Malaya (Abstr.)
De Silva, S.S. and C.H. Fernando, 1980 Recent trends in the fishery of Parakrama Samudra, an ancient manmade lake in Sri Lanka. In Tropical ecology and development, edited by J.I. Furtado. Proceedings of the Fifth International Symposium on tropical ecology, Kuala Lumpur, International Society of Tropical Ecology, pp. 927–37
Fernando, C.H., 1980 The fishery potential of manmade lakes in Southeast Asia and some strategies for its optimization. In Biotrop Anniversary Publication. Bogor, Biotrop, pp. 25–38
Fernando, C.H. and J. Holcik, 1982 The nature of fish communities: a factor influencing the fishery potential and yields of tropical lakes and reservoirs. Hydrobiologia, 97:127–40
Frey, D.G., 1969 A limnological reconnaissance of Lake Lanao. Verh.Int.Ver.Theor. Angew.Limnol., 17:1090–102
Gindelberger, B., 1981 Why Sinarapan almost disappeared from Lake Buhi. ICLARM Newsl., 4(3):3–5
Gindelberger, B., 1982 After Sinarapan: the planned small-scale fish cage industry of Lake Buhi. ICLARM Newsl., 5(1):6–7
Gracia, D.M., 1981 Report on the hydrobiological survey and inventory of aquatic resources of Lake Mainit, Mindanao Island. Terminal report. Manila, BFAR Fish Propagation Division,
Maciolek, J.A., 1969 Freshwater lakes in Hawaii. Verh.Int.Ver.Theor.Angew.Limnol., 17:386–91
Mitchell, D.S., T. Petr and A.B. Viner, 1980 The water-fern Salvinia molesta in the Sepik River, Papua New Guinea. Environ.Conserv., 7(2):115–22
Moreau, J., 1979 Biologie et evolution des peuplements de cichlides (Pisces) introduits dans les lacs Malgaches d'altitude. These le grade de Docteur d'etat. 38 p.
Moreau, J., 1984 Mantasoa (Madagascar). In Status of African reservoir fisheries, edited by J.M. Kapetsky and T. Petr. CIFA Tech.Pap./Doc.Tech. CPCA, (10):155–92
Smith, N.R., 1983 Mismanagement of inland fisheries and some corrective measures. FAO Fish.Rep., (288):88–100
Villaluz, D.K., 1966 The Lake Lanao fisheries and their conservation. Manila, Bureau of Printing, 50 p.
Table 1 Intensity of the utilization by capture fisheries of reservoir and lake fish resources on Indo-Pacific islands
| Country | Type of water body | Intensity of fishery | Type of fishery |
| Fiji | R | ± | E |
| Guam (U.S.A.) | R | ± | Re |
| Hawaii (U.S.A.) | R | ++ | Re |
| Indonesia | R,L | ++ | S,C |
| Malagassy | R | ++ | S |
| New Caledonia | R | ± | Re |
| Papua New Guinea | R,L | ±(R);+(L) | nil(R);C,S(L) |
| Philippines | L,R | +++(L);++(R) | C,S |
| Sri Lanka | R | ++ | C,S |
+++ intensive
++ medium
+ low
± occasional
R reservoirs
L lakes
S subsistence
C commercial
Re recreational
E experimental
Table 2 Major natural lakes in the Philippines and their capture fin-fish fishery1
| Lake | Surface area (ha) | Mean depth (m) | No. of introduced fish species | No. of indigenous fish species | Fish yield kg/ha/year |
| Laguna de Bay | 89 000 | 2.8 | 16 | 15 | 103(1979)2 |
| Lanao | 34 000 | 60.3 | 10 | 29 | 51(1963–64)3 |
| Mainit | 17 430 | 128.0 | 5 | 10(?) | 11(1980?)4 |
| Buluan | 6 134 | 5.5 | 6 | 6 | 2 693(1980)5 |
Table 3 Fish mean yield kg/ha/year for major reservoirs and lakes of the Indo-Pacific islands
| Country | Mean yield kg/ha/year | Range kg/ha/year | Major fish species of commercial importance | Major reservoirs, lakes(4) |
| Fiji | nil | nil | Oreochromis mossambicus | Monasavu, Vaturu |
| Hawaii | 44(1) | 44 | Ictalurus punctatus, Salmo gairdneri, Micropterus dolomieu, Cichla ocellaris, Lepomis macrochirus, Oreochromis macrochir Tilapia zillii, Oreochromis mossambicus, O. melanotheron Micropterus salmoides, Channa striatus, Astronotus ocellatus | Waihiawa, Nuuanu, Waiakea, Kokee |
| Guam | not known but low | not known | Oreochromis mossambicus, Cichla ocellaris | Fena, Masso |
| Indonesia | 99(R) | 22–353 (Baluyut, 1983) | Puntius javanicus, Hampala spp., Macrones spp., Cyprinus carpio O. mossambicus, O. niloticus | Jatiluhur, Peniag, Karangkates, Selorejo, Prijetan, Pacal, Darma, Jombor |
| 18(L) | (Baluyut, 1983) | n.d. | ||
| Malagassy | 88(5) (Moreau, 1979) | 15–100 | O. macrochir, Tilapia rendalli, O. niloticus Cyprinus carpio, Micropterus salmoides | Alaotra, Itasy, Mantasoa |
| New Caledonia | not known | not known | Micropterus salmoides, O. mossambicus | Yate |
| Papua New Guinea | not known | not known | O. mossambicus, Lates calcarifer | Sirinumu (R), Chambri (L), Murray (L) |
| Philippines(2) | 188(L) | 11–2693 (Baluyut, 1983) | Native cyprinids (L.Lanao), C. carpio. O. mossambicus, O. niloticus native gobies, Therapon plumbens, Chanos chanos, Channa striatus | Laguna de Bay, Lanao, Buluan, Mainit, (all lakes) |
| Sri Lanka | 137(3) (De Silva, 1982) | nil to 2230 (Fernando, 1980) | O. mossambicus, Labeo dussumieri, Puntius sarana, Etroplus suratensis Cyprinus carpio | Parakrama Samudra, Moragaswewa, Castlereagh, Nalanda, Senanayake Samudra |
(2) Yields for reservoirs not available
(3) Yield calculated from all country reservoirs
(4) Where not marked, names refer to reservoirs
K.G. Rajbanshi
Fisheries Development Division
Lalitpur, Nepal
INTRODUCTION
Fish and fisheries products play a major role in fulfilling the demand for animal protein in the world. The products are of special importance to the countries of Southeast Asia where they meet more than 50 percent of the total animal protein demand.
The current world production is approximately 75 million tons per year, 55 million tons are utilized for human consumption and the remaining 20 million tons as animal feed for meat production. If the present level of world per caput utilization of fish is to be sustained, fish production must double by the end of the century to keep pace with the world's increase in population.
ROLE OF AQUACULTURE IN THE REGION
The contribution of aquaculture to the overall fisheries production in Asia and the Pacific as of 1980, was 20 percent, with an annual growth rate of greater than 8 percent (Delmendo, 1983). As the nations of this part of the world vary greatly in size, population and stage of development, the status of aquaculture in any one nation may be quite different than that of the area as a whole. Countries such as China, Japan, Korea, India, Indonesia, the Philippines and Thailand have much experience in the field and together contribute the major proportion of the aquaculture production of the area. The other countries of the region have prospects of increasing fish production several-fold by efficiently utilizing existing water bodies including lakes and reservoirs.
Aquaculture development cannot be ignored in the overall development of Southeast Asia since this sector is not only a reliable source of less expensive animal protein but also provides employment for a significant percentage of the world's population. Aquaculture represents an important source of revenue to a state while contributing to an ecologically balanced use of land and water resources.
POTENTIALITY OF LAKES AND MANMADE RESERVOIRS
Lakes
Several countries in Southeast Asia, Bangladesh, Sri Lanka and Thailand have no natural lakes. The natural lakes of India cover an area of 0.72 million ha and are largely situated at high altitude in the north and south of the country (Jhingran and Tripathi, 1977). The lakes of Bhutan (Rajbanshi and Csavas, 1982) and Nepal are scattered in high and mid-altitude regions while those of Pakistan are largely scattered in the lower part of the country where they cover about 0.0785 million ha (Ahmen, pers.comm. 1984). China possesses lakes of various sizes, both in the colder, high altitude region of the west and in the warm, humid eastern plains (Tapiador et al., 1977). The 50 lakes scattered throughout Japan cover 0.2 million ha (Satomi, 1977). Natural lakes in the Philippines cover an additional 0.2 million ha (Baluyut, 1982) with 90 000 ha attributed to the largest natural lake - Laguna de Bay. Lake sizes in Indonesia vary from several hundred hectares to 112 970 ha, the area of Lake Toba (Sarnita, 1977). Altogether, Indonesia possesses 1.78 million ha of lakes (Indonesia, Directorate of Fisheries, 1981). Depending on their altitude and latitude most of the lakes of Southeast Asia could be used for warmwater fisheries.
Manmade reservoirs
The number of manmade reservoirs in Southeast Asia has greatly increased over the last two or three decades. The shape and size of these reservoirs depend on the topography of the area in which they were built as well as on the primary function of the reservoir. Most reservoirs are built for irrigation, hydro-power generation, industrial or domestic use, flood control or navigation or any combination of the above.
In Southeast Asia, reservoirs have existed since rivers have been dammed for irrigation. However, fisheries in such reservoirs are a recent phenomenon, significant only during the last three decades. Most developing countries of the region have not yet fully recognized the importance of aquaculture in reservoirs and therefore do not include provisions for fisheries in the planning of them. Some reservoirs, for example Ubolratana in Thailand, have shown high profits from fisheries (Fernando, 1977) thus supplementing and improving the overall socio-economic benefit of the original purpose, hydro-power production (Interim Comm. Report, 1979). Such cases have induced policy-makers to examine the potential for fishery integration in both lakes and reservoirs. On several reservoirs: Ubolratana in Thailand (Bhukaswan and Pholprasith, 1976), Ganhisagar (Dubey and Mehra, 1959), Bhawanisagar (Chaco and Dinamami, 1949) in India and Tarbela in Pakistan (Ansari, 1977) preimpoundment surveys on fish fauna only were conducted, as a result problems arose in fisheries implementation especially in harvesting and navigation (Ansari, 1977; Natarajan, 1977).
In China, pre-impoundment studies for fisheries are carried out on most manmade reservoirs. The reservoirs are generally constructed for water conservation, fisheries and navigation and have controlled water flow.
An attempt has been made to tabulate the water surface of the lakes and reservoirs of Southeast Asia, as shown in Table 1. However, the data on surface area and production potential is incomplete and urgently needs updating.
Aside from China, Japan, India and Thailand, most countries only partially utilize their available water surface. The Indonesian lakes and reservoirs are considered rich in aquatic resources but have not been managed for fisheries (Sarnita, 1977). Similarly, fisheries potential of the 330 000 ha of water surface in the Philippines had only barely been tapped before 1976 (Baluyut, 1982). Thus, the extension of aquaculture to new areas, along with improved management of areas already developed, is sure to increase fish production in Southeast Asia, and raise this region's contribution to the world market.
AQUACULTURE PRACTICES IN LAKES AND RESERVOIRS
Aquaculture practices vary widely with lake and reservoir conditions, though some practices are widely used, thus common to many countries. Aquaculture in Southeast Asia can be broadly classified under the following headings:
Open-water (lakes and reservoir) fish culture
Pen fish culture
Cage fish culture
Others
Open-water (lake and reservoir) fish culture
Natural lakes and manmade reservoirs can be divided into two categories based on altitude and latitude:
High altitude or latitude water bodies
Lakes and reservoirs at high altitude or latitude are characterized by low water temperature. These temperatures result in slow growth of food organisms and correspondingly, fish. Coupled with the typically small size of mountain lakes, high altitude water resources are generally less productive than low altitude lakes.
Most of the lakes in India, Bhutan, Korea, Japan and Nepal and several lakes in China are high altitude or latitude lakes, suitable only for coldwater fisheries. India, Pakistan, Bhutan, Korea and Japan have successfully introduced the exotic salmonids Salmo gairdnerii and Salmo trutta. Tench (Tinca tinca), Crucian carp (Carassius auratus) and mirror carp (Cyprinus carpio) were also introduced in the high altitude lakes of Uttarpradesh and Tamilnadu states of India. Such exotic fish species have been well established in most of the Southeast Asian countries, though indigenous fish species are generally present in the same waters. In Nepal, attempts were also made on an experimental scale to introduce the salmonids Salmo gairdnerii and Salmo trutta from India and the United Kingdom, and a landlocked trout - amago (Onchorhynchus rhodurus) from Japan. All three species grew and were able to breed under farm conditions but failed to establish themselves in free water.
The introduction of exotic fish species is aimed at increasing the number of available food fish as well as at promoting sports fisheries. However, on the Indian sub-continent, the development of an exotic fish industry is taking place at the expense of indigenous species, e.g., Tor tor, Tor putitora, Achrossocheilus hexagonalepis, Schizothorax spp., Schizothoracthys spp. and Oreinus spp. Fish of the genus Tor are well known for their size and value to sport while the other indigenous species mentioned above, the Asala (Schizothorax or Schizothoracthys and Oreinus group) are considered delicacies by most local populations in Nepal (Rajbanshi, 1976) although it is not favoured in Pakistan (Ansari, 1977). The available information on these coldwater fish species, as well as data on stocking, management and production of the coldwater lakes and reservoirs of Southeast Asia is scant. In Nepal, a study on growth of Asala has concluded that it is very slow as fish attain only 226–362 g in four years and are thus not economically viable for culture (Masuda, 1979). Nevertheless, the possibility of stocking such fish should not be dismissed since the fish would provide animal protein for people living at high altitudes and make use of the water surface in cold or colder regions too. Successful fish seed production of Tor tor, Achrossocheilus hexagonalepis and the Asala group by hypophysation has increased the capability for mass production and stocking of these fish species in high altitude lakes and reservoirs.
Lower altitude or latitude water bodies
The high water temperature of lakes and reservoirs at low altitude or latitude creates an environment conducive to fast growth in fish.
Management practices
Fisheries development and management practices of the region vary as much as the natural and manmade lakes vary in shape, area and depth. Lake Toba in Sumatra, Indonesia and the Tonle Sap of the Mekong are among the largest bodies of fresh water in Southeast Asia. At the other end of the scale, water bodies of less than a few hectares are also found in the region.
Category of lakes and reservoirs: The reservoirs of Sri Lanka have been classified as follows (Mendis, 1977)):
This classification is based not on fisheries management but on irrigation practices and hydro-power generation.
Only in China has lake and reservoir classification been applied to fisheries management. Lakes are divided into three categories, based on surface area (ADCP, 1979):
Similarly, manmade reservoirs are broadly classified as being of one of three shapes (Song, 1980). Shallow lakes on land with only a slight gradient are considered highly productive reservoirs and multi-branched reservoirs are considered to be more productive than river-type reservoirs of mountainous regions. In fish culture, these reservoirs are further categorized on the basis of size:
As a rule the larger the surface area of a lake or a reservoir, the more extensively it is managed and the less is its production per unit area. In China, in an effort to increase the fish production of both lakes and reservoirs the polyculture system has been widely adopted. According to the Chinese system, more attention is focused on small bodies of water where semi-intensive or intensive culture can be applied. Proper stocking rates are combined with the use of organic fertilizers and supplementary feed (aquatic weeds or tender graminiferous plants) to produce high yields of fish (Song, 1980).
In India, any fisheries development programme designed for a larger body of water is done in conjunction with an appropriate sized fish farm able to produce the required quality and quantity of fingerlings.
In addition, governmental restrictions partly aimed at fishing gears and seasons are employed in an effort to protect the fishery. The establishment of cooperatives and the rehabilitation of traditional fishing communities also play important roles in the overall plan.
Stocked fish species: In Southeast Asia, the primary goal of fisheries - to increase the production of food fish for human consumption - is met by stocking both indigenous and exotic fish species.
The polyculture system makes efficient use of available food at all levels in the food chain. The most commonly stocked fish species are:
Chinese carp:
Hypophthalmichthys molitrix (silver carp)
Aristichthys nobilis (bighead carp)
Ctenopharyngodon idella (grass carp)
Common carp:
Cyprinus carpio
Indian major carp:
Labeo rohita (rohu)
Catla catla (bhakur/catla)
Cirrhinus mrigala (naini/mrigal)
African cichlidae:
Oreochromis mossambicus
Oreochromis niloticus
Tilapia rendalli
Chinese carps are generally favoured as they exhibit good growth while utilizing the water body's lower level food organisms (plankton and aquatic macrophytes). In India the filter feeding silver carp, in particular, is noted for its fast growth (Rao and Dwivedi, 1973). Chinese carp species -silver, bighead and grass carp - when stocked with common carp in Nepal's lakes significantly increased fish production. In Hong Kong, the Chinese carp were stocked in a water supply reservoir -Plover Cove - to filter phyto and zooplankton, thus improving water quality (Cheng, 1976; Hodgkiss, 1980).
The introduction of African cichlid fish species can be supported in the absence of lacustrine fish species in the region. Stocking of Oreochromis mossambicus in Sri Lanka has had a tremendous impact on freshwater fish production, particularly in the larger irrigation reservoirs. Production in Parakrama Samudra and many other reservoirs is reported to have increased several-fold (Mendis, 1976). In Thailand, similar cases can be cited (Bhukaswan and Pholprasith, 1976). Fernando (1977) has suggested either the regular stocking of indigenous fry or the introduction of exotic lacustrine species as a means of increasing fish yields to economically desirable levels, since a lack of lacustrine fish species in this region may be the critical factor limiting fish yields.
In India, stocking is largely confined to the Indian major carps - Catla catla, Labeo rohita, Cirrhinus mrigala and Labeo calbasu. In the north these species are combined with certain medium-sized carp such as L. bata, C. reba and Puntius sarana and in the south with peninsular carp such as: L. frimbriatus, L. kontius, Cirrhius cirrhosa, Puntius dubius and P. carnatica (Natarajan, 1972). Experimental stocking of Etroplus suratensis, Osphronemus gouramy, Mugil spp., Chanos chanos and Megalops cyprinoides was also conducted but proved to be of little consequence (Jhingran and Tripathi, 1977). Oreochromis mossambicus which was introduced to a small number of reservoirs in the south of India (Jhingran, 1975) became established to the point of replacing indigenous fishes while yielding high catches (Sreenivasan, 1977).
In Thailand, studies on indigenous fish have revealed 68 species in Ubolratana Reservoir, 39 species in Lan Pao Reservoir (Srisuwantach, 1970), 43 species in Cokh Hora (NIFI, 1980) and 32 species in Kang Krachan (Srisuwantach, 1970). However, the species variety in the above river systems prior to impoundment was invariably greater. The main exotic fish species stocked in thai reservoirs are the Chinese carps - silver carp, bighead carp and grass carp, African cichlidae -Oreochromis niloticus, T. rendalli and T. zillii and Indian major carp -Labeo rohita of these, T. nilotica is favoured by the Thai people (Bhukuswan and Pholprasith, 1976).
The reservoirs of Indonesia are stocked with some exotic species, e.g., Cyprinus carpio, Oreochromis mossambicus and Oreochromis niloticus as well as with indigenous species (Sarnita, 1977). In China, stocking centres on indigenous Chinese carps. Tilapia species have only recently been introduced in Chinese aquaculture.
Stocking size: Fingerling survival in reservoirs and lakes which contain carnivorous species is greatly dependent on the size of fingerlings at the time of stocking.
Information on fingerling size at the time of release is unavailable from most countries of Southeast Asia. However, experience in India, Thailand, Indonesia and the Philippines has shown that production of fish increases with an increase in the size of the fingerlings released. In China the recent trend is to prefer fingerlings of 15–20 cm of 50 g stocked at 1 500/ha over the former practice of stocking 6–7 cm fingerlings at 1 000/ha (ADCP, 1979: FAO, 1983). With larger sized fingerlings recapture rate has increased from 1 to 20 percent of the number of stocked fish (ADCP, 1979).
In Nepal, the stocking of 20–25 g of Chinese and common carps has resulted in adequate survival and improved yield.
Stocking density: Stocking density in open water aquaculture varies according to the fertility of the water and species to be stocked. For the most part, however, stocking information is scanty and difficult to assess.
In India, Indian major carps have been stocked at different densities in several reservoirs. For example, the stocking rate in Nagarjunasagar is 1/ha, in Rehan and Konar Reservoirs 25/ha, in Bhawanisagar Reservoir 82/ha (Natarajan, 1977), in Stanley Reservoir 105–500/ha and in Bhavinisagar 135–475/ha (Sreenivasan, 1977). Information on the size of the stocked fish is unavailable. However, the stocking rate in Indian reservoirs is generally considered as inadequate as reflected by low yield from most of the reservoirs.
In China, recommendations for stocking rates are based on water fertility and the likelihood of predation. Highly fertile water with high predator density should be stocked with 1 200–1 500 fingerlings of 13–16 cm length per hectare or 3 000 fingerlings of 10 cm per hectare. Fertile water with a low likelihood of predator should be stocked with 750–900 fingerlings, 13 cm in length or 1 800–2 250 fingerlings of 10 cm in length per hectare. Sterile water with few predators should be stocked with 450–600, 13-cm fingerlings or 1 200 10-cm fingerlings per hectare. All stocking rates reflect polyculture systems as follows: in plankton-rich water silver and bighead carp are stocked as major species along with grass carp and the mollusc-feeding black carp and Wuchang fish (Megalobrama amblycephali). In water rich in grasses, grass carp are heavily stocked alongside bighead carp, common carp and Wuchang fish.
Fishing gears: Among the gear used for harvesting fish throughout Southeast Asia are gillnets, longline (with or without live bait), hook and line, scoopnets (with or without light attraction), liftnets and traps (bamboo or net). Gillnets used in India are of two types - the surface net, known locally as “Rangoon”, which has floats only, and the bottom set gillnet, known locally as “Uduvalai”, which has a lead line as well as floats (Natarajan, 1977). These gillnets have proved versatile enough to catch fish from different strata, i.e., fish species with different feeding habits.
In China, seine nets are used in conjunction with other gear to increase harvest efficiency. Such nets are typically 1–1.5 km long, but are found as long as 5 km. The use of seine nets is possible because portions of the reservoir were cleared prior to flooding.
Production: Since the management of lake and reservoir fisheries has not yet become well established, yields vary greatly. In general, yields are low to moderate. Exceptions are shallow and eutrophic lakes such as Lake Buluan (1 600 kg/ha/year) and Laguna de Bay (250 kg/ha/year) in the Philippines, whose yields are considered extremely high. Low yields are exemplified by harvests from such deep lakes as Lanao (4.9 kg/ha/year) and Mainit (0.9 kg/ha/year) in the southern Philippines (Baluyut, 1982). Fish production from manmade reservoirs in the Philippines is not yet significant.
Indonesian harvests are not accurately known. The Directorate General of Fisheries has assessed yields at 15–210 kg/ha/year with an average of 18 kg/ha/year, while Sarnita (1977) gives a range of 12–770 kg/ha/year, with lowest production coming from Jatiluhur - Indonesia's most studied reservoir - and the highest from Lake Darma (West Java).
On a per-hectare basis, the most productive Thai reservoir appears to be the 1 800-ha Lam Praplerng, which has a total catch of 252 t/year for an average production of 140 kg/ha/year (Chukajorn and Pawapootanan, 1976). The lowest production, 8.3 kg/ha/year, comes from Sirikit Reservoir. The major Thai reservoirs have an average fish production of 54 kg/ha/year.
Parakrama Samudra Reservoir, Sri Lanka, has an average yield of 442 kg/ha/year (de Silva and Fernando, 1980). Indian reservoirs exhibit relatively low production; Gandhisagar Reservoir - 4.05–20.56 kg/ha/year (Dubey and Chatterjee, 1977); Rihan Reservoir - 4.89–10.91 kg/ha/year (Natarajan, 1977); Stanley Reservoir - 37.30 kg/ha/year; Bhawanisagar Reservoir - 33.88 kg/ha/year. Two other reservoirs in India, Sathanur and Amaravathy yield the greatest harvests with 162.30 kg/ha/year and 187.7 kg/ha/year, respectively.
The production of fish in the natural lakes of China varies from 53 to 750 kg/ha/year (ADCP, 1979), the national average was 135 kg/ha/year in 1978 (FAO, 1983). Production in manmade reservoirs varies greatly, 12–870 kg/ha/year (FAO, 1983); depending on the management system used. small reservoirs under intensive aquaculture provide an average of 750 kg/ha/year (Song, 1980).
Information on fish production from lakes and reservoirs of Malaysia, Bangladesh and Pakistan is scarce. In Nepal, production in Lake Begnas increased from 21.68 kg/ha/year in 1977/78 to 25.87 kg/ha/year in 1981–82 with the stocking of fingerlings of Chinese and common carps. Intensive stocking and better management are sure to enhance the productivity of such lakes in the future.
Constraints:
Stocking of exotic as well as commercially important indigenous fish can be conducted such that maximum use is made of food chains and production optimized. However, several constraints on the rapid development of lake and reservoir fisheries still exist. Among them are:
Paucity of reliable data on various aspects of lakes and reservoirs, including data on various aspects of lakes and reservoirs, including data on the number and size of stocked fish. This situation has created problems in the identification of failures and success and impeded improvements.
Insufficient understanding of the ecology of indigenous fishes and the interactions between native and introduced species. As a result of this problem the success of new introductions cannot be predicted and the reasons for failure are difficult to interpret. The problems mentioned above are illustrated by the effects of the introduction of some fish species into lakes and reservoirs of Southeast Asia.
The exotic species Oreochromis niloticus and Aristichthys nobilis have become well established in some of the Thai reservoirs Ctenopharyngodon idella, Labeo rohita and Hypophthalmichthys molitrix established themselves equally well in Ubolratana Reservoir, however, their adaptation occurred at the expense of several indigenous species (Bhukaswan and Pholprasith, 1976).
In the Philippines, stocking of exotic Oreochromis spp. and Cyprinus carpio together with indigenous Chanos chanos led to catches of significant commercial value. However, the introduction of tilapia to Lake Buhi led to the near extinction of the commercially important small native fish Mistichthys luzonensis Smith (Gindelberger, 1981). Similarly, the accidental introduction of the carnivorous fish Glossogobius giurus and Hypsilotrix agilis has threatened populations of endemic cyprinids in Lake Lanao.
Similar problems are occurring in India where the introduction of Oreochromis mossambicus threatens the population of the endemic Puntius dubius in Amaravathy Reservoir (Sreenivasan, 1977). In other Indian reservoirs, introduced Gangetic major carps - Catla catla and Labeo rohita have caused similar problems. An endemic species, Cirrhinus cirrhosa, which comprised 20–47 percent of the catch in 1943–44 declined to 2 percent of the catch in 1965–66. Labeo fimbriatus and Labeo kontius have completely disappeared from the reservoirs, though they continue to flourish in the river system below the dam. Other endemic species, Labeo fimbriatus and Labeo bata, have disappeared from Bhawanisagar Reservoir since 1968, while Labeo calbasu, an introduced species, has established to comprise 40 percent of the catch (Sreenivasan, 1977). Dubey and Chatterjee (1977) also correlated the decline of C. mrigala once a dominant fish of Gandhisagar Reservoir, with increasing Catla catla harvests. Attempts at stocking exotic fish species in Indonesia have largely failed due to high predation rates and the failure of many species to reproduce naturally (Sarnita, 1977).
Lack of standardization of fish yield records;
Lack of studies on gear used in fisheries, with suggestions for improvements;
Lack of information on the socio-economic impact of lake and reservoir fisheries, which could be used to influence the planners and policy-makers.
Pen fish culture
Pen fish culture, developed in the Philippines, is known to most of the countries in the region, but no other country has adopted this method in lakes or reservoirs. In the Philippines, pen fish culture is primarily located in Laguna de Bay, an eutrophic natural lake. The practice there is intensive and is concerned mainly with the economically important indigenous Bangus - Chanos chanos.
The site of fishpen culture is generally determined by:
Fish pens vary in size (1 ha to greater than 400 ha) and shape (square, rectangular, triangular, circular, half-moon shaped, etc.) (Delmendo 1982). Fish pens are constructed using polythylene netting, nylon ropes and bamboo poles sunk in the mud 25 cm or more depending on the substratum. Usually, the fish pens are stocked with 15–25 g Chanos chanos fingerlings, at a stocking rate of 35 000–60 000/ha (Delmendo, 1982). One stocking per year is common, though some fish pen owners prefer to stock biannually. Fish are harvested when they reach 200–350 g, by means of gillnets or seiners (Delmendo, 1982). Supplemental feeding is not common, though some operators provide bread, crumbs, rice bran, broken ice-cream cones, fish meal, ipil ipil (Leucaena leucocephala) or ipomea leaves.
In 1968 the “Laboratory Scale” fish pen in Laguna de Bay was established; in 1970 it was developed into a 40-ha pilot commercial project and, in 1980, it was expanded to 7 000 ha. It is estimated that this project produces at least 56 000 t/year, with an average yield of 4 t/ha/year (Baluyut, 1982). In the Philippines as a whole, fish pen culture covers an estimated 20 000 ha and produced an estimated 149 557 t, a productive rate of 7.4 t/year (Delmendo, 1983). Fish pen culture alone produces 20 percent of the total Philippines milkfish production.
Cage fish culture
In some parts of Southeast Asia, cage fish culture is still at the planning stage while in other countries commercial production projects are already in operation. Japan (Nambiar, 1970), Democratic Kampuchea (Hickling, 1962) and Thailand (Teng-trongpiros, 1979) have long histories of cage fish culture, with Japan leading production through the use of extensive and intensive methods. The introduction of cage fish culture in China (FAO, 1983), Malaysia (Chua, 1979), India (Natarajan, Saxena and Srivastava, 1979) and Nepal has been relatively recent. In Sri Lanka (Jayamaha, 1979), Bangladesh (Akbar, 1979; Cabangbang, 1979) and Pakistan (Ahmed, pers.comm.) cage fish culture is in the initial stage of development.
There are two types of cages currently used for production of fish. The rigid cage is made of locally available materials such as bamboo, wood or angle iron. Net cages are constructed using nylon netting supported by galvanized pipe, aluminium pipe, wooden or simple bamboo frames. The cage size and shape is variable and dependent on the fish species being cultured. A circular or hexagonal cage is more suitable for fish species which aggregates in shoals and swim incessantly in a circular motion (Chua, 1979). In most countries, however, rectangular or square cages are used. Cages are floated on the water using bamboo, wood logs, sealed empty oil drums, plastic floats or stylofoam.
Availability of seed, the commercial value of different fish species and regional preference determine which species of fish will be utilized for fish culture. In Japan, Cyprinus carpio and salmonids are cultured for domestic consumption and export.
Cages are stocked at the rate of 30 fish of 50–120 g/m2. The fish are fed four to five times a day with commercial pellet feeds with a feed efficiency of about 70 percent. The survival rate is up to 90 percent and the rate of production is 20–50 kg/m2 in a culture period from April to August (Delmendo, 1983).
In the Philippines, four species of African cichlid - Oreochromis mossambicus, O. niloticus, O. aureus and Tilapia zillii - are the preferred fish for use in cage fish culture. Oroechromis niloticus are stocked at the rate of 250–1 000 fingerlings of 5–20 g each per m2. A feed consisting of 23 percent fish meal and 77 percent rice bran is fed to the fish at the rate of 5 percent of the body weight per day. The fish reach weights of 80–100 g within 2–4 months at which time they are harvested (Guerrero II, pers.comm.). Due to the popularity of cage fish culture in the Philippines, the number of cages in Lake Bunot, Laguna de Bay, Lake Paoay and Pantabangan Reservoir is on the increase.
In Indonesia, the studies have been conducted on the use of Cyprinus carpio and Tilapia spp. in cage fish culture of Jatiluhar, Darma, Karangates and Rawa Pening Reservoir (Sarnita, 1977). In Java, similar studies were carried out on Leptobarbus hoeveni and Thyninichthys thynnoides and L. hoeveni (Reksalegora, 1979) and in West Java on Cyprinus carpio (Jangkani and Djajaderedja, 1979) and Oreochromis niloticus.
In Malaysia, cage fish culture of Cyprinus carpio, Ctenopharyngodon idella and Puntius spp. has only been practised in Chendroh and Bukit Merah Reservoirs since 1979 (Baluyut, 1982). Ctenopharyngodon idella is also cultured in floating net cages in Tasik Chenderoh (Delmendo, 1982). Although the Government of Malaysia provides common carp seed without charge, growers prefer grass carp. This preference is due to the feeding habits of grass carp. Grass is abundant and does not cost the farmers money. Net cages are commonly stocked with 200 grass carp. The carp can then be fed hydrilla, soft leaves such as those from tapioca and banana plants and grasses - abundant and inexpensive feed materials. The fish reach 1.8–2.0 kg weight within 7–8 months, whereupon they are harvested.
In Thailand, cage fish culture was initiated in 1950, now it is practised extensively in reservoirs. Many fish species are cultured, such as: Pangasius sutchi, Clarias macrocephalus, Oxyeleotris marmorata, Cyprinus carpio, Puntius gonionotus, Tilapia nilotica and Ophicephalus striatus. Pangasius sutchi is the most popular and commercially viable freshwater species raised in Thailand, Cages are stocked with 2 000 fingerlings of 8–13 cm in length. The fish are fed with rice bran, chopped ipomea, lemna and pelleted commercial feed. Within ten months, the fish reached marketable weights of 1–1.2 kg (Delmendo, 1982).
In China, cage fish culture was initiated in Bailianhe Reservoir in 1976 and has been since expanded considerably. Practices are based on the utilization of natural food organisms by the caged fish. A site is selected on localized productivity measurements and the cage is placed at least 2 m under water. Polyculture is practised using 85 percent silver carp, 4 percent grass carp along with an 11 percent mixture of black carp (Mylopharyngodon piceus) and Wuchang fish (Megalobrama amblycephala) to control the growth of unwanted organisms on the cage wall. The average stocking density is 25 fingerlings of 25 g size (13 cm length) per m2 of cage surface. Average annual production presently stands at 11.2–15 kg/m2/year (FAO, 1983). Further experiments in natural lakes using various indigenous species as well as Oreochromis mossambicus are planned for the near future.
In 1975, Nepal initiated cage fish culture in the lakes of Pokhara Valley (Sharma, 1979). This practice was recognized as economically feasible in 1978 (Pradhan, 1979). The cumulative cage volume used by the private sector exceeds 10 000 m3 (Rajbanshi and Pradhan, 1983).
In Nepal two types of fish cages are used: (a) a rigid angle iron cage with a netlon screen, and (b) a vinylon net cage.
Vinylon net cages are preferred by fish growers because they are easy to transport, to float, to maintain and to harvest the cultured fish. Caged fish polyculture systems have been adopted on the basis of the availability of natural food in lakes. In phytoplankton rich water silver carp are used as the major species. In zooplankton-rich waters bighead carp are used in combination with silver carp, grass carp, common carp, Catla catla and L. rohita is used to clean the side of the cage and is stocked in limited numbers. The general stocking rates is ten fingerlings of 15–20 g each per m2.
Year-round scarcity of bigger sized fingerlings has induced some progressive fish growers to maintain nursery cages along with production cages. In this way, fish growers increase income by ensuring a second or continuous crop as well as by selling larger fingerlings to other growers.
Production of fish varies from 4 to 10 kg/m3/year, in experimental cages. However, average production of private fish growers is 4 kg/m3/year. Details of the development of cage fish culture in Lake Begnas has been described in Annex A.
In India, cage fish culture was attempted with air-breathing fishes in swamps (Dehadrai et al., 1974) and with Indian major carps in Yamuna and Ganga waters between 1972 and 1976.
In an attempt to alleviate the increasing demand for fish seed in India, floating cages were used experimentally to raise collected spawn to fry and fingerlings. The results are encouraging as within 28 days the hatchlings grew to an average of 45.6 mm. Results from another experiment show fry growth of 103.6–121.8 mm in 82–89 days at a stocking rate of 2 500 fry in a hapa (Natarajan, Saxena and Srivastava, 1979).
Others
In addition to fish culture, Japan and China are leading Southeast Asian countries in rearing freshwater mussels for cultured pearl production in lakes and reservoirs.
In Japan, mussels are raised for the commercial production of pearls. In China, because cultured pearls are mainly used for medicinal purposes, their shape and quality is not as important as in Japan (FAO, 1980).
CONCLUSION
Southeast Asian's contribution to the aquaculture production of the world is steadily on the increase. By more effectively exploiting the numerous lakes and reservoirs of the region this increase can be accelerated.
Along with the existing plan for hydro-power or irrigation reservoir construction should accompany a fishery development programme. Planners, policy-makers, engineers and fisheries biologists must work hand in hand to maximize the socio-economic benefits of their projects.
It is also necessary to conduct a systematic data review and compare pre-impoundment with post-impoundment surveys in order to obtain a better understanding of changing ecological and limnological conditions. Careful data must be kept if biologists are to accurately assess the development potential of indigenous as well as introduced species.
Intensification of lake and reservoir exploitation can be made much easier through regional cooperation. A standardization of prevailing data collection to techniques and efficient data exchange are necessities. The various countries of the region must learn from each other's successes or failures and avoid repeating mistakes such as haphazard introduction of exotic and indigenous species.
ACKNOWLEDGEMENTS
The author extends gratitude and sincere thanks to the authorities of the Department of Agriculture and colleagues of the Fisheries Development Division for their continuous encouragement and support in various steps of study as well as in preparing the paper. Acknowledgement is also due to the concerned authorities of FAO Department of Fisheries and to the members of the organizing committee for giving this task.
Thanks are also due to Mrs. M.N. Delmendo and other country colleagues for their help in providing useful references.
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Table 1 Water surface area of lakes and manmade reservoirs in Southeast Asia
| Country | Surface Area of lakes and reservoirs (ha) in million | Source |
| India | 1.814 | Jhingran (1975) |
| China | 8.300 | Tapiador (1977) |
| Bangladesh | 0.090 | Bari (1977) |
| Pakistan | 0.160 | Ahmen (pers.comm.) |
| Sri Lanka | 0.140 | Mendis (1977) |
| Bhutan | 0.004 | Rajbanshi and Csavas (1982) |
| Nepal | 0.005 | |
| Thailand | 0.420 | Baluyut (1982) |
| Malaysia | 0.042 (including Temmenggor Dam) | Baluyut (1982) |
| Hong Kong | 0.001 | Cheng (1976) |
| Philippines | 0.330 | Baluyut (1982) |
| Indonesia | 1.804 | Baluyut (1982) |
| Japan | 0.200 | Satomi (1977) |
| Korea | 0.055 | Korea, Directorate General, Office of Fisheries (1977) |
| Total | 13.365 |
