An aquaculture plan, and a policy for its implementation, ought not be developed until all potential types of culture have been appraised. The appraisal should include economic viability, possible extent of culture and social relevance. As the number of possible culture systems is very large, the Mission initially considered them either in groups of culture systems or in relation to a particular species or species group.
This broad appraisal is carried out in this chapter. It concentrates on the economic viability and the possible extent of the culture. Social relevance will be considered more explicitly in chapter 6. For those groups of culture systems, or species groups, which at first sight appear economically viable, or for which the Government has shown much interest, the Mission assesses in detail the economic viability of a specific culture system (e.g. within the group “small-holder shrimp culture in ponds” the Mission appraised the economic viability of (a) monoculture of Penaeus monodon, or (b) mixed shrimp culture and of (c) polyculture of P. monodon and milkfish).
The main types of system considered for fresh water fish farming in Sri Lanka were pond culture and culture of fish in the seasonal tanks. Cage culture in seasonal and perennial tanks was also appraised by the Mission. Of these, there is little documented experience of pond culture, culture in seasonal tanks or cage culture. All these possible systems require supplies of fingerlings, either from the wild or, more usually, from hatcheries. The stocking of perennial tanks may also require supplies of fingerlings of preferred species from hatcheries. Species that were considered included various carps and tilapias, trout and milkfish.
There are no technical obstacles to the commercial culture of fish in ponds in Sri Lanka. Appropriate species are carps, tilapia and possibly the prawn Macrobrachium rosenbergii. The required inputs (apart from an adequate supply of fingerlings or post-larvae) are available, but they have alternative uses, and the costs and benefits have to be examined and compared. As far as can be estimated in the light of information at present available, economic conditions do not seem to be favourable for pond culture of tilapia in the situations in which most farmers find themselves. Meanwhile, the immediate obstacle to development and subsequent demonstrations, if trials are successful, is the lack of practical experience in this type of fish culture.
Annex 12 contains an appraisal of a corporate-scale fish farm for intensive rearing of tilapia. The conclusion is that such an activity is not at present economic even on very favourable, and probably unrealistic, assumptions (water supply by gravity; cost of pond construction below present rates; no cost for land).
The Mission appraised culture of tilapia on low-yielding paddy land. It may be attractive to the farmer, at least as regards net earnings and/or the input of labour required, although this would have to be borne out by practical experiment. Whether such an enterprise would be attractive from other points of view is perhaps doubtful (see Annex 10).
There may be areas of marginal land with adequate supplies of water where extensive fish culture could be established profitably at small cost. The Mission's impression is that such possibilities are not sufficiently numerous to justify a major effort on the part of Government to develop pond culture.
These tentative conclusions should be reviewed if and when either of two things happen: (1) carp becomes an established part of the local diet, through other developments to be recommended later, or (2) Macrobrachium post-larvae and commercial feeds become readily available.
There is no reason to suppose that raising fresh water fish in cages in Sri Lanka would be technically complicated. It is known that tilapia and carp can be cultivated in this way, and materials for constructing cages are available locally. The major tanks have areas suitable for the installation of cages. As compared with extensive ranching of fish in large open bodies of water, cage culture provides additional control of, and better access to, the farmed stock, at the cost of building and servicing cages. Annex 13 is a tentative appraisal of the economic viability of cage culture in brackish waters; it is not encouraging. The costs of cultivating fresh water species in cages would be similar to those for brackish water species, and fresh water fish fetch lower prices. In the conditions obtaining in 1980, there is no reason to suppose that culture of fresh water fish in cages would pay.
This conclusion would have to be reviewed if a ready market for carp could be established in Sri Lanka as a result of developments to be considered later.
(i) The economic viability of a system of culture involving stocking seasonal tanks with fingerlings and subsequently harvesting the fish, would depend to a large extent upon the cost of the fingerlings as delivered to the tanks and the eventual yield of fish when the tank is harvested. Because the seasonal tanks are highly productive, the yields should be good if appropriate management methods are adopted and if disease, predators and pilferage are not serious. There is no reason to suppose that disease and predators cannot be kept under control.
Good management would ensure that the fingerlings were released into the tank at a time that they could take advantage of the main crop of zooplankton occurring when the tank is nearly full. Later, the stock might have to be fed and guarded against pilfering and avian predators, and the water fertilized. The draw-down of the water would be so conducted as to strike a good balance between the requirements for irrigation and for fish growth. Harvesting when the water level is low should present little problem.
Any one tank would offer a variety of habitats and food for the fish, which would change as the water level falls. A mixture of compatible fish species would probably be needed to make best use of opportunities. Since tanks differ, the best species mix and the best density of stocking may vary and would have to be the subject of experimentation.
As a basis for estimates of probable average yields, it can be assumed that in the early years of farming of a typical seasonal tank, without use of fertilizers or supplementary feed, a stocking rate of 2 500 fingerlings/ha would be reasonable, yielding about 700 kg to 1 ton of fish per ha (full supply level area) in a six month season, at a survival rate of 80 percent. A typical species mix would be bighead carp, grass carp, common carp, tilapia, catla (Catla catla) and rohu in roughly equal numbers; milkfish should also be tried. Later, using supplementary feeding techniques, fertilizers and appropriate stocking densities, the production might be as much as 3 t/ha/6 months.
(ii) The local village council responsible for the tank would have the choice of retaining the rights to cultivate fish in the tank or of leasing these rights to an outside individual or corporate body. The Mission has assumed in all the projections which follow that they would retain the rights. If so, they would have the further choice of allowing approved persons to contribute to the costs of stocking and management and to harvest or receive harvested fish from the tank, according to an agreed sharing system, for disposal as they will, or alternatively to operate the enterprise as a communally-owned self-financing fully commercial venture, with organized harvesting and sale of the crop and distribution or retention of profits as may be agreed from time to time. The latter arrangement should result in more fish being produced and the Mission believes it is the best alternative. Consequently the Mission recommends that the village council appoint an official to be responsible for the management of the fish cultivation enterprise; this manager would work in close collaboration with extension workers and other representatives of Government. His main duties have been indicated in 4.4.1 earlier above. He would receive appropriate training through a scheme organized by the Government extension service.
(iii) Annex 14 presents estimates of the costs of extensive systems of culturing fish in seasonal tanks. The biggest single cost is that of fingerlings: at least this is so if fingerlings have to be produced from special facilities incorporating modern hatcheries, and sold to the villages at cost. Most of the remaining costs would be for salaries and wages. These latter costs are not greatly influenced by the size of the individual enterprise, and it will most likely be uneconomic to cultivate isolated individual tanks of, say, 1 to 2 ha, unless and until relatively more intensive systems are developed involving the use of fertilizers and/or supplementary feeding.
Annex 14 suggests that if the fish can be sold at the tank side for Cey.Rs. 4/kg - a figure which seems reasonable - the estimated costs of production would be recovered, but the village council would not make much profit and would be unable to accumulate funds as a reserve against crop failures or to finance development of more intensive methods. At least this would be so if fingerlings had to be bought at a price which would ensure that all costs were recovered. Since it is the opinion of the Mission that the demand for fingerlings may in course of time be so great that it would be impracticable or inefficient for the Government to produce all that will be needed (see later below), the Mission had assumed that simple small-scale methods of fingerling production will develop where production costs may be significantly lower than in Government hatcheries.
(iv) Culture of fish could have considerable impact on the supply of fish in rural Sri Lanka. The number and area of seasonal/minor tanks in the island have been differently estimated. According to Mendis (1977) these extended over an area of 47 986 ha. The FAO/World Bank Cooperative Programme on village tanks rehabilitation mentions 25 000 minor irrigation schemes, including 15 000 village tanks and 10 000 anicut, or diversion schemes. The project is to cover nine districts in the dry zone, having over 8 000 village tanks as follows:
Distribution of village tanks in dry zone districts of Sri Lanka (FAO, 1980)
| Name of District1 | Number of tanks |
| Amparai | 90 |
| Anuradhapura | 1 406 |
| Hambantota | 311 |
| Kurunegala | 4 203 |
| Mannar | 461 |
| Moneregala | 137 |
| Puttalam | 772 |
| Trincomalee | 192 |
| Vavuniya | 610 |
| Total | 8 182 |
Approximately 3 000 of these tanks are small, not exceeding 8 ha each in area, and have a total water spread of 21 947 ha at full supply level. The total area of village tanks below 80 ha each in water surface in the nine dry belt districts is estimated at 86 000 ha. Including similar tanks in other districts, the total area of seasonal tanks will easily exceed 100 000 ha.
(v) The culture of fish in these tanks will not develop by itself and Government will have to provide fingerlings (at least in the early years) and extension services. In order to get some idea of the scale of effort and amount of resources that might be needed, the Mission examined the requirements for a hypothetical ten-year development project to be started in 1981/82, with the stocking of tanks totalling 1 000 ha, and extending in area in subsequent years. According to this project 10 000 ha would be stocked in 1986 for harvesting in 1987. The details are set forth in Annex 15.
The previous discussion in this section showed that at Cey.Rs. 4/kg at tank side, the culture of fish in seasonal tanks is likely to make economic (as well as social) sense in the long run. The analysis included the cost of Cey.Rs. 0.60 per fingerling, which would cover the Government's costs for producing and delivering the fingerlings. However, as indicated above, the Government will have to incur expenditures also other than those covered by the charge for fingerlings in order for the practice to develop rapidly. These costs are discussed below.
The costs of putting seasonal tanks into good repair are assumed by the irrigation rehabilitation programmes already underway in several dry zone districts, and should not be considered a cost to be charged to the project. The cost of training village workers for the above project at Udawalawe are estimated at Cey.Rs. 0.1 million/year for the first five years. Additional extension services not otherwise required will cost Cey.Rs. 1.2 million/year by about 1986. The Government contribution to a proposed UNDP project is mostly to be used for the production of fingerlings and is therefore part of the Cey.Rs. 0.60 per fingerling direct cost. (This project is described in Annex 16 and discussed in more detail later.)
The total cost of these “additional” Government inputs over the first five years amounts to about Cey.Rs. 7 million. Over the same period, and including the 1987 harvest, it is assumed that at least 14 000 t of fish will have been produced (at 500 kg/ha/year), worth Cey.Rs. 56 million (at Cey.Rs. 4 per kg). This amounts to a cost to Government of Cey.Rs. 0.50 per kg of fish landed. The Mission considers this as an acceptable cost to Government considering the socially favourable aspects of the project.
(i) The indigenous stocks of fish in perennial tanks consist mainly of predatory species that cannot support productive fisheries, and other species of little interest as a source of cheap food. Nevertheless, because the catchment areas are partly cultivated, and cattle are grazed on the areas that are exposed during the dry season, the perennial tanks are remarkably productive, biologically speaking. Efforts have been made over many years to introduce marketable species. Of the several species tried, Tilapia mossambica, introduced in 1951, is well established and supports a valuable fishery. Gourami and common carp are reported to have bred in some tanks, but do not yet contribute significantly to the catches.
(ii) The annual harvest of tilapia averages about 112 kg/ha but, as Annex 7 shows, production varies widely from tank to tank, and in 1975 as much as 1 323 t were taken in Parakrama Samudra, which has an area of 2 520 ha at full supply level. Catches can be improved in some tanks by fishing more intensively, by extending the areas actively fished, and by using fishing gear of more appropriate design in tanks where carps are established. As mentioned earlier, the Government is encouraging such developments by subsidizing the purchase of nets and boats. Other possible measures include removing obstructions on the beds of the reservoirs, such as dead tree stumps. These developments make it all the more necessary to monitor the abundance and reproductive capacity of the stocks and to regulate the fishing effort to ensure that the fisheries remain productive in future years; it is, therefore, essential to collect accurate and comprehensive statistics on catches, species, size of fish, numbers of fishermen and boats and details of fishing gear.
(iii) The standing crops of fish in major tanks vary widely, one estimate is from 500 to 1 500 kg/ha; the variation in catches suggests the same. One reason may be that a typical tank comprises various kinds of habitat and not all of the available ecological niches are occupied. Considering the limnological characteristics of the tanks, and their existing populations, the Mission considers that it should be possible to establish various species of carp without detriment to the existing fisheries. An appropriate selection would include Chinese silver carp (Hypophthalmichthys molitrix) and bighead carp (both phytoplankton feeders); Catla catla (a zooplankton feeder), Labeo rohita (a column-detritus feeder); Cyprinus carpio (an omnivore/bottom feeder); and a small proportion of grass carp to keep macro-vegetation in check. The fact that the common carp has become established only in a very few tanks, despite various attempts, is probably due, in the Mission's opinion, to the small scale and haphazard nature of the efforts made, but it should be noted that the tanks in which it is established are at 300 m altitute and above. A ten-year project for restocking on the scale suggested in Annex 17 (that is to say, 100 fingerlings every year for every hectare of tank) should lead to the establishment of one or more species.
The extensive areas subject to flooding when the tanks fill up during the monsoons seem to be suitable spawning grounds for the above-mentioned species of carps. If and when intensive spawning takes place, it will be possible to collect eggs and hatch them in hapas (fine-mesh enclosures) for stocking other bodies of water.
(iv) Annex 17 outlines a possible pilot project that calls for the production of 10 million fingerlings over a period of ten years for restocking a few selected perennial tanks totalling 10 000 ha in area. At the standard cost of production of Cey.Rs. 0.60 for one fingerling (see Annex 18), the production of fingerlings alone would cost Cey.Rs. 6 million.
Commercial production from an established stock of carp might not be possible before 1990 and Government expenditures on establishing carps should therefore be held much below the Government's support (per kg of fish produced) for the introduction of culture of fish in seasonal tanks. That support was estimated by the Mission at Cey.Rs. 0.50 per kg (see 5.1.3).
The minimum average annual carp catch necessary to justify the stocking programme was estimated by the Mission at 120 kg per ha from 1990 onwards. This carp catch should be in addition to the tilapia the fishermen should have caught anyway. The Mission does not consider this additional catch of carp attainable and therefore recommends against the stocking programme. Most likely such Government development funds would be better used to increase and improve the fishing effort on major tanks. It doubtlessly would pay handsomnly to look into this area of development. The Mission's appraisal is discussed in more detail in Annex 17.
The previous sections have reviewed likely economic results of culture of carps and tilapia in ponds, cages and seasonal tanks and an attempt to establish carps in major tanks. For the immediate future, culture of tilapia and carps in seasonal tanks stands out as the most acceptable of the reviewed culture proposals, economically and socially. Pond culture in low-yielding rice fields might be commercially rewarding. Such culture would be more socially acceptable in marginal agricultural lands, where it would not lead to the reduction of employment opportunities that would result from fish culture instead of rice culture in paddy fields.
The absence of trade, and therefore an established market price, for carps prevents an attempt to appraise the economic merits of carp culture in ponds and cages. The analysis of fish culture in seasonal tanks rests upon the assumption that all fish will be sold ex-tank at a price equal to that now prevailing for tilapia. This may be unnecessarily pessimistic.
The cultures listed above as “economically defensible” will be considered for incorporation in the strategic plan for aquaculture development discussed in chapter 6. Most of the culture systems which the Mission has judged to be of no economic interest now or during the next few years, will not be further considered.
(i) Milkfish (Chanos chanos)
Records of milkfish fry surveys suggest that supplies could be sufficient to support a commercial farming operation. Concentrations of milkfish fry have been identified in several areas on the north-west coast.
Traditional methods of culture of milkfish in ponds are unlikely to succeed in Sri Lanka for a number of reasons. The low tidal range would necessitate pumping to replenish the ponds, involving additional costs. Construction in sandy soils of ponds that will withstand storm conditions is not a well-developed art; in sandy ponds the cultivation of “lab lab” - the blue green algae that form one of the main feeds for the milkfish in conventional culture systems - is difficult; heavy rainfall destroys “lab lab”. Special systems of cultivation of milkfish would therefore have to be developed. Since they grow in fresh water, they could be used to stock seasonal tanks. They might also be grown in salterns and in polyculture with marine shrimp (which are more valuable) in ponds.
The Research Division of the Ministry of Fisheries has recently resumed investigations of the possibilities of using the National Salt Corporation's facilities for the culture of milkfish. There should be few problems in developing this type of aquaculture or in extending the scope of operations to include species other than milkfish (as, for example, penaeid shrimp and mullet), to utilize not only the ponds where the initial stage of concentration of the brine takes place but also those used for later stages, and to operate in the rainy season when salt production is suspended.
Given the fact that the “ponds” already exist, culture of milkfish in salterns will be a paying proposition, provided avian predation and pilferage can be kept under control. As the saltworks have a full time staff, it should be possible to prevent pilferage, at no additional cost.
(ii) Mullet (Mugil cephalus)
The price of mullet, like that of milkfish, is fairly high. The fry occur in abundance, but it is difficult to cull the less desirable species until the fingerling stage. Mullet will grow in fresh water. Since suitable sites for ponds are rare and pond construction is expensive, monoculture of mullet in brackishwater ponds is unlikely to be economical. In some locations, and on some occasions, it may be justifiable to culture mullet in polyculture with penaeid shrimp.
(iii) Pearl spot (Etroplus suratensis)
This species breeds throughout the year in lagoons and is easily acclimatized to fresh water. It is mainly a herbivore. Growth rates are slow and in India it is usually cultured in small numbers in association with other species; it is especially suited to fresh water of high alkalinity. The Ministry of Fisheries is collecting fry for rearing to fingerling size and stocking of tanks. There is a report that it is reproducing in some perennial reservoirs. Price is low. It would appear to be less interesting for cage culture experiments than rabbit fish.
(iv) Rabbit fish (Siganus sp.)
The attractions of rabbit fish are abundant supplies of wild fry, that the fish are primarily herbivores, and that some species tolerate a range of salinities and others enter fresh water at times. The system of culture in Malaysia involves feeding a moist pellet containing a high proportion of filamentous green algae, which is abundant in the lagoons and bays of Sri Lanka. Rabbit fish grown in net cages reach marketable size in nine months. Prices are reasonably high. Rabbit fish may therefore be a better candidate for the current cage culture trials (Annex 5) than fresh water species. Inability to quantify feed costs, in the absence of actual trials, make it unrealistic to attempt to appraise the economic viability of cage or pen culture of rabbit fish.
(v) Tilapia
Tilapia mossambica occur in both brackish and fresh waters. T. nilotica is available in fish culture stations. Both can be cultured in brackish waters but there would seem to be little point in doing so, since the resource of T. mossambica available in the perennial tanks is not fully exploited, although price of tilapia is low. Annex 13 contains an appraisal of the culture of T. nilotica in cages. The breakeven price, Cey.Rs. 12 per kg, makes it unrealistic for the local market, where the price is closer to half of this figure at the most.
(vi) Carnivorous marine fish
Species such as the estuarine grouper (Epinephelus tauvina) and the giant sea perch (Lates calcarifer) can be cultured. They find a ready market in the tourist hotels and restaurants, and command a good price. Similar species are grown commercially in floating cages in Hong Kong and in earthen ponds in Thailand and Malaysia. These two last-named countries are also developing floating cage and fixed pen culture systems.
All commercial systems in use in Asia rely upon capture of wild fry, but one similar species in the Mediterranean is already in commercial production using a hatchery; progress has also been made along these lines in Singapore (Chua, 1977). In Sri Lanka, large numbers of undersized fish are caught in the lagoon fisheries; some of these are of species that may include suitable ones for culture. They do not suffer significant damage when taken in brush pile traps.
An appraisal of cage culture of snappers and groupers is given in Annex 13. The economic viability, like for most cage culture ventures, largely depends on the cost of feed. The feed, a mixture of rice bran, poonac and fish meal, is valued at Cey.Rs. 2.50 per kg. The conversion ratio is high, almost 6. If the conversion ratio can be improved (that is, lowered) or the cost of the feed reduced, the culture might become commercially interesting. The price of the fish is such that it would be unlikely to be used, if grown in small-scale units, by fishermen for home consumption.
There is an abundance of sites around the Sri Lankan coastline at first sight suitable for the cultivation of fish in netting enclosures, either fixed pens or floating cages. These culture systems would be more easily introduced in Sri Lanka than would brackish water pond culture. Apart from availability of feed, particularly for carnivorous fish, potential problems are: disease, predators and the fluctuations in salinity (4.1 above) in the lagoons and their inlets where sites suitable for fixed pens or floating cages are most likely to be found.
The choice between fixed enclosures (pens) and floating enclosures (cages) depends partly upon the topography and hydrography of the particular site - especially as regards flushing of organic waste - and partly upon more general considerations: fixed enclosures may be cheaper in initial costs in relation to the area, or volume, of water enclosed and on some sites will be more accessible; they may provide natural food but afford less control of the farmed stock and be more difficult to harvest. Cage culture, however, implies feeding and feed costs then largely determine total costs.
(vii) Eels
There is no domestic market for eels; one company is engaged in an attempt to culture small eels for export alive to Japan where there is a ready market. Unfortunately the most highly-prized species, Anguilla japonicus, apparently does not occur in large numbers in Sri Lankan waters, although two other species do.
The systems developed for the culture of eels in other parts of the world are sophisticated and require large quantities of water; disease is a major factor in the economics of commercial operations.
(i) Penaeid shrimp
Shrimp fetches high prices both nationally and internationally. There are trawl fisheries on both coasts but most of current production comes from the lagoons. Much of the present catch is of very small size and restrictions on mesh size should be introduced by Government to prevent their capture and to improve yields from these fisheries. There is meanwhile much interest in the possibilities of shrimp culture; in addition to the ventures described earlier above (3.1.2) several applications have been made to Government under the pond subsidy scheme, in relation to proposed shrimp farming operations. Because of the lack of direct practical experience obtained through operating commercially-viable systems, the Government lacks a basis for judging the merits of these applications.
The culture of shrimp on an artisanal scale using rather simple techniques is widely practised in South East Asia; more sophisticated systems are in operation in Japan and Taiwan. Hatchery techniques are well developed. Direct adoption of the simpler techniques in Sri Lanka is hindered by the small tidal range, which makes pond filling and refreshment impracticable except by pump. A good deal is known about the geographical distribution and abundance of the various species of shrimp and the seasonal availability of post-larvae. Surveys are continuing. The catches of the existing capture fisheries are collected and transported to processing plants in Jaffna and Colombo and it should be simple to extend this system to cover small-scale intensive farming enterprises as well.
In order to appraise the economic viability of culture of penaeid shrimps the Mission considered three types of culture: monoculture of Penaeus monodon, mixed shrimp culture and polyculture with milkfish. These systems will now be described. Tentative costs, and earnings, used for appraisal appear in Annex 19.
(a) Monoculture of Penaeus monodon
There would be two production cycles a year. Wild post-larvae would be collected in November–December and June–August and after 30 days in nursery ponds would be released into the rearing ponds at a rate of 32 000/ha. The yield might be 800 kg/ha of shrimp, average weight 33 g, at a food conversion ratio of 4.5:1. The feed would be chopped fish. The requirements for water pumping would probably be on average 10 percent of pond volume per day.
(b) Mixed shrimp culture
In this system the culture unit would consist of one nursery pond and two rearing ponds. Fry of any and all marketable shrimp species available locally would be collected monthly and after 30 days in the nursery, transferred to one of the rearing ponds, which would be harvested alternately, the growing-out period of any one batch being 60 days. Water replenishment would take place every second week by half-emptying and refilling on two successive days, after which urea and triple superphosphate would be added to support growth of natural feed. There would be no supplementary feeding. At rates of application of 12 kg/ha of urea and 1.8 kg of superphosphate, the kind of yield that could be expected is 120 kg/ha per month of mixed shrimp, about half smaller than 100/kg and half in the range 60 to 100/kg.
(c) Polyculture with milkfish
In this system, water management of the ponds would be as in (b) above. Since the peak of abundance of milkfish fry in Sri Lankan waters occurs before that of P. monodon, the former would have to be collected and held in nursery ponds pending the collection of the shrimp fry. With stocking rates of 40 000/ha of shrimp and 750/ha of milkfish, the yields after six months in the rearing ponds could be expected to be about 500 kg of shrimp with an average weight of 22 g and 200 kg of milkfish averaging 0.5 kg each.
The appraisal of economic viability attempted in Annex 19 shows that monoculture of P. monodon, would be the economically most rewarding activity. Mixed culture of shrimps and polyculture with milkfish are doubtful activities, at least in farms smaller than one ha. All three cultures would be socially relevant in the forms proposed.
The system most appropriate to the conditions in any particular locality may be one of the three described above or some variation (for example, involving mullet); the choice will be best made as a result of practical trials of the various possible systems at typical sites in various districts, to ascertain which system best suits local conditions and makes best use of local opportunities including availability of fry. The choice also depends very much on the amount of knowledge, skill and experience possessed by the operator: the three systems described above carry different kinds and degrees of risk. For example, in system (a), the loss of one crop of shrimp may mean the loss of six months' income. In method (b), the loss of one crop involves the loss of only one month's income. The frequency of receiving income in system (b) makes it especially attractive to smallholders with little capital and no access to credit; this offsets the reduced productivity from a given area of pond as compared with system (a).
The extent to which it would be possible to develop pond culture of shrimp is uncertain, not only because of the issues related to appropriate species mix and management schemes, but also because very few sites with suitable heavy clay type soils have been identified. If ponds can be constructed above the low water mark, water can be drained by gravity, while the low tidal range means that pumps must be used to replenish the ponds. This is the normal management procedure when shrimps are cultured in ponds in locations with low tide difference.
Light sandy soils are likely to give rise to problems, the solution of which will involve additional capital expenditure as compared with sites where there is clay, and which in some cases may require development of special designs of ponds and methods of construction. The problems include leaking, either through erosion or the burrowing of crabs, which leads to further erosion. Another problem is damage to the embankments or dikes by wind, storm waves or waves generated by the wind on the pond surface itself, or by heavy rain. Yet another problem that may arise in some areas is excessive acidity: the extent and severity is unknown, but its remedy may require flushing over a period of months or years.
(ii) Mangrove crab
Techniques of culture are not well established and, since prices on the local market are low, it is unlikely that effort to develop its culture will result in the development of an economically viable activity.
(i) Oysters
So long as the substantial resources of naturally-occurring oysters in Sri Lanka go virtually unexploited, even for the tourist industry, there is no economic or social reason for expecting that culture would become a self sustaining activity within the next few years.
(ii) Pearl oyster
The former fisheries in the Gulf of Mannar and near Trincomalee were destroyed by bad weather in the late 1950s. Large oysters do not at present occur in sufficient numbers to support a fishery, but it has been suggested that small oysters might be collected from the surviving natural beds and re-laid in the shallow waters of the Kaller-Silvaturai estuary, where conditions seem conducive to rapid growth. Also, the production techniques used in Japan for Pinctada martensi might be adaptable to the local Pinctada vulgaris.
The Mission does not have the data required to appraise the economic aspects of pearl oyster culture. They would best be obtained through trials.
(iii) Cockles
Cockles of one or the other of three species that occur in Sri Lanka are abundant in many of the lagoons. They seem to be consumed in fair quantities by the poorer sections of the local population and also in the dried form in Colombo. Possibly demand could be stimulated in other areas and in other sections of the population.
Simple and cheap culture systems are in use elsewhere, that are well suited to the capabilities of poor, rural people. They involve transplanting of young cockles and are of interest primarily when over-exploitation has taken place. Presently this appears not to be the case.
(iv) Mussels
No species of mussel is abundant and there is no domestic utilization. In this situation it is unlikely that commercially viable mussel culture units can be established in the near future. Economic and social appraisal would have to wait for pilot trials. However, mussel culture has several economically advantageous aspects. Raft culture is cheap, both with regard to capital investment and with regard to operating costs. As no feeding is involved, and virtually no forms of imported energy, the cost of production is linked to the use of manpower, which is comparatively low.
Of the species of seaweed from which agar can be extracted, two occur in Sri Lankan waters in significant quantities and with significant content of extractable agar. These resources form the basis of a spasmodic export trade in dried seaweed to Japan, worth perhaps about US$ 80 000 in 1979. The price received is low because nearly all of the weed is collected from the beaches, after being broken loose from the beds by the monsoons, and it is usually dirty. The principal exporters state that if they could assure their Japanese customers of regular supplies of clean dried weed, the trade would be much more valuable. They also assert that if regular supplies amounting to 200 metric tons wet weight equivalent could be assured, this would justify establishment of a processing plant in Sri Lanka, which could lead to substantial import savings.
It seems unlikely that the wild resources could provide a continuing crop on this scale, but in Japan, seaweeds of the same genus (Gracilaria spp.) as the two principal species in Sri Lanka, formed about one-quarter of the total production of cultured marine plants in 1977; cultured seaweeds provided two-thirds of all supplies and more than that in value. Culture techniques that may be adaptable to Sri Lankan conditions therefore exist, and already (Sivapalan, 1975) experiments in Puttalam lagoon have indicated that annual production figures of 2.8 kg (wet weight) are achievable per square metre. If this is repeatable on a large enough scale, it would be necessary to cultivate between 80 and 90 ha of sea bed to produce the 200 t/month said to be required to justify a processing plant. The Executive Director of the firm concerned, Mark International, expressed a willingness to undertake trials of seaweed culture if evidence could be produced that the chances of success were sufficiently high in his estimation.
Given the relatively high export price for seaweeds, it would seem that seaweed culture could pay. Culture of seaweeds have the same economic attractions as have culture of mussels; no feed costs, operating costs being mostly labour, and comparatively low investment in rafts.
“Valli” culture is practised mainly in Italy. The mouth (or mouths) of a suitable lagoon is closed off by screened weirs incorporating fish traps, so that tidal flow in and out of the lagoon can be controlled by operating the weirs or sluices; the flow can all be made to pass through the fish traps. The operator, therefore, has control of the water and of the entry of aquatic animals of a size that cannot readily pass the screens or traps; the fish that grow in the lagoon are trapped when they try to make for the open sea. The rise and fall of tide in the Mediterranean is similar to that around Sri Lanka.
The lagoons in the Jaffna area offer the opportunity for experiments in “valli” culture as practised in Italy, especially Thondai Mannar, where sluices were installed some years ago in an attempt to turn the lagoon into a fresh water lake. This attempt has been unsuccessful, apparently because fresh water inflow is insufficient; salinity varies widely. Meanwhile, the rather haphazard operation of the sluices appears to have destroyed the fisheries, especially the shrimp fisheries, formerly occurring in and near the lagoon. Modification of the weirs and a rational programme of control of water flow to and from the sea might result in the production of a significant quantity of fish. It would seem reasonable to hope for an improvement, over the present production, of 10 kg/ha per year, or a total of nearly 800 t/year more from Thondai Mannar as a whole.
In order to appraise the economic merits of such a programme the Mission has used an argument similar to that applied to the possibility of a Government programme aiming to establish carps in major tanks (reservoirs). The Mission assumes that the Government will be willing to subsidize the development of valli-culture with an amount of Cey.Rs. 0.50 per kg of (additional) fish produced by the scheme. The subsidy would correspond to payment for such things as modification to the weirs, maintenance of weirs or water control structures and management of the fishery (over and above what would have been the case without the proposal). The maximum Government expenditure to manage Thondai Mannar would thus be Cey.Rs. 0.4 million per year (800 t × Cey.Rs. 500). This amount might be sufficient.
Section 5.2 contains a review of the economic aspects of potential culture of various marine fishes, crustaceans, molluscs and seaweeds, in a variety of culture systems, including ponds, pens, cages. Monoculture of Penaeus monodon could become a good money-earner for small holders or larger companies. Seaweeds might, if suitable sites are available, also earn a good living for those who venture into their culture. Culture of fish or shrimps in salterns should add to the net income of the National Salt Corporation. It is possible, but not certain, that culture of marine fish (snappers, groupers) would be commercially rewarding.
Of these cultures only culture of seaweeds would seem ideally suited for the small-holder; only culture of fish in salterns (mullets, milkfish) would add much to the local supply of fish. The shrimps and seaweeds would both be earners of foreign exchange.
For lack of data on national markets the Mission was not able to carry out appraisals of mollusc culture. Culture of molluscs is economically interesting; investment in culture facilities is low (for cockles virtually non-existent), no cost for feed (and little energy spent by the organisms for activities other than growth) and very little running expenditures other than for manpower. Also the culture of rabbit fish in cages might become economically interesting as they feed on vegetation.
Most of those culture systems which the Mission judged to be of no economic interest now or during the next few years, will not be further considered.
