SYMPOSIUM ON AQUATIC RESOURCES OF KENYA
Marine and Freshwater
(Organised by Kenya Marine and Fisheries Research Institute, Mombasa)
BASIC APPROACH TO MARICULTURE, PROBLEMS AND DEVELOPMENT STRATEGIES
(KEN/77/014 )
By
S. SIVALINGAM
AQUACULTURIST
Government of Kenya/UNDP/FAO Pilot Project
“Development of Coastal Aquaculture”
P.O. BOX 583, MALINDI
JULY, 1981
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THE MARINE ENVIRONMENT AND STRUCTURES FOR CULTURE
The Environment
Structures for Culture Operations
Species for Culture
PRESENT STATUS OF MARICULTURE DEVELOPMENT IN KENYA
SUMMARY
The paper discusses the environmental conditions in the open marine and inland brackishwater areas and the type of structures that can be constructed in both areas for mariculture purposes. For the open marine environment cages are suitable but for cage culture, both cheap materials for constructing cages and cheap fish feed have to be developed. For the inland brackishwater areas earth ponds are recommended. The tidal range for earth ponds is quite favourable and soil conditions in Gongoni area is suitable. In developing countries in the far east, herbivores and prawns are popular for culturing in brackishwater ponds and these are recommended for culture in Kenyan waters in the inland brackishwater areas.
Majority of the culture activities in the developing countries in the far east, concentrate on extensive practice without supplementary feed. It is recommended that initially extensive practice be adapted and once adequate manpower has been trained and culture practices perfected then move into semi intensive systems with fertilizers and then into fully intensive system, by when cheap fish feed can be developed.
Details of the pilot project at present underway to test the feasibility of brackishwater fish culture including the biological survey for fish and prawn seed is given. The indications are that mariculture would be profitable specially culturing prawns.
The term “Mariculture” in its present usage may be defined as the culture of organisms, both plants and animals, in an aquatic medium or environment which may be completely marine (sea), or sea water mixed to various degrees with fresh water. This definition would include both the sea and inland brackishwater areas. The problems encountered in these areas for aquaculture purposes are quite different, necessitating different approaches to solve them.
For example, in the sea or marine environment, the water is in constant motion due to tides, currents and wind action. This does help in oxygenation and distribution of the various elements, but it also does cause considerable difficulty in constructing enclosures or confined area for culturing organisms. The familiar “ponds” which we normally associate with aquaculture in developing countries is not a practical idea in the sea. Culture then has to be in a different type of enclosure and the type in popular use are cages anchored in protected bays. This may be in the form of a metal frame with netting material forming the walls or the entire cage is made of metal screens with or without a coating of corrosion resisting material. In recent years the metal has been replaced by stiff synthetic material - but this requires a metal frame work. Though the netting is cheaper it has disadvantages. It can be easily damaged with the loss of the cultured organisms.
In cages it is necessary to maintain a larger number of individuals inside the cage to make the venture profitable. This in turn necessitates supplementary feeding, since the quantity of natural/available food in the volume of water ly inside the cage cannot sustain the larger number normally cultured in these cages. Where cages are used for fish culture carnivores are commonly cultured in them. But in developing countries culture of herbivores is more popular due to inadequate supply of high protein fish feed which is required for predatory or carnivorous species. The popular cultivated herbivores do do not do well in cages. Also cages are expensive and require heavy capital investment which involves a high foreign exchange component. For these reasons development of culture practices in the marine environment has been slow or not taken off at all in developing countries.
Therefore to make a start in this field it will be necessary to develop two items
cheap enclosures which can withstand the wave action and occasional storms in the sea and
cheap high protein fish feed which would make cultivation of carnivorous species profitable.
In developed countries in addition to culture in cages in the sea in protected bay area, they also practise producing seed in very large numbers in hatcheries and continuosly seeding the natural fishing grounds thus guaranteeing recruitment. There has been success in this field. The natural waters which are stocked are well known rich fishing grounds. In addition these countries were in a position to take the risk and foot the bill without guaranteed success during the initial stages of research and development. Equally important to the success of this approach is the fact that they were in a position to have treaty agreement with the other nations exploiting the same fishing grounds thus being assured of a fair return for their investment. These practices involve not only heavy outlay both in the form of manpower and capital but also the existence of natural rich fishing grounds and understandably developing countries have been slow in progressing in this field.
Compared tot he sea the brackishwaters present a calmer environment often with heavy vegetation. Two types of brackishwater areas with different ecological conditions can be identified. In one, the source of water is the sea with hardly any influx of freshwater while in other the water comes both from the sea and from inland streams and rivers. The former is characterised by high salinity, the salinity being the same as that of the sea or higher. The water levels are predictable since it depends entirely on tides which can be predicted with a great of accuracy. Management of ponds are also easier under such predictable situations. For example, the exchange of water inside the ponds can be pre-planned. But in the second type while the incoming sea water is predictable, the influx of fresh water from streams and rivers can be unpredictable because the inflow depends on the rains which is variable. The variation in the influx of fresh water causes considerable fluctuations in salinity and water levels. The fish farm structures therefore have to be designed to accommodate these fluctuations. In addition, one has to be prepared for problems like unexpected heavy floods during the construction stage. These difficulties have been tackled at a rural level in many developing countries and as a result mariculture in inland brackishwater area has been profitably practised in the rural area for so long.
On the question of the choice of a structure that is best suited for inland brackishwaters, experience in developing countries has shown that for fish and prawn farming the practical way is to construct ponds and impound high-tide water. This is done without difficulty where the land is more or less flat or has only a slight slope. For an efficient unit of this type it is necessary to have a high tidal range i.e. the difference in water levels between high and low-tides should be at least 1.5 m. Higher the range easier the operation and management of the farming activities. But nevertheless, there are instances in developing countries where private individuals have successfully carried out prawn farming activities in unfavourable areas with lower tidal range using water pumps where necessary and still make the operation profitable.
The other alternatives are cages or intensive, constant water circulation units. But large earth ponds suggested above have many advantages over cages or intensive constant water circulation units. Cages and water circulation units have a higher foreign exchange component in their construction costs, while for the establishment of earth ponds the foreign exchange component is nil or negligible. Further, ponds permit extensive culture practices i.e. it is possible to stock smaller numbers sufficient to exploit the natural food production within the pond. Supplementary feeding which requires heavier financial outlay is then not necessary. On the other hand, culture in cages and constant circulation units require feeding involving heavy financial outlay. It will be noted that on the average the conversion ratio for fish is about 3:1 and for prawns about 12.5:1 that is, one requires 3 tons of fish feed to produce 1 ton of fish and 12.5 tons of feed to produce 1 ton of prawn (Bardach et al 1972). Feeding is profitable where cheap feed is available and any efficiently managed farming system would end up in this phase. But gradual development from an extensive to a semi intensive and finally fully intensive phase permits the development of man power which is a major constraint in developing countries where mariculture practice is new. This approach would in addition permit the orderly establishment of other connected secondary industries like collection and supply of seed for the commercial farms and most important of all, it involves lower financial risks in the early stages of development. Any heavy loss due to inexperienced handling in the developing stages can be very discouraging to other prospective farmers both small and big.
Parallel with the above decisions on the type of enclosure and practice to be adapted it is also necessary to decide on the species to be cultured for, the design of the structures to be constructed would depend on the species to be cultured. In developing countries where mariculture is popular, they specialise in herbivores like mullet (Mugil sp) or milk fish (Chanos chanos) which is more profitable to a rural fish farmer than predatory species or carnivores. These two varieties can be cultured in a wide range of salinity levels. But others like common carp or Tilapia can only be cultivated in very low salinity areas. Herbivores have been the preferred species in rural areas because for the same inputs a larger poundage of herbivores can be produced than carnivores. Carnivores require high protein food and in addition tend to be choosy in their food habits. Cultivation of herbivores can be in monoculture i.e. as a single species in a pond or in polyculture i.e. a suitable combination of two or more species in the pond.
Polyculture exploits a wider spectrum of the natural food available within the pond and thus gives better production results.
Among the cultivated species, prawn forms a special category. It is omnivorous in habit and feeds on any type of detritus on the pond bottom in addition to feeding on smaller live organisms. They also seem to do well on the algae growing on the pond bottom. The very high price of the end/the fact product that it can be cultured on an extensive scale depending on and the natural food available within the pond, encouraged fish farmers in developing countries to take upto prawn farming. In the traditional areas in the far east prawn culture practices vary from constant trapping and harvesting to complete culture from post larvae to marketable sizes. This is often in polyculture in combination with herbivores like mullets or milk fish. In some of the developing countries which have recently taken upto prawn farming with considerable success, the rural farmers start their prawn culture with juveniles instead of post larvae and grow them in monoculture. This practice is popular in South India.
As mentioned earlier, prawns have a special place in mariculture and is popular not only with the rural backyard fish farmer who does it on a subsistence level but also with industrialists who culture it on an industrial scale in developed countries. Upto now Japan is unique in this respect. They have developed intensive constant circulation systems where the adult female lays the eggs and they are hatched and grown to marketable sizes under controlled conditions. This development has been restricted to Japan mainly because of the high cost of production which is matched by the existence of equally expensive clientelle who are prepared to pay the high price for live prawns. It will be necessary to first create such a demand before this type of culture practice can be profitably tried. Until then for developing countries where prawn culture is yet to start, traditional extensive methods offer better scope for success and expansion.
Edible oyster culture, which has not yet been mentioned upto now, is also common in many developing countries. Culturing of oyster is a different procedure from that of fish and prawns. The very young oysters called spat are allowed to settle on suitable hard collectors which are later thinned out and suspended in growing areas where they grow to marketable sizes. The oyster feed on naturally available plankton and no supplementary feeding is possible.
Culturing of oysters has its share of problems or probably more. In addition to other factors like pollution etc. oysters are known to carry various forms of human infection and as a result handling storage and marketing needs much more care than other fish products. The problems are not insurmountable and needs to be tackled by the appropriate authorities. It is necessary to create a steady market to encourage oyster culture.
Upto now we have been discussing various mariculture systems and practices in various countries and how they can be applied by developing countries like Kenya where mariculture practice is new; in order to exploit their natural resources and increase food production, also creating employment in this process. We may now turn our minds to get a picture of the present status of mariculture development in Kenya and specific project details.
Kenya has a coastline of approximately 450 km (270 miles) with more or less a continous coral reef all along the shoreline. The coast is characterised by the presence of
Inland closed lagoon systems namely Mida, Kilifi, Mtwapa and Mombasa and of these Kilifi and Mombasa receive fresh water from perenial rivers and the other two do not have a permanent fresh water supply. These closed lagoon systems open to the sea by a very narrow entrance.
Open lagoon systems which have many entrances to the sea separated by many islands. These are at Lamu, Gongoni and Shimoni.
River Estuaries. Tana river estuary is the biggest with extensive acreage of swamp land on either side of the river forming the estuary. In the case of the Sabaki river the banks on either side are steep and as a result open directly into the sea without any swamp or lagoons on either side of the river mouth. In the southern part of the country around Shimoni area there are three smaller rivers opening into the lagoon system around Shimoni.
What are the favourable conditions that are required for establishing coastal mariculture farms and which of the above areas offer such conditions? The most important are
The soil conditions in two areas have been investigated in detail - i.e. the Mida Creek and the Gongoni Lagoon area. Of these two, Gongoni area where Ngomeni is situated is better. The water retaining capacity of Mida creek area is lower and appropriate designs have to be developed to construct ponds to be in a position to maintain adequate levels of water. This can be done, but probably at a higher cost. On the other hand in the Gongoni area the soil conditions are very favourable with good water retaining capacity. Also the pH is satisfactory.
As for the tidal range, all along the coast the range is 3 to 4 meters which is very favourable. In both Mida and Gongoni areas the land is almost flat with a very gradual slope, traversed by narrow deep creeks along which the tidal water flows from and to the sea. This situation is very favourable for the construction of mariculture farms.
For culture purposes three species of fish - namely mullets, milkfish and rabbitfish offer good prospects and in addition three species of prawns have so far been identified for culture work. While the general biology and natural habits of all these species are well known, information on the local characteristics is inadequate. For example we all know that mullets in general breed in the open sea and the fry enter the lagoons and estuaries when they are about 20mm long and grow to larger sizes in the lagoons. At a later stage before matuarity they migrate back to the sea, spawn there and the cycle starts all over again. But, there are many species of mullets and if experience in other parts of the world is any guide, these species spawn at different times. As at present we have very little information on the identification of the species of mullets available along the Kenya Coast, and their spawning seasons. Some species of mullets grow better in ponds than others and to be in a position to select the faster growing species we should know their spawning seasons. It is very difficult to identify mullet fry from its external features and it is easier to go by their spawning seasons and therefore this information is essential. In our program we have carried out a survey for the availability of mullet fingerlings and we now know that we can get them twelve months a year - but we have not been able to identify the species. We have forwarded some specimens to specialists in this field and awaiting reply.
For the prawns we have carried out detailed investigations of the species available, their relative abundance and seasonal variation with particular reference to the Gongoni lagoon. As to whether these results would apply to other lagoons along the Kenya coast - we are not in a position to confirm without carrying out some investigations in the other areas. There are three commercially important species of penaeids - P. indicus, P. monodon and M. monoceros. All three can be cultured and fortunately are available year round. But of these three, P. indicus forms about 80% of the penaeids followed by M. monoceros and P. monodon forming the smallest percentage, around 8% or less. P. monodon is the popular “jumbo” prawn, the largest of the three species. The smaller percentage P. monodon may be due to the fact that this species prefer lower salinity for its post larval development while in the Gongoni lagoon area the salinity is close to 35ppt most of the time coming down to about 30ppt for a few weeks along the western shores of the lagoon during heavy rains.
Penaeids usually breed in the open sea and the hatched larvae are planktonic. They drift with the tide into the lagoon and once they enter the lagoon settle down and lead a demersal life.
Before maturity, like the mullets they migrate back to the sea to mature and breed in the open waters.
In most of the traditional prawn farming areas the rural farmers collect the post larvae in the stage before settling to lead a demersal life, and rear them in nursery ponds to a juvenile stage and then grow them to marketable sizes in larger production ponds. In some other countries the farmers stock their ponds with juveniles thus avoiding the nursery pond stage. This is necessitated specially in South India, by the extended heavy rainy season which shortens the growing period available for the prawn farmers.
The results from the project's biological survey program have been very encouraging. But even before the biological surveys it was known that the conditions for mariculture in brackishwaters were favourable and the Government realised that a start should be made. With the Government initiative and financial assistance form United Nations Development Programme and Technical Assistance from the FAO, the present pilot mariculture project was established and is underway at Ngomeni. Although the farm is designed on a large commercial scale there will be smaller units for small scale farmers. Production from different sized ponds is often not directly proportional to the area. So that production from these small units would provide the necessary information to prospective small holders. As recommended earlier in this pilot project it is proposed to start with an extensive systems and then move into a semi-intensive and finally an intensive systems with supplementary feeds etc. The primary species for culture will be prawns which will be tried in association with mullets and possibly rabbit fish. The question naturally arises as to whether there is adequate seed both prawns and fish available in natural waters for extensive development of mariculture along the coast. From the work we have carried out so far we are assured of adequate supplies of both prawn and mullet seed from the Gongoni lagoon for the mariculture farms that can come up around this lagoon. The question of the need for hatcheries has been mentioned quite often. The technology for breeding prawns in hatcheries has been perfected for quite some time and a hatchery can be fitted in any time required. But breeding of mullets on a commercial scale in hatcheries is still not popular and I am sure that by the time the need arises breeding of mullets in hatcheries on a commercial scale would become popular and can be applied here However it should be realised that it is expensive to operate hatcheries and that the smallest unit can supply an extensive acreage. It is therefore necessary to first encourage expansion of mariculture activities with naturally available seed which are cheaper to collect, and gradually create a demand for seed which would then necessitate the establishment of hatcheries.
Finally it may be said that all indications are that the conditions along the Coast are favourable for profitable mariculture purposes and the present pilot project would give the necessary results. But what is needed more than results is man power. Mariculture is so new to East African Coast that every effort should be made to improve the situation. This subject has been mentioned by many of the previous speakers and as such no further emphasis is necessary on my part. However, in this connection it may be mentioned that the present pilot project would go a long way in meeting the man power requirements to make a start and if at the end of the present project activities the facilities are turned into a training centre, it would solve the problem to a great extent and it is hoped that this would be done.
Bardach, John E., John H. Ryther and William O. Mc Larney: 1972.
Aquaculture the Farming and Husbandry of
Freshwater and Marine Organisms.
John Wiley & Sons Inc. London: 868p