Fish culture practices as paddy-cum-fish culture, small scale subsistance fish culture, fish culture in small scale experimental farms and fish seed production centres are going on in Madagascar since long. To give a new impulse to the development of commercial fish culture and further ramification of this type of animal protein production (fish culture in reservoirs and dams), improving the fish stock in natural waterbodies, cage and pen culture (enclosure), integration of fish culture with animal husbandry etc… makes necessary to establish a commercial fish farm as a sort of pilot project.
The purpose and targets of the project can be determined as follows:
Production of market fish in commercial scale,
This farm will serve for demonstration purposes as well,
To execute practical experiments for improving the production and find out the local possibilities of fish culture development,
Besides the market fish production fish seed production will be carried out and the excess fingerling will be sold,
The integration of fish culture and animal husbandry can be practiced here,
A fish culturist staff can be trained in this pilot project who can proceed with the further extension and ramification work.
Considering the mentioned targets of the project, the water surface of the ponds should be about 30–35 hectares; 25–30 ha from that is for fish meat production. The remaining 4–5 ha will be used as breeders' and breeder recruitment ponds, nursery and fingerlingrearing ponds and ponds for hypophysis donor production. (For hypophysis production 1.5–2 kg common carp is the best).
About 50–60 ha terrain should be secured for the total farm area.
Because the farm needs and will utilise great amount of fresh manure, it would be highly advisable to join this farm with a 1000–1500 heads of piggery. The fresh pig manure could be utilised on the best and most economical way through the fish ponds.
The piggery has to be integrated to the fish farm and constructed in the vicinity to avoid transportation costs of the manure. According to the litterature data, from 100 kg fresh pig manure about 5–7 kg or even more fish meat production can be expected.
The fish culture here should be polyculture (or combined culture). The number one fish will be the phytoplancton eater, column feeder, filterer silver carp. (HYPOPHTALMICHTHYS MOLITRIX). About 1000–2500 young silver carp will be stocked per ha. The second fish shall be the bighead carp (ARISTICHTHYS NOBILIS) which is a zoo and bigger phytoplancton eater, column feeder, filterer fish. About 500–1000 will be stocked per ha. The third fish will be the common carp which is mainly bottom and zoo-plancton feeder. Stocking rate here without feeding 400–500 per ha or according to the available food 800–1500. Further, Tilapia nilotica as the only Tilapia species could be stocked in restricted number in the production ponds.
The project has to deal with the propagation and nursing of the mentioned fish species.
A general rule has to be kept here, that no other fish allowed to enter into the farm area.
The minimum production in this farm has to be 2 metric ton per ha. But depending on the market size of the produced fish (0.5 or 1 kg in average or less) further the management and utilisation of fresh manure, it is possible to produce up to 4 m ton per ha as well.
The total production of the farm, if the production area is 25 ha, will be between 50 and 100 metric ton per year.
Because the silver carp does not accept artificial feed and the bighead takes it only in restricted quantity, only the feeding of the common carp is to be considered. If cheap feed as rice bran, oil cakes, agriculture wastes are available on a reasonable price, the feeding of the common carp could be practiced. The extent of the feeding will be about 1–1.5 kg feed for producing 1 kg carp meat. The production of the two other fish species (silver carp and bighead) will be secured by regular manuring of the ponds.
Calculating 2 ton per ha per year, 1 ton will be provided by silver carp, 0.6 ton by bighead and 0.4 ton by the common carp. Supposing 4 ton per ha production, 2 ton will be silver carp, 1 ton the bighead and around 1 ton the common carp (with feeding).
In tropical and subtropical countries the silver carp has to grow about 1 kg in its first year. The bighead should grow up to 1.2–1.5 kg and common carp 0.5–0.8 kg. Tilapia nilotica may grow here 0.2–0.3 kg individual weight.
The ponds have to be stocked accordingly, calculating 4000–5000 fingerlings per ha.
If the market accepts smaller fish at reasonable price, for example 0.3–0.5 kg in average, two or one and a half crop can be harvested in one year. The stocking rate has to be adapted to that production.
It is totally senseless to construct fish farm without stable and reliable continuous water supply. This is due especially in the tropics and subtropics, where the lack of water during the dry season may endanger or upset the normal and economic course of fish meat production. The water supply has to be stable round the year. The water could be provided from a dam or reservoir which has a continuous and sufficient water supply during the dryest season as well. Good, stable water source can be a river, which water can be deviated toward the fish farm. One of the best is a well managed canal (irrigation canal) with continuous water supply.
The water entering into the farm area has to be filtered so far that unwanted fish can not enter into the ponds.
The ponds have to be totally drainable. The production ponds will be drained and harvested only once in a year. It will happen practically in that season, when the refilling of the pond short after the harvest is possible. Partial harvest with net without draining the pond can be executed whenever the stocked fish attains the marketable size.
To fill up 1 ha pond with 1–1.2 m deep water 16000–20000 m3 water are needed. It takes 400,000–500,000 m3 for 25 ha and 480,000–600,000 m3 for 30 ha pond surface. Supposing 300 l per sec continuous (24 hours) water supply, about 1.5 ha pond could be filled up in one day. When the water supply lasts only 10 hours long per day, no more than 0.5 ha can be inundated only. This water quantity is needed only during the harvesting and refilling time, 30–60 days long respectively. During the dry season only the nursery ponds have to keep dry. All the other ponds should be kept inundated. Roughly 2 cm per day water loss (evaporation, seepage, percolation) can be calculated supposed that the dikes are well constructed, the soil keeps the water and the outlet structures are closed, not allowing tickling of the water. To maintain the normal water level in the ponds, 200 m3 water is needed per ha per day. For the 30 ha unit it is 6000 m3 per day. To provide that water quantity, a continuous water supply of 70 liters per sec. is needed.
In the refilling time, if 300 l water per sec is not available, 150 l per sec would be acceptable in a longer time span (2–3 months). During the dry season, at least 50–70 l water per sec would be necessary. This latter includes also the water used for the hatchery and nursery. The spent water of the hatchery and nursery ponds should be used for replacing evaporated water of the production ponds.
The maximum water need of a medium size hatchery is about 7–10 l. per sec. To refill one nursery pond 500–1000 m3 water is needed. Calculating half day refilling time (6 hours) 25–50 l. water per sec is necessary.
The general lay-out, size and arrangement of the ponds depend on the terrain. There are some general rules which are advisable to follow.
The hatchery, nursery unit and breeders' ponds should be constructed nearest to the water supplying structure (Outlet gate of the reservoir, or where the feeding canal enters the farm area). Here is the safest water supply. These parts of the farm have to be situated on the highest part of the terrain.
The production ponds and donor ponds are located in the lower and farther part from the main water intake structure.
All ponds should have independant water supply and draining structure. If there is no other feasible solution, exceptions can be allowed in the case of production pond (draining or/and feeding through each other).
The breeders' ponds and nursery ponds should be constructed with independant water supply and draining. If the terrain allowes, the drained water of these ponds should be used for the water supply of production ponds.
No through-flowing water is allowed in warm water fish ponds.
The breeders' ponds are conveniently about 1000–3000 m2 each. Considering the number of cultivated fish species, at least 5 such ponds are necessary. For the common carp 4–6 extra segregation ponds are needed 500 m2 each. It takes 1–2.5 ha in total. The depth of these ponds should be 1.2–1.5 m in average.
Nursery ponds. The convenient size of the nursery pond is 600–1000 m2 of elongated form (60 × 10 or 50 × 20 m). The necessary number of nursery ponds is 10 or 20 if possible. One nursery unit may produce 50000 fingerlings in 3–4 weeks time. One unit will be used 3–4 times in a year. The depth of the nursery ponds is 0.5–0.8 m in average.
Production ponds. The size of production ponds are from 1 ha up to 5 ha. Bigger ponds are not advised in this farm because the difficulties of cropping and handling. Strickt rules concerning the size of production ponds do not exist, but the mentioned size seems to be convenient in the tropics and subtropics. Because strong carp fingerling will be stocked, the overgrowth of obnoxious water weeds has not to be feared. Weed control will be necessary only in the nursery ponds. The average depth of the production ponds should be 1–1.2 m. Considering that the column feeder fishes need rather deep water ; 1.5 m water depth would be very useful here.
Fish farm used to be constructed on a more or less plain area, where are not too great level differences on the terrain. That helps to spare construction costs.
The main necessary structures to be constructed in a fish farm are the follows:
Bigger ponds need higher dikes with wider dam crown and slanter slope. The dikes are different according to their function. The main dikes or contour dikes which are around the farm, or keep the deepest water in the lowest part of the pond, are constructed stronger and higher. Such dike which protects the farm from inundation (is between the farm and the river, or inundated area of the river) has to be planned and constructed with special care, considering the highest possible flood, the strength of the current, duration of the flood, etc…
The contour dikes of a pond or a farm are constructed 0.75–1 m higher above the planned water level kept in the pond. It is necessary even in such case if the pond has not a catchment which may provide ample water during the heavy rains. The width of the damcrown should be minimum 2 m but possibly 3–3.5 m especially if there, vehicular traffic is planned. The slope of these dikes should be minimum 1 : 2 if the soil is clay, and 1 : 2.5–3 if the soil contents sand or gravel.
The separating dikes which are between the ponds can be less strong ; their height is about 0.5 m above the planned water level and their crown width is 1–1.5 m if vehicular traffic is not planned on it.
The settling of the soil should be taken in account if the soil is not packed layer by layer, during the construction. In this case 20–25% settling has to be calculated.
Generally speaking, if the deepest water in the pond is 1.5 m, the
dike which keeps this water has to be 2.25–2.5 m high (main dike) and 2 m
high of the separating dikes. The construction difference between the main
dikes and separating
The slopes of the dikes have to be planted with suitable grass, mostly made with bricks of turfs, to prevent erosion and damages. Material for the dike construction. The dikes are made of earth. The best is the clay for dike construction. Soils which let percolate the water are not suitable for this purpose (gravely, sandy soil).
To have an idea about the earth quantity needed to the dike construction some data is given here.
Dike size in m.
| height | width of dam crown | slope | Type of the dike | soil for construct 1 m long dike | costs of 1 m long dike |
| 3 | 3 | 1:2 | contour | 27 m3 | |
| 3 | 2 | 1:2 | -"- | 24 m3 | |
| 2.5 | 3 | 1:2 | -"- | 20 m3 | |
| 2.5 | 2 | 1:2 | -"- | 17.5 m3 | |
| 2 | 3 | 1:2 | separating | 14 m3 | |
| 2 | 2 | 1:2 | -"- | 12 m3 | |
| 2 | 1 | 1:2 | -"- | 10 m3 | |
| Nursery pond dikes | |||||
| 1.5 | 1 | 1:2.5 | 4 m3 | ||
| 1 | 1 | -"- | 2.5 m3 | ||
It has to be determined by the planning, that from where will be obtained the soil for the dikes. It can be excavated from the nearby hillocks, excavated from the pond bottom. Sometimes the levelling of the pond bottom produces certain amount of superfluous soil which is used for the dikes. When the soil excavated, 10–15 cm topsoil has to be removed first and not build in into the dike. The base of the dike also has to be cleaned and the topsoil removed. To facilitate the joining of the base soil with the dike the base of the dike used to be ploughed deeply.
All ponds have to be totally drainable. The excavation has to be made so far that the drainability is not endangered.
Although it is more expensive, it is highly advisable to construct cement-concrete or plastered brick feeding canals in tropics and subtropics.
Its maintenance is easy, and cheap ;
seepage, percolation of water is quite nil, other possibility of loss of water is far less than in the case of earthen canals
water transporting capacity is high therefore the narrow concrete canals have the same water transporting capacity as wide earthen canals
erosion or sliting up does not occur as in the earthen canals ;
boring animals could not cause damages ;
elevated canals can be constructed on the top of the dikes.
The main feeding canal should be 0.6 m width and 0.6 m height, or 0.5 × 0.6 m or 0.4 × 0.5 m ; the side canals used to be 0.3 × 0.3 m. It is advisable to construct suitable base to the canals to prevent crackings.
For keeping or diverting the water in the canal control boards are used ; for that, pairs of grooves have to be made on the adequate part of the canal.
It is a very important structure built according to the feature of the river or canal. If the water is taken from a river feeding a reservoir, this structure can be a more simple one. This structure needs a strong fundation and protection against flood caused damages etc…
Easy to handle, filter has to be constructed near the beginning of the main feeding canal to prevent the invasion of unwanted fishes. Usually a simple stone chips filter is enough for this purpose.
More accurate filtering structure is needed for cleaning and filtering the hatchery water. The water, for filling up the nursery ponds, also has to be carefully filtered. Such structures require to apply different type and effective filters, adequate construction and maintenance.
Pipes of suitable diameter and strengh are used as inlet structures if the feeding canal is made of cement-concrete. The pipe connects the feeding canal with the pond. The inlet pipe is closable with a simple control board. To prevent backwashing and erosion below the inlet pipe, the soil should be paved with stones or cement slabs.
Monks or sluice gates are used for draining the pond in the fish culture practice. The gate of the sluice, or the front opening of the monk and the diameter of culvert pipe determine the draining capacity of the structure. Ponds of 1–10 ha size need 40–50 cm diameter culvert pipe and the same gate opening. Ponds of 1000 m2 up to 1 ha need only 30 cm of diameter culvert pipe.
Sluice gates are constructed mainly there, where many ponds have one common cropping pit, or the cropping device is placed on the dry side of the dike. The inlet and outlet structure is placed on the same dike by the up-to-date fish ponds.
The ponds of a modern fish farm are arranged in fan form if the terrain allowes, so that many ponds have the same cropping pit. That cropping pit is about 1 m deeper as the deepest parts of the related ponds, and the main controlling draining structure is constructed there. Between the ponds and the common cropping pit, sluice gates are constructed with about 30–40 cm wide gate. Fish pass without difficulty through the open sluice gate, not so as through the long and dark culvert pipe of the monk.
Breeders' ponds and segregation ponds are constructed with conventional cropping pit, or cropping trench excavated before the draining structure.
The draining structure of the nursery ponds has to be constructed with a paved cropping pit on the dry side of the structure. Two or four nursery ponds can have a common paved cropping pit, in which fish catching net box can be fixed to facilitate the harvest of frail small fish.
They are usually earthen canals deepend under the level of the draining structures. It transports off the drained water from the pond. To avoid water loss through the draining canal water level controlling structure is constructed on this canal. To retain the escaped fish, wire box or screen is fixed on this structure.
A complete fish farm is constructed with roads, office, store building for storing equipment, tools, materials, feeds, fertilizers etc… garage, workshop, manager and fishermen quarters, guest rooms etc…
