This paper details proposals for the construction of family/small-scale fish farms and has been prepared in accordance with the brief of Project LIBFISH to provide advisory and training support for the aquaculture sector.
The designs presented arc for two basic types of units, the 'pond model' and the 'raceway model. Both are modular in concept, so that an initial farm installation can be extended as needed.
Semi-intensive techniques are specified for pond operations because they involve:
low construction costs for soil ponds;
availability of suitable areas of land with waterproof soils, flat terrain, and proximity to the sea (for water supply);
technological requirements that are fairly straightforward and easy to adopt; and
equipment costs, mainly for pumps and aerators, that are comparable to traditional small-scale irrigated farm operations throughout the coastal zone.
2.1 Site Suitability
The development of a family/small-scale pond type of fish farm requires drainable flat land with sandy clay soils and a location near the sea. The seawater supply must be secure from any risk of pollution. Ready access to road communications and an electricity supply are also advisable, since the level of investment would otherwise be prohibitively high.
2.2 Construction Details
Construction and management of farm units would be rendered easier and more convenient if four ponds were to be built at the very outset. Each unit should be 0.5 ha in size (100 × 50 metres), as illustrated in Annexes I, II/1 and II/2. Construction will require bulldozer work for cleaning the site, levelling, and building the dykes (Annex III). The detail of the excavation should be as follows:
0.05 m of upper soil should be removed (salty sand) from an area of about 3 ha.(l,500 m3) where the ponds will be built.
0.15 m of sandy clay should then be removed (4,500 m3).
This soil is used to build the dykes to a level of 1.5 m high and a width of 4.5 mat the lower part and 1.5 m at the upper part.
|Total cross section:||4.50 m|
|Total length of dykes:||900 m|
|Total volume of dykes:||4,050 m3|
A drainage channel should be excavated on the lower side of the ponds; length of channel will depend on the location of the farm (proximity to a lower basin or return wastewater route to the sea); for a channel depth of I m the cross section should be 2 m2, so that for a minimum length of 250 m excavation of 500 m3 is required (Annex IV).
One concrete drainage device (‘monk’) should be built for each pond (see Annexes V, VI, VII, & VIII).
2.3 Seawater Supply
Seawater can be pumped either directly from the sea or, preferably, from a well drilled near the shore. Due to the major importance of water quality in aquaculture, a feasibility study is needed for each site to determine quality parameters and best draw (intake) configuration (see Annex IX).
Whenever possible ground water (salinity: 30 to 38 g/l; pH: 7 to 8; yield: 25 m3/h minimum) should be used in place of water pumped directly from the sea, since the latter is subject to high turbidity during stormy periods and extremes of temperature especially during summer.
Water in semi-intensive ponds is stagnant. It is therefore necessary to compensate losses incurred through evaporation and seepage. Evaporation can reach 2 cm per day in summer and seepage 1 cm per day even in good soil conditions. Thus it is necessary to have pumps able to correct for a reduction of water level of at least 3 cm per day, which represents a minimum requirement of 300 m3 per hectare per day (12.5 m3/hour or 3.5 l/second). Annex X graphically represents the relationship between water flow, head (vertical lift or height from source level to pond inlet), and power of pump.
A farm of 2 ha needs 600 m3 of water per day (25 m3/h or 7 l/S). When properly installed, a 3 kw/4 hp pump is in theory sufficient to meet this requirement (24 hours operation). In fact, two pumps are advisable. More water is needed when empty ponds have to be filled and it is better to operate pumps for alternate 12 hour periods each day in order to avoid motor overheating. Furthermore, a second pump is necessary in case of a breakdown, so that repair work can be carried out without risk to the farm. Considering ail these factors, the power of each pump should be 10 hp.
During summertime water temperatures will be high (28–30°C), and it will therefore be necessary artificially to increase the concentration of dissolved oxygen. Paddle type aerators are recommended due to their efficiency and low cost of operation (Annex XI).
2.4 Pump house
The pump house is a critical part of the farm operation. A small concrete structure should be built close to the shore, at as low a level as practicable so that the pumps can deliver the maximum possible yield (Annex XII). The size of the house should be large enough to shelter two pumps and associated piping, as well as an electric board (4×3 metres and 2 m high). It should allow enough room for easy servicing of equipment inside.
The diameter of the suction pipe should be at least 15 cm, so that flow friction losses are minimum. In case water is to be pumped directly from the sea, suction should be made at a depth of at least 3 m in order to avoid turbid water during storms and warm water in summer. Outlet pipes from the pumps to the ponds should have a minimum diameter of 10 cms. All pipes and fittings should be of PVC in order to avoid corrosion. The pumps can be either ordinary irrigation pumps designed for fresh water or special ones designed for corrosive liquids. The former are available in many places, their price is quite low, and they should last for 2 or 3 years. Special pumps for corrosive liquids may last longer, but they are much more expensive and both the units and their spares are difficult to obtain. Ordinary pumps are probably the best choice.
2.5 Store / Housing
Some sort of a storage facility will be required at the farm site, and it should be of sufficient size to contain two rooms of about 4 × 5 m with 3 m ceiling height. The first room should be used to store equipment and the second feed. Stores need to be built to be safe, dry, dark, cool in summer, and protected from rodents and insects.
The size and the comfort-level of any housing will mainly depend on the people who will be using it (family,watch keepers). In any event the investment should remain realistic and proportional to the planned output of the farm.
2.6 Summary of Equipment Needed
The inventory of basic equipment needed to establish operations on the model scale proposed here is not extensive. Principal items are as follows:
Day-to-day work chiefly consists of controlling water supply, feeding the fishes, and minor maintenance routines. Two persons can perform it quite easily. Casual labourers may be hired for short periods of heavy labour, such as may occur at times of harvest, repair of dykes, and cleaning out excess mud from ponds and drainage channel. It should be kept in mind that the number of staff must always be compatible with the level of investment and expected production.
Aquaculture presents major advantages compared to capture fisheries in that production can to a large extent be scheduled and controlled according to market demand. It is assumed here that harvests will be staggered over the course of the year. As far as possible given the availability of fingerlings, one pond should be harvested every 3 months. Obviously the supply of fingerlings should be planned well in advance with the management of the supplying hatchery.
2.8.1 Fish species selection
Species selected for farming should exhibit several essential features. They should be:
For these reasons sea bass and sea bream are the species of choice for finfish aquacultural operations around the Mediterranean coastline and are in fact the most commonly farmed species within the region. For the 2 ha pond model some 10,000 fingerlings per year would be required. Stocking density is assumed to be two 20–30g fingerlings per m2.
Since managing a hatchery is a very risky activity and one that requires a high level of training and skill, and since profitability is only achieved at levels starting with a production of two million fry a year, it is not advisable to incorporate a hatchery into a small-scale farming operation,
Fingerlings can easily be transported by road on adapted trucks in wintertime and there are hatcheries within a manageable distance from Tripoli.
2.8.2 Cycle of production
Two major constraints must be taken into account when planning the cycle of production: (i) the availability of fingerlings; and (ii) the demand for high quality fish on the market. Other constraints such as water temperature, quality of feed, and experience of the staff will obviously influence the cycle of production.
The breeding season at regional hatcheries lasts from November to March. Larvae and then fry are kept in the nursery up to the next winter. They are about one year old (20 to 50 g each) when they can effectively be supplied to farms -- i.e. again during the November to March period. Therefore it is recommended to place two orders of 20,000 fingerlings -- the first in November and the other in March. Fingerlings must be supplied when a pond is ready to be stocked, with dykes in good condition, bottom clean (excess mud removed) and if necessary disinfected, clean water at the proper level, etc. A whole consignment of fingerlings will initially be stocked into one pond and after a period of two months divided between two ponds, according to the scheme laid out in the table provided as Annex XIII.
2.8.3 Expected production
Annual production for the pond model farm is estimated at around 9 tonnes, based on the stocking figures proposed in Annex XIII and the following assumptions:
|Number fingerlings per pond per year:||5000 m2 × 2 = 10 000|
|Expected mortality (improvements when staff experienced):||25%|
|Expected number of fishes at the end of a cycle:||40,000 - 25% = 30 000|
|Individual weight when harvested:||300 g|
|Expected production (kg):||30,000 × 0.300 = 9,000|
2.8.4 Required feed
Bass and bream need about 2.5 kg of pelleted feed to produce 1 kg of fish (this is an average value which can be lower or higher according to the quality of the feed). Therefore some 22.5 t (9,000 × 2.5 = 22 500 kg) of feed will be needed at the pond model farm every year. Feed must be of suitable composition (Annex XIV), and it must be stocked with care. If feed is kept in store for excessively long periods, serious quality deterioration (vitamins and proteins) will occur. It is thus recommended that 5 to 6 tonnes of feed be ordered every three months
Daily distribution of feed must be done in a very accurate way. It is absolutely necessary to control the growth of the animals and to adjust the distributions accordingly. Temperature must be recorded two times a day in order to calculate the exact requirements of the fishes.
Proper use of feed is fundamental. On the one hand, excess feeding is not only a waste, but may lead to the contamination of the entire farm by fungae and bacteria. On the other hand, the fishes cannot grow if they are not given enough food.
The raceway model represents another kind of small-scale fish farm that can be established in places where sandy clay soil is not available, and also where land is in shorter supply. The model which is described here is planned to produce the same outputs as the pond model, but in a smaller site through the use of more intensive techniques.
3.1 Site suitability
For reasons of proper management it is proposed that four raceways initially be built. This would require a site of only one hectare (including space for facilities).
The site should be flat and located near the sea or near another proper water supply. Soil should be soft, but not necessarily waterproof. It is possible to develop the prototype on sandy sites, provided that there is access to a road and to a power supply,
3.2 Construction Details
Four raceway trenches are required, each 100 m long, 10 m wide, and 1 m deep (Annex II/2). Construction details for the dykes, inlet, and drainage channel are similar to those described in section 2.2 above. The main difference consists in the use of plastic liner in order to allow optional construction on sand rather than the waterproof soil needed for ponds. In either case a liner is recommended for raceways because it also serves to protect dykes from erosion due to constant water currents. The liner consists of a plastic sheet (green house type) which covers all the bottom of the raceway up to the top of the dykes. It should last for one or two cycles of production.
3.3 Seawater supply
Clean water can be pumped directly from the sea or preferably from a marine well. Water quality considerations are the same as those which apply for the pond model (section 2.3). In raceways, water is constantly circulating from the inlet to the drain. The main advantage is that wastes are automatically eliminated. However, water requirements are much higher than for ponds. Therefore, two 30 HP pumps are needed. Due to the high rate of water replacement, aerators are not needed.
3.4 Pump House
Details for the raceway model pump house are the same as those reviewed for the pond model in section 2.4.
3.5 Store /Housing
Store / housing specifications noted in section 2.5 for pond type units apply also to the raceway model.
3.6 Summary of equipment
The basic equipment needed to establish operations on the model raceway unit proposed here can be summarised as follows:
Personnel requirements are as discussed for the pond model (section 2.7). However, due to the more intensive technique of production used, a somewhat greater level of labourer skill is desirable.
Points of management are generally as already reviewed for the pond model. With raceways, though, extra attention should be given to the water supply, since any reduction or interruption may cause fish mortality. Also, with reference to species selection, each raceway should be stocked with 10,000 fingerlings (same number as in a 0.5 ha pond).
A small scale fish farm can be profitable as long as there is control of inputs in order to avoid any useless expenses (Annex XV/1 for ponds, XV/2 for raceways). Whilst the models elaborated here assume sea bass or sea bream as the farmed species, the layouts could theoretically be utilised for other types of species.
Another possibility is to associate these models with irrigated agricultural projects. Fish ponds can be used to stock water for further use. In that case, water is enriched with minerals by the wastes produced by the fishes. It is also possible to use water from irrigated field drains, which is too salty for irrigation re-use but is suitable for aquaculture. Appropriate species for this type of activity are tilapia, carps and mullets.
Coche, A.G. & J.F. Muir. 1992 Pond construction. FAO Training Series No. 20/2. Rome.
Huet, M. 1970 Textbook of fish culture breeding and cultivation of fish. Fishing News (Books) Ltd. London
Milne. P.H. 1972 Fish and shellfish farming in coastal waters. Fishing News (Books) Ltd. London.