GLOBAL – Oreochromis niloticus (Nile tilapia) is a hardy and omnivorous fish that is ideally suited for farming at temperatures between 31 and 36C. This guide focuses primarily on how tilapia can be raised in ponds, tanks, floating cages and recirculating aquaculture systems (RAS).
A variety of inputs such as agricultural by-products (brans, oil cakes, vegetation and manures), inorganic fertilisers and feed are used for pond cultivation of tilapia.
Annual fish yields of tilapia in carp polyculture, high levels of agricultural by-products and good stock management can hit or exceed five tons/ha, respectively.
Animal manures provide nutrients that stimulate the growth of protein-rich phytoplankton in monoculture tilapia systems, consumed by filter fed Nile tilapia. The content of nutrients in manure varies. In contrast with duck and chicken manure, water buffalo manure has much lower nutrient levels.
The acquisition of adequate nutrient levels from manures presents a risk of depletion of oxygen from excessive organic matter loading. Therefore, in low-input production systems, a mixture of manure with inorganic fertilisers is used.
In Thailand, the weekly application of chicken manure at 200-250 kg DM (dry matter)/ha and the addition of urea and triple super phosphate (TSP) to chicken manure at 28 kg N/ha/week and 7 kg P/ha/week results in a net harvest of 3,4-4,5 tons/ha per 150 days at a stocking rate of 3 fish/m2 or an extrapolated net annual yield of 8-11 tons/ha.
It is only with inorganic nutrients that equivalent yields are obtained if alkalinity, a source of carbon, is sufficient.
In Honduras, yields of 3.7 tonnes/ha are obtained at a stocking rate of 2 fish/m2 with weekly doses of 750 kg DM/ha of chicken litter and 14.1 kg N/ha of urea.
Sufficient natural phosphorus is present. Fertilisation techniques grow fish in five months to a size of 200-250 g. In order to produce larger fish and obtain a higher market price, formulated feeds are important.
Two methods are practised for lowering production costs for domestic markets in developing countries: delayed feeding and supplementary feeding.
In Thailand, tilapia is stored at three fish/m2 and grown with fertiliser alone to 100-150 g in approximately three months, and then supplemental feeding is provided at 50 percent satiation until the fish reaches 500 g.
The average net harvest is 14 tonnes/ha, which equals a net annual yield of 21 tonnes/ha. In Honduras, with a weekly application of 500 kg DM/ha of chicken litter and a feed application of 1.5% of fish biomass for six days per week, yields of 4.3 tonnes/ha can be achieved. This management regime, however, is less lucrative than the use of chicken litter and urea.
To grow tilapia in ponds, many semi-intensive farms rely almost exclusively on high-quality feed.
Depending on the water temperature, male tilapia are stored at 1-3 fish/m2 and grow to 400-500 g in five to eight months. Normal yields range from 6-8 tonnes/ha/crop, but in northeast Brazil, where climate and water quality are optimal, yields as high as 10 tonnes/ha/crop are reported.
By exchanging 5-15 per cent of the pond volume daily, dissolved oxygen is retained. In other areas, higher yields of large fish (600-900 g) are obtained by the use of high-quality feed (up to 35 per cent protein), multiple growth phases (restocking up to three times at lower densities), high exchange rates of water (up to 150 per cent of daily pond volume) and continuous aeration (up to 20 HP/ha).
In general, fish produced using these costly methods are filleted and sold on export markets.
In wide lakes and reservoirs of many nations, including China, Indonesia, Mexico, Honduras, Colombia, and Brazil, the high-density Nile tilapia culture is conducted in floating cages. In order to preserve free water movement, mesh size has a major effect on development and should be 1.9 cm or larger.
Several significant benefits are provided by cage culture. In cages, the mating cycle of tilapia is interrupted, and mixed-sex colonies can also be reared in cages without recruitment and stunting problems. If they are fertilised, eggs fall through the cage bottom or do not grow. Other benefits include:
Usage of aquatic bodies that can not be drained and otherwise would not be ideal for aquaculture.
Management versatility of several units of output.
Simplicity and low cost of harvesting.
Near observation of responses to fish feeding and wellbeing.
Compared to other cultural strategies, capital investment is comparatively poor.
There are a variety of drawbacks, however, which include:
Chance of loss from poaching or damage by predators or storms to cages.
Less fish tolerance to low quality water.
Dependence on diets that are nutritionally full.
Greater chance of outbreaks of illnesses.
Cages differ greatly in size and materials for building. Cage volumes and stocking densities in Brazil range from 4 m3 cages stocked at 200-300 fish/m3 to cages stocked at 100 m3 or greater at 25-50 fish/m3.
The yield varies from 50 kg/m3 for cages of 100 m3 to 150 kg/m3 for cages of 4 m3. Cages vary in volume from 2.7 to 45 m3 in Colombia and are stocked with 30 g of male sex-reversed fingerlings and raised to 150-300 g in six to eight months.
Extruded feed with 24-34 per cent crude protein is fed to the fish. Streptococcal infections are a problem, and survival is 65 percent on average. Annual yields are 76-116 kg kg/m3 at final densities of 160-350 fish/m3.
Raceways and Tanks
In tanks and raceways of different sizes (10-1000 m3) and forms, tilapia are cultivated (circular, rectangular, square and oval). Successful solid waste removal is an important aspect of the tank design; the most effective design is a circular tank with a central drain.
The exchange of water varies from <0.5 percent of the volume of the tanks per day in tanks to 180 per day in raceways. In order to eliminate harmful nitrogen waste, low-exchange tanks rely on nitrification in the water column, while raceways rely on water flow to flush waste from the tank.
Water between culture tanks and large earthen reservoir ponds that act as biofilters to preserve water quality is recycled by one form of tank culture, known as a combined extensive-intensive (CEI) method, or Dekel system.
The volumetric ratio of the culture tank to the reservoir pond varies between 1:10 and 1:118 or more. To improve efficiency in tanks, aeration is used because dissolved oxygen is normally the limiting factor in water quality.
The overall raceway tilapia density varies between 160-185 kg/m3 and the maximum load ranges between 1.2-1.5 kg/litre/min. A typical raceway output level is 10 kg/m3/month, as the availability of water is often inadequate to achieve maximum rates.
In tanks with minimal water exchange, output levels are considerably lower, but the quality of water usage is much higher in these systems.