2020-10-10
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Usually culture systems are classified according to three criteria:
(A) Type of culture structure. Culture structure describes what encloses or
supports the aquaculture organisms. Broadly, aquaculture structures include
ponds, tanks, raceways, cages and pens.
(B) water exchange. Water exchange describes the amount of water exchanged or the control over water flow to the system. Broadly, the levels of water exchange are static, open, semi-closed and recirculating (closed).
(C) Intensity of culture.
Intensity of culture reflects the number of aquaculture organisms per unit area or water volume and also the ability of the natural productivity to support the crop. Broadly, the intensity of culture is described as intensive, semi-intensive or extensive.
(D) Fish farming methods.
Monoculture and polyculture number of fish species reared in the same pond.
The type of system used for aquaculture production is a combination of the above criteria. For example, there may be a pond system that is:
• extensive and static: to grow major carp in ponds in China and India;
• semi-intensive and semi-closed: to grow silver perch in ponds in Australia;
• semi-closed and intensive: to grow shrimp in ponds in Asia;
• open and intensive: to grow Atlantic salmon in sea cages in Canada.
Exercise 47. Read and translate the following words and word combinations from Russian into English.
Пруды, резервуары, рыбоходный каналб монокультура, клетки, загоны, водообмен, рециркуляция, сток воды, полуинтенсивный, атлантический лосось, аквакультурное производство, серебристый окунь.
Exercise 48. Make up collocations using words from both columns.
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| water | perch |
| silver | cages |
| sea | exchange |
| atlantic | system |
| aquaculture | flow |
| pond | salmon |
| water | production |
Exercise 51. Test yourself by answering these questions and summarize given information.
What are culture systems classified?
What types of aquaculture do you know?
What is water exchange?
How is the intensity of culture described?
What are extensive and static systems in aquaculture used for?
Text B
Type of culture structure.
1. Earthen ponds consists of:
- Rearing ponds which are larger preferable between 0.5 to 1 feddan in size and 1.25-1.5 m in depth.
- Auxiliary ponds
- Ponds for segregation of food stock.
- Spawning ponds
- Fry nursing ponds
- Fry holding ponds
- Storage ponds for marketable fish
- Overwintering ponds
They usually much smaller ponds and may serve different functions in different
seasons as, the same, pond may be used for carp spawning in spring, fry nursing in summer, storage of marketable fish in autumn and fry over-wintering in winter. Generally, the rearing ponds may constitute about 85% while auxiliary ponds constitute about 15% of the total pond area of the farm.
The primary culture system used in the world today is the earthen pond. A typical pond is about 3 feet (1m) deep at the upper end and 6 feet (2 m) deep at the drain. The bottom and sides are made from compacted earth sides slope at a ration of 2:1 or 3:1. Steeper slopes make entry and exit from the pond difficult and promote erosion of the banks, while shallower slopes promote the establishment of aquatic weeds. Pond size varies greatly-some are only a few square yards (square meters) in area, but most are an acre (0,4 ha) or larger. Management and harvesting become difficult if a pond is too large, so most culture ponds do not exceed about 20 acres (8 ha). A well designed pond should have a drain that allows the water to be completely removed within a day or two and should be provided with an inflow pipe of sufficient size that the pond can be filled within a reasonable period of time. Ponds can be stocked at various densities. If water is exchanged continuously or frequently, higher densities of culture animals can be maintained than when static conditions are employed. Cat-fish farmers in Mississippi are annually producing over 4,000 pounds per acre (kg/ha)
n ponds.
Raceways
Raceways are linear channels or circular tanks through which water continuously flows at a rate that will provide a minimum of several exchanges each day. Raceways are commonly used in hatcheries for the rearing of young animals and are employed by the trout industry for production from fry to harvest size. In ponds, fish are exposed continuously to the same water during the growing period, while in raceways, the water may be exchanged completely every several minutes to every few hours. Culture cages and net pens are structures placed in a natural environment and stocked with fish for growout. The only real difference between the two is size. Cages tend to be relatively small (a typical cage has a volume of 1 or 2 m), while net-pens are often several meters on a side and 10 to 20 meters deep. Cage culture has been practiced to a limited extent by catfish farmers. For example, in Arkansas (where leasing of state lakes for cage culture operations is possible), catfish have been commercially produced in cages. Cages have also been used by researchers. Most cage culture is conducted in freshwater environment, while net-pens are most commonly used in the marine environment. Net pen culture has been restricted to protected waters, but recently, net pen engineering has advanced to the stage that open sea pens are now available that can withstand storms without damage.
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1. The pioneer for intensive production.
2. Usually comprise a parallel sets of a narrow channels constructed in sequential blocks with two to three raceways sets in series.
3. Typically is about 30×3×1 m and they may be smaller or larger.
4. Fast water flow rates.
5. Mainly from cement and may be constructed above or in the ground.
