Monday, November 10, 2008

Cage Culture

Cage is constructed by various materials of various sizes and shape with closed bottom or the bottoms of the cages are not fixed in the ground of cultured water bodies. Cage can be fitted in any water bodies with any depth. Cage is installed by means of floats and sinkers. The main advantages of the cage are that it can be shifted from one place to another place in any time and it can be installed in deep sees also or any deeper waters. Depth of the water body is not a factor of cage culture. It can be installed in lentic or lotic water.

Certain invertebrates and vertebrates are reared in cages, but mainly warm water fishes are culture in the system. Fishes in the cages are confined in natural environment with known quantity. After stoking, generally no attentions on feeding and diseases treatment are paid. Sometimes in case of some super intensive marine farms, attentions are given to the organisms confined in the cages.

Cage culture is practiced in Cambodia rather traditionally. In Japan, some cage based marine farms are developed in recent years. Now Japan is the leading country for cage based fish production. Now many maritime countries are adopted this culture technique. The cage culture opens a new way of easy exploitation of natural water body or marine water as well as fresh waters.

Shape, Size and density of Cages: Cages are of varying shape and sizes according to the need. It may be circular, rectangular or square etc. Cages for research purpose is not more than 1m3 in volume and may contain several hundred organisms with 500gm at the time of harvest.

Large cages of marine or fresh water farms are of 3.6×3.6×2.4m3 to 7.2×7.2×2.4m3 deep. For growing market sizes the cages are measured from 35 to 100m2 in area with 3.6m of depth.

The cages should be placed in that place where water freely flows through the cages.

Materials Used for Cage Culture - The traditional cages are made up with bamboo screen. Modern cages are made with metals, rubber, fibre glass, plastic coated metal wire with a mesh size of 1.3 – 2.5cm2. Plastic coated wire can be attached to a steel frame to produce cages that can lasts for several years. Cages must have good buoyancy and installed in water by floats and sinkers. The netting materials should be hard enough to with stand the attack of marine predators.

Fish Culture – The following fishes are cultured in cages

Yellow tail (Japan)
Carps (Indonesia)
Trout (USA)
Eels (USA)
Puffer (Japan)
Red Porgy (Japan)

Production: Cages of 1.2m deep×2.4m wide×2.4m long can support 1800 – 2000kg of fish when stoked with 350 – 505fish/m­3. Although the density of fish in per unit volume is high (248-276kh/m3).

Advantages of cage Culture:

The management cost in cage culture is low
High densities of stocking can be possible
Relatively simple and cheap technique
Plenty of natural food is available in natural water so need of supplementary food is less
Fishes can be reared in natural environment, but the cultured organisms can not escape
Cages provide well protection of fry and fingerling stages with plenty of water flow
Harvesting is simple and easy
Free from the attack of predators
The growth of the fish is much higher

Problems in Culture:

The construction of cages and initial investment to make a such type of farms are quite high
The netting materials of the cages have to be periodically changed due to the damage by predator attacks or fouling organisms
Some organisms tend to attach with the cages which are not economical but they obstruct the easy flow of water inside the cages and cause further damage due to the pathogens carried by them
Theft or loss of cages due to the extreme environmental conditions in the sea
Pollute the water bodies used by human beings

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