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Monjit Paul


 Pen Culture:


Pen is someway can be considered as transitional structures between pond and cages as so far as environmental and stock control are concerned. Some times large cages of 200m3 are called pen. For some farmers the word pen means only those cages with no top netting. Generally the bottoms of the pens are fixed into the ground of water bodies. Pens were first used in culture of milk fish Philippines.


Site Selection for Pen Culture: For pen culture, site selection is necessary for sustainable production of fish. The design of pens may depend upon the characteristics of water bodies. The water bodies for pens may be categorized by two ways –


Category – I: Narrow rivers irrigation canals – ox-bow lakes: A part of this type of pen can be divided by a number of connective sections by erecting portion of fencing across the narrow water bodies. Thus one or several pens are arranged in a series.


Category – II: The Shallow Reservoirs Margins or Tanks: In this type pens are four walled. This may be constructed according to the depth of the water bodies.


Shape, size and design of the pens:-


On the basis of the pen culture it may be circular, square, and rectangular in shape for depending upon the harvesting.


The size of pens depends upon the number of physical factors such as location, water depth and biotic parameters. Large cages of 200m3 or above may construct for pen culture. The height of the pens depends upon the water level during entire culture periods. The height also depends upon the jumping behaviour of cultured species. The height of pen may be at least 50cm. But about 30cm of the cages are fixed into the bottom to keep the pen wall secured.


Materials Used for Pens:


Screen – The screen materials used for pen should be

  • Small meshed to prevent the escape of fry and fingerlings
  • Resistant to long exposure in sun and water
  • Steady enough to resist current, wind action and wave action
  • Resists the attack of crabs and other animals
  • Cheap and easily available, easy to handle

The screens are usually made of split bamboo mats in eastern countries. Metal or metal coated with resin, nylon or HDPE, even rubber are used in western countries and Japan.


Supporting Structures – Matured and well seasoned bamboo are generally used as supporting materials, relatively in shallow waters. Other supporting materials like floats and heavy sinkers like stones are used as supporting materials.


Types of Pens:


Bamboo Screen Pens – This is the simplest type of pen made with fixed bamboo poles in the bottom soil of water bodies, surrounded with fine meshed netting materials. Bamboo screen fencing is suitable in narrow and shallow rivers, flooded fields and other very shallow water bodies.


Monofilament Cloth Fencing Pens – This type of pens are surrounded by monofilament netting material with required size. The screen wall is arranged just like a fry net.


Production: The pen culture is experimentally conducted in kalli backwaters. The net production is about 250kg/ha/year of Penaeus monodon. Similar experiment is also done in Chilka Lake with average production in three months – 100kg/ha with 50% survivality. In kakinada calm waters pen culture is conducted in submerged condition @ 100 individuals/m2 with monthly yield of 385kg/ha (survival rate – 88%). Pens are also used in nursery pond production of carp seeds. In Howrah and South 24 Parganas the culture of ornamental fish is done in pen constructed in pond or in irrigational canal. Fry stages to grow out are sometimes cultured in that manner. Some report says that experimental culture of catla, mrigal and rohu with 3:1:4 ratios may yield upto 4t/ha/6 months. How ever main advantages of that type of culture is that the fish can be cultured in natural environment of river streams or irrigation canal without any supplementary food or little supplementary food.


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