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.
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.
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