Pens and cages provide suitable environment for fish growth, if the security is assured and water pollution free. Pen and cage fish culture is mostly practiced in India. In Nigeria, culturing fish in pens and cages are new practices, but the potential are high.
PENS
Pen is a fixed enclosed in open water body made of either bamboo or wooden poles and nets which allow interaction with immediate environment and prevent entry of undesirable animals and fish that may harm the fish stocked.
In the construction of fish pen the following need to be considered:
Location
Pen are located in marginal or near offshore areas of large body of water or sometimes in large ponds. This method is considered eco-friendly as it does not pollute the environment.
Construction
Bamboo or wooden poles planted into a lakebed or shoreline bottom form the pen frame. Nets strung from pole to pole and weighted using lead or large stones attached to the nets are fixed into the lake bottom to form the enclosure into which dish are placed.
Advantages of Pen Fish Culture
The use of pen in aquaculture has the following advantages:
• Commercial fish grown in pens in fertile lakes generally have very good growth rates.
• This method is also successful in unproductive water when supplementary feeding is provided
• It considered eco-friendly method of fish culture as it does not pollute the environment.
• Little maintenance, except for care of netting, is required
Disadvantages of Pen Culture
• Setup costs can be expensive as nets must be made of nylon or plastic to avoid rot and water logging.
• Pens have short lifespan ranging from 3 – 5 years, thereby requiring periodic replacement.
• Because pens are often set up in shallow water where fish spawn, they sometimes reduce natural production in some lakes.
CAGES
A cage is a floating enclosure in water body for fish culture. Cages are widely used in commercial aquaculture. The culture of fish cages has shown the possibilities of production of different fish species. Cages are of various sizes and shapes. Locally available materials like cheap materials like bamboo is suitable for cage construction. However, PVC pipe may be used for cage construction. Cages can be used in both freshwater and marine environments with adequate security to prevent losses into high tides and poaching.
Types of Cages
1. Floating cage. It is convenient to use in water bodies where depth of the water is more than 5m.
2. Fixed cage: This cage type is convenient for water bodies where depth of water is less than 5m.
Shapes of Cages
1. Rectangular (most convenient)
2. Square
3. Round
Cage construction
The cages can be constructed using available bamboo at cheaper PVC pipe may also be used for cage construction. From practical experience, it is seen that the body of the cages of required size and shapes can be constructed readily using bamboo and nylon ropes. Inside the bamboo frame a well stitched inner hapa or nylon cloth cage with a closable lid is tied. The success of the fish culture in cages depends the mesh size f the bamboo woven main cage and the much size of the inner nylon cage. Cleaning of bamboo cage and the inner nylon cage at regular intervals is essential for good growth of fish. Cages constructed with matured bamboo may last for 3 – 4 years , while the mature and seasoned bamboo made cages may last for 8 – 10 years.
Advantages of Cage Culture
• It provides private ownership in public waters, control competitors special of fish and predators are easy.
• Cost of construction of cage and initial expenditure is low.
• There is high yield of fish, and good economic return.
Disadvantages of Cage Culture
• Problems of experienced by the cage culture are damage during storms pollution, theft and vandalism.
• The viability may also be affected through increased expenditure on security