Pens can be constructed with frameworks of wood, bamboo, metal, etc, on which netting or other fencing materials is stretched to form an enclosure. The netting is fixed to the bottom of the water to prevent fish from swimming under it. This can be done by using pegs or sand bags.
The mesh of net used for the pen should be small enough to prevent the fingerlings from escaping through it.
The cage units should be built to withstand prevailing winds and waves in the water.
Pen Culture: It is the system of culturing fish within a fixed net enclosure either at the bank or in a water body. The bed of the water body serves as the bottom of the pen.
Good water exchange is essential in both pen and cage culture to ensure a replenishment of oxygen and flash away waste. In this regard, pens should be placed in such a way that flow of water through them is enhanced, while cages should have sufficient space between their bottom and the bottom of the water body.
Advantages of Pen/Cane Culture
– Existing water bodies can be used.
– Lower capital cost compared with land-based fish culture.
– Easier stock management and monitoring compared to pond culture.
– Growth offish in pens and cages is fasterthan in ponds.
Suitable Fish Species
The most popular pen and cage culture species in Ghana has been Tilapia However other species such as Catfish, Carp Heterotis, etc could be stocked in cages.
Stocking rates in pens and cages depend on the fish species and the carrying capacity of the water body. Tilapia can be stocked in pens at the rate of 30-50 fingerlings per m3, while It is advisable to fix the netting so that the meshes open horizontally rather than vertically
It is the system of culturing fish within floating net enclosures, each supported by a framework in water bodies such as borrow pits, rivers, streams, reservoirs or lakes. Cages could be rectangular, square or circular in surface area.
The fish in pens and cages should be fed with formulated feed with a good protein content. Generally, floating feeds are preferable in order to prevent wastage and pollution of the water.
Duration of culture
Culture periods depend mainly on water quality, the type of species, and quality of feed. For tilapia and catfish the culture period is between 6 and 10 months.
Pens and cages attract predators like birds, crocodiles, predatory fish, mammals etc. Poaching is also a serious problem. Measures should be put in place to control such problems.
In Ghana the establishment of any cage culture facility requires a permit. An Environmental impact assessment may be required by the Environmental Protection Agency (EPA).
– Fish stocks are vulnerable to external water quality problems e.g. Algal blooms, low oxygen.
– Growth rates are significantly influenced by ambient water temperatures.