Cage Culture: an alternative commercial fish enterprise

Today, freshwater cage culture is practiced to a limited extent in Asia and the United States of America, usually as an alternative type of agriculture for small and limited-resource farmers.

Freshwater cage culture also allows farmers to use existing water resources that may or may not be used for other purposes. The fish produced are usually sold to local niche markets. As wild-capture fisheries have declined and aquaculture has expanded, these niche markets have also grown. The result may be opportunities to increase cage production with the optimal utilisation of our water bodies mostly in the South- South region of Nigeria.

Types of cage culture

Fish can be cultured in one of four culture systems-ponds, raceways, recirculation systems, or cages. A cage or net pen is a system that confines the fish or shellfish in a mesh enclosure. By strict definition, a cage and a net pen differ based on their construction. A cage has a completely rigid frame (on all sides) and a net pen has a rigid frame only around the top. However, the terms "cage" and "net pen" are often used interchangeably. Marine cages are often called net pens, even though they have completely rigid frames, and vice versa. Structural differences have little effect on production practices or the environmental impact of these systems. Cage culture uses existing water resources (ponds, rivers, estuaries, open ocean, etc.) but confines the fish inside some type of mesh enclosure. The mesh retains the fish, making it easier to feed, observe and harvest them. The mesh also allows the water to pass freely between the fish and surrounding water resource, thus maintaining good water quality and removing wastes.

Cage culture probably originated with fishermen who used cages to accumulate fish for market. Over time, they learned to feed the fish in these cages to increase their size and improve their overall health. The first cages used for culturing rather than just holding fish were probably developed in Southeast Asia about the end of the 18th century. These cages were constructed of wood or bamboo and the confined fish were fed trash fish and food scraps.

Freshwater cage research in the U.S. has been limited because large-scale, open-pond culture was more economically viable and received most of the research focus. There has been little research on marine cage systems because of regulatory issues, a limited number of good quality sites, and the high cost of research. Currently, however, there is renewed interest in marine cage or net pen culture worldwide.

Freshwater cage culture is not foolproof or simple. On the contrary, it is more intensive in many ways than pond culture and probably should be considered as an alternative commercial enterprise only where open-pond culture is not practical because of excessive depth, obstructions that prevent harvest, or predator problems.

Benefits of cage culture

Resource use flexibility - Cage culture can be established in any suitable body of water, including lakes, ponds, mining pits, streams or rivers with proper water quality, access and legal authority. This flexibility makes it possible to exploit underused water resources to produce fish.

Low initial investment- Relative to the cost of pond construction and its associated infrastructure (electricity, roads, water wells, etc.), cage culture in an existing body of water can be inexpensive. At low densities (relative to pond surface acreage) cages often do not require aeration or any electrical source. Cage materials are not especially expensive and many kinds of cages can be constructed with little experience.

Simplified cultural practices - Cages lend themselves to straightforward observation of the fish. The observation of fish behaviour, especially feeding behaviour, is critical to anticipating and avoiding problems with stress and diseases, which often occur in cage culture.

Simplified harvesting - Cages are usually harvested by moving them into shallow water, crowding the fish into a restricted area, and simply dipping the fish out of the cage. Or, the cage can be lifted partially out of the water so that the fish are crowded into a smaller volume, and then the fish dipped out. This makes it possible to partially harvest fish from cages as needed for local niche markets or personal consumption.

Multi-use of water resources - The confinement of fish in cages should not hinder other uses of the water resource, such as fishing, boating, swimming, irrigation or livestock watering.

These advantages are appealing, particularly the low capital investment required. A farmer could try producing fish in an existing pond or other water resource with minimal financial or environmental risk. If successful, the farmer could expand production with additional cages or intensify production by increasing aeration or fish densities.

For a species to be practical for cage culture, we must know its culture requirements and be able to satisfy them. That means supplying the water quality it needs and having access to commercial feeds that meet its nutritional requirements. Some species do not do well in cages because they cannot tolerate the crowding that is necessary for efficient cage production.

Before attempting to raise fish in cages, the producer should carefully analyse the potential markets, the production site, water quality, construction and production costs, and legal requirements. Of these, the market is the most often overlooked by novice fish producers. Cage culture is best recommended for artisan farmers during the off season period in Nigeria.

The writer can be reached via email: amoo85@hotmail.com