Cages lend themselves to straightforward observation of the fish. The observation of fish behavior, especially feeding behavior, 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.
Disadvantages of Cage Culture:
Complete diets needed
Feed must be nutritionally complete and kept fresh. Caged fish will get no natural food and so depend on the manufactured diet for all essential nutrition. Feed must provide all necessary proteins (down to specific amino acids), carbohydrates, fats (including essentially fatty acids), vitamins and minerals for maximum growth. Nutrients start to deteriorate quickly when exposed to heat and moisture.
The shelf life of feeds is less than 3 months from the date of manufacture. Therefore, foods must be stored properly and fed quickly.
Water quality problems:
Localized water quality problems, particularly low dissolved oxygen, are common in cage culture. The high fish densities, along with the high feeding rates, often reduce dissolved oxygen and increase ammonia concentration in and around the cage, especially if there is no water movement through the cage. Low dissolved oxygen within cages may not affect other organisms in the lake, pond or stream.
Diseases:
Diseases are a common problem in cage culture and they can cause catastrophic losses. Wild fish around the cage can transmit diseases to the caged fish. The crowding in cages promotes stress and allows disease organisms to spread rapidly.
Vandalism and poaching:
Caged fish are an easy target for poachers and vandals. Cages must be placed where access can be controlled and poaching risks reduced.
Predation:
Predation can be a problem if cages are not constructed or managed properly. Turtles, snakes, otters, raccoons and fish-eating birds will take fish or damage cages unless precautions are taken.
Limited production:
Fewer pounds of fish per acre are produced in cages than in open pond culture systems. This is mostly because of the stress associated with fish density, the poorer localized water quality, and the increased incidence of disease.
Overwintering problems:
It is difficult to overwinter warm- water fish in cages. There is usually a high mortality rate because of bacterial and fungal diseases. The disadvantages of cage culture should be considered carefully before production begins. Many of these problems can be dealt with through proper construction, location and management.
Species selection:
Research in the southern U.S. has centered primarily on the cage culture of channel catfish and rainbow trout, with some studies conducted on carp, hybrid striped bass, tilapia and sunfish. 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, like blue catfish, 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 analyze potential markets, the production site, water quality, construction and production costs, and legal requirements. Of these, the market is most often overlooked by novice fish producers. Research the markets in your area before deciding whether or not to culture fish.
Finally, check with your local Extension office or state department of natural resources about the permits needed for aquaculture and the processing and transportation of fish.
Author:
Michael Masser
