Trout:
Rainbow, brown, and brook trout can all be reared in cages. Rainbow trout are most often cultured because of the availability of fingerlings, established market, and adaptability to cages.
Basic culture of all three species is similar. Rainbow trout will be described here, but the information should apply to other trout species.
Trout are coldwater species. Optimum growth temperature for trout is between 55 and 65o F, but good growth is attained between 50 and 68o F. At 70o F severe heat stress begins, usually followed by death if exposure is prolonged.
Below 45o F feed conversion drops significantly and, therefore, growth. These temperature regimes make cage culture of trout a wintertime only activity in most of the southeastern United States, except where cold spring water or high altitude lowers summertime water temperatures.
It is necessary to stock a 6- to 8- inch fingerling trout in most of the Southeast to obtain 1 /2- to 1- pound trout by the end of the growing season.
Stocking should begin in the fall as soon as the water temperature drops below 65o F. Failure to harvest before water temperatures reach 70o F in the spring will mean loss of your product and profit.
Stocking densities for trout in cages may be a little higher than those for catfish. The higher oxygen levels maintained by cooler water and smaller sizes at harvest allow trout to be stocked at the higher densities (Table 1) without much concern for low dissolved oxygen problems. In fact densities as high as 15 trout per cubic foot may be acceptable.
Tilapia:
Several species of tilapia and their hybrids have been reared in cages. Species most often cultured are T. nilotica, Florida red tilapia, Taiwanese red tilapia, Aurea red tilapia, and T. aurea. Some tilapia species or hybrids are illegal or restricted in many states.
Check with your state Department of Natural Resources, Fish and Wildlife, or an Extension fisheries (or aquaculture) specialist before culturing these species.
Tilapia are truly a tropical fish with origins in central Africa. They tolerate high temperatures well, can feed on plankton and detritus, are resistant to water quality deterioration, reproduce readily, and have excellent flesh quality.
For these reasons they have been stocked all over the tropical world and probably rank as the most widely cultured tropical freshwater fish. In temperate climates, however, they cannot survive winter water temperatures.
Optimum temperatures for tilapia are from 80 to 90o F, but good growth is maintained between 75 and 95o F. Death occurs at approximately 50 to 55o F depending on the species, and diseases become common below 60o F. Tilapia should not be stocked until the water temperature reaches 70o F.
Fingerlings should be stocked at 4 to 5 inches long (or larger) and can be stocked at the densities described in Table 1. One distinct advantage in the cage culture of tilapia is that they are unable to reproduce in cages and, therefore, do not overpopulate the pond. Better growth is achieved if all male populations are stocked.
At the lower stocking densities tilapia will have excellent feed conversion because they filter feed on plankton passing through the cage. Tilapia should be harvested before water temperature reaches 60o F. Tilapia can be stocked in the same cage with channel catfish (called polyculture).
Research has shown that tilapia polycultured with catfish will increase catfish growth because they stimulate the catfish to feed more aggressively, increasing feed consumption. In polyculture with catfish, tilapia should be stocked at rates between 1 and 3 tilapia per 10 catfish.
Striped bass:
Striped bass and their hybrids have been successfully reared in cages. Striped bass are illegal or restricted in many states. Check with your state Department of Natural Resources, Fish and Wildlife, or an Extension fisheries (or aquaculture) specialist before culturing these species.
Striped bass temperature tolerances and preferences are similar to those for channel catfish (described previously). One observed problem with striped bass is their poor growth and survival in soft water.
Because of this, it is recommended that striped bass and their hybrids should be stocked in waters with total alkalinity of at least 50 ppm. Stocking densities recommended are the same as given in Table 1.
At present the greatest problem in cage culture of striped bass is the availability of large or advanced fingerlings. Most fingerlings are sold at sizes too small to be stocked into cages. A minimum 4-inch fingerling is needed for stocking and 8-inch fingerlings would be preferable. Fingerlings should be graded closely as cannibalism is a problem in young striped bass.
Red drum:
The culture of red drum (redfish) is a recent phenomenon. The research in cage culture of red drum is very limited. At present temperature tolerances and preferences of red drum appear to be about the same as those for channel catfish (described previously), except that red drum do not appear to tolerate rapid temperature drops and require water of high alkalinity and total hardness.
For this reason, harvest is recommended before the temperature drops sharply in the late fall. Do not overwinter these fish in cages. At present the greatest problem with red drum, like hybrid striped bass, is the availability of large fingerlings for stocking. The recommended stocking size is a 6- to 8-inch fingerling. Cannibalism is also a problem in red drum, so fingerlings need to be graded closely.
Bluegill:
Bluegill sunfish and their hybrids have been reared in cages with some success. Temperature tolerances and preferences of bluegill are similar or slightly lower than those for channel catfish (described previously).
Bluegill are aggressive and will take food at lower temperatures than catfish and should be stocked before the water temperatures reach 60o F. Limited research on bluegill culture in cages has shown poor feed conversions.
Fingerling bluegill/hybrids should be 3 to 4 inches or larger at stocking and should be graded carefully to assure uniformity. Stocking densities for bluegill should be in the upper range of those given in Table 1.
Crappie:
Limited research has been conducted on the cage culture of crappie (black, white and hybrids) in the Midwest. These crappie were captured from the wild then transported and stocked into cages.
Results of these preliminary studies indicate that black crappie adapted best to cage conditions but overall survival and growth were poor. The fish were fed a high protein (43 percent) semisoft diet. More research needs to be conducted on the culture of crappies in cages.
Carp:
Common carp (including German, Israeli, mirror, and other varieties) have been successfully cultured in cages and are commercially produced in cages in much of Europe, Asia and the Middle East. Total production of common carp in cages is usually higher than that of most other species. It is not uncommon to produce up to 400 pounds of common carp per cubic yard of cage.
Chinese carp (grass, silver, bighead, and silver x bighead hybrids) also have been reared in cages. These Chinese carp are illegal or restricted in many states. Check with your state Department of Natural Resources, Fish and Wildlife, or an Extension fisheries (or aquaculture) specialist before culturing these species.
Common, grass, silver, and bighead carp (and silver x bighead hybrids) have approximately the same temperature preferences and tolerances as channel catfish (described previously).
Fingerlings should be stocked into cages at a minimum of 4 to 5 inches in length at the same stocking densities listed in Table 1. Common and grass carp are usually fed a 32 to 36 percent protein complete floating pellet.
Silver and bighead carp (and their hybrid) are filter feeders and can be placed in cages in nutrient rich ponds (eutrophic) without any supplemental feeding.
The reason for stocking grass carp in cages is to produce a larger fingerling for stocking into recreational ponds (for weed control) with large predatory fish. One research study has been done using silver x bighead carp hybrids cultured in cages.
The hybrids were stocked at densities of approximately two per cubic foot or 120 in 8 x 4 x 4 rectangular cages. The cages were not fed and no artificial water circulation provided.
These fish fed on plankton and grew quickly from 10 inches to average 3.7 pounds in one growing season.
Choose species carefully:
Picking the fish species that will do well in cages in your particular location is important. For example, it is difficult to get enough growth on trout during the short winters in Gulf coastal plain locations but not in the longer winters in states like Kentucky.
Probably the most important decision in determining which species you should culture in cages is: Is there a market for them? Furthermore, is that market local or must they be transported for long distances? Is it a live market or a processed market? What size is preferred in the market? All potential producers should evaluate markets before selecting the species to be cultured.
Author:
Michael P. Masser
