Many species of fish are suitable for cage culture. Species which have been researched and successfully reared in cages in the southeastern region of the U.S. include: catfish, trout, tilapia, striped bass, red drum, bluegill sunfish, crappie, and carp.
Other species may be suitable for cage culture but research has lagged behind other aquaculture research in recent years. Interest in cage culture has been revived as an alternative crop for farmers outside traditional fish farming areas and in areas with topography not conducive to levee ponds.
As this interest continues to increase, more research into cage culture techniques and alternate species will no doubt occur. A great deal of variability exists in the research and commercial literature about suitable pond sizes, growing season, stocking densities, and size of fingerlings to stock.
Stocking rates or densities are dependent on species, cage volume and mesh size, pond surface area, availability of aeration, and desired market size.
In general, stocking densities are calculated on the number of pounds of fish which can be reared per surface acre of pond and per cubic foot of cage. A pond without aeration can produce from 500 to 1,500 pounds of fish per surface acre.
In a pond with aeration, 2,500 to 4,000 pounds of fish per acre have been achieved. The maximum pounds of production per cubic foot of cage seldom exceed 14 pounds in small cages and 11 pounds in large cages (< 270 cubic feet). Commonly, cage production will be between 5 and 8 pounds per cubic foot.
Cage production is possible in ponds, lakes, reservoirs, strip pits, rivers and streams, and in cages which range in size from 27 cubic feet to several thousand cubic feet (in large reservoirs). In this fact sheet, ponds will be the frame of reference and only cages smaller than 300 cubic feet will be considered.
Catfish:
The channel catfish is the species most commonly cage cultured today in the Southeast. Channel catfish have a well established market and fingerlings are generally available. They tolerate many extremes in water quality and generally adapt to cages. Channel catfish are warm water fish. Optimum growing temperature for channel catfish is between 80 and 85o F. Good growth occurs between 70 and 90o F. Above 95o F fish feeding is reduced and deaths may occur. Below 70o F feeding slows and, therefore, growth slows. Feeding essentially stops below 45o F.
Channel catfish should be stocked only in a certain range of water temperatures. Handling stress associated with stocking and quality of fingerlings stocked are critical factors to be considered. Channel catfish can be stocked into cages almost any time when the water temperature is above 50o F. However, stocking at temperatures above 80o F may adversely stress the fish and lead to disease and possibly death.
Stocking poor quality fingerlings before the water reaches 60o F (when predictable feeding occurs) can lead to handling stress compounded by nutritional stress from the lack of food intake. For these reasons it is probably best to stock when water temperatures are between 60 and 70o F. Of course, fish farmers may have to learn how to handle and stock fingerlings at any range of temperatures to be competitive and meet their marketing objectives.
Size of catfish fingerlings to be stocked depends on the length of growing season, availability, and marketing strategy. The minimum size fingerling which can be stocked into a cage made of 1 /2- inch mesh is approximately 5 inches. Generally 6- to 8-inch fingerlings are stocked into cages. If a 1 1 /4- to 1 1 /2-pound fish is the desired market size at harvest it may be necessary to stock a larger fingerling or stock at a lower stocking rate.
A larger fingerling must be stocked in the northern part of the southeastern region (or at high elevations) where the growing season is shorter. It is not uncommon to stock 8- to 10-inch fingerlings where the growing season is 180 days or less.
Availability and cost of larger fingerlings may make stocking these sizes prohibitive. A fingerling over 10 inches in length may not adapt well to a cage. Uniformity of fingerling size is also important. Research has shown that catfish fingerlings of uniform size (all within 1 /2 inch of the same length) will grow more homogeneously, reaching a larger average size and increasing total cage production over fingerlings with a 1 inch or longer variation in length.
The strain or variety of channel catfish stocked into cages can make a great difference in production or yield. Different strains have been developed or selected at both public and private hatcheries throughout the Southeast.
Not all of these strains do equally well in cages even though they may grow well in open ponds. In fact, strain research in cages suggest that some strains can grow as much as 50 percent faster than other strains.
Therefore, probably the best general advice is to talk to other cage producers in your area and ask which fingerling source they like and have been successful with. Research done at Auburn University has shown that strains with a Kansas or Marion (named after the Federal hatcheries) ancestry do well in cage conditions.
This same research has shown that many private hatcheries, but certainly not all, have channel catfish strains that grow well in cages. Ask other cage producers and use a strain that has a good reputation. Stocking densities for catfish fingerlings in cages range from 5 to 14 per cubic foot of cage.
This equates to 250 to 600 fish in a 4 x 4 feet cylindrical cage. Generally speaking it is best to stock at the low densities (5 to 8 per cubic foot) when first attempting cage culture, particularly if supplemental aeration is not present. Do not stock below a density of 5 per cubic foot or catfish may fight, leading to injury and disease.
Some recommended stocking rates for small cages are given in Table 1. Even with supplemental aeration available it may be advantageous, for stress reasons, to stock additional cages rather than overstock individual cages.
Overstocking can reduce growth and increase disease problems. Blue catfish, hybrid catfish (blue catfish male x channel catfish female), and bullhead catfish have been stocked in cages with limited success. Blue and hybrid catfish do not grow as well in cages as channel catfish. Bullhead catfish have been raised in cages and appear to do relatively well.
Recommended stocking size is a 6-inch fingerling. Bullheads do not grow as large as channel catfish, however, and are expected to get to only 1 /2 pound in a growing season. Bullhead fingerlings are generally difficult to find and may be expensive.
Author:
Michael P. Masser
