Location of the cage in the pond can be critical to its success. Two factors to consider in cage placement are access to the cage and maintenance of water quality. Daily feeding and management of the cage necessitate easy access under almost any weather condition.
Access may be by pier or by boat. Probably more critical to the success of the cage will be a location in the pond that allows for good water circulation.Critical factors:
Critical factors for locating a cage to maximize water quality are:
Windswept. It is important that the cage be in an area where it will receive maximum natural circulation of water through the cage. Usually, this is in an area that is swept by the prevailing winds (usually prevailing summer winds are from the southwest).
At least 6 feet of water depth. A minimum of 2 feet of water is needed under the cage to keep cage wastes away from the fish.
Away from coves and weed beds. Coves, weed beds and overhanging trees can reduce wind circulation and potentially cause problems.
Away from frequent disturbances from people and/or other animals (e.g., dogs, ducks, etc.) Disturbances from people frequently walking on the dock, fishing or swimming near the cage, and/or from animals which frequent that area of the pond will excite the fish and can cause stress, injury, reduced feeding, and secondary disease.
Fish are shy creatures and should never be disturbed needlessly. At least 10 feet between cages (unless aeration is available). Cages should not be too close together (Figure 4). Close proximity to other cages may increase the likelihood of low dissolved oxygen (See SRAC Publication No. 161, Cage Culture – Site Selection and Water Quality) and spread of diseases between cages.
Access to electricity or to a location where a tractor-driven paddlewheel, irrigation pump, or other aeration device can deliver aerated water to the cages should be considered when locating cages.
Aeration:
Aeration can enhance water quality, reduce stress, improve feed conversion efficiency, and increase growth and production rates. Research has shown that aeration can improve cage production by 20 percent or more. Aeration is most commonly needed at night or during still, overcast days. Aeration for cages can be provided by several types of mechanical aerators.
The key to aeration of cages is to create a current that moves water through the cage. Mechanical aerators like paddlewheels, vertical pumps, or propeller-aspirators can be placed near cages where they create currents through the cages. These types of aerators work well to aerate cages near them and within their current pattern.
However, aerators may not work well in creating currents that aerate multiple cages, particularly cages staggered along both sides of a pier. Air-lift pumps powered by highvolume, low-pressure regenerative blowers can be an efficient and cost effective means of aerating many cages spaced along a pier.
Placing air stones in cages appears to agitate and stress catfish, while aerated water pouring into the top of the cage from airlifts does not disturb them. Figure 5 shows how air-lifts can be constructed from 3-inch (or 4-inch) PVC pipe and connected by 5/8- inch garden hose to a 2-inch or larger air supply manifold attached to the pier.
Each air-lift will move approximately 60 gallons per minute into the cage. One air-lift is usually sufficient to aerate a single small cage (4×4 or 6×6 foot cages), but larger cages (12×6 feet) need 2 or more air-lifts.
As many as 27 air-lifts can be powered from a single 1-horsepower regenerative blower. The keys to using multiple air-lifts in multiple cages are: construct all air-lifts to exact dimensions (so all are identical), place or attach all air-lifts at the same depth in relation to the water surface, and construct restriction orifices at the connection of the air manifold and the air line (going to each air-lift).
Most air-lifts should be constructed to be approximately 36 inches long with an “elbow” at the upper end (elbows at the bottom are optional). Air-lifts can be attached to the outside of the cage or hung in the cage (see Figure 6).
Air-lifts will not lift water more than a few inches above the pond’s surface and therefore should be attached to the cage as close to the water surface as possible. Air-lifts must be attached to the cage(s) at the same level and held straight vertically, not tilted.
The place the hose connects to the air-lift must be between 30 and 34 inches below water level, and all air-lifts must have hoses attached at the same level. A constriction orifice (see Figure 7) must be placed in the air line going to each air-lift, where it attaches to the air manifold.
Orifice size should be between 1/8 and 3/16 inch in diameter (3/16-inch diameter is common) and all the same size. The constriction orifice equally distributes air to all air-lifts and stabilizes water flow through each airlift.
Large cages:
Larger cages than the ones described here have been built and utilized particularly in large lakes, reservoirs, rivers, bays, and estuaries. Many times large cages are called net pens because they are constructed from nylon netting. Most commercial ventures in warmwater cage culture using large cages (e.g., 20x20x12) have failed. Most of these failures appear to have been caused by water quality and associated disease problems.
Some research and demonstration projects have been conducted in the southeastern states using large cages with aeration devices. These aerated cages have worked well in producing fish but little effort has been made to evaluate the cost effectiveness of these systems.
It would appear, however, that large cages can be designed which will maximize the number of fish sustainable by the pond and actually support increased densities above present recommended levels by including aeration systems in the design. For further information on these cages contact your state Extension fisheries or aquaculture specialist.
Author:
Michael P. Masser
