Fish Cage Design. Handout 6.1a

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Theodore Fields
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1 Fish Cage Design Handout 6.1a Fish cages or small net-pens can either be purchased from commercial dealers or made at home. Commercially made cage or net-pen systems are available in a wide range of sizes. Aquaculture operators working in large ponds, lakes, rivers, or bays use netpens 50 x 50 feet or larger with a coated netting that resists fouling. These commercially produced systems require considerable investment, labor, and time. Mesh Consider a mesh size small enough to hold the smallest fish, yet large enough to allow water to flow through. Water movement removes waste products and brings in fresh oxygenated waters. Mesh 1/2 inch or larger often works best for fish 5-8 inches or more in length. Algae buildup fouls mesh smaller than 1/2 inch and restricts water flow through the cage. Size Cages range in size from 30 to 300 cubic feet. Cages are usually rectangular, 3 x 4 x 3 feet in size; however, any variation of cage may be constructed, including circular, square, or oval. Size and design are restricted only by imagination, practicality, and suitability for the intended purpose. Cage Components Frames for cages or small net-pens may be made of rot-resistant wood (Cypress or redwood), steel, plastic, or aluminum. Avoid copper or zinc as both can be toxic to fish. Smaller cages benefit from the addition of covers. A hinged mesh or solid cover over the top of the cage prevents birds or other animals from preying on the fish. A sturdy cover allows for the additional of a lock on the cage to thwart theft of the crop. A fine mesh collar, or feeding ring, is essential. Without the ring, water currents caused by wind and splashing fish carry the feed through the cage wall. The ring, suspended inside the cage, prevents feed from floating away. The feeding ring is open at the bottom and made of screen small enough so that floating feed pellets cannot pass through the mesh. It should extend from the cage lid to about 8 inches beneath the water surface. The ring can be attached to the top of the inside cage wall, or it can be fastened to the cage lid. 139

2 The ring should be at least one half the size of the surface area of the cage top. In addition, a feeding screen of 1/4-inch mesh helps prevent the food from floating away during feeding activity. The screen is attached to the top of the cage and extends 3 inches above and 6 inches below the surface of the water. Flotation PVC pipe, plastic jugs, steel barrels, and styrofoam floats serve as types of flotation devices. Flotation devices must be attached to allow the cage to float at a height of 3 to 4 inches above the water surface. Some netting materials are lightweight, with a specific gravity less than water, and are therefore buoyant. In commercially produced cages, styrofoam is often used. As a guide for determining the amount of styrofoam needed, consider that one cubic foot of styrofoam supports 30 pounds. Polystyrene foam is enclosed in a net to hold the foam together in case it breaks apart. Balance the flotation on opposite sides of the cage to prevent it from tipping over in strong winds. 140

3 Cage Construction Procedures Handout 6.1b 1. Construct the feeder ring. a. Form feeder ring out of 13 x 1 inch mesh. b. Attach the feeder ring mesh with wire ties to the top inside of the larger mesh. Lace the bottom edge of the feeder ring to the larger mesh to prevent the fish from getting caught between the two layers of mesh. Connect the feeder ring with plastic wire or wire tags. 2. Construct the sides of the cage. a. Stand a 13 x 4 inch piece of mesh on one end. Form a cylinder with 4-6 inches of overlap where the two ends are joined. b. Lace both overlapping edges with plastic wire or ties. Lace as close to the edge as possible to keep the interior of the cage smooth. c. Ensure all rough edges of cage wire face the outside of the cage. d. Fasten four wood slats equal distances apart to the outside of the cage. Slats should touch the top and bottom of the cage. 3. Construct the lid and the bottom of the cage. a. Use two 4-feet square sections for the top and bottom. b. Attach the top with plastic wire or ties halfway around the cage. The unattached portion forms the door. Trim excess. c. Attach the bottom wire all the way around the cage. Remove excess. 4. Construct flotation devices. a. Form two circular rings of plastic pipe to fit inside or outside the perimeter of the cage. Fit one ring to the top; place the bottom ring 4 inches from the bottom. b. Attach the ring to the cage with ties 6 inches apart or use plastic wire to lace the ring to the cage. c. Attach the flotation squares. Use two 21-inch wire tires to attach each styrofoam square next to the top pipe ring. 5. Make final inspection to repair rough edges or skipped spaces. Test floatability. 141

4 Handout 6.1c Sources of Cages Charles Glass Seven Springs Fish Farm P. O. Box 176 Burkeville, VA Bruce Simpson B & P Farm 2608 Livermore Drive Hopewell, VA Duro-Cage Fish Farming Cage Kit P. O. Box 1294 Garner, NC Ken s Hatchery & Fish Farm, Inc. Dept. AGB Hwy. 129 North P. O. Box 449 Alapaha, GA or Inqua Corp. Box 86 Dobbs Ferry, NY or Irving Arnold Rt. 1, Box 515 Crewe, VA J. Paul Custom Made Cages Richmond, VA Coosa Catfish Cages c/o Shep Phillips Rt. 1, Box 126 Equality, AL

5 Transparency 6.1a ADVANTAGES OF CAGE CULTURE If an existing body of water is available, investment costs are relatively low. Harvesting is simplified: The entire cage can be lifted from the water, and the fish removed, or fish can be dipped out of the cage with a net. Fish are easier to observe and monitor for general health and feeding behavior. Cages facilitate the treatment of fish disease. Fish losses from predatory birds and animals are reduced. Fish may be grown in cages as a food source for larger fish. Uncaged areas of the pond may be used for recreational fishing. 145

6 Transparency 6.1b FISH CAGES A fish cage is a screened enclosure usually consisting of plastic-coated wire, plastic extruded mesh or nylon, or polyethylene netting. Cage material should be light for easy handling buoyant strong enough to withstand lifting resistant to weather affordable. 147

7 Transparency 6.2a CAGE MAINTENANCE Remove algae and other attached debris regularly. Use golden shiners, a native fish, to control algae growth. Clean cages to prevent the spread of contagious diseases. Net fish and inspect for disease. Apply antibiotics and other drugs to the feed. In public waters, purchase either certified disease-free fish or use fish from the same body of water. 151

Winter Culture of Caged Rainbow Trout in the South.

Winter Culture of Caged Rainbow Trout in the South. Forrest Wynne, State Extension Specialist for Aquaculture, Kentucky State University Cooperative Extension Program, Graves County Extension Office, 251