In-Pond Raceways consist of rectangular boxes that can be constructed in various sizes and from several types of materials depending on the intended use. IPRs have been used in research and commercial production at several locations in the South and Midwest since 1992.
The smallest IPRs have been used for production of fish fry and were only about 84 cubic feet in volume (6x4x3.5 feet). The largest to date have been used for commercial production of catfish and were approximately 670 cubic feet in total volume (24x8x3.5 feet).
IPRs have been constructed from marine and treated plywood, plastic sheets, and plastic liners. Each of these materials has advantages and disadvantages. Plywood becomes saturated with water and extremely heavy unless coated with non-toxic water-resistant marine paint. Plastic sheets (usually 1 /4 inch thick) expand and contract with heat, making their shape irregular.
Plastic liners (80 mil) cannot be walked in (during harvest or grading) and may collapse due to wave action. A frame around the outside of the IPR is used for attachment of the plywood or plastic. Both treated lumber and metal frames have been constructed.
All IPR materials, including screws and nails, need to be water-resistant and non-toxic. Although treated lumber contains some toxic compounds, these have not been a problem in the IPRs because of the high water exchange rates. However, it may be advisable to coat the wood with non-toxic marine paint.
The IPR is designed to float in any body of water; therefore, a recommended component is a dock or pier for ease of management (e.g., feeding, water testing, etc.). It is possible to anchor the IPR to a stationary pier or to the pond bottom if water levels do not fluctuate.
However, if anchored to the pond bottom without a dock, then daily activities must be conducted from a boat. The IPR pier should be constructed of walkways (3 to 4 feet wide) to allow access to all sides of the IPR and provide space for attaching equipment . For ease of management the pier must be constructed so that the IPRs are positioned close to the walkways. Security should also be considered in construction.
Theft and vandalism can be a problem in any type of high density fish culture system. One of the most common IPRs has been built of treated plywood, framed with treated 2×4 lumber or steel, and coated with epoxy paint. Sizes have been either 16 or 24 feet long, 4 feet wide, by 4 feet deep (only 3 feet underwater).
Figure 2 shows the basic design of this raceway. The air-lift pump is attached to the front or “intake” end of the IPR, and the waste collection system (if needed) is attached to the “discharge” end.
The intake end wall of the raceway is constructed so its upper edge is approximately 9 inches below the sides of the raceway. This space allows the air-lift pump to be adjusted for flow control (see air-lift pump section).
The rear discharge wall of the raceways is constructed so that its lower edge ends about 4 inches above the raceway bottom. This allows discharged wastes to be drawn off the bottom of the raceway for removal.
An “eddy board,” usually 2×6 or 2×8, is placed across the width of the raceway about 4 to 6 feet from the water discharge of the air-lifts. This board should be attached with about 1 inch extending above the water surface when the pumps are running.
The eddy zone behind this board is the feeding area of the raceway. Feed dropped in this area is held against the board, keeping it from being washed out of the raceway. Cage-type mesh material (usually 1 /2-inch mesh) is used to keep cultured fish inside the IPR and exclude wild fish from entering, without restricting water flow.
Mesh is placed in front of the airlifts and at the discharge end of the raceway. The mesh in front of the air-lifts should be in an “L”- shape, forming a trough across the raceway about 6 to 8 inches in front and 4 to 6 inches below the air-lift’s water discharge. This trough traps debris and wild fish that enter through the air-lifts, without restricting water flow.
A second mesh screen is placed about 1 foot from the rear of the raceway and extends completely across the width and height of the raceway. The rear screen keeps the cultured fish from leaving the raceway and wild fish from entering through the water discharge opening.
Hinged lids or doors should cover the top of the IPR to discourage predators and stop fish from escaping by jumping out. Usually several small lids are preferable to one or two large ones because of weight and the need to access only certain sections of the raceway at a time. Mesh material (similar to that described above) should be used in the section over the feeding area so feed can be dropped into the raceway without opening the lid.
The remaining lids can be constructed of a solid material or can be covered with a material such as shade cloth to reduce light and its associated stress on the fish. A 16x4x4 foot IPR has an effective culture volume of 210 cubic feet (15x4x3.5 feet) or 1,571 gallons. A 24-footlong IPR would have an effective culture volume of 322 cubic feet (23x4x3.5 feet) or 2,409 gallons. An IPR with dimensions of 24x8x4 has an effective culture volume of 644 cubic feet (23x8x3.5 feet) or 4,817 gallons.
IPRs have also been constructed using plastic liners. There are several synthetic compositions (i.e., chemically different) of plastic liners. These are commercially available in 19 to 80 mil thickness, with 40 mil being adequate for use in most IPR situations. Liners are ultraviolet light-resistant and have a lifetime of at least 10 years.
Liner manufacturers can fashion liners in many shapes and sizes, so it is possible to have a liner custom-made for a specific IPR design. The flexible nature of a liner allows the raceway to be moved to the pond bank or pier and collapsed for easy harvesting of the fish.
A disadvantage of plastic liner construction is that the walls can collapse inward from wave action, reducing the raceway volume unless a frame is used to maintain its shape. Also, the attachment of solid waste collection systems and air-lifts is more difficult since it is hard to glue materials to the liner.
Cost of plastic liners is also a consideration. Depending on thickness, the type of liner, and custom shaping, they can range in price from $0.50 to several dollars per square foot. This cost is only for the liner and does not include frame, blower, air-lifts, etc.
A small IPR (8x3x3 feet) of 23 mil plastic liner has been tested for use as a fry rearing unit. For this purpose an IPR offers advantages as mentioned before and also provides a steady supply of planktonic food organisms essential for good growth and survival of fry.
A saran mesh sock of 250 microns was placed over the air-lift discharge or outflow to prevent any predaceous insects or fish from entering the raceway. The saran sock will not screen out plankton in the water. Problems were encountered with fouling of the rear mesh screen because of its small mesh size and removing solids from the bottom of the raceway.
Results of this study on fry production were promising, however.
Authors:
Michael P. Masser and Andrew Lazur
