Information bulletin

NO. 88-85 Nov. 1988

Floating Raceway System Can Expand Production of Striped Bass

An innovative system has been developed to culture striped bass (Morone saxatilis) in bodies of water containing trees, stumps, predators, and other items normally not compatible with fish husbandry. Striped bass have been routinely reared in warmwater ponds at State and Federal hatcheries for more than 20 years. Although production has increased in recent years, the capacity of existing hatcheries is inadequate to meet the demand in many locations. Presently, brood fish taken from Chesapeake Bay are spawned in Maryland and Virginia, and larval fish arc shipped to several Federal and private hatcheries to be reared to the phase II size (about 15-20 cm). These fish are then returned to the Chesapeake Bay area, marked, and released in the area from which the brood fish were taken.

Floating System Previously Used Only in Flowing Water

The development of mobile, on-site production facilities would eliminate the need to ship fish to and from distant hatcheries, would allow fish to imprint on water into which they are released, and should improve the efficiency of restoration programs. Such facilities could stimulate the commercial production of striped bass and hybrids. A prototype floating raceway system, modified from the design of a unit used commercially to produce channel catfish Ictalurus punctatus in a river, has been developed for striped bass. The prototype unit, constructed of wood and steel, consists of two boxes approximately 38 m long x 1.3 m wide x 1.3 m deep, which are maintained at the water surface by two floating walkways (1.3 m wide x 16 m long).

Airlift Pumps Provided Water Flow for the Raceway

Water flow through the raceway was provided by airlift pumps. Each pump consisted of 14 parallel tubes (7.5 cm x 7.5 cm) arranged side-by-side in a panel that fit into one end of the raceway. Compressed air from a 1.8-kw regenerative blower was injected about 1 m below the water surface, and water was lifted 5 cm into the end of the raceway. The intake to the airlift pump was screened to exclude vegetation, debris, and large fish. The outflow of the airlift pump was released behind a screen to prevent predators larger than the striped bass from entering the raceway. Water flow rates of about 3,284 28 L/min could be achieved with an air flow of 1027 L/min.

Striped Bass Fry and Fingerlings Grew in the Raceway

The floating raceway unit was placed in a warmwater pond and two short trials were conducted with striped bass. In 1987, fingerlings averaging 5.9 0.9 cm in standard length and 3.9 2.3 g in July reached a size of 14.0 11.0 cm and 55.9 13.3 in October after 99 days of growth During this period, fish were fed a commercial salmon diet (55% protein). Cannibalism and predation by birds and snakes were major problems; survival of the 5,085 stocked fish was only 64%. The raceway was fitted with grading screens to separate the sizes and reduce losses about midway through the trial; however, snakes and birds continued to prey on the fish.

The second trial was conducted in June 1988. Approximately 2,500 17-day-old striped bass were stocked into one raceway to evaluate screens and water flow rates and to determine if the zooplankton pumped into the raceway would provide sufficient nutrition. Growth was excellent during the 2-week trial. The retaining screens were small enough to prevent escape of larval fish, yet large enough to allow passage of zooplankters.

Floating Raceway Unit Also Useful in Hatchery Ponds

Placement of floating raceway units in ponds would allow larval fish of different ages or strains to be reared side-by-side without mixing stocks. Culturists could also monitor survival of larval fish. stocked in a unit and empty and restock units in which survival was low. This is in contrast to conventional culture, where ponds must be drained to remove the few surviving fish, refilled, and the zooplankton base reestablished before ponds can be restocked

The floating raceway also has the advantage of keeping all fish. in confined areas so that their condition can be readily determined and they can be quickly graded as needed. The fish benefit from the zooplankton base, which is supported by the entire water volume in the pond. In estuarine environments the intake could be extended to lower depths to take in the more saline water and possibly avoid the upper freshwater layers that may be low in pH or contain toxic substances. Deepwater intakes might also provide the optimum thermal requirements for striped bass or hybrids and support growth of subadult fish. and development of brood stock..

The prototype unit we tested was provided on loan to the Government at no charge by a commercial firm (Stripers, Inc., Marion, Alabama). Commercial-size units would have multiple raceways in one cluster and be similar to floating net cages. Production capacity for striped bass could be quickly expanded at a relatively low cost by using floating raceway units.

This bulletin is an interim report for information only. The data are considered provisional, pending completion of the research and analysis and interpretation of final results. Use of trade names does not imply U. S. Government endorsement of commercial products.


For more information, contact:
Nick C. Parker
Southeastern Fish Cultural Laboratory
Rt. 3, Box 86
Marion, Alabama 36756