Falls, W.W., Dennis, C.W., Hindle, P.A., Young, J.C.
Abstract:
Conventional methods of inducing spawning for red drum, Sciaenops ocellatus, have been refined so that tank maintenance and labor costs have been reduced while husbandry and adherence to a progressive genetics program have been improved. The following refinements have been in place since 1993: 1) broodstock are kept in ponds for initial reproductive maturation; 2) light cycles are set so that spawning occurs during the day; 3) broodstock are genetically fingerprinted, exchanged between tanks, and replaced when necessary to maintain high levels of genetic diversity; and 4) "mentor" broodfish are used to train mature, non-spawning fish.
Wild red drum broodstock were first matured under ambient conditions in 0.93-acre plastic-lined ponds for eight months; harvested in late summer; and then transferred into environmental control room tanks for final maturation and spawning. Allowing fish to acclimate and mature in ponds was more economical than having them mature in tanks. With tank conditions of 10h light:14h dark, 24-26 C, and 30-ppt salinity, spawning began within 30-50 days after transfer.
Light cycles in the environmental control rooms were set so that lights came on at 0000 h and went off at 1000 h. This caused the broodstock to spawn during staff's normal working hours, so eggs could be collected, evaluated, and transferred to incubators immediately. Because the eggs were not left overnight in the eggcollector, both egg and water quality were improved.
Oocytes collected during routine ovarian biopsies were used so that each female could be genetically fingerprinted using mtDNA. Subsequent genetic analyses of offspring (n = 50/brood) allowed us to determine the relative reproductive contribution of each female parent to a given brood. Broodstock were periodically exchanged between tanks and replaced with new wild stocks on a regular basis to maintain high levels of genetic diversity in offspring. The genetic diversity of offspring was monitored and compared to that of wild red drum populations. We are also investigating the possibility that genetic fingerprints can be used to identify hatchery-produced fish after they are released into the wild.
Actively spawning red drum females have been used to train non-spawning or new fish to spawn. One spawning female mentor was placed into a tank with three males and three mature females who had not yet spawned. The non-spawning females followed the example of the mentor and begin to spawn. When the mentor fish was removed, spawning continued. These refinements enhanced red drum spawning while reducing costs.
(Florida Department of Environmental Protection, Stock Enhancement Research Facility, 14495 Harllee Road, Port Manatee, Florida 34221-9620, USA)
***************