CHROMOSOME SET MANIPULATIONS IN THE BLACK CARP

The mollusc-eating black carp (Mylopharyngodon piceus) has economic an d health-care potential for biological control of nuisance aquatic mol luscs. The present study investigates the production of gynogenetic-mo nosex and triploid-sterile populations of black carp. The goal was to provide a method which would eliminate unwanted biological and environ mental impacts of introducing this exotic species into areas with nuis ance mollusc infestation. Meiotic gynogenesis was induced by inseminat ing black carp eggs with UV-irradiated (800 Jm(-2)) sperm of common ca rp (Cyprinus carpio) or Japanese ornamental (koi) carp. Diploidy was r estored through retention of the second polar body (2PB), by shocking activated eggs at 1-8 min post-fertilization (embryological age of 0.0 7-0.57 tau(0), a parameter defined by the cell cycle duration) at 1 mi n intervals, with heat-shocks (41.0 +/- 1.0 degrees C for 1 min) or pr essure-shocks (7500-7600 psi for 1.5 min). Highest survival was found when embryos were heat-shocked 1.5-4.5 min post-fertilization (0.10-0. 25 tau(0)). The highest survival of free-swimming larvae from pressure -shocked eggs, was achieved at 7500 psi at 1-2 min post-fertilization (0.08-0.16 tau(0)). Triploidy was induced by retention of 2PB followin g normal fertilization. Batches of 30 000 eggs were fertilized with in tact sperm and pressure-shocked (6000-8500 psi for 1.5 min) 2 min post -fertilization (0.15-0.16 tau(0)). The highest survival of triploid sw im-up larvae was 5.1% in eggs shocked with 7500 psi. In random samples of individual larvae taken from each treatment, triploidy was analyse d by cytofluorometry of the cellular DNA content. In DNA analysis perf ormed in fingerlings (N greater than or equal to 15), 50% of the fish were triploids.