Chromosome set manipulations in the black carp

The mollusc-eating black carp (Mylopharyngodon piceus) has economic and health-care potential for biological control of nuisance aquatic molluscs. The present study investigates the production of gynogenetic-monosex and triploid-sterile populations of black carp. The goal was to provide a method which would eliminate unwanted biological and environmental impacts of introducing this exotic species into areas with nuisance mollusc infestation. Meiotic gynogenesis was induced by inseminating black carp eggs with UV-irradiated (800 Jm(-2)) sperm of common carp (Cyprinus carpio) or Japanese ornamental (koi) carp. Diploidy was restored through retention of the second polar body (2PB), by shocking activated eggs at 1-8 min post-fertilization (embryological age of 0.07-0.57 tau(0), a parameter defined by the cell cycle duration) at 1 min intervals, with heat-shocks (41.0 +/- 1.0 degrees C for 1 min) or pressure-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 following normal fertilization. Batches of 30 000 eggs were fertilized with intact 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 swim-up larvae was 5.1% in eggs shocked with 7500 psi. In random samples of individual larvae taken from each treatment, triploidy was analysed by cytofluorometry of the cellular DNA content. In DNA analysis performed in fingerlings (N greater than or equal to 15), 50% of the fish were triploids.