Genome and gene manipulation in the common carp

Genetic and physiological manipulations can be carried out easily in teleost fishes due to their external fertilization and embryogenesis. These procedures are performed in the early stages of ontogenesis to produce the required characteristic, which then leads to an altered phenotype. Two trends in effective modification of genotype of fishes have been developed: (a) manipulation of the genome by inducing gynogenetic and androgenetic reproduction and (b) manipulation of ploidy. In both of these modifications the sex ratio is modified by genome manipulation, allowing the establishment of monosex populations and inbred lines. Individuals of sterile populations produced by genome manipulation usually show better growing rate than their fertile mates. Moreover, sterilization substantially reduces the risk of acclimatization, when exogenous fish species are imported into different aquatic ecosystems. In the early stages of ontogenesis — before the sex-determining genes are switched on in the progenitors of germ cells — physiological processes can also be manipulated with remarkable effects on phenotype. Alteration of the sex of young fish populations by hormonal treatments is a well-known example. For some commercially important species this method can be applied very effectively and has become general in the practice of breeding, while there are still many unelucidated questions in other species, including common carp. Present methods could be rapidly improved by combination of certain genetic and physiological manipulations. The genetically identical individuals of fish clones have both experimental and practical importance. A large number of clones can be produced and sustained in carp using a combination of different manipulations. Insertion of recombinant DNA constructs into the genome of fish provides a new, efficient way of improving current stocks of farm fish. Methods of production, selection and characterization of transgenic individuals of fish, gene transfer experiments performed on and availability of presently cloned genes of farmed cyprinids with special emphasis on common carp as well as possible developments of the area in the future are discussed in this review. The experimental results produced by using these new techniques will increase our knowledge of the basic processes of fish biology. Together with traditional methods they will also hopefully contribute to the development of a more efficient and rapid carp breeding system in the future. Although application of these methods will obviously require efficient measures for protection of natural populations, overreaction resulting in regulations with prohibitive effects concerning the use of these procedures in laboratories should be avoided