| Summary: | During the last decade the existence of genetic diversity within species and populations has been generally accepted. The complex structure of populations as well as the variations within populations is believed to be of fundamental importance for adapting to a changing environment and for further evolution. Several genetic studies have suggested a complex population structure for the cod in Norwegian waters. Cod stocks in enhancement programmes may suffer the unwanted loss of genetic variation which has been observed in stocking and enhancement programmes for anadromous species. In preliminary experiments with cod in the laboratory, differential selection against some genotypes was observed and is in fact likely to take place when producing cod fry. When producing large quantities of fry from a few parent fish, genetic drift will also greatly effect the gene pool. At present, however, methods for genotyping parental fish and genetic analysis of cod eggs and larvae offer the opportunity of genetic control at different stages of development. The importance of genetic surveillance of local populations, application of genetic principles and methods to prevent loss of genetic variation, and the possibility of using "genetically tagged" cod fry are discussed in relation to artificial propagation programmes for cod.
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