HETEROSIS FOR GROWTH-RATE IN COMMON CARP

The growth of crossbreds of common carp and their parental strains was compared. Heterosis, defined as growth of the crossbred exceeding tha t of its faster growing parent, was demonstrated in cases involving is olates from different farms or countries. As a rule, heterosis was not found when one of the parental lines was Dor-70, a line generated in a long-term mass selection experiment for faster growth. Heterosis was found commonly in young-of-the-year carp during their first summer. I n winter and adult tests, significant differences between crossbreds a nd their better parent were rare. The crossbred between the Chinese an d European races of common carp was heterotic only in an environment p ermitting an intermediate growth rate. We conclude that heterosis for growth is a common but not universal phenomenon in carp. It is limited by genetic factors, genotype-environment interactions, and age and we ight of fish. The application of heterosis to aquaculture is discussed .