Massive mortalities of edible and ornamental (koi) carp (Cyprinus carpio L.) have been encountered in several fish farms worldwide, including Israel. The disease-causing virus has been identified as koi herpes virus (KHV). Based on its pathogenic effect in fish, it has also been termed carp interstitial nephritis and gill necrosis virus (CNGV). The first objective of this work was to select virus-resistant fish by crossbreeding sensitive domesticated strains with resistant wild strains of carp. Frozen wild carp [Cyprinus carpio haematopterus; Sassan] sperm was brought from the Czech Republic to achieve heterosis by producing crossbreds. We compared growth rate, food consumption, survival and behavior among strains and crossbreds. Two strains of domesticated carp—Našice (N) and Dor-70 (D) and the wild Sassan (S) were used. A large quantity of Našice eggs were fertilized with semen of Našice, Dor-70 or Sassan to produce the N×N, N×D and N×S crossbred groups, while a large quantity of Dor-70 eggs were fertilized with semen of Dor-70 or Sassan to produce the D×D and D×S groups. Resistance to the viral disease was evaluated by exposure to the virus in ponds and in the laboratory.
