Virologists have demonstrated that different strains of carp and hybrids between strains have differing resistance to Koi Herpes Virus.
A team of Israeli researchers from a number of institutions including the Hebrew University of Jerusalem, the Agricultural Research Organization and the Ministry of Agriculture and Rural Development studied resistance to the virus in several strains and hybrids of carp, and have just reported their findings in the journal Aquaculture.
By sourcing a number of different wild carp strains from around the world, the team managed to select a group of mix which had differing levels of resistance to the virus.
Wild Sassan carp (S), Cyprinus carpio "haemopterus", sperm was imported from the Cezch Republic, along with two strains of domestic carp Nasice (N) and Dor-70 (D). The various strains were then crossed to produce hybrids between NxD, NxS and DxS.
The various thoroughbred strains and hybrids between strains were then experimentally-infected with the virus by keeping them alongside other carp known to be carriers of the virus.
The study found that one cross, DxS, had much more resistance to KHV than the others, with a 60.7% survival rate, while others, such as the pure strain of the Nasice variety were much more sensitive, with just 8% of fish surviving.
Others didn't differ significantly from each other in their susceptibility, with most having survival rates of 17.7-33.7%.
The study also demonstrated the use of a new technique which involves detecting the levels of virus particles in the fish by doing a touch-imprint of the kidney on a slide and then examining it with indirect immunofluorescence microscopy.
Koi Herpes Virus (KHV), which is also known as Carp Interstitial Nephritis and Gill Necrosis Virus (CNGV) on account of the symtoms it produces, has caused mass mortalities around the world, particularly in Israel and Japan.
For more details on the new study see the paper: Shapira, Y., Magen, Y., Zak, T., Kotler, M., Hulata, G. and B. Levavi-Sivan (2005) - Differential resistance to Koi Herpes Virus (KHV) or Carp Interstitial Nephritis and Gill Necrosis Virus (CNGV) among common carp (Cyprinus carpio L.) strains and crossbreds. Aquaculture, Vol. 245, 1-4, pp. 1-11.