A specific region in the genome of Nile tilapia has a major effect on mortality levels during an outbreak of Tilapia Lake Virus (TiLV), a study led by the Roslin Institute and WorldFish has found. Fish with specific genetic variants in this region were substantially less likely to die in an outbreak of the virus than fish without these variants. Survival rates improved by approximately one-third, scientists observed. By selecting parent fish for breeding based on these variants, tilapia strains with innate resistance can be developed. This will reduce the number of outbreaks and mortality rate of TiLV, which is one of the biggest threats to tilapia aquaculture, with mortalities up to 90% and for which vaccines are not yet available. Scientists analyzed the genome of almost 1,000 fish from a pond that had experienced an outbreak of TiLV. Comparing the genomes of fish that survived the outbreak with fish that did not enable scientists to find the region in genome containing variants associated with survival. “This information will be invaluable in creating resilient tilapia breeds that can help maintain production of fish in the face of increasing disease risks that threaten food security in many parts of the world. WorldFish plans to incorporate TiLV resistance in the new strains of Genetically Improved Farmed Tilapia (GIFT) we are developing,” said Professor John Benzie, WorldFish.