Tiger shrimp is widely used in aquaculture in Asia. If genomics can be used to prevent white spot disease, it will be of major economic significance (Photo: Nofima).
Shrimp aquaculture is carried out in large parts of Asia and Latin America. White spot syndrome is one of the most serious diseases of farmed shrimp, and there is currently no effective way of combating this disease. Scientists have recently discovered markers for genes that determine how well black tiger shrimp (P. monodon) resist the disease. They are now planning to look for the genes in the white shrimp (L.vannamei).
If the markers are used to breed shrimp that are more resistant to the disease, problems caused by the disease in the shrimp aquaculture industry will be significantly reduced.
The virus that causes white spot disease (WSSV) is capable of killing all the shrimp in a pond within 10 days of infection. The disease can, on occasions, totally devastate shrimp aquaculture in a complete region. There are currently no treatments available to effectively prevent outbreaks of the disease.
Indian and Norwegian scientists have been looking for a preventative solution in the shrimp genes. They have collaborated in the search for gene markers, which are locations in the genome, that code for the level of immunity the shrimps have against the virus. Senior scientist at the Norwegian food research institute Nofima, Nicholas Robinson, believes the findings will have a large impact on future generations of shrimp:
“Now that these markers have been found in the tiger shrimp, it will be possible to select for higher immunity to the disease in the next generation by implementing what is known as ‘marker-assisted selection’ into an advanced breeding program. Since the generation time of the shrimp is short, we can expect a clear effect within a few years,” says Robinson.
This is the first extensive experiment in which genes markers related to disease have been found in shrimp.
The research has been carried out by Nofima and the Indian CIBA (Central Institute of Brackishwater Aquaculture), and financed by the Research Council of Norway and the Indian Department of Biotechnology.
In addition to finding markers for disease resistance in the black tiger shrimp, the scientists have also found markers for genes that determine sex. The gene markers for sex could assist hatcheries to produce exclusively female shrimp for distribution. Male shrimp are small and grow slowly, so the discovery of sex-determining markers can enable aquaculture personnel to produce healthier shrimp that grow more rapidly.
The genetic code (DNA sequence) in the genes of various shrimp was analysed, as the scientists sought for the markers. Variation in the DNA sequence of nearly 4,000 genes was compared within large groups that had been exposed to the disease. The scientists were looking for correlations between the duration of survival of the shrimp after being infected and the genetic code in their genes. It was possible in this way to reveal nine gene markers that were associated with resistance to the disease. Some of these were present in, or close to, genes that are known to have a function related to immunity in fish.
The scientists are now planning to examine whether the same genes affect the resistance to white spot disease in white shrimp. This will be financed by the same sources, and new partners will be involved. White shrimp is also used in aquaculture in India and several Asian countries.
“We are now in the process of starting a project for the white shrimp with the same goals – to discover genetic tools that can reduce a disease that is widespread in shrimp aquaculture,” concludes Robinson.
