THE RIGHT FEED FOR FARMING LOUSE EATERS The genome of the ballan wrasse has been mapped Cooperation: Centre for Ecological and Evolutionary Synthesis (CEES), University of Oslo Funding: The Norwegian Seafood Research Fund
Scientists at NIFES have now mapped the DNA of the louse-eating ballan wrasse. They combined two different methods to solve this great puzzle. Ballan wrasse is a relatively new species in fish farming and is used as a louse eater to combat the problem of salmon lice. Scientists at NIFES have now also sequenced the fish's genome. This means that they have mapped the total DNA of the species. The starting point for the genome sequencing was a lucky ballan wrasse selected from a fish farming facility in Ă˜ygarden. It was sequenced by combining two technologies. This was done because the two technologies cover each other's weaknesses. The first method of sequencing (Illumina) can take readings of many, but short chains of nucleotides. Nucleotides is the appellative for the four types of molecule that code a genome. Illumina sequences are also very reliable since they contain very few mistakes. The other method (PacBio) produces very long readings of
the genome's nucleotides, but it is more often incorrect. It is assumed that between 10 to 15 per cent of the nucleotide readings taken will be incorrect. When all these pieces of a genome are in place, the work on solving the puzzle begins. The pieces have to be put together. To do this, the genome has to be sequenced many times. In this project, the scientists sequenced the whole genome 111 times using the Illumina method and 33 times using the PacBio method. In this way, the pieces of the sequence overlap many times. It is then possible to use computer programs to put the pieces together and pick out the nucleotides that have been incorrectly read. The completed map of the ballan
wrasse genome is 805 megabases, a commonly used unit of length for DNA. This is in the same magnitude as the genomes of cod, medaka and tilapia. For the sake of comparison, the genome of salmon is assumed to be around 3,000 megabases. The project has also demonstrated that it is possible to produce a complete, complex and commented genome for a 'new' species of fish in a relatively short period of time and at an increasingly lower cost. Now that we have knowledge about this genome, we can identify the genes and variations in genes that control the fish's physiology, immunology and metabolism and use these to study the fish's nutrition and welfare.
AQUACULTURE
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