Farming the sea, cleaning up our act
Amy Fitzpatrick, PhD candidate, Munster Technological University and Teagasc Food Biosciences Department won third prize with this article at the MTU Postgraduate Research Competition 2021. She discusses Farming the sea and cleaning up our act to make fish safer to eat
The Irish relationship with fish
Seagrass, periwinkles, oysters - while nowadays such delicacies feature on Michelin-starred menus, they were the scrapings which sustained starving Irish peasantry during the Great Famine of 1840-1847. Ireland and its people have a complicated relationship with seafood, owing in part to its reputation as a poor man’s food (‘bia bocht’) and the dangers that came from eating filter feeders. Oysters filter up to 150 litres of water per day, making them an excellent source of nutrition but also disease-causing pathogens. The fishmonger Molly Malone likely died from typhoid fever after eating shellfish, a common fate in the 17th century before advances in sanitation.
Today, systems are in place to limit the pollution of waterways and monitor how safe our food is. However, Ireland’s water network is largely unmapped. How many of us grew up in houses connected to a septic tank rather than the mains? This makes it difficult to identify where raw sewage is entering our waterways. As our cities and towns have expanded, the wastewater treatment plants are not large enough for the ever-increasing population – the frequent ‘Boil Water’ notices issued after periods of heavy rainfall are a testament to this.
Norovirus and shellfish
One virus which accumulates inside shellfish is norovirus, also known as the winter vomiting bug. This virus can survive for long periods in cool water with low salt content such as the Atlantic Ocean during the winter. As sewage contains waste from many people, multiple genotypes of norovirus can end up inside oysters. Symptoms of norovirus include explosive diarrhoea and vomiting and it spreads like wildfire.
Work at the Teagasc Sequencing Facility
At the Teagasc Sequencing Facility, Moorepark, Co. Cork, in collaboration with MTU and the Marine Institute, Galway, we are ‘fingerprinting’ all the genotypes of norovirus found inside oysters. Sequencing or ‘fingerprinting’ involves reading a series of bases, or letters. We all have a unique series of letters and that makes up our genome. Usually we don’t need to read the entire series of letters that makes up human or viral genomes and instead we target a small region that provides enough information to identify an individual or group. Oysters contain RNA from genes being expressed by the oyster and bacteria and viruses living in the oyster gut alongside the inactive norovirus. Less than 0.1% of the RNA inside an oyster is viral RNA and only some of that viral RNA is from norovirus.
We are improving sequencing of norovirus by removing some of the oyster RNA or targeting the norovirus RNA. This is akin to looking for a needle in a haystack by making the haystack a lot smaller or by making the needle easier to find. We monitor norovirus genotypes circulating in Ireland or in an outbreak situation. By collecting and sharing this information we help target vaccine development and antiviral research and it allows us to watch for new viruses that could cause illnesses.
Shellfish farming is sustainable and has a positive environmental impact but we need to clean up our act to make it safe to eat all year round.
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