Oysters can’t survive in just freshwater for more than three months. If exposed to it for long periods of time, they’ll die.
This is because they need saltwater or brackish water to stay alive. These waters have high salinity levels which are crucial to oysters’ survival. Clams and mussels can live in saltwater or freshwater, but oysters’ habitats are brackish water and salt waters.
A slightly lower level of salinity won’t reduce their safety in terms of consumption and plenty of oysters live in brackish water (mixture of freshwater and salt). Still, they need the salinity level to be medium or high in order to thrive.
Saltwater differs from freshwater by being mostly present in seas and oceans. It also has a high level of salinity which is improper for human consumption, yet ideal for oysters.
On the other hand, freshwater is mostly the water in lakes, rivers, streams, wells, and ponds, and its level of salinity is low.
So, does this mean that you must never keep oysters in freshwater?-Let’s find out!
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Where do Oysters Live?
Estuaries are the perfect ground for fish and oysters.
An estuary is partially protected by land and oysters need a hard bottom because soft bottoms will cause them to get buried and die.
Estuaries are partially enclosed water bodies where freshwater and salt mix and this is known as brackish water.
They’re one of the most productive ecosystems of the earth and plenty of diverse habitats thrive there. Oysters also thrive at the edge of channels because of the good flow of water that brings them food. Oysters live in brackish waters between 2 and 26 feet in depth.
The ideal temperature is also important for the survival of oysters and it’s between 68 and 90 degrees F.
However, an adult oyster can survive in water as cold as 38 degrees and as hot as 120 degrees F, though this is only for a short period of time.
Oysters can survive in above-20-percent dissolved oxygen saturation while some marine life needs this percentage to be at least 30. Dissolved oxygen is oxygen in the water that marine organisms need.
Why Do Oysters Need Saltwater?
Oysters need saltwater that has a salinity of at least 8ppt in order to survive.
Different strains of oysters need different levels of salinity; however, salinity that goes beyond 20ppt seems to provide optimal productivity.
The lower the level of salinity in the water, the higher the risk of oyster diseases and death. This is why oysters can’t live long-term in freshwater, though they can survive in it for a certain period.
Salinity is the amount of salt that’s dissolved in water. This percentage varies in estuaries. Namely, water that’s closer to the mouth of the freshwater source usually has a lower salinity while the water closer to the ocean has a higher one.
Oysters need a salinity in a range between 14 and 28 ppt, but they can also survive in a ppt between 5 and 35. Below 12 ppt is low salinity, 12-20 ppt is medium, and 20+ ppt is high salinity.
How to Store Oysters Properly?
When properly stored and still in their shell (in the fridge, or on ice and covered with a damp cloth at the coldest part of the fridge), oysters can stay alive and fresh for up to 20 days, although it’s always the best to consume them as soon as possible.
They must never be placed in regular water because they’ll die as they’ll try to “feed” on the water they’ve been immersed into.
Oysters are filter feeders: they eat by pumping water through their bodies. Interestingly, an oyster can filter up to 50 gallons of water daily!
When you buy oysters and you don’t plan to eat them right away, keep them as cold as possible, but never in the freezer. If you keep them in the freezer, their freshness will diminish and they’ll no longer be safe for consumption.
How to Handle Oysters Safely?
When it’s time to prep the oysters, take them out of the fridge.
Put on household gloves and transfer the oysters into a colander. Bring them into the sink and rinse them well. Inspect each oyster and clean any debris. If some oysters seem “odd”, check if it’s alive.
You can do this by lightly tapping on them. If the shell closes, it means it’s fresh and alive, and safe for consumption. If not, throw it away. Once they’re all clean, it’s time to put on the protective shucking gloves and take the shucking knife to open them.
If you’re not very skilled at shucking oysters with a knife, you can always invest in an oyster shucking machine. The risk of injury with a machine is lower and it’s the ideal way to shuck oysters without having to use a knife, which can get dangerous if you’re not experienced!
Although oysters are popularly consumed raw and straight out of the shell, there are plenty of awesome dishes that you can make with them. Also, they can be cooked in different ways, that is, baked, steamed, boiled, etc.
Final Thoughts
Oysters shouldn’t be kept in freshwater because it will eventually kill them and you end up wasting precious seafood.
Oysters need saltwater or brackish water to survive. They’re filter feeders and feed on microscopic plankton which they filter through their gills. They need a medium or high salinity that these waters provide.
On the other hand, the salinity levels of freshwater are very low. Oysters thrive at higher salinity and therefore live in estuaries in brackish water and near edges of channels with a high flow of water.
The ideal way to store oysters and keep them fresh and alive is on top of ice which is placed on a perforated pan and dripping down.
They should be lightly covered with a damp cloth and eaten as soon as possible, although they can be kept like this for up to 20 days.
When handling oysters, always choose the proper equipment, i.e., an oyster shucking knife or an oyster shucking machine and protective gloves.
