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The terminology Seafood encompasses a very broad scope of products, because it includes the raising of seafood (mariculture and aquaculture which relates to fresh water seafood), the washing  of seafood (shellfish) after harvest (depuration), the storage of fresh seafood and fish, and finally to the processing of such products.  In each of these applications ozone has found significant commercial application, to wit:  


The sensitivity of fish eggs (roe) and juvenile fish (fry) to ubiquitous microorganisms and natural predators can result in significant losses.  Screening of tanks protects against predators, and ozone protects against microorganisms and disease epidemics these can cause.  Primary advantages of treating influent hatchery waters with ozone are that it is self-regulating and does not create byproducts that are toxic to the eggs or fry.  How is ozone self-regulating?  Over-treating influent waters with ozone will be toxic to the eggs and fry, and too little ozone will be microbiologically ineffective.   

Ozone has been in use at U.S. Fish & Wildlife Service hatcheries for decades to hatch and raise fingerlings for annual stocking of rivers, lakes and even commercial fisheries.  Many catfish farmers also have discovered the benefits of ozone.  


Shellfish (oysters, clams, mussels) feed by opening their shells to allow seawater to pass through their bodies.  As this happens, algae are filtered to provide food for growth.  On the other hand, microorganisms and viruses also are filtered into the mollusk meat.  Therefore, when harvested, the contaminated shellfish are held several days in a clean water supply so that over time (4-7 days), the microorganism loadings will pass out of the edible shellfish meat.  Treating the depuration station influent water with ozone decreases the time required for the harvested animals to rid themselves of toxic microorganisms and viruses by at least 33%.  This technique has been in commercial practice in Mediterranean depuration stations since the 1920s.  


Once fish have been harvested, the natural processes of decomposition begin, both externally (bacterial degradation) and internally (enzymatic changes), ultimately resulting in putrefaction.  Routinely, freshly caught fish are stored under ice to lower their temperature, which decreases the rates of both internal and external decomposition mechanisms.  

For decades, ozone has been in use on-board fishing vessels to treat water used to make ice for storing fish harvests.  Such ice is microbiologically cleaner than ice made from raw water.  Adding ozone to water used to wash fresh caught seafood also lowers the number of microorganisms on fish surfaces, increasing their storage times and delaying spoilage.  


Some fish processing plants recently have adopted the addition of  ozone to all waters used throughout the plant for washing fresh fish, but also for sanitizing processing equipment, workers clothing and boots, for making ice, and for washing drains at the end of the work day or shift.  

A Swiss sushi processing plant has adopted ozone, along with other processing steps including ultrasound, UV radiation, electrolyzed water, and modified atmosphere packaging, to extend the conventional shelf lifetimes of fresh sushi from three to seven days.  Since a single product recall by public health authorities can result in very poor press and lowered product sales (to say the least), the use of ozone coupled with the other processing steps listed provides an insurance policy that allows the Plant Manager to finally sleep well each night.  

R.G. Rice, August 26, 2010

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