Tuna Seafood Safety

Tuna meat contains mercury, and too much of it is bad for you.

Seafood safety should be taken seriously by those of us who catch our own and by those of us who purchase it from specialty seafood shops, supermarkets or fish houses.

We tend to lump all shellfish into one category, but shellfish are not really fish. They can be molluscs or crustaceans and there are significant differences regarding procuring and eating them safely.

Molluscs, such as oysters, clams and scallops, are filter feeders, moving large amounts of water through their systems daily. As they filter, their internal organs can trap bacteria like Vibrio vulnificus and Escherichia coli. And since oysters and clams are sometimes eaten whole, and often raw, they are two of the most highly regulated species, statewide and nationally. Water testing is an ongoing and frequent exercise in the waters that produce oysters and clams. In Florida, our scallop harvest is possible due largely to the clean and clear Gulf of Mexico waters that are open to that fishery, from Bayport to Mexico Beach. Since scallops are rarely eaten whole (the adductor muscle is usually eaten) the filtering organs are usually discarded. In either case, these bacteria can cause severe intestinal discomfort. Just the thought that Vibrio vulnificus is a relative of Vibrio cholerae, the causative agent for cholera, is enough to make me sit up and pay attention to the oysters and clams I eat. And how I eat them. Bacteria are just one reason to pay attention to the source of your molluscan shellfish. Viruses like hepatitis A can also be present and cause liver damage in humans.

Crustaceans, such as crabs and shrimp, are more closely related to insects and spiders than to fish. The quality of their harvest waters is monitored by a number of regional and national agencies. Harvest areas in Florida are regulated as well. As soon as crabs and shrimp die, spoilage begins. This can be caused by oxidation, bacteria or from the natural enzymes in the animal, and the best way to slow spoilage is rapid refrigeration. This is particularly true with regards to shrimp. Blue crabs are usually sold live, or in the case of soft-shell crabs, dressed and quickly frozen. Stone crab claws must be cooked immediately and then refrigerated before they can be sold. Most of the shrimp we buy from reputable dealers (not from roadside stands!) has been either carefully iced or frozen aboard the boat.

Finfish are another story when it comes to human consumption. The most talked-about contaminant is mercury, which is an industrial waste and serious neurotoxin. Some species we regularly eat in Florida, such as king mackerel, grouper and tuna show high levels, according to the U.S. Environmental Protection Agency. Certain individuals, especially those with autoimmune disease, children and pregnant or wanting-to-be-pregnant women, should limit or totally avoid fish that are high in mercury.

Ciguatera is a serious illness caused by eating large specimens of reef fish contaminated by toxins produced by reef organisms. Ciguatera toxin is not wide spread through the tropics and subtropics, but isolated in localities. When traveling to fish, investigate for incidents of ciguatera in local waters.

Scombroid poisoning can occur when bacteria grows during improper storage of the dark meat of the fish, which can produce scombroid toxin. Symptoms of scombroid poisoning generally begin quickly, about 30 minutes to one hour after ingestion of the poison and may include fun symptoms like nausea, diarrhea, and vomiting. Cooking will kill the bacteria, but not the toxin it produced.

Finally, a few hints on buying fresh fish, oysters, crabs or clams. Buy from a licensed fish market, grocery store or fish house. Don’t be afraid to ask if you can smell or touch the fish you wish to purchase. If it smells overly “fishy” or a slight poke to the flesh with a finger feels soft and mushy, reject it. If the fish’s eyes are cloudy, reject it. See if there’s plenty of ice in the shop’s showcase. That’s a sign the fish has been handled properly. And last, if the odor of spoiled fish hits you when you enter the shop or walk past the seafood case, turn around and go the other way.

First published Florida Sportsman May 2016

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