Shellfish That Glows Not Safe to Eat


If your shellfish glows, that’s a sign it’s not safe to eat. A new technique that identifies contaminated shellfish by causing the toxins to glow has been developed by chemists at the University of California, San Diego, but this early warning system is still in the early stages.

Red tides can make shellfish unsafe to eat

Red tide, also known as algal bloom, is a large concentration of microorganisms that typically form in coastal areas. These blooms can be caused by dinoflagellates, a type of phytoplankton that contain pigments ranging in color from red to brown and green.

During warm summer months, blooms of dinoflagellates can develop and play havoc on marine life, as these unicellular organisms produce a neurotoxin that affects the muscle function in susceptible organisms. Humans who eat fish or shellfish such as mussels and oysters contaminated by these toxins can develop diseases including ciguatera (contaminated fish) and paralytic shellfish poisoning.

Oysters and mussels feed by filtering seawater through their digestive systems. In the process they accumulate dinoflagellates, which are usually harmless but in some cases produce dangerous poisons. At the University of California, San Diego, chemists developed a new marker to detect toxic dinoflagellates in shellfish.


A team of scientists led by chemistry professor Michael Burkhart devised a system that adds a fluorescent tag to an enzyme that produces a toxin called okadaic acid. Because the tag is added to the molecule that turns the enzyme on, the scientists are able to ensure they will “light up” only the parts of cells that can make the toxin.

Although the technique currently requires an expensive fluorescence microscope to see the tagged cells, Burkhart and his team believe advances in technology will eventually allow the tags to be detected using a handheld device.

A recent study published in Marine Drugs noted that neurotoxic shellfish poisoning is caused by eating molluscan shellfish contaminated with brevetoxins, which are produced mainly by the dinoflagellate Karenia brevis. Symptoms of shellfish poisoning include nausea, vomiting, abnormal sensations of the mouth, lips, and tongue, as well as slurred speech and dizziness. Neurological symptoms can progress to partial paralysis.

The new technique has proved effective in cultures and in live mussels, whose guts glow with toxin-producing dinoflagellates for the scientists. In theory, this approach could identify shellfish that are not safe to eat, thus reducing the risk of shellfish poisoning.

University of California, San Diego
Watkins SM et al. Marine Drugs 2008 Sept; 6(3): 431-55