News | December 28, 2015

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Researcher studies toxins that cause fish poisoning

Last year, an estimated 50,000 people around the world were struck ill with ciguatera fish poisoning (CFP) after eating their favorite fish. CFP is insidious in that there are no simple methods to test for the ciguatoxins that cause the illness; so people who like fish take their chances at the fish market, and they take their chances in a restaurant.

FGCU graduate students Alex Leynse and Adam Catasus prepare a damselfish for transport on a boat in the Florida Keys. The students will conduct toxin analysis on the sample reef fish in FGCU laboratories.
FGCU graduate students Alex Leynse and Adam Catasus prepare a damselfish for transport on a boat in the Florida Keys. The students will conduct toxin analysis on the sample reef fish in FGCU laboratories. / Photos by Pete Bacheler: Petebachelerphotoshelter.com

The symptoms are often frighteningly bizarre. While deaths are rare, people suffering from CFP report experiencing abdominal cramps, diarrhea, nausea and vomiting followed sometimes by neurological or cardiovascular events. Headaches, muscle aches and numbness are common. Other symptoms can include strange sensations, like loose teeth, intense itching or confusion between hot and cold temperatures. The illness can linger for weeks, months or even years.

In the past, ciguatera was primarily a concern in tropical and subtropical areas, but fish from those waters are exported to markets across the globe, making the illness a worldwide concern. Today, it is the most common form of phycotoxin-borne seafood poisoning in the world; phycotoxins are toxic chemicals produced by marine algae.

Mike Parsons, FGCU Professor of Marine Science, is leading a team of researchers studying ciguatera. They are in the final year of a five-year, $4 million ECOHAB (Ecology and Oceanography of Harmful Algal Blooms) grant from The National Oceanic and Atmospheric Administration (NOAA). The grant, named CiguaHAB, is the largest competitive grant ever awarded to an FGCU researcher.

In preparation for writing the grant, Parsons assembled an international team of researchers from universities and laboratories with a focus on the Caribbean region, including the Woods Hole Oceanographic Institution of Massachusetts, the University of Texas Marine Science Institute, the University of South Alabama, the University of Veracruz, the Food and Drug Administration Gulf Coast Seafood Laboratory and the University of the Virgin Islands.

In addition to his partner institutions and universities, Parsons works closely with FGCU graduate students Amanda Ellsworth, Alex Leynse, Adam Catasus and Jeff Zingre. They’ve been collecting samples of algae and reef fish once a month at four primary research sites in the Florida Keys. The samples are examined in labs and tested for toxins that cause ciguatera poisoning.

FGCU Professor of Marine Science Mike Parsons, left, and grad student Alex Leynse process samples for testing. Parsons is in the final year of a five-year, $4 million grant from the National Oceanic and Atmospheric Administration to study ciguatera fish poisoning.
FGCU Professor of Marine Science Mike Parsons, left, and grad student Alex Leynse process samples for testing. Parsons is in the final year of a five-year, $4 million grant from the National Oceanic and Atmospheric Administration to study ciguatera fish poisoning.

Ciguatoxins are heat-stable, meaning they remain dangerous even after the fish has been cooked. Like many marine toxins, ciguatoxins biomagnify, that is, they become more concentrated in the fish tissue as the toxin moves up the food web. In general, the larger fish that eat the smaller reef fish store higher levels of the toxin, and therefore are more likely to pass on ciguatera to people.

Poisoning is caused by eating reef fish — grouper, snapper, barracuda, hogfish and triggerfish to name a few — that are contaminated with ciguatoxins produced by a single-celled microalgae called gambierdiscus that attach to macroalgae, which serve as the diet of many reef fish.

According to Parsons, some species of gambierdiscus are toxic, while others are not. “To identify the toxicity of the microalgae we collect,” he says, “we analyze samples collected monthly at our primary research sites and send them to one of our CiguaHAB partners for a molecular workup to determine which species are out here in abundance and which are toxic.”

Parsons says that because gambierdiscus is a microagla , he anticipates that there will be blooms — much like red tide — when fish will be exposed to more microalgae with ciguatoxins and therefore increase the risk for CFP. “Ultimately, we want to identify conditions that are ideal for ciguatoxins,” says Parsons, “which will help us predict when the toxins will most likely affect fish.”

“Our work here is very complex,” Parsons says. “We’re compiling the data that will give us an understanding of the overall marine system at work at our research sites. When we understand the system at work on the reefs, we’ll be in a better position to make predictions about when outbreaks of ciguatera are most likely to occur.

“Once we have a definite understanding of the system, we’ll be able to develop a predictive model that NOAA can use to forecast the likelihood of CFP. That’s the goal for the next phase of our research.” Once that goal is reached, the CiguaHAB research will impact tens of thousands of people worldwide as fewer and fewer people suffer from ciguatera fish poisoning.