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The thiocyanate detector publicized in 2017 was an experimental research sensor, not a product shown to be available for fish screening. More importantly, an independent study later failed to find the expected thiocyanate signal in water from cyanide-exposed clownfish. Follow-up work found thiocyanate in fish plasma, but did not establish a dependable field test across species. The idea remains scientifically interesting; the claim that it could end illegal cyanide fishing goes far beyond what the evidence demonstrates.
What the reported detector was designed to do
Cyanide exposure can prompt an animal to form thiocyanate, a chemical metabolite. The proposed screening idea was that an exposed fish might release thiocyanate into the water where it was being held, allowing investigators to test the water rather than kill the fish.
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A 2017 Chemistry World report described researchers led by Clifford Murphy at Roger Williams University developing an electrochemical sensor with metalloporphyrins attached to a substrate. The report said the experimental sensor could detect thiocyanate at 1–2 parts per billion and described blind identification of samples associated with fish exposure. Those figures and results are claims reported about the research, not independently established specifications for a commercial device. The report did not identify a product model, vendor, or retail availability. Chemistry World’s 2017 report.
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A sensor detecting a chemical under research conditions is not automatically a test that can reliably determine how a fish was caught. That broader use requires a sampling method that works consistently, validated performance across relevant species and conditions, and a way to apply results in trade or enforcement.
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Why the holding-water test faced a reproducibility problem
The proposed water test followed earlier work describing a non-invasive optical-fiber and high-performance liquid chromatography (HPLC) approach. In 2018, Breen and colleagues attempted to reproduce the expected signal in common clownfish (Amphiprion ocellaris).
Across four cyanide-exposure experiments conducted over three years, the team analyzed more than 100 water samples. They detected no thiocyanate in water from exposed fish using either HPLC with ultraviolet detection or liquid chromatography–tandem mass spectrometry (LC-MS/MS). Standards and positive controls showed that the analytical methods could detect thiocyanate. The authors concluded that the water-based approach was not viable on their evidence; if thiocyanate was present in the tested aquarium water, its concentration was below 0.6 μg/L. These findings concern the study’s clownfish experiments and do not establish results for every species or holding condition. Breen et al., PLOS ONE (2018).
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The authors summarized the practical problem this way: “Currently, there is no easy, reliable and universally accepted method to detect if a fish has been exposed to cyanide during the capture process.”
What plasma measurements added—and what they did not
A 2019 study measured thiocyanate in the plasma of A. ocellaris after controlled cyanide exposure. Plasma levels peaked 12–20 hours after exposure. The researchers reported elimination half-lives of 1.01 ± 0.26 days after a 45-second exposure and 0.44 ± 0.15 days after a 20-second exposure. Those are results from the study’s controlled exposures, not a timetable that can be assumed for all fish.
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The authors said the findings needed to be extended to other species. They also noted that baseline thiocyanate levels in wild fish would need to be established before plasma measurements could be used as an exposure marker. Plasma sampling is also different from the proposed non-invasive holding-water screen. The study therefore improved understanding of thiocyanate kinetics without validating a cross-species, field-deployable test. Breen et al., PeerJ (2019).
The authors of that paper put the remaining gap plainly: “A field-deployable test for detecting fish caught using CN would assist in combating the use of this destructive practice, however, no reliable and robust test exists.”
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Why detecting cyanide fishing is difficult
Cyanide fishing uses sodium or potassium cyanide solution to stun reef fish for collection, including for the marine aquarium and live reef food trades. Exposure can affect target and non-target fish and corals, and many exposed fish die during capture or transport. A useful test has to work within this varied biological and trade context, not simply register a chemical in one laboratory sample.
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Existing detection approaches differ in whether they require sacrificing a fish, their detection limits, ease of use, and robustness. A historical account in the 2018 study describes the Cyanide Detection Test developed by the International Marinelife Alliance at the request of the Philippine Department of Agriculture’s Bureau of Fisheries and Aquatic Resources. The paper reports that the test was historically used in eight Philippine laboratories. It also records concerns about false positives, sample-size constraints, fish sacrifice, and a laborious 2–3 hour analysis. These are historical details reported by the study, not a description of current laboratory operations.
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The same paper reports that 48,000 fish were tested over eight years and 25% tested positive in that historical Philippine testing account. That figure describes the past testing reported by the authors; it should not be read as a current prevalence estimate for the fish trade.
A detector is only one part of enforcement
Even a reliable analytical signal would need to fit into a defensible process: who collects the sample, how and when it is stored, how results are confirmed, and what action follows. A test also needs validation across species and conditions likely to arise in the relevant trade. Without those links, a promising sensor cannot by itself establish a fish’s capture history or stop illegal practices.
That broader challenge was recognized in NOAA’s 2008 International Cyanide Detection Testing Workshop, which brought together forensic chemists and government and nongovernment representatives, including participants from the United States, the Philippines, Indonesia, and Vietnam. Its focus included testing options as well as management and enforcement. A 2020 evidence review likewise reported that the holding-water thiocyanate approach had not been successfully reproduced and highlighted outstanding toxicokinetic, test-development, and management questions. NOAA’s workshop report; Murray et al., 2020 review.
What readers can conclude
- The 2017 story described a research-stage electrochemical sensor for thiocyanate, not a demonstrated retail screening product.
- The expected thiocyanate signal in holding water was not detected in an independent 2018 study of exposed clownfish using two analytical methods.
- Later plasma measurements in clownfish helped characterize when thiocyanate appeared and declined, but did not validate a field test for other species.
- The evidence supports continued test development, not the claim that this detector ended—or could alone end—illegal cyanide fishing.
The literature discussed here centers on ornamental and live reef fish, controlled clownfish experiments, and work published between 2008 and 2020. It does not establish current country-by-country law or enforcement conditions. The sound reading of the headline is therefore that thiocyanate sensing was a promising research direction whose proposed water-based signal remained unresolved.
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