Can excreted thiocyanate be used to detect cyanide exposure in live reef fish?

Abstract

Cyanide fishing, where a solution of sodium or potassium cyanide is used to stun reef fish for easy capture for the marine aquarium and live fish food trades, continues to be pervasive despite being illegal in many countries and destructive to coral reef ecosystems. Currently, there is no easy, reliable and universally accepted method to detect if a fish has been exposed to cyanide during the capture process. A promising non-invasive technique for detecting thiocyanate ions, the metabolic byproduct excreted by exposed fish, has been reported in the literature. In an effort to validate this method, four cyanide exposure studies on Amphiprion ocellaris (common clownfish) were carried out over three years. Fish were either exposed to the same (25 ppm) or twice the concentration (50 ppm) as the previsouly published method. Over 100 water samples of fish exposed to cyanide were analyzed by reverse phase HPLC with a C30 column treated with polyethylene glycol and UV detector operating at 220 nm. No thiocyanate was detected beyond the analytical standards and positive controls prepared in seawater. As an alternate means of detecting thiocyanate, water samples and thiocyanate standards from these exposures were derivatized with monobromobimane (MBB) for LC-MS/MS analysis. Thiocyanate was detected in standards with concentrations as low as 0.6 μg/L and quantified to 1 μg/L, but thiocyanate could not be detected in any of the water samples from fish exposed to cyanide with this method either, confirming the HPLC results. Further, we calculated both the mass balance of thiocyanate and the resultant plausible dosage of cyanide from the data reported in the previously published method. These calculations, along with the known lethal dosage of cyanide, further suggests that the detection of thiocyanate in aquarium water is not a viable method for assessing fish exposure to cyanide.

Wild caught ornamental fish: a perspective from the UK ornamental aquatic industry on the sustainability of aquatic organisms and livelihoods

“…() and has been called into question by Breen et al . (). Nevertheless, the issue of cyanide fishing is one that the legal and legitimate trade is determined to address.…”

“…Most recently, the test methodology described by Vaz et al (2012) could not be repeated in the field by Herz et al (2016) and has been called into question by Breen et al (2018). Nevertheless, the issue of cyanide fishing is one that the legal and legitimate trade is determined to address.…”

On the half-life of thiocyanate in the plasma of the marine fish Amphiprion ocellaris: implications for cyanide detection

“…While development of such a test has long been the goal of anti-CN fishing proponents, no test meeting the aforementioned criteria has proven viable for routine use (Breen et al, 2018). A more systematic approach to solving this long-standing problem would be to first investigate the toxicokinetics of CN absorption and its subsequent detoxification and elimination in a variety of marine fish.…”

The determination of thiocyanate in the blood plasma and holding water of Amphiprion clarkii after exposure to cyanide

“…The same group used this technique to monitor the MAT in the EU for the presence of cyanide fishing in the exporting countries ( Vaz, Esteves & Calado, 2017 ). The hope was that this technique could serve as a test for CN exposure in marine fish, but in the nine years that have passed since it was first reported, it has never been replicated by any other lab even though multiple laboratories have attempted to do so ( Breen et al, 2018 ; Herz et al, 2016 ; reviewed by Murray et al, 2020 ). Breen et al (2018) demonstrated by using a mass balance calculation that the SCN concentrations reported by Vaz et al (2012) and the concomitant dose of CN that the fish would have had to receive given the reported SCN concentrations were an order of magnitude higher than all known LD50s for CN in vertebrate species.…”