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International Waters: New Cyanide Test Holds Promise

Posted: July 25, 2012, 5:55 p.m., EDT

Marine ornamental fish collection using cyanide is a contentious issue that has been hotly debated for decades. Its great advantage is that it facilitates collection of wild specimens by knocking fish out, thus allowing their easy capture, even from hard-to-access nooks and crannies.
Its main negative properties include the internal damage it causes to the captured fish, as well as the indiscriminate destruction, not just of target and non-target fish species, but of reef invertebrates as well, including corals, by disrupting the symbiotic relationship between corals and their resident zooxanthellae.

New Cyanide Test Holds Promise
Cyanide facilitates the collection of fish from hard-to-access nooks and crannies. Image by John Dawes

The use of sodium or potassium cyanide is frowned upon and condemned by all the ornamental aquatic trade organizations, in addition to consumer disapproval and condemnation of the practice, and its use has declined over the years as a result of this. Nonetheless, it still continues to be employed in some collecting regions, largely for food fish, but also, though to a lesser extent, for ornamental fish.

Several analytical methods aimed at detecting cyanide in collected fish have been developed and applied over the years. However, there have always been either uncertainties regarding the validity or consistency of the tests or perceived limitations, such as the need to sacrifice specimens for tissue analyses. Gaps in knowledge regarding a number of aspects of cyanide metabolism have also impaired progress.

This is not to say that progress has not been made. It has, but there has always been a need to find a way of reliably testing for cyanide without having to kill any fish. Ideally, if one could find a way to accurately test the waste products of fish for any sign of cyanide poisoning, this would open the door to major advances in the fight to eliminate the practice.

Well, there now is such a way. It is based on the formation of thiocyanate, a metabolite ion fish produce as cyanide passes through their bodies. Being a waste product, fish subsequently excrete thiocyanate via their urine. So, in theory at least, if the urine can be tested successfully, this would eliminate having to sacrifice any test subjects.

However, before any test can be regarded as universally acceptable, it has to be shown to work under real-life conditions. For instance, research into cyanide metabolism in freshwater fish has largely concentrated on long-term—or chronic—exposure to cyanide in aquaria. Yet, when fish are collected from reefs using sodium or potassium cyanide, they are subjected to what is referred to as an “acute pulse dosage” of these compounds.

In addition, marine fish produce very little urine when compared to freshwater fish, and thus retain cyanide traces for longer periods. This means they will continue to excrete thiocyanate over a long period of time.
While the longer retention period may be detrimental to some fish, it is an advantage with respect to testing, since it could allow a sufficiently long period for the metabolite to be present in water through the supply chain. This opens up the possibility of testing at every stage, from collection to sale.

In a recently reported experiment, 27 Amphiprion clarkii were divided into three groups: Group one, the control group, was given no cyanide; Group two was subjected to a bath of 12.5mg/L-1 sodium cyanide; Group three was given 25.0mg/L-1 sodium cyanide. After rinsing in cyanide-free water to remove all traces of external contamination, water samples were analyzed daily for thiocyanate.

The water in the control group tank showed no thiocyanate at all throughout the duration of the tests, which ran for 28 days. Group two showed detectable levels of thiocyanate from the sixth day onward. Group three showed the presence of thiocyanate from the second day onward. Significant levels were detectable even at the end of the experimental period.

Clearly, these results hold great promise for the future, although some very important questions remain unanswered. Nonetheless, this non-intrusive, non-destructive, fast method of analysis could pave the way for major advances in the near future, once some of the key questions are answered.

Encouragingly, there has been a positive initial reaction from the industry, which received the news with cautious optimism. One exciting possibility the new approach provides is that of self-policing, with companies being able to employ the tests themselves and being able to identify any cyanide-contaminated consignments.

There are, obviously, several important issues that need to be resolved. However, if these can be resolved, cyanide use within the ornamental aquatic industry could, at long last, be eliminated in the not too distant future.

Marcela C.M. Vaz, Teresa A.P. Rocha-Santos, Rui M. Rocha, Isabel Lopes, Ruth Pereira, Armando C. Duarte, Peter J. Rubec and Ricardo Calado, Excreted Thiocyanate Detects Live Reef Fish Illegally Collected Using Cyanide—A Non-Invasive and Non-Destructive Testing Approach. PLoS ONE 7(4): e35355.doi: 10.1371/journal.pone.0035355. <HOME>

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