Excreted Thiocyanate Detects Live Reef Fishes Illegally Collected Using Cyanide—A Non-Invasive and Non-Destructive Testing Approach

Marcela C M Vaz,Peter J Rubec,Rui J M Rocha,Armando C Duarte,Ruth Pereira,Ricardo Calado,Isabel Lopes,Teresa A P Rocha-Santos,Sebastian C A Ferse

doi:10.1371/journal.pone.0035355

Abstract

Cyanide fishing is a method employed to capture marine fish alive on coral reefs. They are shipped to markets for human consumption in Southeast Asia, as well as to supply the marine aquarium trade worldwide. Although several techniques can be used to detect cyanide in reef fish, there is still no testing method that can be used to survey the whole supply chain. Most methods for cyanide detection are time-consuming and require the sacrifice of the sampled fish. Thiocyanate anion (SCN−) is a metabolite produced by the main metabolic pathway for cyanide anion (CN−) detoxification. Our study employed an optical fiber (OF) methodology (analytical time <6 min) to detect SCN− in a non-invasive and non-destructive manner. Our OF methodology is able to detect trace levels (>3.16 µg L−1) of SCN− in seawater. Given that marine fish exposed to cyanide excrete SCN− in the urine, elevated levels of SCN− present in the seawater holding live reef fish indicate that the surveyed specimens were likely exposed to cyanide. In our study, captive-bred clownfish (Amphiprion clarkii) pulse exposed for 60 s to either 12.5 or 25 mg L−1 of CN− excreted up to 6.96±0.03 and 9.84±0.03 µg L−1 of SCN−, respectively, during the 28 days following exposure. No detectable levels of SCN− were recorded in the water holding control organisms not exposed to CN−, or in synthetic seawater lacking fish. While further research is necessary, our methodology can allow a rapid detection of SCN− in the holding water and can be used as a screening tool to indicate if live reef fish were collected with cyanide.

Highlights

Coral reefs currently face an increasing number of anthropogenic threats worldwide [1,2,3,4] which are magnified by global climate change [5,6].Coral reefs in Indonesia and the Philippines are currently the most at risk, due to the use of destructive fishing techniques [7]
(21 day post-exposure (DPE)), SCN2 levels in the water had increased to 6.9660.03 and 9.8460.03 mg L21, respectively, for fish pulse exposed to 12.5 and 25.0 mg L21 of CN2, and remained significantly higher in specimens pulse-exposed to a higher concentration of CN2 (p,0.0001)
The present work confirms that our optical fiber (OF) methodology can be used to determine elevated concentrations of SCN2 in seawater samples collected from containers holding fish previously pulseexposed to CN2.This non-invasive and non-destructive approach, with an analytical time of less than 6 min [34], allowed us to monitor during a 4 week period the daily excretion of SCN2 by fish previously exposed to CN2

Summary

Introduction

Coral reefs in Indonesia and the Philippines are currently the most at risk (about 95% of existing reefs), due to the use of destructive fishing techniques [7]. Millions of fish are collected illegally from coral reefs every year using cyanide, with over 500 metric tons of cyanide being used annually for this practice on Philippine reefs alone [8,9,10]. Despite leaving the reef physically intact ( corals may be broken to extract stunned fish), cyanide kills coral polyps by disrupting their symbiotic association with the zooxanthellae [15,16]. Cyanide fishing is illegal in most exporting countries, it is still a common practice, and is often encouraged by corrupt authorities taking advantage of poor rural communities [17]

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Results

Conclusion