How many of these tropical fish can you name? If you're an avid snorkeleror scuba diver, probably all of them (1). Seeing them in their natural habitat - a coral reef - is anamazing experience.But, the fish that you might see insalt water aquariums (usuallynot these) may have gotten there in a way that is also amazing, but not in a good way.

This is because of a barbaric method of catching tropical fish, which not only kills many of the fish before they get to your tank, but also does significant damages to coral reefsabout the last thing the world needs. The method is called cyanide fishing, and it is comparable to slash and burn agriculture that threatensrain forests.

Cyanide Fishing - An ecological travesty Photo: Vice

Above is an example of how it is done. In order to make it easier tocollect tropical fish, diversswim down to shallowreefs with a bottle of cyanide solution, and spray around thereefthe home to an enormous variety oftropical fish. The cyanide stuns the fish, making it easy to collect them. Then they are brought to the surface, where they are revived in sea water. Some of them recover, some don't. But the real damage is done to the reef. The fish at least have a fighting chance, but the reefs do not. Cyanide fishing is one of the causes of coral bleaching, which is occurringat an alarming rate in many tropical waters. It is estimated that 500 metric tons (2,3,4) of cyanide is used annually in the Philippines alone.

A cyanide-bleached reef in the Philippines Photo: The Nature Picture Library.

So, how do you stop this abomination? It is illegal, but much of Southeast Asia - the area where most cyanide fishing takes place -is impoverished. The combination ofa $200 million global market for pet tropical fish (5), and poverty make poaching of these fish inevitable, and enforcement of this illegal practice a real challenge. But now, some clever analytical chemistry, which was reportedat the 2017 American Chemistry Society meeting in San Francisco may provide a tool to identify fish that were caught in thismanner, and identify areas where it was used.

The research, which makes use of the disciplines of analytical chemistry, toxicity, andmetabolism, was presented at the meeting by Professor Clifford Murphy of Roger Williams University. Murphy and colleagues described a very sensitive method of detection, which makes use of dye-sensitised solar cells,can measure low concentrations ofthiocyanatein water.

An enzyme in the fish called rhodaneseis known to detoxifycyanide by converting itthe less toxicthiocyanate anion, so the detection ofthiocyanate, either in the fish (3) or the water near the reef is evidence that cyanide was used.Murphy's group invented an easy and sensitive method to detect thiocyanate at concentrations there are up tothree-times lower than current methods. The method employs electrochemistry, and involves simply dipping the detector into the waterand observing a change in color and/or electrical current a positive sign for thiocyanate.

"If you're going to forensically determine that a fish has been caught by cyanide fishing, it would be really helpful to have a portable device so you can test for it on site when fishing boats return to the docks."

Professor Clifford Murphy

Here's how it works.

Porphyrins arestructurallyunusual, but essentialclass of biomolecules, whichare miracles of nature that areresponsible for multiple life processes in animals and plants. They consist of four pyrrolerings that are connected in a way that all four nitrogen atoms are pointing at thecavity in the middle of the molecule (Figure below). Metal ions fit into the cavity, and are held in place by the nitrogen atoms, a type of binding called coordination. The complexes ofmetals andporphyrins, which are called a metalloporphrin, are ubiquitous and biologically essential. They act as transporters, delivering the metal to the site that it is needed to perform a specific function.For example, ironthe metal in hemoglobinhas a strong affinity for oxygen, so it is not surprising that hemoglobin is the transporter of oxygen inthe blood of vertebrates. When the metal is magnesium, the function is different conversion oflight into energy (photosynthesis).

Murphy and his colleagues described a very sensitive method of detection,using materials similar todye-sensitized solar cells, can measure low concentrations of thiocyanate in water.. When thiocyanate is present, it binds to and reacts with the iron in the metalloporphrin. The sensor turns from purple to grayand generates a tiny electrical current. Measurement of the amount of current can quantitatively determine the amount of thiocyanate that is present in the water. Very cool.

Schematic drawing of the thiocyanate detector. Courtesy of Dr. Clifford Murphy

The sensor can be used in either of two ways. First, it candetect thiocyanate in the ocean, which can identify areas where cyanide fishing have been used. Murphy's group tested this by collecting water samples from Narragansett Bay. They added different amounts of thiocyanate and dipped the sensor into the salt water, and determined that it could measure thiocyanate concentrations in the range of1 to 5parts per billion, about 2-3 times more sensitive than previous detection systems.

Second, the sensor can also be used to identify which fish have been caught with cyanide. Fish detoxify cyanide rather slowly (over the course of a few days), and excrete the thiocyanate in urine. So, when afish is placed in clean water, the absence or presence of thiocyanate is a surrogate marker for whether cyanide fishing was used to catch it.

Good for them. Our coral reefs are in bad enough shape in many areas of the world. We do not need to make thingsworse by dumping 500 tons of cyanide into the ocean, andkilling healthy reefsso that people can have pretty fish tanks. Enough already.

Notes:

(1) Here are the answers:

Note: The fish in the photos are not meant to be a representation of those that are found in aquariums, or were necessarily caught using cyanide. They arejust some of my favorites.

(Anyone have a favorite snorkeling site they'd like to share?)

(2) Rubec PJ, Cruz F, Pratt V, Oellers R, McCullough B, et al. (2001) Cyanide-free net-caught fish for the marine aquarium trade. Aquarium Sci Conserv 3: 3751.PJ RubecF. CruzV. PrattR. OellersB. McCullough2001Cyanide-free net-caught fish for the marine aquarium trade.Aquarium Sci Conserv33751

(3) Sadovy YJ, Donaldson TJ, Graham TR, McGilvray F, Muldoon GJ, et al. (2003) While stocks last: The live reef food fish trade: Asian Development Bank, Philippines. 169 p.YJ SadovyTJ DonaldsonTR GrahamF. McGilvrayGJ Muldoon2003While stocks last: The live reef food fish trade: Asian Development Bank, Philippines169

(4) deRivera C, Hitchcock N, Teck S, Steves B, Hines A, et al. (2007) Larval development rate predicts range expansion of an introduced crab. Marine Biology 150: 12751288.C. deRiveraN. HitchcockS. TeckB. StevesA. Hines2007Larval development rate predicts range expansion of an introduced crab.Marine Biology15012751288

(5) Some of the fish caught in this manner are also eaten.

Originally posted here:
Protecting Coral Reefs With Some Clever Chemistry - American Council on Science and Health