Some marine fish are collected for the fishkeeping trade via the use of cyanide. Fish collectors squirt a cyanide solution onto the reefs and in the nooks and crannies of the reef to stun the fish they are trying to collect. This oftentimes leads to sick fish that end up in the fish trade, and it damages wild reef systems. The practice of cyanide fishing occurs primarily in Indonesia and the Philippines, island archipelagos in Southeast Asia that both maintain bans against cyanide fishing but do little to enforce such laws.
Currently the only way to test for cyanide involves taking muscle or blood samples of suspect fish, which often kills them. But Portugese researchers may have found a way to test for cyanide exposure in marine ornamental fish. The researchers used captive-bred Clark’s clownfish (Amphiprion clarkii) to determine levels of metabolized cyanide (SCN) in their water. Captive-bred fish were used to eliminate any chance that specimens had been exposed to cyanide prior to the experiment. The clownfish were kept in a way that simulates the travel time it takes to get from reef to fish store. Marine fish exposed to cyanide excrete thiocyanate (SCN) in their urine, and this urine is present in their transport water. The goal was to determine if SCN levels in a fish’s transport water, days after capture, could prove that the fish had been or had not been exposed to cyanide.
The clownfish were acclimated for 60 days in a 70-gallon aquarium complete with a circulation pump, lighting system and feeding schedule. They were then divided into three groups of nine fish. The first group served as the control group and was not exposed to cyanide. Group two was exposed to a nominal concentration of cyanide (12.5 mg/L), and the third group was exposed to twice as much cyanide (25 mg/L) as the second group. The exposure, called a pulse exposure, was performed in three steps: an exposure bath, first cleaning bath and second cleaning bath.
The researchers tested for the metabolized cyanide using an optical fiber to detect SCN levels in the water. They determined that the test could detect SCN levels from the fish exposed to 25 mg/L of cyanide beginning the next day after exposure. Fish exposed to 12.5 mg/L of cyanide had detectable SCN levels in their water after one week of exposure. While this non-invasive and non-destructive test may vary based on the size of the fish and other factors, the research may lead to a commercial test that can easily test marine species that end up in the aquarium trade.
Reference: Excreted Thiocyanate Detects Live Reef Fishes Illegally Collected Using Cyanide—A Non-Invasive and Non-Destructive Testing Approach