Molecular identification in the marketplace - Fish genetics

Molecular identification in the marketplace

The PCR technology that allows researchers to recover DNA data from small bits of tissue is now recognized as a major forensic tool, both in criminology and wildlife management. The first organized effort at species identification in the marketplace with PCR technology was directed at the Japanese and South Korean whale fisheries (Baker et al. 1996). To date the applications of forensic genetics to fish products have been few, but these cases are instructive.

Sturgeon caviar represents the ultimate luxury product from fishes, commanding prices upwards of US$50 per ounce. However, native stocks of the most prized species have crashed in the aftermath of the Soviet Union, as poorly regulated fisheries and high price have driven up the harvest, while pollution and dams have reduced habitat. In these circumstances, there is strong incentive to find substitutes for the premium caviar of the Volga River–Caspian Sea region. DeSalle and Birstein (1996) surveyed 23 lots of premium black caviar purchased from reputable dealers in New York City, using mtDNA sequences. They found that five of the lots (22%) were mislabeled eggs from less desirable but imperiled species, including three species listed on the Internation Union for the Conservation of Nature (IUCN) Red List (http://www.iucnredlist.org/) as Vulnerable (Siberian Sturgeon, Acipenser baerii) or Endangered (Amur River Sturgeon, A. schrenckii, and Ship Sturgeon, A. nudiventris).

Red Snapper (Lutjanus campechanus) is an esteemed fish in the restaurants and markets of North America, and commands a premium price. Yet few consumers have the discriminating pallet needed to be sure they are consuming the right species, and the genus Lutjanus has many members that are widespread, abundant, and delicious. In 1996 the Gulf of Mexico Fisheries Management Council imposed fishing restrictions after finding that the Red Snapper was overfished, driving down supply and driving up prices. Marko et al. (2004) surveyed specimens of Red Snapper purchased in eight states in the USA. The mtDNA cytochrome b sequences were compared to reference sequences available in Genbank (see above, Fish genomics). Seventeen of 22 specimens (77%) were not Red Snapper. Among the fraudulently labelled specimens, five were identified as other Atlantic snappers, two were Pacific Crimson Snapper (L. erythropterus), and the remaining 10 could not be identified because sequences from the corresponding species have not been submitted to Genbank. Some of these may be rare or unknown to science, invoking the possibility of overfishing before these species can be identified for management purposes. The fact that over half of the putative Red Snapper came from international sources indicates that this problem is global in scale.

Shark fin is one of the most contentious items in international wildlife trade, a commerce that takes an estimated 10 to 100 million sharks annually, and generates revenues equivalent to over a billion US dollars. In response to sharp declines in abundance worldwide, many countries have banned the practice of finning (harvesting the shark fins and discarding the rest of the fish), and three sharks (Whale, Basking, and Great White) are banned from international trade by the Convention on International Trade in Endangered Species. In these circumstances it is useful to know what species are entering the marketplace, and whether prohibited species are present. In response to this conservation concern, Shivji et al. (2002) developed diagnostic species-specific markers based on a nuclear ribosomal DNA sequence. In preliminary trials, 10 out of 55 putative Silky Sharks (Carcharhinus falciforis) proved to be other species. Subsequently Clarke et al. (2006) surveyed markets in Hong Kong and found that Blue Shark (Prionace glauca) predominated among auctioned fins (17%). Other sharks in the auctions included Shortfin Mako (Isurus oxyrinchus), Silky (C. falciformis), Sandbar (C. obscurus), Bull (C. leucas), hammerhead (Sphyrna spp.), and thresher (Alopias spp.).

These genetic surveys provide two lessons about the wildlife trade:

1 Legal markets such as those for Red Snapper in the USA are often a cover for poaching, smuggling, and illicit products entering the marketplace. Some of these products are from endangered or overutilized species.

2 Esteemed species are replaced by fraudulent alternatives. The practice of species mislabelling, dubbed “mock turtle syndrome”, is observed in 15–95% of luxury products surveyed to date, including caviar, fish fillets, shark fins, seal penises, whale meat, and turtle meat (Roman & Bowen 2000).

The response of wildlife management agencies to this illicit trade remains to be seen, but clearly the commerce in scarce fish products should be monitored. If you find some suspicious fish (or other wildlife) products, take a fin clip, a small tab of tissue, or a skin swab, and consult your local conservation geneticist.