These two species look extremely similar but DNA barcodes can tell us that A is a species of barb called Puntius filamentosus while B is Putius assimilis

 When you have a young family, a good and entertaining way to spend some time is to visit a local pet shop. Toddlers love to look at the kittens and puppies. When they tire of that there are more exotic pets to examine. One that seems endlessly fascinating is the aquarium fish. There are usually a number of species in different tanks in all shapes and sizes and colours. Not being a fish expert I am sometimes overwhelmed by the diversity, tanks with lesser spotted whatsits sitting next to blue-striped dodads and sometimes swimming with clown thingamys. Although I’ve never succumbed to getting fish, many obviously do. Aquarium fish account for about $20 billion in global trade each year! That’s an estimated one billion fish moving mostly from tropical to temperate countries. That’s a lot of fish! The fate of most of these fish is to live comfortable lives in an aquarium before going belly-up. For a few there is the prospect of liberation as they make it into the wild. Of 59 fish species colonisations into the USA, 37 of them are as a result of the aquarium trade. So there is a significant biosecurity problem here. If these fish establish then they may outcompete native species, modify habitats and so on.

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New Zealand is a country that works hard to maintain its borders from entry by potential pest species. We have a fragile native fish fauna that is already under threat from previous introductions and habitat change. In order to manage the possible threat of aquarium fish the government has developed a list of species that are allowed to enter the country as they can be easily managed or are unlikely to survive in the wild. Of course this relies on being able to identify individuals coming into the country as belonging to the right species. For some species this is obvious but for most, especially if they are larval forms which haven’t developed their species traits, this can be very difficult and time-consuming. You don’t want to bring a pest species into the country that happens to look like a safe species. What to do?
Rupert Collins with many colleagues, mostly from Lincoln University, has thought long and hard about this. Rupert realised that using the appearance of fish, known as morphology, was not ideal as species often look very similar. One thing that always differs between species is their DNA. Even if two species look exactly the same they still differ in their DNA. Taking DNA samples from individuals would remove doubt about the species. This approach has been termed DNA barcoding (as each species has its own DNA code). Rupert checked to see whether this approach would work for aquarium fish species and his study is now published in PLOS One. Rupert collected DNA from 678 fish from 172 species entering New Zealand. Rupert was able to match over 90% of the DNA sequences with known named species. He was also able to show that there were at least 10 cryptic species (species that happened to look like another species on the safe list). From this study, Rupert was able to develop a procedure that can be used to make fast and accurate identifications of fish coming into New Zealand. So the next time a toddler asks you what that fish is you can be confident in the name written on the tank!