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Study reveals ‘hidden’ species in aquarium fish trade

Rupert Collins

A recently published study in the open-access journal PLoS ONE documents the trade in a popular family of fishes—the cyprinids—and reveals new information about some of the hobby’s favourite species.

Puntius filamentosus (A) and P. assimilis (B) are not easy to tell apart. © Rupert Coliins

The cyprinid family includes the barbs, danios, rasboras, carps and freshwater “sharks”, to name but a few of this diverse group. Despite their popularity in the hobby, there is a great deal of uncertainty in which species are actually traded, and this includes both familiar species, and the new ones cropping up. This can cause a headache for government organisations in countries wishing to restrict the availability of certain species.

The ornamental fish industry is one of the world’s largest transporters of live animals, and thousands of species from far-flung corners of the globe can be easily purchased in local pet stores. This trade is mostly unregulated, however, and an unfortunate downside is the liberation of exotic fishes into local waterways. If the released species become invasive pests, there can be serious environmental and financial consequences.

Trigonostigma heteromorpha. © Rupert Collins

Our work, funded by the New Zealand biosecurity agency MAF, aimed to set up a DNA barcode reference library for the cyprinid fish species in the trade. DNA barcodes are short sequences of DNA, and are used to associate an unknown fish with pre-identified reference specimens held in museums. One benefit of such research is the DNA barcodes can be used as a permanent resource, available free of charge to any individual or organisation seeking to understand the patterns or risks associated with the ornamental fish trade in their country.

In addition to their use as an identification tool, DNA barcodes are helpful for investigating biodiversity. In our study of 172 cyprinids from the trade, many were found to be genetically different to what was expected, indicating there may be several species known under a single name. Some of these, such as the orange-finned danio Danio kyathit, has long been suspected by hobbyists to be two different species—a spotted and a striped form—and this was confirmed with DNA.

The diminutive golden dwarf barb (Puntius gelius) was also another case where aquarists had noticed several different varieties were being traded. Even the ever popular harlequin (Trigonostigma heteromorpha) was found to harbour diversity. An example of the two genetic forms of the harlequin is shown below, and can be distinguished by the difference in body shape and the orange spot on the anal fin.

Trigonostigma cf. heteromorpha. © Rupert Collins

Others, such as Puntius denisonii, the famous red-line torpedo barb from India, also showed signs of substantial diversity, but the groups did not appear to be morphologically different to one another; these are termed “cryptic species” by scientists. The finding has important implications for conservation, in fact, as P. denisonii is understood to have a limited distribution in Southern India, and is highly vulnerable to being over-harvested for the aquarium trade.

Interesting patterns were also observed in other aquarium species, and included: Danio choprae, D. dangila, Devario devario, Epalzeorhynchos kalopterus, Microdevario kubotai, Microrasbora rubescens, Puntius assimilis, P. fasciatus, P. lateristriga, P. stoliczkanus, Rasbora dorsiocellata (now Brevibora cheeya), R. einthovenii, Boraras maculatus, Trigonopoma pauciperforatum and Sundadanio axelrodi (recently described as multiple species).

There also appeared to be a lot of mislabelling and misinformation in the trade, with many of the commonly traded species turning out to be something else entirely. A good example here being the Siamese algae eater “Crossocheilus siamensis“, which are actually much more likely to be C. langei, C. atrilimes or even Garra cambodgiensis.

The article can be read here, and comes with extensive supplementary data including images of live and preserved fishes, as well as a full list of references and characters for the morphological identification of cyprinids. The images and figures are also creative commons licenced, allowing free use and reproduction.

Rupert A. Collins, Bio-Protection Research Centre, Lincoln University, New Zealand

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