People who were concerned that transgenic living forms might escape containment and prove the end of nature may feel vindicated by the finding of glow-in-the-dark fish in Brazilian wild waterways. However, zebrafish genetically modified for luminescence appear to be less harmful than many other invasive species, and may perhaps be no worse than normal zebrafish.
Even the vibrant hues of tropical reef fish aren’t enough for some folks. As a result, zebrafish with fluorescent protein genes have found a ready market in the home aquarium sector.
Unfortunately, neither aquarium fish owners nor sellers are universally responsible for their assets, and at least 70 non-native aquarium fish have been discovered in Brazilian inland waters alone, 31 of which are known to have established themselves in their new environments. Glowing zebrafish have been added to the list in an article published in Studies on Neotropical Fauna and Environment.
Scientists choose zebrafish as a model animal because they are easy to maintain in the lab, the larvae are transparent, and we know so much about their genetics. The National University of Singapore demonstrated in the late 1990s that adding genes from jellyfish and sea anemones to zebrafish caused them to glow red and green, respectively. Yorktown Technologies, based in Texas, recognized a commercial opportunity and began distributing GloFish® shortly thereafter, expanding the range of colors available. Since then, several competitive luminescent aquarium fish have reached the market, employing zebrafish and other species.
Glow-in-the-dark fish have been seen in the wild since 2013, and transgenic fish have been outlawed in Brazil since 2017, however the rule is not implemented.
Dr. André Magalhes and colleagues from the Universidade Federal de Sao Joa del Rey studied five creeks in Brazil’s Paraba do Sul freshwater ecoregion. The area was chosen because it is close to a massive ornamental aquaculture center, from which fish have been known to escape during water releases, sometimes settling in nearby seas. The zebrafish thrive in the warm and somewhat steady climate.
Red zebrafish were discovered in four sites and green zebrafish in three, but only in two creeks were they prevalent enough to warrant further investigation. Both types of fish, particularly the green strain, have a diverse diet of aquatic invertebrate larvae in their stomachs. They appeared to be capable of reproduction for much of the year, and as creatures that reproduce prodigiously, their numbers have the potential to rise quickly. On the other side, the authors discovered a scarcity of juvenile fish, which they blame to a lack of vegetative areas where zebrafish larvae normally thrive.
The authors are concerned that if GloFish® become abundant enough, they will threaten native invertebrates or outcompete local species. The waters in which they were discovered were predator-free, but the colors could attract unwanted attention if they spread further.
There’s no reason to believe GloFish® is worse for the environment than wild-type zebrafish, and a 2015 study found the luminous proteins would be detrimental in the wild. However, any species lacking local predators can be devastating in a new environment, and the chance that one or several colors will aid transgenic animals in taking over cannot be ruled out.