People who worried transgenic life forms would escape from captivity and prove the end of nature may feel they have had their fears confirmed with the discovery of glow-in-the-dark fish in Brazilian wild creeks. On the other hand, so far zebrafish genetically modified for luminescence seem to be less damaging than plenty of other invasive species and maybe no worse than unmodified zebrafish.
For some people, even the gorgeous colors of tropical reef fish just aren't bright enough. Consequently, zebrafish with genes for fluorescent protein production have found a ready market in the home aquarium industry.
Unfortunately, neither the owners nor sellers of aquarium fish are universally responsible with their possessions, and at least 70 non-native aquarium fish have been found in Brazilian inland waters alone, of which 31 are known to have established themselves in their new ecosystems. In a paper published in Studies on Neotropical Fauna and Environment, glowing zebrafish have now been added to the list.
Zebrafish are a model animal, heavily used by scientists because they are easy to raise in the lab, the larvae are transparent, and we know so much about their genetics. In the late 1990s, the National University of Singapore showed that if you added genes from jellyfish and sea anemones to the zebrafish they would glow red and green respectively. Texas company Yorktown Technologies saw a market, and began selling GloFish® soon after, and have since expanded the range of colors on offer. Several competing luminescent aquarium fish have hit the market since, using both zebrafish and other species. Reports of glowing fish in the wild date back to 2013, and transgenic fish have been banned in Brazil since 2017, but the law is not enforced.
Dr André Magalhães of the Universidade Federal de Sao Joa del Rey and co-authors surveyed five creeks in Brazil's Paraíba do Sul freshwater ecoregion. The region was chosen because it is close to an enormous ornamental aquaculture center, from which fish have been known to frequently escape during water releases, sometimes establishing themselves in the waters nearby. The warm and relatively stable climate is friendly to the zebrafish.
Red zebrafish were found at four locations and green at three, but only in two creeks were they common enough for further study. Both sorts of fish, particularly the green strain, had a wide variety of foods in their stomachs, particularly larvae of aquatic invertebrates. For much of the year they appeared to be capable of reproduction, and as animals that breed prodigiously, their numbers have the potential to grow fast. On the other hand, a shortage of juvenile fish was found, which the authors attribute to a lack of the vegetated areas in which zebrafish larvae usually thrive.
The authors fear that if the GloFish® become abundant enough they could pose a threat to some native invertebrates, or out-compete local species. The waters they were found in were predator-free, but the colors could draw unwelcome attention if they spread further.
There's no reason to think GloFish® would be any worse for the environment than wild-type zebrafish, and a 2015 study suggested the luminescent proteins would be a disadvantage in the wild. However, any species that lacks local predators can prove disastrous in a new environment, and the possibility one color or another will help transgenic species take over can't be ruled out.