The Growing and Glowing Threat to Native Brazilian Freshwater Fish

By: Ashlyn Halseth

Glow-in-the-dark fish were first created in the late 1990s by the National University of Singapore by genetically modifying zebrafish (Danio rerio) with fluorescent proteins obtained from sea anemones (Entacmaea quadicolor) and jellyfish (Aequorea victoria; Wan et al. 2002). In 2001, an Austin-based company began to commercialize these fluorescent zebrafish, and rebranded them with the name, GloFish. GloFish took the exotic pet trade by storm and was sold to Spectrum Brands for $50 million in 2017 and is continuing to grow in popularity (Ho 2017). As of 2022, the Glofish company has expanded its collection of fluorescent fish, and now produces and distributes genetically modified bettas (Betta splendens), short-fin and long-fin tetras (Gymnocorymbus ternetzi), barbs (Puntius tetrazona), and sharks (Epalzeorhynchos frenatum), together known as the GloFamily.

Photo is property of GloFish

The entire GloFamily is available for purchase in the USA and Canada, but is prohibited for sale in Mexico, South Africa, India, Indonesia, Australia, New Zealand and throughout the entire European Union (Van Den Akker & Wassenaar 2012). Most recently, Brazil has prohibited the commercialization of the first species of GloFish, the green-fluorescent zebrafish, after hearing reports of this fish making its way out of aquariums and into the local waterways (Tuckett et al. 2017). The non-fluorescent species of zebrafish, from which the GloFish is modified from, is native to the freshwater streams and rivers of the Western Ghats and parts of the Himalayas in India (Magalhaes et al. 2021). It was previously thought that the GloFish wouldn’t be able to survive outside of its native home ranges or controlled aquariums as they were modeled to be unable to forage for food or reproduce efficiently (Khee 2006). However, since the GloFish introduction to Brazilian waterways within the past decade, this has not been the case.


Brazil is home to the Muriae Ornamental Aquaculture Center, the largest Brazilian fisheries establishment that has 250 different species of aquarium fish, 350 fish farms, and 4,500 production ponds (Magalhaes et al. 2021). In practice to maintain these facilities, routine pond drains happen eight times a year, only 1-6 meters away from local waterways full of native fish. Many fish farms have physical barriers to prevent the introduction of non-native fish into local waterways; however, the Muriae Ornamental Aquaculture Center has no retention or detention ponds and is hypothesized to be the source for some non-native introductions (Magalhaes et al. 2020). As mentioned above, the green variant of the zebrafish, referred to as GloFish, has been detected in Brazil’s streams and rivers, and are thriving.

GloFish, in their native home range, are prompted to start reproducing in response to the South Asian monsoons; however, the GloFish have easy acclimated to Brazil’s climate, as the summer months experience similarly high levels of rainfall as well (Magalhaes et al. 2021). This increase in water levels allows for easier communication between breeding pairs and even allows for increases in breeding grounds and food availability for their young after they hatch. In fact, the climate of Brazil is so favorable, that the GloFish breeding season ranges from 8 months to the entire year. Furthermore, GloFish are generalist feeders, meaning they have the ability to consume almost any species of prey to meet their energetic demands. With this natural history tactic, GloFish can feed across the entire Brazilian water column, with the dominant prey source being aquatic insects, but also algae, zooplankton, terrestrial prey, and more (Magalhaes et al. 2021).

Although more studies need to be conducted to understand the full impact GloFish have on their introduced community, it is thought that this non-native species could be detrimental to the native freshwater fish populations found in Brazil’s waterways. Being a generalist feeder, Glofish have the potential to consume large quantities of small prey species, harming the invertebrate community and therefore putting a strain on other species of fish that consume the same prey (Magalhaes et al. 2021). Furthermore, GloFish in laboratory settings have been documented to be aggressive towards other fish, through nipping and biting (Karga & Mandal 2017). Their large diversity of diet and aggression towards other species could lead to them out-competing native Brazilian fish, which serve important ecological and economic roles (Magalhaes et al. 2021).

While the individual species of GloFish in Brazil’s waterways still need to be addressed, there is hope for preventing the introduction of introduced species in the future. In Brazil, it is illegal to release genetically modified species, intentionally or unintentionally, like GloFish, into the environment. Also, many biologists, like Magalhaes et al. (2021) have proposed steps to prevent future introductions. Education remains at the forefront of this plan, with a push towards the production of native species instead of non-natives for aquariums, installation of filters to prevent unintentional introductions, introducing native predators into contaminated areas, and more legislative bans to prevent the commercialization of non-native species. With all of these practices and more innovative approaches, highlighting the impacts GloFish have on native fish communities, one can hope that GloFish will remain a sought-after pet, and not an ecosystem terror.



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