Transgenic Glowing Fish Escape and Thrive in the Wild in Brazil

TWN Info Service on Biosafety
23 May 2022
Third World Network

Dear Friends and Colleagues

Transgenic Glowing Fish Escape and Thrive in the Wild in Brazil

Native to Southeast Asia, zebrafish (Danio rerio) were engineered to glow for research purposes in the late 1990s by inserting genes from fluorescent jellyfish (for blue and green colors) and coral (for red). In the 2000s, companies saw the potential of the neon fish as pets.

Researchers in Brazil have published a paper documenting the escape and successful reproduction of these GM aquarium fish in the wild. The fish have escaped fish farms in southeastern Brazil and are multiplying in creeks in the Atlantic Forest all year round. They could threaten local species by competing for food or preying on them in one of the most biodiverse spots on the planet. This is the first documented case of a genetically engineered animal breeding in the wild.

Despite Brazil’s ban on sales of the fish, local farms keep breeding them, and stores all over the country sell them as pets. They may soon colonize other parts of the country. Isolated individuals were spotted in ponds and streams in south and northeast Brazil in 2020.

The abstract of the paper is reproduced below. A further article in Science is available here:

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Third World Network


The fluorescent introduction has begun in the southern hemisphere: presence and life-history strategies of the transgenic zebrafish Danio rerio (Cypriniformes: Danionidae) in Brazil

André Lincoln Barroso Magalhães, Marcelo Fulgêncio Guedes Brito & Luiz Gustavo Martins Silva (2022),


Transgenic ornamental fish that fluoresce are becoming popular in the aquarium trade worldwide. Some transgenic zebrafish (TZF) records in natural water bodies have been published, but there are no data on their biological attributes in the new areas. This study aimed to evaluate the distribution, trophic ecology, and reproductive condition of the non-native TZF in headwater creeks located in the largest Brazilian ornamental aquaculture center. Insect fragments – identified as chitinous material in the ‘false stomach’- and aquatic insects were the most consumed item. TZF adults were found in breeding conditions during almost all sampling periods. The Gonadosomatic Index of females and males showed peaks during the rainy season and matched with the rising water levels. Breeding females and males were found at small body sizes, indicating early maturation, and these transgenic females produced a moderate amount of small oocytes. Sex-ratio assessment showed that females and males had the same frequencies in one site, while females were significantly more frequent than males at another location. Management recommendations, such as utilization of best management practices (e.g. screens on outlets), not using unapproved genetically modified organisms in aquaculture, and awareness with fish farmers about transgenic animals, are suggested to avoid new introductions.

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