Greedy goldfish cause massive damage in the wild

They’ll fool you with their googly eyes and cute chubby bellies, but goldfish are unknowingly one of nature’s greatest threats. How? Due to the fact that they have been released into the wild by their owners.

The pet trade is responsible for a third of all aquatic invasive species as pet owners release unwanted wildlife into the wild. While owners generally believe this is a humane option for the pet, it has been shown that it could have catastrophic impacts on native biodiversity.

To better understand how these invasive species respond in the wild, a study looked at two commonly traded fish: the golden (Carassius auratus) and the white cloud mountain roach (Tanichthys albonubesThe goldfish was domesticated more than 1,000 years ago and has an extensive global invasive distribution, while the white cloud has only been marketed in recent decades and has relatively limited invasive ubiquity.

Goldfish and White Clouds belong to the Cyprinidae family of carp, a highly successful group native to Europe and Asia, but an invasive pest in parts of Africa, Australia, and the United States.

To assess dispersal properties, three behaviors were compared between the two species, as well as with two analogous natives – the stonecreeper (Barbatula-barbatula) and the common whitefish (Phoxinus-phoxinus)† These behaviors were per capita feeding rates, foraging interactions (being fed together), and level of boldness.

Goldish had the highest maximum feed rates of the four species, while white clouds had the lowest. In the foraging experiments, neutral interactions were observed for all four species, with goldfish still having the highest feeding rates regardless of which fish they shared the environment with. Goldfish also showed the greatest audacity, were more active during the trials and were more inclined to approach new objects.

Relative invasion risks (RIR) of these three behaviors were assessed. Goldfish were considered to be of the highest risk and required high priority for management, reflecting the extensive invasive history of this fish.

“Our research suggests that goldfish pose a triple threat,” said lead author Dr James Dickey of Queen’s University Belfast, Northern Ireland. “Not only are they readily available, but they combine insatiable appetites with daring behavior.

“While northern European climates often present a barrier to non-native species surviving in the wild, goldfish are known to be tolerant of such conditions and can pose a real threat to native biodiversity in rivers and lakes, eating up the resources that other species depend on.

“Our research highlights that goldfish pose a high risk, but we hope the methods developed here can be used to assess others in the pet trade in Ireland and beyond.

“Most likely to release readily available species, so limiting the availability of potentially impactful species, along with better training for pet owners, is one solution to prevent harmful invaders from settling in the future.”

The results of the study were published in NeoBiota

Giant goldfish found in WA waterways represent a huge problem for native wildlife. Credit: Murdoch University



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