Import and keep of crustaceans in freshwater aquaria – risks posed to biodiversity in Norway


Report no: 2021:02

Published: 15.02.2021

Key message:

Crustaceans can spread pathogenic organisms. This is primarily why importing and keeping crustaceans in aquariums can pose a threat to biodiversity in Norway.

This is the conclusion from the Norwegian Scientific Committee for Food and Environment (VKM) in a risk assessment of the negative impact of importation and keeping of freshwater crustaceans. The assessment was commissioned by the Norwegian Environment Agency.

Crustaceans as pets

VKM assessed species of crayfish, crabs and shrimps that are currently in trade in Norway, in addition to species that are likely to be in trade within the next ten years.

Many of the species are kept separately in special setups, but especially shrimps are kept in ordinary aquariums as decorative and useful pets for removing algae. It is estimated that several thousand people in Norway keep different kinds of freshwater crustaceans as pets.

Ecological risk

VKM assessed 112 different species of crustaceans kept in freshwater aquariums: 38 species and genera of crayfish, 28 species of genera of crabs and 45 species of shrimps. In addition, one species of saltwater crab was included in the assessment.

“Five of the crayfish species we’ve assessed are able to establish and spread in Norway today. There is a high risk that these species can have a negative impact in Norwegian biodiversity through ecological effects like competition and predation,” says Gaute Velle, Scientific Leader of the project group.

The species in question are Faxonius virilis, Faxonius spp., Procambarus clarkii, P. virginalis and Pacifastacus leniusculus.

Were these species to be released or escape from the aquarium, they could thrive in Norwegian nature, and out-compete the native noble crayfish. They could also have a negative impact on the already threatened amphibian populations, and cause negative cascading effects on the ecosystem,” adds Velle.

Seven species of crayfish, one species of crab and two species of shrimps were assessed to pose a medium risk.

“It is unlikely that the species associated with a medium risk are able to survive for long in the Norwegian nature, but the likelihood of establishment and negative effects will increase with increasing temperatures,” Velle explains.

Risk associated with hitchhiking organisms

Most of the species VKM has assessed pose little threat as they are not able to survive in Norwegian nature. However, many of the species can still carry diseases that can survive and spread without the original host.

The Norwegian law on food production and food safety lists four pathogenic organisms as potential threats in Norway: Aphanomyces astaci which causes crayfish plague, white spot syndrome virus (WSSV) which causes white spot disease, Taura syndrome virus which causes Taura syndrome, and Yellow head virus genotype 1 which causes Yellow head disease. These were assessed individually regarding the threat they pose in relation to the importation and keeping of freshwater crustaceans.

VKM concludes that primarily A. astaci and WSSV are of concern in this regard.

25 species of crayfish were assessed to pose a high risk in relation to spreading of A. astaci and WSSV, while another 13 species of crayfish pose a medium risk in this regard. Four species of crabs and 14 species of shrimps were found to pose a medium risk, while 25 and 31 species respectively pose a low risk regarding the spread of these diseases.

“These pathogenic organisms can spread through both live and dead hosts, as well as by water. The likelihood that they spread is therefore greater than for the crustacean hosts, and the consequences are also far more severe. Our conclusion is therefore that the disease-causing organisms pose the biggest threat in relation to importing and keeping freshwater crustaceans,” says Velle.

According to the Norwegian Regulation on Alien Organisms, it is forbidden to import species that can survive temperatures below 5°C. Organisms that cannot survive are exempt. Velle points out that this regulation does not protect against spreading of the pathogenic organisms that the crustaceans might carry.

Risk-reducing measures

An important measure to reduce the risk of importing and keeping crustaceans is to ensure that neither live or dead individuals, eggs or aquarium water are discarded in nature. Different treatments, to ensure that both water and gear are safe, is discussed in the report.

The disease-causing agents are present in the water where the crustaceans live. Therefore, another risk-reducing measure is to diagnostically test for these agents in the water which they are imported in, or during quarantine.

The assessment is approved by the VKM Panel on Alien Organisms and Trade in Endangered Species (CITES).


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