26 June 2020

Link roundup for June 2020

Friend of the blogGünter Vogt has a write-up for non-specialists about Marmorkrebs at the Atlas of Science.

• • • • •

Great Lakes Now has a story about the efforts to keep invasive species out of the Great Lakes. It starts with Marmorkrebs being banned in Michigan, saying that the new policy made headlines. Other crayfish are discussed more in the article, mostly Louisiana red swamp crayfish.

24 June 2020

Rusch and colleagues, 2020

NeoBiota volume 58 cover featuring crayfish image
Rusch JC, Mojžišová M, Strand DA, Svobodová J, Vrålstad T, Petrusek A. 2020. Simultaneous detection of native and invasive crayfish and Aphanomyces astaci from environmental DNA samples in a wide range of habitats in Central Europe. NeoBiota 58: 1-32. https://doi.org/10.3897/neobiota.58.49358


Crayfish of North American origin are amongst the most prominent high-impact invasive invertebrates in European freshwaters. They contribute to the decline of European native crayfish species by spreading the pathogen causing crayfish plague, the oomycete Aphanomyces astaci. In this study we validated the specificity of four quantitative PCR (qPCR) assays, either published or newly developed, usable for environmental DNA (eDNA) screening for widely distributed native and non-native crayfish present in Central Europe: Astacus astacus, Pacifastacus leniusculus, Faxonius limosus and Procambarus virginalis. We then conducted an eDNA monitoring survey of these crayfish as well as the crayfish plague pathogen in a wide variety of habitat types representative for Central and Western Europe. The specificity of qPCR assays was validated against an extensive collection of crayfish DNA isolates, containing most crayfish species documented from European waters. The three assays developed in this study were sufficiently species-specific, but the published assay for F. limosus displayed a weak cross-reaction with multiple other crayfish species of the family Cambaridae. In the field study, we infrequently detected eDNA of A. astaci together with the three non-native crayfish species under examination. We never detected eDNA from A. astaci together with native crayfish, but in a few locations eDNA from both native and non-native crayfish was captured, due either to passive transport of eDNA from upstream populations or co-existence in the absence of infected crayfish carriers of A. astaci. In the study, we evaluated a robust, easy-to-use and low-cost version of the eDNA sampling equipment, based mostly on items readily available in garden stores and hobby markets, for filtering relatively large (~5 l) water samples. It performed just as well as the far more expensive equipment industrially designed for eDNA water sampling, thus opening the possibility of collecting suitable eDNA samples to a wide range of stakeholders. Overall, our study confirms that eDNA-based screening for crayfish and their associated pathogen is a feasible alternative to traditional monitoring.

Keywords: crayfish plague • eDNA monitoring • eDNA sampling methods • quantitative PCR • TaqMan assay validation

Open access

01 June 2020

Bans on Marmorkrebs could hurt research

If you want to talk about a success story in invasive species management, you might want to talk about the province of Alberta, Canada. Alberta like to boast that it is rat free.

But I can let you in on a little secret. I’ve seen rats in Alberta many times, when I was a student at the University of Lethbridge. Last year, the university got a government grant to build a new rat facility.

So there was a disconnect between declaring “We don’t want this invasive species!” and actually having that species in research labs. The two situations are separable.

I am not sure if that separation will exist for Marmorkrebs, though.

This year, Saskatchewan and Michigan banned Marmorkrebs. Ontario and some other US states are thinking about it.  I have been thinking about what the bans might do for Marmorkrebs research. There are several issues.

First, researchers in those states and provinces might not be able to have Marmorkrebs at all. Some of the Marmorkrebs legislation does not appear to have exceptions for bona fide academic researchers.

For example, the Canadian province of Manitoba has a law against owning all crayfish species, not just Marmorkrebs. In the course of doing research, I once asked officials in Manitoba if a researcher might keep crayfish, and was told, “No.”

Second, if the laws work as intended, fewer people in general would have Marmorkrebs. It’s possible that some pet owners would stop keeping Marmorkrebs, even in jurisdictions where it is completely legal. Aquarium keepers might see “the writing on the wall” and decide not to keep Marmorkrebs any more, in case they become illegal.

This could affect researchers, too. When an animal is widely available in the pet trade, it’s easy for researchers to get them, either for a one-off study or to start a colony.

Crayfish researchers have a long history of asking for regulation of the movement and trade of crayfish. It has been hard to get those regulations, but it would be a shame if new laws were not nuanced enough to allow original research.

If there can be rats in labs in Alberta, we should be able to have crayfish in labs, too. After all, an escaped crayfish in a university building probably has a harder time getting far than an escaped rat would.

Poster from here.

28 May 2020

Velisek and colleagues 2020b

Velisek J, Stara A, Zuskova E, Chabera J, Kubec J, Buric M, Kouba A. 2020. Effects of chloridazon on early life stages of marbled crayfish. Chemosphere 257: 127189. https://doi.org/10.1016/j.chemosphere.2020.127189


The effects of chloridazon exposure at concentrations of 2.7 μg/L (maximal real environmental concentration in the Czech Republic), 27 μg/L, 135 μg/L and 270 μg/L on early life stages of marbled crayfish (Procambarus virginalis) were evaluated. Significantly higher glutathione S-transferase activity and reduced glutathione level was observed at all tested concentrations of chloridazon compared with the control. Chloridazon in concentrations 27, 135 and 270 μg/L caused delay ontogenetic development and slower growth. Histopathological changes in hepathopancreas were found in two highest tested concentrations (135 μg/L and 270 μg/L). Crayfish behaviour was not altered in control vs. exposed animals, while the activity parameters tend to decline with increasing chloridazon concentrations.

Keywords: antioxidant biomarkers • behaviour • early ontogenetic • pyridazinone • toxicity

26 May 2020

Marmorkrebs illegal in Saskatchewan

Map of Canada with Saskatchewan highlightedLast month, Saskatchewan became the first Canadian province to specifically prohibit Marmorkrebs, according to this news article.

“New for this year is a regulatory change that prohibits the collection of crayfish from any Saskatchewan waterbody, as well as prohibitions related to their use as bait for angling,” (Environment Minister Dustin) Duncan said.

Rusty crayfish and marbled crayfish were added to the province’s prohibited species list in April.

I am trying to find the specific policy on Saskatchewan’s Ministry of Environment, but I found nothing through a generic Google search. Will continue to search. The difficulty in finding news about this provincial legislation from last month stands in sharp contrast to the ease of finding about the new policy in Michigan just days ago. Ten points from Saskatchewan.

I found it in the April 3 edition of the Saskatchewan Gazette (PDF) (Table 10 on page 193, to be specific) in a list of prohibited fish.

Yes, a crayfish can be legally considered a fish. Policy is not always about entirely accurate biology. You should read about the legal battles that erupted when scientists started to realize that a whale was not a fish.

External links

Saskatchewan remains free of zebra and quagga mussels
Sakskatchewan Ministry of Environment
Saskatchewan Gazette, 3 April 2020 (PDF)
Trying Leviathan: The Nineteenth-Century New York Court Case That Put the Whale on Trial and Challenged the Order of Nature

23 May 2020

Marmorkrebs in The Times

This a Jeopardy! style post. The answer is:

17 Marbled crayfish or marmorkrebs (Procambarus virginalis). It makes clones of itself from eggs unfertilised by sperm.

The question is one of twenty in today’s Saturday Quiz in The Times!

External links

The Times Saturday Quiz: May 23, 2020

15 May 2020

No Marmorkrebs in Michigan

As expected, Michigan has become the fourth American state (that I know of) to specifically prohibit Marmorkrebs.

This article is quite detailed, and includes a FAQ about what to do if you have marbled crayfish already. To wit:

  • Dispose of it humanely
  • Do not flush it
  • Don’t sell it to someone in another state (that’s also illegal)

It is probably the best resource I have seen from any state that has regulated Marmorkrebs so far.

Update, 18 May 2020: Associated Press (AP) has put this out as one of their syndicated wire stories (e.g., here and here), which is surprisingly wide coverage.

Update, 23 May 2020: Michigan has definitely done the best job of publicizing the policy on Marmorkrebs, probably because of the AP wire story. It’s been reprinted and redistributed by more news organizations than I’ve ever seen for a state. ANd it’ not just reprints. There is some journalism here. For instance, this is a new quote, I think:

“It’s pretty popular in the pet trade, and the decision was not made lightly in terms of it will impact some of the pet trade industry,” said Lucas Nathan, aquatic invasive species coordinator for the Michigan Department of Natural Resources.

As sometimes happens when Marmorkrebs makes the news, I’m happy to see a picture I took being used to illustrate the species.

The coverage here made me laugh:

The (Department of Natural Resources) warns against flushing them down toilets because they may survive. What the DNR probably MEANT to say is, “that's how you get giant self-cloning crayfish roaming the sewer system.”

Related posts

Michigan considering prohibiting Marmorkrebs

External links

Invasive, self-cloning marbled crayfish now a prohibited species in Michigan (Michigan Department of Natural Resources)

Marbled crayfish added to Michigan’s prohibited species list (Associated Press)

Michigan adds invasive marbled crayfish to prohibited species list

Michigan bans marbled crayfish, which reproduces rapidly by genetic cloning

Michigan Outlaws Self-Cloning “Marbled Crayfish”

Self-cloning marbled crayfish banned from Michigan

Great Lakes Commission

Marbled crayfish placed on Michigan’s prohibited species list