31 December 2020

2020 was not the best year for Marmorkrebs research

As if there weren’t enough reasons to hate 2020, the number of Marmorkrebs papers published was down from the last two years.


Graph showing journal articles about Marmorkrebs from 2003 to 2020.


It’s impossible to tell if the dip in number of publications is the result of a global pandemic or just the regular up and down you see in these sorts of data.


Marmorkrebs did make international news again this year, mainly because a cloning crayfish invading a cemetery is a great story for Halloween. That was the first record of Marmorkrebs in Belgium, but another first record – on the island of Taiwan – made for fewer news stories but may have been more important in showing how Marmorkrebs are spreading globally.


On the legislative front, Marmorkrebs (and other crayfish) were banned in Japan, the American state of Michigan, and the Canadian province of Saskatchewan. Several jurisdictions like North Carolina and Ontario are considering following suit.


Update, 4 January 2021: Have just found another paper with a 2020 release (Stein and colleagues, 2020), so the count shown in the graph is one too low.


Related posts


2008 was the best year ever for Marmorkrebs research

2009 was tied for the best year ever in Marmorkrebs research

2010 was the best year ever for Marmorkrebs research

2011 was not the best year ever for Marmorkrebs research

2012 was an average year for Marmorkrebs research

2013 was the second best year ever for Marmorkrebs research

2014 was a good year for Marmorkrebs research

2015 was the best year ever for Marmorkrebs research

2016 was the best year ever for Marmorkrebs research

2017 was the second best year ever for Marmorkrebs research

2018 was the second best year ever for Marmorkrebs research

2019 was the second best year ever for Marmorkrebs research

Kawai and Patoka, 2020

Cover of The Journal of Crustacean Biology, volume 40, number 6
Kawai T, Patoka J. 2020. Morphology of gastric mills and mandibles of New Guinean parastacid crayfishes, with comparisons with other Astacidea (Decapoda). Journal of Crustacean Biology 40(6): 692-703. https://doi.org/10.1093/jcbiol/ruaa081




Knowledge of the morphological features of crayfishes native to New Guinea is limited in many cases, the internal morphology, gastric mills, and mandibles of six species of Cherax species (Decapoda: Astacidea: Parastacidae) from this island were described and illustrated. The measurements were compared with those of parastacid crayfish from Madagascar and New Zealand, with Enoplometopoidea from coral reefs, and Nephropidea from deep sea. Characters peculiar to the family Parastacidae were found both in gastric mills and mandibles, and differences between the morphology of mandibles in freshwater and marine species from the infraorder Astacidea were found. Relationships between functional morphology and feeding behaviour were discussed.


Keywords: None provided.

26 December 2020

Laurenz and colleagues, 2020b

International Aquatic Research cover
Laurenz J, Brendelberger H, Lehmann K. 2020. Effects of Diclofenac on the embryonic development of freshwater crayfish. International Aquatic Research 12(4): 255-265. https://doi.org/10.22034/iar.2020.1905475.1074, http://submission.intelaquares.com/article_677597_0.html




In recent years, there has been increasing concern about the ecotoxicological consequences of the drug Diclofenac on freshwater organisms. Influences on the largest freshwater invertebrates, the freshwater crayfish, are especially interesting in the context of cascading effects due to their important role as keystone species. In this study, lethality, influences on body weight, embryonic development and histological changes in embryos of marbled crayfish (Procambarus virginalis) as well as noble crayfish (Astacus astacus) were investigated in response to their exposure to different concentrations of Diclofenac. Additionally, the suitability of marbled crayfish as a model organism for endemic freshwater crayfish was established when studying the effects of Diclofenac. For both species, lethal effects started at concentrations of 10.24 mg/L Diclofenac, weight was not affected, embryonic development slowed down from concentrations of 0.16 mg/L and histological changes were visible from concentrations of 0.64 mg/L. The similarity of LOEC (Lowest Observed Effect Concentrations) between the two species showed that marbled crayfish can serve as a model for native crayfish when investigating the effects of exposure to Diclofenac. 


Keywords: marbled crayfish • noble crayfish • juveniles • Diclofenac • embryonic

Open access

22 December 2020

Vogt 2021

Hydrobiologia VOlume 848 Number 2 civer featuring Marmorkrebs
Vogt G. 2021. Evaluation of the suitability of the parthenogenetic marbled crayfish for aquaculture: potential benefits versus conservation concerns. Hydrobiologia 848(2): 285298. https://doi.org/10.1007/s10750-020-04395-8




The parthenogenetic marbled crayfish, Procambarus virginalis, is currently being discussed as a promising new candidate for aquaculture that could supply people in developing countries with high-quality protein and income. The main advantage of marbled crayfish is parthenogenetic reproduction. Comparison of growth between marbled crayfish and red swamp crayfish, Procambarus clarkii, the leading species in crayfish aquaculture revealed inferior body size and considerably slower growth in marbled crayfish. Only a very small proportion of the production would meet the size requirement of the international market and could serve as a cash crop. Aquaculture for local markets in extensive outdoor systems is probably economically feasible in developing countries, but the highly invasive and competitive marbled crayfish could easily escape from such sites, invade natural ecosystems and impair the autochthonous fauna and flora. Culture in closed indoor systems would be a safe alternative but this cost-intensive approach is economically not profitable. Because of small body size and slow growth, conservation concerns, and economic reasons, the marbled crayfish is considered unsuitable for aquaculture. It should not be spread around the globe for aquaculture and sustainable fisheries as was earlier done with the congeneric Procambarus clarkii, resulting in devastating ecological effects in numerous countries.


Keywords: marbled crayfish • aquaculture • conservation • growth • Procambarus clarkii


Update, 3 January 2020: The journal   added these notes on the cover illustration.


The marbled crayfish Procambarus virginalis is the only known parthenogenetic freshwater crayfish. It was detected in 1995 in the German aquarium trade and is now widespread among aquarists. It is also used as a research model in many laboratories. Releases have led to the establishment of wild populations in 18 countries in Europe, Africa and Asia. Due to parthenogenetic reproduction, it was suggested to establish this species in aquaculture. However, because of relatively small body size, conservation concerns resulting from high invasiveness, and economic reasons the marbled crayfish is considered unsuitable for aquaculture. Photograph by Chris Lukhaup.

Parthenogenesis 2020 stories

Christmas – or, as we crustacean researchers like to call it, Crustmas – is one of the best times of year to talk about Marmorkrebs, because many interested in the idea of virgin birth at this time of year.


No idea why. 😉


Here are a couple of good articles about parthenogenesis making the rounds this holiday season.

Virgin births from parthenogenesis: How females from some species can reproduce without males: I can’t help but wonder if this article from The Conversation may have inspired the SyFy article below, given that both feature Asian water dragons at the top of the page. No Marmorkrebs.


Some unnatural creatures can replicate themselves without even trying, no mate required: This SyFy Wire piece looses points for calling parthenogenesis shaming in the title and no Marmorkrebs. Otherwise pretty good.

P.S.—Sadly, about that Asian water dragon? It has joined its ancestors in the great beyond.

18 December 2020

North Carolina eyes Marmorkrebs ban

North Carolina is considering banning Marmorkrebs, along with several other crayfish species, according to the Smoky Mountains News.


A list of proposed changes to regulations from the state’s Wildlife Resources Commission include (emphasis added):

Add the African Longfin Eel, Creole Painted Crayfish, Bigclaw Crayfish, Marbled Crayfish or Marmorkrebs, Applesnail, Olive Mysterysnail, European Eel, Oriental Weatherfish, Brown Hoplo, Yellow Bass, Shortfin Eel, Crucian Carp, Prussian Carp, European Perch, European Minnow and Amur Sleeper to the list of species for which it is unlawful to transport, purchase, possess, sell or stock in the public or private waters of North Carolina. These non-native species can become invasive and nuisance species in North Carolina.


Public comment is running until 1 February 2021. My impression is that usually by the time these things are proposed for regulation, it’s unusual for the proposals to change.


External links


North Carolina Wildlife Resource Commission proposed regulations (PDF)

06 December 2020

Wiśniewski and colleagues, 2020

Wiśniewski K, Szarmach D, Poznańska-Kakareko M. 2020. The role of abiotic and biotic factors in interspecific competition of Polish crayfish – comprehensive literature review. Oceanological and Hydrobiological Studies 49(4): 428-441. https://doi.org/10.1515/ohs-2020-0038


Invasive species are those that have been transferred by humans out of their natural range. Native crayfish species in Polish waters include: Astacus astacus and Pontastacus leptodactylus, whereas invasive species are: Pacifastacus leniusculus, Faxonius limosus, Procambarus clarkii and Procambarus virginalis. The objective of this study was to determine how abiotic and biotic environmental factors contribute to interspecific competition of Polish crayfish based on the available literature. Abiotic factors affecting the interspecific competition include tolerance to extreme pH values, calcium ion content, temperature, oxygenation, water salinity, preferred substrate and the type of water bodies. Biotic factors are, inter alia, pathogens, food base, plant cover and interactions in the prey–predator system, as well as interactions between crayfish species. The most important abiotic factors are water temperature and oxygenation, while the most important biotic factor is the crayfish plague – a deadly disease for native species. Each invasive species has a different set of traits and adaptations that enable a successful invasion. However, a successful invasion of a given species is not determined by one, but many adaptations that coexist.

Keywords: invasive species • native species • agonistic interactions • negative impact

28 November 2020

Weiperth and colleagues 2020

Weiperth A, Bláha M, Szajbert B, Seprős R, Bányai Z, Patoka J, Kouba A. 2020. Hungary: a European hotspot of non-native crayfish biodiversity. Knowledge and Management of Aquatic Ecosystems 421: 43. https://doi.org/10.1051/kmae/2020035


There is a long history of crayfish introductions in Europe and numbers keep increasing. In Hungary, spiny-cheek crayfish Faxonius limosus, signal crayfish Pacifastacus leniusculus, red swamp crayfish Procambarus clarkii, marbled crayfish P. virginalis and Mexican dwarf crayfish Cambarellus patzcuarensis have become established. Here we report on monitoring at two localities with novel crayfish assemblages closely linked to releases associated with the pet trade. Florida crayfish Procambarus alleni were recorded from the Gombás brook near Vác living in syntopy with the established spiny-cheek crayfish. Dozens of Florida crayfish individuals including egg-carrying females have been detected. The short lifespan of this species and its documented presence including two overwintering in at least two years suggests possible establishment. However, the lack of juvenile records calls for further monitoring as long-term propagule pressure cannot be ruled out. We also identified a single marbled crayfish in the Danube floodplain at the end of the monitoring campaign. The second locality (Városliget thermal pond in Budapest) harbours an even more diverse crayfish assemblage. Here, we identified numerous red swamp and marbled crayfish in syntopy with dozens of monitored redclaws Cherax quadricarinatus and seven individuals of New Guinean Cherax species − C. holthuisi, C. snowden, as well as two scientifically undescribed species. These findings clearly indicate the attractiveness of urban and, especially, thermal waters for the release of even expensive aquatic pets and highlight the hitherto poorly known biodiversity of New Guinean crayfish species.

Keywords: pet trade • biological invasion • animal release • invasive species • thermal water

Weiperth and colleagues 2015

Pisces Hungarici Volume 9 cover
Weiperth A, Csányi B, Gál B, György ÁI, Szalóky Z, Szekeres J, Tóth B, Puky M. 2015. Egzotikus rák‐, hal‐ és kétéltűfajok a Budapest környéki víztestekben. Pisces Hungarici 9: 65-70. http://haltanitarsasag.hu/ph9/Weipert_et.al_Pisces.Hungarici_2015b.pdf


Our recent faunistic surveys revealed some new exotic crayfish, fish and amphibian species recorded for the first time from the River Danube, as well as from several streams and warm water ponds located at public areas in Budapest. The most important discovered species are the red swamp crayfish (Procambarus clarcii (sic) Girard, 1852) originating from North America, several fish species belonging to different families (Callichthyidae, Cichlidae, Cyprinidae, Doradidae, Poecilidae) and originating from Africa, Asia, Central and South America, and the African dwarf frog (Hymenochirus curtipes Noble, 1924). All these species are presumably released by aquarists into the warm‐water ponds and by the floods into the Danube river system. An adult southern striped raphael (Platydoras armatulus Valenciennes, 1840) and armoured catfish (Megalechis thoracata Valenciennes, 1840) were caught in the water system of the River Danube after the record flood in 2013. Several individuals of blue streak hap (Labidochromis caeruleus Fryer 1956) and doctor fish (Garra rufa Heckel, 1843) were found in the Lake Városliget. Furthermore, adults, subadults and juveniles of convict cichlid (Amatitlania nigrofasciata Günther, 1867), molly (Poecilia sp.) and swordtail (Xiphophorus sp.) appeared in all major urban warm‐water ponds in Budapest. Consequently, we presume that these fish species are not only surviving but also breeding in these water bodies.

Keywords: pet trade • stocking • thermal water • Danube

21 November 2020

Citizen science detected Marmorkrebs

Observations.org logo
I’d read a lot of news articles in late October about the discovery of Marmorkrebs in Brussels. Ariana Remmel managed to add an important detail I hadn’t seen before: that the Marmorkrebs were spotted as the result of citizen science.

A research team led by Kevin Scheers... first realized there might be a problem when he saw a marbled crayfish photo misidentified on a citizen science website called Waarnemingen.be.

The site is a local iteration of Observations.org, a website for recording observations of species in nature.

This is important, because as Marmorkrebs becomes more and more widespread, I am deeply worried researchers will lose interest in documenting where they are. Good monitoring is important to management and without it, the spread of Marmorkrebs – already difficult to detect – will be even harder.

External links

Turkey troubles and cantankerous crustaceans

14 November 2020

Why sex? (Why not?)

Quanta Magazine has a nice article about the evolution of sexual reproduction. I had hoped it might also focus on cases where sex is lost, as in Marmorkrebs, but worth a peek regardless.

External links

Why Sex? Biologists Find New Explanations.

13 November 2020

Laurenz and colleagues 2020

Water, Air, & Soil Pollution cover
Laurenz J, Lietz L, Brendelberger H, Lehmann K, Georg A. 2020. Noble crayfish are more sensitive to terbuthylazine than parthenogenetic marbled crayfish. Water, Air, & Soil Pollution 231: 548. https://doi.org/10.1007/s11270-020-04921-3




We investigated the sensitivity of two freshwater crayfish species (Astacus astacus and Procambarus virginalis) during embryonic development to chronic exposure to the herbicide terbuthylazine under laboratory conditions. The assessed parameters included time of embryonic development, survival rate, hatching weight and histopathology of hepatopancreas. LC50 (median lethal concentration) and ED50 (median effective concentration) were estimated. We were able to determine effects of terbuthylazine for every investigated parameter. For noble crayfish, the LC50 value after 45 days was 0.11 mg/L, and the histology of the hepatopancreas showed effects starting from 0.025 mg/L. Other parameters revealed effects starting at concentrations of 1.6 mg/L for weight and 6.4 mg /L for embryonic development time and hatching rate. Marbled crayfish only showed effects concerning the hatching rate and survival rate at concentrations without a clear dose-effects curve. As a conclusion, our data shows the risk of terbuthylazine in existing concentrations in freshwater ecosystems to non-target organisms and also the need of toxicological studies on directly affected species in addition to the use of model organisms.


Keywords: marbled crayfish • noble crayfish • juveniles • terbuthylazine • embryonic



07 November 2020

Lost in translation

"The Interpreter" movie poster
It’s been a busy few weeks here on the Marmorkrebs newswatch. 


Three new countries added to the list of known introductions: Belgium, Poland, and the island of Taiwan.


One country banning most crayfish, including marbled crayfish: Japan.


What is nagging me after these last few weeks is this question: how much am I missing?


The news about crayfish in Poland had been out for some time. I missed it because it wasn’t in English. I stumbled upon when I was updating the marbled crayfish Wikipedia page


The news about Marmorkrebs in Taiwan and new regulations in Japan could have easily slipped by me if they hadn’t been reported on English news websites.

I have strong suspicions that there are many more introduced populations out there that aren’t getting into the scientific literature, because marbled crayfish introductions have happened so much that they aren’t considered notable. And I’m not finding them, because they are not being reported in English.

I don’t think I can set up Google alerts for every language, and I'm not even sure what people would call Marmorkrebs in most languages. So I don’t know how to fix this yet.

06 November 2020

Marmorkrebs’ second Asian invasion

Map showing location of Taiwan island in Asia

Mere days after Marmorkrebs made international news by invading a cemetery in Belgium, they appear set to take over a park in Taiwan Island. 


This is only the third time Marmorkrebs have been reported in Asia, and this seems to be the most substantial population so far. Previous discoveries of Marmorkrebs in Japan consisted of only single individuals.


There are more individuals in this one bucket fron Daan Forest Park than have been discovered in all of Japan.


Perhaps the one piece of good news is that it sounds like these are isolated, managed park ponds. If authorities want to get serious, they might be able to remove all of them (emphasis added):


Wang Shu-ya, director of the Youth Park Management Office said that park staff have been cooperating with the Friends of Da’an Park Foundation to trap the crayfish. Wang said that the situation has improved slightly, however, they have not ruled out the possibility of draining the ponds in the future to completely remove the pests.

One interesting trend I am starting to notice in news coverage is the use of the term “mutant.” Strictly speaking, yes, Marmorkrebs are mutants. But many other similar organisms are not described that way. 


An all-female species of whiptail lizards are not called “mutants.” 


Amazon mollies, reasonably popular aquarium fish, are all female and have even weirder reproduction than Marmorkrebs (sperm stealing?!) and they aren’t called “mutants.” 


What is it about Marmorkrebs that leads people to describe them this way?

The main news article is quite good, although I am surprised it uses the old species name and not Procambarus virginalis, which has been widely adopted by the community.


I have updated the map of Marmorkrebs introductions.


External links


Mutant invasive crayfish found infesting ponds in Taipei City park


Daan Forest Park crisis! Invasion of exotic species "Marbled crayfish"  (Video in Chinese; title loosely translated)

02 November 2020

Marmorkrebs banned in Japan

Flag of Japan
A wire story from Jiji Press is reporting that Marmorkrebs — along with many other nonnative crayfish — are being effectively outlawed in Japan.


Raising and selling of all nonnative species of crayfish, excluding red swamp crayfish, became prohibited in principle in Japan on Monday... Species newly added to the list are foreign crayfish belonging to four groups, including marbled crayfish, which reproduce without fertilization(.)


I’m not sure what “prohibited in principle” means. Unfortunately, the article does not give a source for this story, meaning I will probably have to spend some time trying to search and translate Japanese government websites.




It seems to be this press release from the Ministry of the Environment. If Google Translate can be trusted, this PDF says:

All species of the crayfish family, America Among the species belonging to the crayfish family, the United States
Other than crayfish (Procambarus clarkii), Asian crayfish
Other than Japanese crayfish (Cambaroides japonicus) among the species belonging to
All species of crayfish, Minamizari

I’m surprised the Jiji Press story specifically mentioned Marmorkrebs, since it is not mentioned by name in the press release.


It’s been a busy week for Marmorkrebs news.


External links


About partial revision of the law enforcement regulations concerning 14 kinds such as Hayatogefu Shiari designated as a specific alien organism based on the Alien Organism Law


Raising, Selling of Nonnative Crayfish Banned in Japan (also at Nippon.com)

31 October 2020

Marmorkrebs map update

I am experimenting with a change to the map of Marmorkrebs introductions. A new paper (Son et al. 2020) describes a location where Marmorkrebs seem to have been eradicated with some certainty.


One of the first recorded localities of P. virginalis — a cascade of ornamental ponds in Odesa, where three live individuals were observed in June 2015 — was also surveyed. Shortly after that discovery, those reservoirs underwent multi-stage cleaning and renovation. During the winter-spring period of 2017–2018, a consistent complete drying of all ponds was carried out. In the course of those activities, large animals such as fish and turtles, including invasive red-eared sliders Trachemys scripta (Schoepff, 1792), were placed in aquariums and released back later. Conversely, soft sediment accumulated at the bottom along with benthic invertebrates was removed from these water bodies. As a result, we can confidently assert that P. virginalis was eradicated in that locality.


Günter Vogt emailed me to say that there are no known active populations in Sweden or the Netherlands.


I have added a new symbol to the map: a vertical line on top of a horizontal line. This is a symbol used in Japanese maps to indicate a graveyard. I am aware that maps like this sometimes can solidify hypotheses or tentative claims into “fact,” so I am not sure right now what criteria to use for adding an “removed” symbol to the map.


The map is, as always, a work in progress.




Son MO, Morhun H, Novitskyi RO, Sidorovskyi S, Kulyk M, Utevsky S. 2020. Occurrence of two exotic decapods, Macrobrachium nipponense (de Haan, 1849) and Procambarus virginalis Lyko, 2017, in Ukrainian waters. Knowledge and Management of Aquatic Ecosystems 421: 40. https://doi.org/10.1051/kmae/2020032

Son and colleagues, 2020

Knowledge and Management of Aquatic Ecosystems coverSon MO, Morhun H, Novitskyi RO, Sidorovskyi S, Kulyk M, Utevsky S. 2020. Occurrence of two exotic decapods, Macrobrachium nipponense (de Haan, 1849) and Procambarus virginalis Lyko, 2017, in Ukrainian waters. Knowledge and Management of Aquatic Ecosystems 421: 40. https://doi.org/10.1051/kmae/2020032




New information on the occurrence of two alien decapod crustaceans, Macrobrachium nipponense and Procambarus virginalis, was summarized for Ukraine. The invasive potential of both species was estimated in the context of local environmental and socio-economic issues. Their history as non-native species is marked by the early use of alien decapods as a natural resource by local residents. Both intentional and unintentional introductions occurred for M. nipponense, while the ornamental trade was an important source of non-native P. virginalis. New records of M. nipponense and P. virginalis from open freshwater habitats in the Odesa and Kharkiv provinces suggest continuing expansion of these decapods. We conducted a molecular phylogenetic analysis of COI sequences, which confirmed morphological identifications of invasive M. nipponense. This reinforces the presumed pathway of this species, including its pathway from China to south-western Ukraine. Procambarus fallax was found to be paraphyletic in relation to P. virginalis, which was probably caused by analyzing only one mitochondrial gene, which could be impacted by the recent emergence of the latter species.


Keywords: Decapoda • Macrobrachium nipponenseProcambarus virginalis • Ukraine • invasive species



24 October 2020

Poland also has Marmorkrebs

Map of Poland in Europe

While I was busy updating the marbled crayfish Wikipedia page with yesterday’s news that Marmorkrebs had been found in the waters of Belgium, I noticed another country on the list I hadn’t seen before.


Poland. Poland?


Yes. Last month, news reports came out about Marmorkrebs in Poland. And nobody told me! Presumably my automatic email alerts failed because I don’t have alerts for whatever the Polish word for “crayfish” is.


Not only are they in Poland, one article says that these may be amo ng the largest populations. The Polish lakes are estimated to have tens of thousands of individuals.


As usual, I have some fact-checking to do on the news report, since there is no scientific paper yet. Both articles say:


(T)he young produce eggs by themselves after about 2-3 months.


That’s much faster than the reproductive cycle in the literature. From hatching to first reproduction usually takes 7 months (Seitz et al 2005).


One article says:

The lack of males in this species makes it impossible to use pheromone methods or introduce genetically modified males as competition - the scientist explains.


Agree that genetically modified males wouldn’t work. 


I’m not sure what “pheromones” is referring to. I don’t know off the top of my head of any attempt to use pheromones to control crayfish populations. But the lack of males may not be an obstacle, since Marmorkrebs still show sexual behaviour (Vogt et al. 2015). They might still respond to pheromones.


Predatory species of fish also cannot cope with it. Marbled crayfish kills catfish, pike, zander and perch.


This is a weird claim. I don’t know of any fish that has too much of a problem taking out crayfish. Marbled crayfish could kill fish when they’re small, maybe. But this makes it sound like Marmorkrebs are somehow invincible to these fish regardless of size.

The Epicrates Foundation has been doing quite a bit of work on this, working with a nearby national park to try to stem the Marmorkrebs from entering park waters.

Additional: Gregor Kalinkat mentions a 2018 survey in Poland found no Marmorkrebs.

External links


Epicrates Foundation (Facebook)


Raki mutanty już tu są. Niosą zagrożenie koło Włodawy i nie potrzebują do rozmnażania samców (Translation: “Crayfish mutants are already here. They pose a threat near Włodawa and do not need males to breed”)


W naszym regionie odkryto ogromną populację zmutowanych raków. Stanowią one ogromne zagrożenie dla ekosystemu (zdjęcia) (Translation: “A huge population of mutant crayfish has been discovered in our region. They pose a huge threat to the ecosystem (photos)”


Rak marmurkowy zagrożeniem dla Poleskiego Parku Narodowego (Translation: Marbled crayfish as a threat to the Poleski National Park) 




Seitz R, Vilpoux K, Hopp U, Harzsch S, Maier G. 2005. Ontogeny of the Marmorkrebs (marbled crayfish): a parthenogenetic crayfish with unknown origin and phylogenetic position. Journal of Experimental Zoology A 303(5): 393-405. http://dx.doi.org/10.1002/jez.a.143


Vogt G, Falckenhayn C, Schrimpf A, Schmid K, Hanna K, Panteleit J, Helm M, Schulz R, Lyko F. 2015. The marbled crayfish as a paradigm for saltational speciation by autopolyploidy and parthenogenesis in animals. Biology Open 4(11): 1583-1594. http://dx.doi.org/10.1242/bio.014241

23 October 2020

Belgium falls to Marmorkrebs

Map of Europe highlighting Belgium

The Brussels Times is reporting that Marmorkrebs popping up in several locations in Brussels. It’s not clear when they were first spotted, but their success in one location, a cemetery in Antwerp, was enough to warrant coverage.


The map of Marmorkrebs introductions has been updated accordingly.


It’s almost reaching the point where it will be faster to list European countries without Marmorkrebs rather than with.


An article in the Telegraph is paywalled, but I’m not hopeful about it given the preview text says:


 Escaped self-cloning mutant crayfish created in experimental breeding programmes...


No. That’s some bullshit right there. There is no evidence Marmorkrebs were “created” by experiments. It’s a weird myth that seems to have no discernible origin.


Additional, 25 October 2020: The story has made it into a US newspaper. Weirdly, they chose to illustrate the story with what appears to be a signal crayfish (Pacifastacus leniusculus) instead of Marmorkrebs.


External links


Hundreds of self-cloning crayfish invade Antwerp cemetery


Escaped cloned female mutant crayfish take over Belgian cemetery


Self-cloning mutant crayfish take over Belgian cemetery


Mutant crayfish clones take over cemetery after aquarium escape


Self-cloning mutant crayfish are invading a Belgian cemetery


Self-cloning mutant crayfish are invading a Belgian cemetery and will wreak havoc on the local biodiversity if not controlled, expert warns


Honderden rivierkreeften in slotgrachten Schoonselhof (With video clip)


What are marbled crayfish? Know everything about these dangerous species invading in Belgium


Self-cloning crayfish have taken over a cemetery in Belgium


Belgium: Self-cloning mutant crayfish invade historic cemetery, scientists concerned


Hundreds of self-cloning mutant crayfish invade cemetery in Belgium. 2020 isn't over yet

Maagdelijke kreeft op Antwerpse begraafplaats (roughly translated, “Virgin crayfish in Antwerp cemetery”)

20 October 2020

Linzmaier and colleagues 2020

BIological Invasions cover
Linzmaier SM, Musseau C, Matern S, Jeschke JM. 2020. Trophic ecology of invasive marbled and spiny-cheek crayfish populations. Biological Invasions 22: 33393356. https://doi.org/10.1007/s10530-020-02328-z




North American cambarid crayfish have been highly successful in establishing and spreading across Europe and are now over-invading earlier arrivals in many water bodies. Parthenogenetic marbled crayfish (Procambarus virginalis), which originated from aquarium stocks, are relatively recent invaders and have established in lakes previously invaded by spiny-cheek crayfish (Faxonius limosus). However, the feeding ecology of marbled crayfish and consequential impacts on the non-native species’ coexistence are largely unexplored. By combining laboratory experiments with stable isotope analyses of field samples, we were able to (1) determine food preferences of both species under controlled conditions and (2) explore their trophic niches in three lakes where both species co-occur. In the food-choice laboratory experiments, the two species showed similar food preferences and consumption rates. Consistently, the stable isotope analyses (δ13C and δ15N) highlighted the intermediate trophic position of both species. Marbled crayfish and spiny-cheek crayfish occupied a wide range of trophic positions corresponding to a very generalist diet. However, marbled crayfish were more relying on arthropod prey than spiny-cheek crayfish which fed more on mollusks. This is the first work providing evidence for trophic plasticity of marbled crayfish in lake food webs. Our results suggest that the addition of marbled crayfish increases grazing pressure on macrophytes and macrophyte-dependent organisms and the allochthonous detritus decomposition in ecosystems already invaded by spiny-cheek crayfish. Since both species are listed as invasive alien species of EU concern, further assessments of potentially endangered food organisms are needed.

Keywords: prey choice • food selection • stable isotope analysis • over-invasions • MixSIAR • functional equivalence • trophic niche

Roje and colelagues 2020

Aquatic Sciences cover
Roje S, Švagrová K, Veselý L, Sentis A, Kouba A, Buřič M. 2020. Pilferer, murderer of innocents or prey? The potential impact of killer shrimp (Dikerogammarus villosus) on crayfish. Aquatic Sciences 83(1): 5. https://doi.org/10.1007/s00027-020-00762-8


Freshwater ecosystems worldwide are facing the establishment of non-native species, which, in certain cases, exhibit invasive characteristics. The impacts of invaders on native communities are often detrimental, yet, the number and spread of non-native invasive species is increasing. This is resulting in novel and often unexpected combinations of non-native and native species in natural communities. While the impact of invaders on native species is increasingly well-documented, the interactions of non-native invaders with other non-native invaders are less studied. We assessed the potential of an invasive amphipod, the killer shrimp Dikerogammarus villosus (Sowinsky, 1894), to cope with other established invaders in European waters: North American crayfish of the Astacidae family—represented by signal crayfish Pacifastacus leniusculus (Dana, 1852), and the Cambaridae family—represented by marbled crayfish Procambarus virginalis Lyko, 2017. The main goal of this study was to investigate if killer shrimp, besides their role as prey of crayfish, can significantly influence their stocks by predating upon their eggs, hatchlings and free-moving early juveniles. Our results confirmed that killer shrimp can predate on crayfish eggs and hatchlings even directly from females abdomens where they are incubated and protected. As marbled crayfish have smaller and thinner egg shells as well as smaller juveniles than signal crayfish, they were more predated upon by killer shrimp than were signal crayfish. These results confirmed that the invasive killer shrimp can feed on different developmental stages of larger freshwater crustaceans and possibly other aquatic organisms.

Keywords: freshwater • Crustacea • amphipod • invasive species • interaction • predation

Open access

01 September 2020

Hossain and colleagues 2021

Science of the Total Environment cover

Hossain MS, Kubec J, Guo W, Roje S, Ložek F, Grabicová K, Randák T, Kouba A, Buřič M. 2021. A combination of six psychoactive pharmaceuticals at environmental concentrations alter the locomotory behavior of clonal marbled crayfish. Science of The Total Environment 751: 141383. https://doi.org/10.1016/j.scitotenv.2020.141383


Pharmaceutically active compounds (PhACs) are ubiquitous in the aquatic environment worldwide and considered emerging contaminants. Their effects on growth, behavior, and physiological processes of aquatic organisms have been identified even at very low concentrations. Ecotoxicological investigations have primarily focused on single compound exposure, generally at a range of concentrations. In the natural environment, pollutants seldom occur in isolation, but little is known about the effects and risks of combinations of chemicals. This study aimed to investigate the effects of concurrent exposure to six psychoactive PhACs on locomotory behavior and life history traits of clonal marbled crayfish Procambarus virginalis. Crayfish were exposed to ~1 μg L−1 of the antidepressants sertraline, citalopram, and venlafaxine; the anxiolytic oxazepam; the opioid tramadol; and the widely abused psychostimulant methamphetamine. In the absence of shelter, exposed crayfish moved significantly shorter distances and at lower velocity and showed significantly less activity than controls. With available shelter, exposed crayfish moved significantly more distance, showed higher activity, and spent a significantly more time outside the shelter than controls. Molting, mortality, and spawning frequency did not vary significantly between the groups. Hemolymph glucose level did not vary among groups and was not correlated with observed behaviors. Results suggest that environmental concentrations of the tested compounds in combination can alter the behavior of non-target aquatic organisms as individual exposure of these compounds, which may lead to disruption of ecosystem processes due to their reduced caution in stressful conditions. Further research is needed using varied chemical mixtures, exposure systems, and habitats, considering molecular and physiological processes connected to behavior alterations.

Keywords: antidepressant • ethology • emerging contaminant • opioid • Procambarus virginalis

21 August 2020

Benson 2020

Illinois State UNiversity seal
Benson AM. 2020. Identification of innexins contributing to giant-fiber escape responses in marbled crayfish. Master's thesis, School of Biological Sciences, Illinois State University. Stein W, Vidal-Gadea A, advisors. http://doi.org/10.30707/ETD2020.Benson.A


Gap junctions form intercellular pores that coordinate the flow of electrical signals between adjacent cells in the nervous system. While the physiology of electrical synapses has been investigated in sophisticated detail, the molecular underpinnings of electrical signal spread between neurons are not well understood. Even in the crayfish tail flip escape circuit, where electrical synapses have been studied for more than six decades, the gap junction proteins underlying electrical synaptic transmission are unknown. Invertebrate gap junctions are assembled from a diverse family of proteins called innexins (inx), and previous studies have suggested that in each species multiple innexins can contribute to electrical signal spread between cells. In this study, I used the genome and transcriptome assembly of the marbled crayfish, Procambarus virginalis, to identify which innexins are present and expressed in crayfish, and which contribute to the giant fiber tail flip escape response.

My bioinformatics analyses identified 8 putative innexin genes (termed inx1- inx8), only five of which were present in the transcriptome, suggesting that inx6-8 are not necessary for the tail flip. A conserved domain search of inx1 - 5 revealed that only inx1 - 3 contained the sequence signature common to innexins, indicating that inx4 and 5 may not contribute to the functioning of electrical synapses. RNA isolation from the ventral nerve cord (VNC) and brain, which contain distinct giant neurons that mediate the two major crayfish tail-flip responses, further suggested that inx1 - 3 could contribute to the tail flip: the brain expressed two innexins (inx2- 3), whereas the ventral nerve cord expressed three innexins (inx1-3). Basic Local Alignment Search Tool (BLAST) comparisons additionally revealed that inx1 and 2 were homologous to two innexins previously identified to contribute to giant fiber escape responses in insects. To test whether inx1 or 2 contribute to giant fiber tail flips in crayfish, I reduced inx1 and 2 gene expression through RNA interference (RNAi) and measured the behavioral consequences of this diminishment on the tail flip escape response. To elicit RNAi, I created innexin-specific double-stranded RNA (dsRNA) and verified the presence of intact innexin-½ dsRNA at the expected product size of 547 bp.

Animals receiving treatment were injected with 3 µg dsRNA/ g of body weight. A comparison of innexin expression levels between untreated (n = 2), control dsRNA (n = 1), and RNAi (n = 10) treatment groups using quantitative real-time PCR (qPCR) revealed that innexin expression levels diminished two days post-treatment. Behavioral measurements showed that the response latency onset of the tail flip response correlated with innexin expression levels (n = 6). A linear regression revealed a significant correlation between innexin expression and differences in response latency onset for abdominal flexion (p < 0.05, R2 = 0.77) and subsequent extension (p < 0.05, R2 = 0.82). In contrast, the tail flip strength was unaffected by the RNAi treatment (Fig. 20; p > 0.05, R2 = 0.27). Thus, at least one of the two innexins contributes to electrical synaptic transmission in the crayfish tail flip circuit.

Keywords: None provided.

28 July 2020

Marmorkrebs and messed-up childhoods

"What Do You Think You Are?" cover
Brian Clegg is promoting his new book, What Do You Think You Are?, which is coming out next week. As part of his promotion, he has an article in i newspaper about what shapes adult life. (Really, the name of the paper is a single lower case letter i.) The thesis of the article is that your parents and school don’t matter much to your adult life.

Somewhat strangely, Marmorkrebs make an appearance to argue for “chaos” in life outcomes. Clegg writes:

Batches of Marmorkrebs were raised in nearly identical environmental conditions, yet they differed widely. Some were 20 times bigger than others. Some lived twice as long. Their behaviour was totally different. The tiny genetic and environmental differences made a huge difference in outcomes.

The claims here seem to be based on Vogt and colleagues (2008), and they deserve a little examination.

The “nearly identical” environment is bit misleading. Vogt and colleagues noted that the most variation in growth came when crayfish were raised together, and “without shelters, i.e. under conditions of social stress” (emphasis added).

It’s like saying Harry Potter and Dudley Dursley were raised in “nearly identical” conditions. Well, yes, they were generally in the same physical space. But the social reality for the two boys could hardly be more different. Dudley is spoiled. Harry is tolerated at best and harassed at worst.

Similarly, crayfish fight and form hierarchies. Just because crayfish were in the same tank and had ample food does not mean that their experience in the Dursley house – I mean, crayfish tank – is necessarily the same. Nor is it accurate to call that a “tiny” environment difference.

“20 times bigger” is a bit ambiguous. I image that people might imagine one crayfish an inch long and another 20 inches (over a foot and a half) long. But the measurements are mass, not length. Since mass increases with the cube of length, that means one crayfish is about 2.5 longer than another.

I am not sure how different behaviour has to be to count as “totally different.” I’ve watched a lot of crayfish. You can tease differences apart in experiment, but I think most people would have a hard time distinguishing the behaviour of one Marmorkrebs from another. It’s not obvious, like the relaxed dog you see chilling in the dog park and the barky aggro dog you have to keep on the leash.

I don’t know if Marmorkrebs also appear in the book. I hope they do but with perhaps a little more nuance than in this short article.

Related posts

External links
What makes us ourselves? Why your parents might not f*** you up as much as you think


Vogt G, Huber M, Thiemann M, van den Boogaart G, Schmitz OJ, Schubart CD. 2008. Production of different phenotypes from the same genotype in the same environment by developmental variation. The Journal of Experimental Biology 211(4): 510-523. http://jeb.biologists.org/cgi/content/abstract/211/4/510

15 July 2020

Map of Marmorkrebs introductions, now with Austria!

Map of Europe highlighting Austria
I made multiple additions to the big map of Marmorkrebs introductions. The biggest change is the addition of Austria to the list of countries with established Marmorkrebs populations.

The discovery of Marmorkrebs in Salzburg, Austria was published back in 2018 (Latzer and Pekny 2018), but I only just caught up to it today.

Trying to understand that paper (since it was in German) led me to another short abstract describing another Marmorkrebs finding in Austria, this time in Vienna (Moog et al. 2019). This description is brief, so the map position is not precise:

According to Thomas Ofenböck (Municipal Department 45 - Water Management), in August 2018 a single specimen was found in the 22nd district and released in the Mühlwasser.

Released? Oh, that hurts to read.

Finally, I have a more precise position for the location where Marmorkrebs were found in France. Previously, I only had a description of the area from Marc Collas’s tweet. Again, I stumbled upon a much lengthier description of the finding (Collas 2019), which included a map. That allowed me to get a more exact position.

And just to round things out, I added a couple more of sites from Hungary mentioned in Szendőfi and colleagues (2018).

Busy day. Wish I had done this before this year!


Collas M. 2019. Premier signalement de l’écrevisse marbrée (Procambarus virginalis) en Centre de ressources espèces exotiques envahissantes. http://especes-exotiques-envahissantes.fr/premier-signalement-de-lecrevisse-marbree-procambarus-virginalis-en-france/

Latzer D, Pekny R. 2018. Erstnachweis des Marmorkrebses für Österreich in Salzburg. Salzburgs Fischerei 49(3): 24-30. https://issuu.com/lfvs/docs/safisch_3-18

Moog O, Leitner P, Huber T, W. R, Graf W. 2019. Marbled Crayfish (Procambarus virginalis Lykow, (sic) 2017) – a supplement to the list of Aquatic Invertebrate Neozoa in Austria. ECOPROF. https://www.ecoprof.at/index.php/faunaaquaticaaustriaca.html?file=files/ep_downloads/faa/New_Neozoon_Marbled%20Crayfish.pdf

Szendőfi B, Bérces S, Csányi B, Gábris V, Gál B, Gönye Z, Répás E, Seprős R, B. T, Kouba A, Patoka J, Weiperth A. 2018. Egzotikus halfajok és decapodák a Barát‐ és Dera‐patakban, valamint a torkolatuk dunai élőhelyein. Pisces Hungarici 12: 47-51. http://www.haltanitarsasag.hu/ph12/Szendofi_et.al_Pisces.Hungarici_2018.pdf

Collas, 2019

Collas M. 2019. Premier signalement de l’écrevisse marbrée (Procambarus virginalis) en France.   Centre de ressources espèces exotiques envahissantes. http://especes-exotiques-envahissantes.fr/premier-signalement-de-lecrevisse-marbree-procambarus-virginalis-en-france/

(Approximate English translation of title: First report of the marbled crayfish (Procambarus virginalis) in France)


Without abstract. Translated excerpt: 

Following surveys carried out by the Moselle fishing federation, P. virginalis has just been reported for the first time in a natural environment in France, in a body of water in the context of ballast pits on the Moselle catchment area, near Metz. This morphological identification was confirmed by molecular analysis using a mitochondrial gene.

Keywords: None provided.