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

Wiƛniewski and colleagues, 2020

Wiƛniewski K, Szarmach D, PoznaƄska-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