18 January 2022

Marmorkrebs feature in The Guardian

The Guardian
Kate Connolly has written a substantive summary of the state of Marmorkrebs in The Guardian that includes new interviews with several researchers.


The article also prompted some coversation on Twitter about how likely it is that crayfish can help regulate schistosomiasis.


I think my favourite part of the article is a previously undescribed pattern of behaviour: that they are nocturnal:


Lyko recalls driving to a lake about 15 minutes from his lab with his students. Donning head torches and waders and standing ankle deep in the water, “we waited until it got dark, then suddenly they emerged in their hundreds and thousands”, he says.



External links

‘We started eating them’: what do you do with an invasive army of crayfish clones?

Marmorkrebs in Canada?

Premek Hamr drew attention to this record on iN today: a potential Marmorkrebs sighting in City View Park, Burlington, Ontario.


Guenter Schuster suspects that it might be Procambarus, but keying out to species from these pictures is effectively impossible.


That said, local park in an urban environment has been almost exactly the most common pattern we have seen in other locations: someone with an aquarium dumps some unwanted animals into a local park.


This was last October – mere months before Ontario banned Marmorkrebs at the start of 2022. Although Marmorkrebs have done well in some northern locations, it’s hard to tell if they could overwinter in Canada.


Has our luck finally run out? Is this the thin end of the wedge that will be the start of many more invasions of North America?


External links


Marbled crayfish on iNaturalist






15 January 2022

Maiakovska, 2021

University of Heidelberg
Maiakovska O. 2021. Origination, monoclonality and evolution of the marbled crayfish genome Procambarus virginalis. Doctoral dissertation, The Faculty of Bio Sciences, Ruperto Carola University Heidelberg, Germany.




The parthenogenetic marbled crayfish (Procambarus virginalis) sparked interest within the scientific community due to its unique features. Its polyploid and monoclonal genome, high environmental adaptability and phenotypic diversity made the marbled crayfish a suitable laboratory model for genomics, epigenetics and ecology research. The previously established marbled crayfish genome sequence of 3.5 Gbp represents a highly fragmented draft assembly. Initial comparative genomic analyses resulted in confirmation of P. virginalis genome origination from the sexually reproducing freshwater crayfish P. fallax. However, in-depth genomic analysis and interspecies genome comparisons require further refinement of the fragmented genome reference of the marbled crayfish. In this PhD thesis, the first refinement of the marbled crayfish genome has been performed with application of the PacBio Single Molecule Real Time (SMRT) sequencing technology. The new and improved genome assembly of the marbled crayfish resulted in 3.7 Gbp of sequence length and an N50 of 144kb. The refined genome assembly enabled searching parental haplotypes and understanding species origination. The absence of evidence for loss of heterozygosity in the various monoclonal marbled crayfish generations suggests the lack of recombination process during oogenesis. Thus, marbled crayfish suggest to be apomictic parthenogens which are characterized by generating identical copies of the maternal genotype. Moreover, despite of the limited genome variability, monoclonal marbled crayfish genomes consisted of population-specific genetic polymorphisms within the global population. Comparative genomic analysis between geographically distant populations resulted in the identification of population-specific mutational signatures. The calculation of genomic variability of marbled crayfish from the growing population in Lake Reilingen allowed to estimate population dynamics. Thus, the population in Lake Reilingen demonstrates a rapid growth, following the density-independent exponential model. This PhD thesis provides fundamental insights into marbled crayfish research, particularly via making use of an improved genome assembly for comparative genomic analyses, epigenetic studies, and for research on the evolution and genomic adaptation to asexuality.


Keywords: None provided.

14 January 2022

Tŏnges, 2021

University of Heidelberg logo

Tönges SM. 2021. Context-dependent DNA methylation variants in marbled crayfish (Procambarus virginalis). Doctoral dissertation, The Faculty of Bio Sciences, Ruperto Carola University Heidelberg, Germany. https://doi.org/10.11588/heidok.00029299



The marbled crayfish is a recently discovered freshwater crayfish. It is the only known decapod crustacean that reproduces by obligate apomictic parthenogenesis resulting in a clonal, all-female population. All known marbled crayfish have a single origin, and the species is estimated to have an age of about 25-30 years. Furthermore, it has spread already into several countries globally and shows high adaptability to different environments in the absence of genetic adaptation. Epigenetic mechanisms were suggested to play a role in the rapid adaptation of this species. This thesis aims to identify context-dependent DNA methylation variants in marbled crayfish. Samples from two tissues and four distinct habitats were analyzed with a capture-based bisulfite sequencing approach to identify methylation variants. The results were validated by deep amplicon sequencing of tissue-specific and location-specific regions and with newly collected samples from the same tissues and locations as before. The location-specific methylation patterns suggest the existence of epigenetic ecotypes and allow the tracing of the origin of marbled crayfish populations by their DNA methylation fingerprint. In a laboratory trial, single rearing conditions were changed to see the influence of specific parameters on the methylation pattern. Within six months, methylation changes could be observed for the group kept at a lower temperature compared to the control group, indicating the adaptation of the methylation pattern caused by an environmental trigger. Furthermore, the laboratory population showed a different methylation pattern compared to the wild populations. Lastly, the potential of marbled crayfish as an aquaculture livestock was explored, and a framework for an environmentally safe aquaculture was established. Additionally, tracing the origin of marbled crayfish using location-specific methylation patterns was proposed for certifying sustainable and transparent aquaculture practices. These re-sults provide insight into the rapid adaptation in invasive species and provide a proof of concept for environmental origin tracing with DNA methylation fingerprinting.

Keywords: Epigenetics • ecology • aquaculture

Open access

05 January 2022

Marmorkrebs at the ready

Spotted on Reddit:


Marmorkrebs in glass jar labelled, "In case of emergency break glass"


I always worry if Redditors are okay.


External links


Weaponized Marmorkrebs! Don't leave home without one.

31 December 2021

2021 was the third best year ever for Marmorkrebs research

Graph of number of Marmorkrebs journal articles from 2003 to 2021, with 19 papers in 2021.

At least it was the third best year as judged by number of journal articles. But there were more than just journal articles! At the start of the year, we had what was probably the best popular article written to date about Marmorkrebs.


It was a slow year for new introductions, but the one in Macau was a significant expansion in Asia.


And finally, I learned of two North American jurisdictions regulating Marmorkebs: Ohio, which seemed to have done it quietly in 2020, and Ontario, which did so quietly starting in 2022.


Previous year end reviews


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


2020 was not the best year for Marmorkrebs research


Ontario prohibits Marmorkrebs

Welcome to the Environmental Registry of Ontario.
The Gananoque Reporter reminds me of a story I have been watching for almost two years: Marmorkrebs have been added to a list of prohibited species in Ontario under the Invasive Species Act.


Marbled crayfish (Procambarus virginalis) and Louisiana red swamp crayfish (Procambarus clarkii) prohibited in Ontario, as of 1 January 2022. Happy new year. 


What does this mean in practical terms?


Prohibited species cannot be brought into Ontario, deposited, released, possessed or transported in Ontario and cannot be propagated, bought, sold or traded in Ontario.

The regulation includes species-specific exceptions to certain prohibitions, including: Marbled Crayfish, Red Swamp Crayfish: Exceptions allow for incidental capture of these species while fishing in Ontario.


This is a weird exemption, because as there are no marbled crayfish to be caught in Ontario, as far as I know.


This is the most significant regulation concerning marbled crayfish in North America to date, because Ontario is the largest and most populous jurisdiction that has yet tried to regulate marbled crayfish.

We’ll see if it works.


That I am just learning about this today – one day before it takes effect – emphasizes yet again how hard it is to keep track of this sort of legislation. I have alerts set for marbled crayfish and try to track this material as closely as possible. I am making an effort. But this passed me by for eight whole months.


Related posts 


Canadian province of Ontario asks for input on Marmorkrebs (February 2020)


Ontario seeks public comment on regulating marbled crayfish (April 2021)


External links


New Ontario boating rules Jan. 1 to stem spread of aquatic invasive species


Regulating 13 invasive species and watercraft as a carrier of invasive species under Ontario’s Invasive Species Act, 2015 (decision)


Regulating 13 invasive species and watercraft as a carrier of invasive species under the Ontario Invasive Species Act, 2015 (Analysis, April 2021)