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)

02 December 2021

The newest version of Marmorkrebs.org

Marmorkrebs.org is moving to Google Sites.




One major advantage of this change is that Google Sites are much better at switching between desktop and mobile versions of the site, which will make people visiting by using their phones much happier!


Since its beginning, the main Marmorkrebs.org website has been hosted by my former employer, The University of Texas Rio Grande Valley (formerly The University of Texas Pan American). Last year, I took a new position. Because of that, I will soon be losing all access to the web hosting provided by that university.


I have updated the domain name pointers, so typing “marmorkreb.org” in your browser bar should now go to the new site. If, for some reason, you still need to visit the old, more complete site in the next couple of days, you can go to:




Thank you!

23 November 2021

Captivity does not cause cloning

An >article about Marmorkrebs by Paul Hetzler is showing up in a wide array of places, from New York state to India. It’s generally accurate, although I have to raise eyebrows as to the description of the origin of Marmorkrebs.

Sometime in the 1990s, a mutant crayfish able to conquer and degrade aquatic systems emerged as a result of secret German experiments gone awry. (What the what? - ZF) The marmorkreb (sic), a.k.a. marbled crayfish (Procambarus virginalis), is a destructive new species that first appeared aquariums in Germany. However, it’s more likely the result of too much inbreeding in captivity, rather than some mad-scientist scheme, that led to their mutation.


I think – I hope – Hetzzler meant the bit about “secret experiments” as a joke. I am willing to be that some people will take it as real and won’t make ti to the second part of the paragraph. But the second part of the paragraph is also pretty dubious. 


There is no evidence that inbreeding can cause triploidy. Inbreeding increases homozygosity. It doesn't create extra chromosomes, particularly a whole new set of chromosomes.

By weird coincidence, a technical paper in press also seems to think that just being in captivity is enough to make a species parthenogenetic.

The marbled crayfish Procambarus virginalis probably evolved clonal parthenogenetic reproduction while in the captive aquarium trade. ... With growth in human cultivation of invertebrates for food and other services, the potential for evolution and escape into the wild and subsequent rapid spread of other clonal species is increasing.


This stands in contrast to a recent paper by Gutekunst and colleagues that argues that there are triploid individuals in the natural slough crayfish population, from which Marmorkrebs ultimately emerged.

We need to stop with this narrative that somehow the origin of Marmorkrebs in humans’ fault. It’s not as though there is a shortage of crayfish guilt in the world. It’s our fault we spread them around the globe. That’s on us.


Hetzler also mentions a controversy that... I don’t think exists?

Perhaps the only amusing thing about these nasty aberrations of nature is the mild squabbling as to how one should describe them. Experts disagree on whether the new organisms are mottled, freckled, speckled, spotted, variegated, or something else.

I have never seen a single written comment arguing about what to call the pattern on Marmorkrebs.

Update, 2 December 2021: Yet another article implies that “captivity is to blame for asexual reproduction:

Some insects and other invertebrates have evolved a novel solution to the “can’t get a date” problem: They can reproduce without sex. ... At least one invertebrate, the marbled crayfish, evolved the ability to reproduce asexually in captivity and is now spreading rapidly across Europe, Africa and Asia, carrying with it disease that harms native species. As we cultivate other invertebrates for food or hobbies, we raise the risk that something similar might happen with other species.

I say again: just the act of keeping a species in a tank does not increase the chance of it becoming parthenogentics. It increases the chance we notice it.


Update, 31 December 2021: Even The Guardian gets in on the act by reprinting the Ensia article.




Gutekunst J, Maiakovska O, Hanna K, Provataris P, Horn H, Wolf S, Skelton CE, Dorn NJ, Lyko F. 2021. Phylogeographic reconstruction of the marbled crayfish origin. Communications Biology 4(1): 1096. https://doi.org/10.1038/s42003-021-02609-w


Sutherland WJ, Atkinson PW, Butchart SHM, Capaja M, Dicks LV, Fleishman E, Gaston KJ, Hails RS, Hughes AC, Le Anstey B, Le Roux X, Lickorish FA, Maggs L, Noor N, Oldfield TEE, Palardy JE, Peck LS, Pettorelli N, Pretty J, Spalding MD, Tonneijck FH, Truelove G, Watson JEM, Wentworth J, Wilson JD, Thornton A. 2021. A horizon scan of global biological conservation issues for 2022. Trends in Ecology & Evolution: In press. https://doi.org/10.1016/j.tree.2021.10.014


External links


Marbled Crayfish: The Mutants Have Landed


Help keep marbled crayfish from spreading


The Mutants Have Landed


Horizon scan: the opportunities and threats facing Earth’s biodiversity

05 November 2021

Chucholl and Chucholl 2021

Cover of Freshwater Biology, volume 66, issue 11.
Chucholl F, Chucholl C. 2021. Differences in the functional responses of four invasive and one native crayfish species suggest invader-specific ecological impacts. Freshwater Biology 66(11): 2051-2063. https://doi.org/10.1111/fwb.13813




  1. Invasive non-native species represent a leading threat to global freshwater biodiversity and non-native crayfish species frequently cause extensive ecological damage. However, the extent to which their impact: (1) depends on invader identity and (2) differs from the natural state with native crayfish remains unclear. Comparison of the functional responses of invasive and native species represents a promising approach in this regard.
  2. Here, we explored whether four invasive crayfish species (calico crayfish Faxonius immunis, spiny-cheek crayfish Faxonius limosus, signal crayfish Pacifastacus leniusculus, and marbled crayfish Procambarus virginalis) in European freshwaters and the most widespread native species (noble crayfish Astacus astacus) overlap in function in their potential effects on key resources of benthic food webs. First, the impact on gammarids and zebra mussels was assessed by means of comparative functional response analysis using the functional response ratio as impact metric; second, the consumption of macrophytes (Chara sp.) and detritus (leaf litter) was quantified and compared using feeding experiments.
  3. Both invader- and resource-specific effects were observed. Invasive calico crayfish and signal crayfish exhibited the strongest per capita effects on gammarids and zebra mussels, respectively, with functional response ratios being 2-fold higher than those of native noble crayfish. Marbled crayfish showed an intermediate effect on both prey species, whereas spiny-cheek crayfish had lower impacts than noble crayfish. In the feeding experiment, calico crayfish consumed the highest amount of detritus, while the consumption of macrophytes did not differ among the five crayfish species.
  4. Our work demonstrates as-yet unrecognised differences in functional responses among the four North American crayfish invaders and the European noble crayfish. The lack of congruence across the observed impacts suggests a mostly species-specific pattern and stresses the importance of species and resource identity when considering the ecological impact of crayfish. An initial assessment of invader-specific potential impacts positions calico crayfish and signal crayfish among the most impactful invaders.

Keywords: ecological impact • ecological redundancy • functional response • invasive crayfish risk assessment

Open access.


Scholz and colleagues 2021

Zoomorphology journal cover
Scholz S, Göpel T, Richter S, Wirkner CS. 2021. High degree of non-genetic phenotypic variation in the vascular system of crayfish: a discussion of possible causes and implications. Zoomorphology 140: 317-329. https://doi.org/10.1007/s00435-021-00536-2




In this study, the hemolymph vascular system (HVS) in two cambarid crayfishes, i.e. the Marbled Crayfish, Procambarus virginalis Lyko, 2017 and the Spiny Cheek Crayfish, Faxonius limosus (Rafinesque, 1817), is investigated in regard of areas of non-genetic phenotypic variation. Despite their genetic identity, specimens of P. virginalis show variability in certain features of the HVS. Thus, we describe varying branching patterns, sporadic anastomoses, and different symmetry states in the vascular system of the marbled crayfish. We visualize our findings by application of classical and modern morphological methods, e.g. injection of casting resin, micro-computed tomography and scanning electron microscopy. By comparing our findings for P. virginalis to the vasculature in sexually reproducing crayfishes, i.e. F. limosus and Astacus astacus, we discuss phenotypic variation of the HVS in arthropods in general. We conclude that constant features of the HVS are hereditary, whereas varying states identified by study of the clonal P. virginalis must be caused by non-genetic factors and, that congruent variations in sexually reproducing F. limosus and A. astacus are likely also non-genetic phenotypic variations. Both common causal factors for non-genetic phenotypic variation, i.e., phenotypic plasticity and stochastic developmental variation are discussed along our findings regarding the vascular systems. Further aspects, such as the significance of non-genetic phenotypic variation for phylogenetic interpretations are discussed.


Keywords: Evolutionary morphology • phenotypic plasticity • circulatory system • heart • artery

Open access logo.


01 November 2021

Celbrate diversity: Charasmatic California condors can without consumation

California condor in flight


It’s been fascinating to watch species that have been well studied suddenly and unexpectedly show that they can reproduce by parthenogenesis. The latest entry to the club is perhaps the most surprising yet: the critically endangered California condor.

The story is making the rounds on science news, but the original technical article is here.

Two males were generated by parthenogenesis. This is in contrast to many other cases of parthenogenesis, where offspring are exclusively female. Birds have a ZW chromosome system, where the females have different sex chromosomes. The males have two of the same sex chromosome. I suppose that in theory, the condors could produce offspring of either sex by parthenogenesis?



Ryder OA, Thomas S, Judson JM, Romanov MN, Dandekar S, Papp JC, Sidak-Loftis LC, Walker K, Stalis IH, Mace M, Steiner CC, Chemnick LG. Facultative parthenogenesis in California condors. Journal of Heredity: In press. https://doi.org/10.1093/jhered/esab052


External links


After 30 Years of Breeding Condors, a Secret Comes Out

17 September 2021

Gutekunst and colleagues, 2021

Communications Biology
Gutekunst J, Maiakovska O, Hanna K, Provataris P, Horn H, Wolf S, Skelton CE, Dorn NJ, Lyko F. 2021. Phylogeographic reconstruction of the marbled crayfish origin. Communications Biology 4(1): 1096. https://doi.org/10.1038/s42003-021-02609-w




The marbled crayfish (Procambarus virginalis) is a triploid and parthenogenetic freshwater crayfish species that has colonized diverse habitats around the world. Previous studies suggested that the clonal marbled crayfish population descended as recently as 25 years ago from a single specimen of P. fallax, the sexually reproducing parent species. However, the genetic, phylogeographic, and mechanistic origins of the species have remained enigmatic. We have now constructed a new genome assembly for P. virginalis to support a detailed phylogeographic analysis of the diploid parent species, Procambarus fallax. Our results strongly suggest that both parental haplotypes of P. virginalis were inherited from the Everglades subpopulation of P. fallax. Comprehensive whole-genome sequencing also detected triploid specimens in the same subpopulation, which either represent evolutionarily important intermediate genotypes or independent parthenogenetic lineages arising among the sexual parent population. Our findings thus clarify the geographic origin of the marbled crayfish and identify potential mechanisms of parthenogenetic speciation.


Keywords: None provided.

29 August 2021

Tönges and colleagues 2021

Frontiers in Ecology and Evolution
Tönges S, Masagounder K, Lenich F, Gutekunst J, Tönges M, Lohbeck J, Miller AK, Böhl F, Lyko F. 2021. Evaluating invasive marbled crayfish as a potential livestock for sustainable aquaculture. Frontiers in Ecology and Evolution 9: 651981. https://www.frontiersin.org/article/10.3389/fevo.2021.651981



The marbled crayfish (Procambarus virginalis) is a recently discovered freshwater crayfish species, which reproduces by apomictic parthenogenesis, resulting in a monoclonal, and all-female population. The animals were widely distributed through the aquarium trade and have established numerous stable wild populations through anthropogenic releases. They are highly prevalent in Madagascar, where they have become a popular source of nutritional protein. As freshwater crayfish aquaculture in open systems is a thriving, but ecologically damaging global industry, alternatives are urgently needed. Although marbled crayfish are often branded by their invasive mode of reproduction, their overall invasiveness is not higher than for other cultured crayfish species. Furthermore, their resiliency and high adaptability provide a strong rationale for evaluating them for closed, and environmentally safe aquaculture approaches. Here we describe a novel population of marbled crayfish in a former German coal mining area that is characterized by acid and polluted water. Even under these adverse conditions, animals grew to sizes, and weights that are comparable to commercially farmed freshwater crayfish. Tailored feed development and laboratory testing demonstrated highly efficient feed conversion, suggesting a considerable capacity for sustainable production in closed systems. We further show that marbled crayfish meat can be readily introduced into European meals. Finally, chemical analysis of marbled crayfish exoskeletons revealed comparably high amounts of chitin, which is a valuable source for the synthesis of chitosan and bioplastics. Our results thus suggest that production of marbled crayfish in closed systems may represent a sustainable alternative for crayfish aquaculture.

Keywords: livestock • invasive species • feed conversion • chitin • sustainability • aquaculture • marbled crayfish • tailored feeds

Open access

Francesconi and colleagues 2021

Frontiers in Evology and Evolution.
Francesconi C, Makkonen J, Schrimpf A, Jussila J, Kokko H, Theissinger K. 2021. Controlled infection experiment with Aphanomyces astaci provides additional evidence for latent infections and resistance in freshwater crayfish. Frontiers in Ecology and Evolution 9: 647037. https://doi.org/10.3389/fevo.2021.647037




For 150 years the crayfish plague disease agent Aphanomyces astaci has been the cause of mass mortalities among native European crayfish populations. However, recently several studies have highlighted the great variability of A. astaci virulence and crayfish resistance toward the disease. The main aim of this study was to compare the response of two crayfish species, the European native noble crayfish (Astacus astacus) and the invasive alien marbled crayfish (Procambarus virginalis), to an A. astaci challenge with a highly virulent strain from haplogroup B and a lowly virulent strain from haplogroup A. In a controlled infection experiment we showed a high resistance of marbled crayfish against an A. astaci infection, with zoospores from the highly virulent haplogroup B strain being able to infect the crayfish, but unable to cause signs of disease. Furthermore, we demonstrated a reduced virulence in the A. astaci strain belonging to haplogroup A, as shown by the light symptoms and the lack of mortality in the generally susceptible noble crayfish. Interestingly, in both marbled crayfish and noble crayfish challenged with this strain, we observed a significant decrease of the detected amount of pathogen’s DNA during the experiment, suggesting that this A. astaci haplogroup A strain has a decreased ability of penetrating into the cuticle of the crayfish. Our results provide additional evidence of how drastically strains belonging to A. astaci haplogroup B and haplogroup A differ in their virulence. This study confirmed the adaptation of one specific A. astaci haplogroup A strain to their novel European hosts, supposedly due to reduced virulence. This feature might be the consequence of A. astaci’s reduced ability to penetrate into the crayfish. Finally, we experimentally showed that marbled crayfish are remarkably resistant against the crayfish plague disease and could potentially be latently infected, acting as carriers of highly virulent A. astaci strains.


Keywords: marbled crayfish • noble crayfish • host-pathogen co-evolution • crayfish plague • experimental infection

OPen access

25 August 2021

Fishing for Marmorkrebs

Man in pond with nets and buckets fishing for crayfish.

I missed a story from back in spring about how Marmorkrebs are being commercially fished in Berlin.

German newspaper Die Zeit reports that Marmorkrebs are an addition to an existing crayfishing operation. About a ton of Lousiana red swamp crayfish have been caught every year over the last few years. 

NPR reported on this a couple of years ago, and did not paint a rosy picture of the fishery. Despite jokes about “How can they be a problem if we can eat them?” every time I talk about invasive crayfish, not everyone likes to eat them. Few restaurants are interested, and supply is irregular.

We’ll see.

External links

Erstmals sollen Marmorkrebse ins Netz gehen

For Berlin, invasive crustaceans are a tough catch and a tough sell

09 August 2021

Lemmer and colleagues, 2020

Lemmers P, Spikmans F, Volk L. 2020. De Marmerkreeft (Procambarus virginalis), een nieuwe invasieve exoot in Limburg. Natuurhistorisch Maandblad 109: 260-266.




In terms of crayfish, the province of Limburg is a province poor in species by Dutch standards. Until 2020, only three invasive alien crayfish species were known. However, Marbled crayfish (Procambarus virginalis) were found at two isolated locations near Venlo within a short period of time in the spring of 2020. The origin and release of one of the populations could be traced via an internet vendor, who had released ten animals in 2017. A dipnet survey in 2020 at this site showed that the density was at least 30.8 specimens per 100 m of embankment. At the other site, length-frequency data suggest the species has been present since 2018. Here, the density was estimated at 5.4 individuals per 100 m of embankment. Further expansion of the populations via overland migration can be expected. It is likely that negative effects on nearby native amphibian populations will occur when no action is taken. The conclusions drawn from this study are that Marbled crayfish (1) are still offered for sale in the aquarium trade even after EU legislation, (2) are actively being released into the wild and (3) are able to establish populations in the Dutch countryside.

29 July 2021

Lemmer and colleagues, 2021

Cover to Living Nature, volume 122, issue 4.
Lemmers P, Frank Spikmans F, Koese B. 2021. Is de opmars van de marmerkreeft in Nederland nog te stuiten? De Levende Natuur 122(4): 138-140. https://delevendenatuur.nl/tijdschrift/2021-4




The first marbled crayfish in the Netherlands was recorded in 2004. The next was observed a decade later, in 2014. Since then the number of observations has increased significantly up to 14 sites in 2020, spread all over the country. The marbled crayfish became established in at least four sites of which one has been eliminated in 2020. Animals are mainly found in vegetation- rich, shallow parts of isolated waters. Other crayfish species were not present in these sites. The main introduction route of marbled crayfish is release by pet keepers. The EU Regulation 1143/2014 on Invasive Alien Species seems to have limited effect on the ongoing invasion of this species yet, as both trade and new introductions are still taking place. Swift actions, considered both cost effective and mandatory under EU legislation, are urgently needed to eliminate the species while this is still feasible.


Note: The main text of article is in Dutch. The English title is roughly, “The expansion of the marbled crayfish in the Netherlands.”

24 July 2021

Illinois State University logo.
DeMaegd ML. 2021. Physiological consequences of neuromodulation and the cellular properties that underlie them. Dissertation for Doctor of Philosophy (PhD), School of Biological Sciences, Illinois State University. https://doi.org/10.30707/ETD2021.20210719070603173187.87




Neuronal activity is a product of more than the underlying neuronal connections. Modulatory influences like changes in the animal’s environment, the animals physiological state, or the release of neuromodulators can dramatically alter neuronal activity. Modulatory influences can be beneficial for the animal because they are a source of neuronal and behavioral plasticity, and they can provide neuronal circuits with the robustness needed to continue to function in new conditions, states, or tasks.However, malfunctions of the modulatory system can disrupt neuronal activity and lead to pathologies. Predicting how modulatory influences will alter neuronal activity is challenging because the underlying cellular and circuit properties are delicately balanced and often respond in nonlinear and multifaceted ways to modulatory influences. In my thesis I address how several types of modulatory influences affect neuronal activity in the crustacean stomatogastric nervous system, and seek to characterize the circuit and cellular mechanisms that underlie them. In Chapter II I show that the activation of chemosensory pathway alters the frequency of backpropagating action potentials in a proprioceptive sensory neuron that measures muscle tension when the animal chews. These backpropagating action potentials invade the most distant regions of the proprioceptive neuron where muscle tension is encoded, including the spike initiation site and sensory dendrites. They alter the latency, the number, and the frequency of action potentials in response to muscle stimuli. When the chemosensory neurons become active, backpropagating action potential frequency decreases, thereby granting greater sensitivity to the muscle tension receptor. Since the chemosensory pathway is activated by food before the chewing starts, the modulation of backpropagating action potentials prepares the muscle receptor for future changes in muscle tension. Thus, my results demonstrate that one sensory pathway can prime another for upcoming tasks via the modulation of backpropagating action potentials. In Chapter III I show two ways that neuronal activity can be sustained during temperature modulation. First, I show that axons of different pyloric neurons maintain action potential timing between them over a large temperature range, despite their distinct morphological and intrinsic properties. I used computational model axons to determine if, and if so, how, axons with different diameters that are exposed to varying temperatures can maintain action potential timing with one another. I found that the temperature sensitivity of most ion channel properties mattered little to action potential timing. Conversely, the ratio of two Sodium channel parameters were critical: how much the maximum conductance and activation gate time constant in one axon changed with temperature relative to the other axon strongly influenced action potential timing between two. Since the ratio was critical, but not the actual values, this demonstrated that even highly temperature-sensitive ion channels can support temperature-robust action potential timing between neurons. Second, I show that acutely warming the stomatogastric ganglion by 3°C disrupts a gastric mill rhythm by diminishing the spread of electrical signals in the dendrites of the Lateral Gastric neuron (LG). I also show that a substance P-related peptide restores dendritic electrical spread and consequently the gastric mill rhythm at the warmer temperature. Specifically, the peptide rescues electrical spread through the activation of a modulatory cation current (the 'modulatory induced current' (IMI)). These data demonstrate the cellular mechanisms by which this peptide neuromodulator induces temperature-robust neuronal activity. A realization during my work on the previous chapters was that few peer-reviewed protocols exist that provide detailed and reproducible workflows of electrophysiological and molecular approaches for the study of modulatory influences. Many laboratories use 'homegrown' protocols or protocols that were inherited by word of mouth and are not widely available. This leads to a lack or reproducibility of research approaches and results and impedes the widespread use of these techniques. Chapters IV and V address these issues. In Chapter IV, I first, provide detailed protocols on how to generate action potentials in an axon using extracellular stimulation. Second, I provide a detailed protocol on how to measure action potential conduction velocity using extracellular recordings. In Chapter V, I expand on the concept of providing easily understandable and reproducible protocols to the processes of integrating genetic and molecular techniques with electrophysiological one in both lab and classroom settings. I establish a workflow that guides undergraduates or physiologists in the manual identification, confirmation, and curation of putative genes involved in neuronal function. I implement this workflow in a Course in Undergraduate Research Education (CURE) – like setting, that brings undergraduate students of all levels to actively participate in research labs by allowing students to work under supervision of graduate students and faculty mentors. The workflow outlines a efficient protocol for gene identification in marbled crayfish, clear leaning objectives, and several quality control and assessment processes that enable students to conceptualize the interconnectedness of genetics, molecular, and physiological neuroscience. By following this workflow, I identified the transcript and gene sequences for two Gamma Aminobutyric Acid (GABA) receptors subunits in the marbled crayfish (Procambarus virginalis). In addition to its educational purpose, the provided protocol serves as a first step toward integrating genetic and molecular techniques with electrophysiological ones to study the impact of receptor diversity for the cellular mechanisms of modulation in the marbled crayfish.


Keywords: None provided. 


Note: This document is embargoed until June 28, 2022.

25 June 2021

Sanna and colleagues, 2021

Logo for journal "Life".
Sanna D, Azzena I, Scarpa F, Cossu P, Pira A, Gagliardi F, Casu M. 2021. First record of the alien species Procambarus virginalis Lyko, 2017 in fresh waters of Sardinia and insight into its genetic variability. Life 11(7): 606. https://doi.org/10.3390/life11070606




In the fresh waters of Sardinia (Italy), the non-indigenous crayfish species Procambarus clarkii has been reported from 2005, but, starting from 2019, there have been several reports of a new nonindigenous crayfish in southern and central areas of this Mediterranean island, and its morphology suggests that this species may be the marbled crayfish Procambarus virginalis. Forty-seven individuals of this putative species were analyzed, using the mitochondrial gene Cytochrome c Oxidase subunit I as molecular marker to identify this crayfish and investigate the level of genetic variability within the recently established population. Phylogenetic and phylogeographic analyses were carried out on a dataset including sequences from the Sardinian individuals and from all congenerics available in GenBank. Results showed that the new Sardinian crayfish belong to the species P. virginalis. All the sequences belonging to P. virginalis from European countries are identical, with only few exceptions found among Sardinian individuals. In conclusion, this paper highlights the occurrence of a new further alien species in the Sardinian fresh waters, which are already characterized by the high presence of non-indigenous species.


Keywords: alien species • invasive species • non-indigenous crayfish • biological invasion • marbled crayfish • Sardinian fresh waters • mtDNA


Open access


19 June 2021

Fun for people of all ages! Marmorkrebs colouring

I stumbled across a page with a coloring book style blank illustration of Marmorkrebs! While the page says it’s for kids, there’sa a lot of fine detail that makes me think some young ones may find it a little on the high end of the difficulty scale.


Black and white outline of crayfish for colouring.


The shape of the claws looks much more like Louisiana red swamp crayfish than Marmorkrebs, though.

01 June 2021

Muuga 2021

Muuga J-M. 2021. Effects of temperature on marbled crayfish (Procambarus virginalis, Lyko 2017) invasion ecology. Master’s thesis, Hydrobiology and Fishery, Institute of Agricultural and Environmental Sciences, Estonian University of Life Sciences. http://hdl.handle.net/10492/6695




Biological invasions are crucial issues worldwide and marbled crayfish (Procambarus virginalis, Lyko 2017) is one of the examples of freshwater invaders spreading across Europe and beyond. Marbled crayfish has high growth rate and reproduces via parthenogenesis, making it unique among other decapod species. Even though it is a warm water species, they can resist colder temperatures and are highly adaptable. Furthermore, it is also a vector for Aphanomyces astaci, causing crayfish plague. Due to its high adaptability, fast growth and reproduction, since one individual is enough to start a new population, it is important to understand its invasion ecology in order to implement better management plan in the new invaded ecosystems. In this thesis the main goal was to assess whether the temperature is the main factor of marbled crayfish establishment and distribution in the artificially warm outflow channel of Balti Power Plant in Narva. We hypothesised to find temperature gradient along the channel which reflects marbled crayfish distribution and trophic niche. We analysed marbled crayfish and their potential food sources for stable carbon (13C) and nitrogen (15N) isotopes to assess its trophic niche. Temperature data did not show the gradient in the channel, however the channel was significantly warmer than Narva Reservoir. Stable isotope results showed change in marbled crayfish diets and trophic niche along the channel and between seasons, indicating a shift from enriched carbon to depleted carbon values from head to mouth of the channel and a shift from high to lower trophic level from spring and summer to autumn. Moreover, results showed diets being similar in head and middle of channel where crayfish mostly rely on macroinvertebrates and macrophytes, while in the mouth of the channel diet seems to shift more towards periphyton. Diet also changed from protein-rich in spring to vegetation-based diet in autumn. Based on the results, temperature had important role in the marbled crayfish establishment in the invaded channel, however the distribution of its population might have been affected by ecological aspects rather than temperature, like better food availability in the head of the channel.


Keywords: invasive species • trophic niche • temperature • Procambarus virginalis • stable isotopes

Note: Embargoed until 3 September 2021.

27 May 2021

Marmorkrebs in Taipei update

Last November, I reported on Marmorkrebs were found in Taipei, but they seemed to be confined to a single park pond. A brief mention in a new story suggests there is a second location that has become home to a population of Marmorkrebs. 

The firefly restoration ecological pond in Taipei’s Daan Forest Park is being invaded by an exotic species, the many-rayed sailfin sucker catfish, while Neihu District’s (內湖) Bihu Park is being invaded by the invasive marbled crayfish, causing ecological balance issues, the office said.


Emphasis added.


Marmorkrebs were previously reported in Daan Forest Park, so it is not entirely clear to me if Marmorkrebs are in two parks, or id the reporter inadvertently switched the two locations. I have updated the map of Marmorkrebs introductions with the second Taipei location, but noted the uncertainty.


External links

Taipei to issue fines for feeding wildlife in parks


Related posts


Marmorkrebs’ second Asian invasion

14 May 2021

Roje and colleagues 2021

Roje S, Richter L, Worischka S, Let M, Veselý L, Buřič M. 2021. Round goby versus marbled crayfish: Alien invasive predators and competitors. Knowledge and Management of Aquatic Ecosystems 422: 18. https://doi.org/10.1051/kmae/2021019



Aquatic biodiversity is threatened by spread of invasive alien species. Round goby Neogobius melanostomus is an invasive fish in large European rivers as well as in coastal waters near their mouths and marbled crayfish Procambarus virginalis is a highly invasive crustacean. Both are small, bottom-dwelling species occupying similar habitat and shelters and utilizing similar food sources. We hypothesized that goby presents a threat to both native and non-native astacofauna in invaded ecosystems. We tested this through laboratory experiments designed to determine aggressiveness and competitiveness of goby against marbled crayfish as a model for other North American cambarid crayfish, assessing goby prey size selection and competition with marbled crayfish for space and shelter. Gobies showed high aggressiveness and dominance over the crayfish. Goby predation on juvenile crayfish was limited by mouth gape size. In goby/crayfish pairs of similar weight, gobies were more aggressive, although each affected the behavior of the other.


Keywords: Biological invasion • freshwater • predation • shelter competition • species interaction


Open access


11 May 2021

Kouba and colleagues 2021

Biology journal logo

Kouba A, Lipták B, Kubec J, Bláha M, Veselý L, Haubrock PJ, Oficialdegui FJ, Niksirat H, Patoka J, Buřič M. 2021. Survival, growth, and reproduction: Comparison of marbled crayfish with four prominent crayfish invaders. Biology 10(5): 422. https://www.mdpi.com/2079-7737/10/5/422



Biological invasions are increasingly recognized ecological and economic threats to biodiversity and are projected to increase in the future. Introduced freshwater crayfish in particular are protruding invaders, exerting tremendous impacts on native biodiversity and ecosystem functioning, as exemplified by the North American spiny-cheek, signal and red swamp crayfish as well as the Australian common yabby. The marbled crayfish is among the most outstanding freshwater crayfish invaders due to its parthenogenetic reproduction combined with early maturation and high fecundity. As their introduced ranges expand, their sympatric populations become more frequent. The question of which species and under what circumstances will dominate in their introduced communities is of great interest to biodiversity conservation as it can offer valuable insights for understanding and prioritization of management efforts. In order to examine which of the aforementioned species may be more successful as an invader, we conducted a set of independent trials evaluating survival, growth, claw injury, and reproduction using single-species stocks (intraspecific interactions) and mixed stocks (interspecific interactions) of marbled crayfish vs. other crayfish invaders since the onset of exogenous feeding. In both single and mixed stocks, red swamp crayfish and yabby grew faster than marbled crayfish, while marbled crayfish were superior to both spiny-cheek and signal crayfish in terms of growth. With the exception of signal crayfish, the faster-growing species consistently reached a higher survival rate. The faster-growing species tended to negatively impair smaller counterparts by greater claw injury, delayed maturation, and reduced fecundity. Only marbled crayfish laid eggs as early as 14 weeks in this study, which is earlier than previously reported in the literature. Thus, the success of marbled crayfish among invasive crayfish is significantly driven by relatively fast growth as well as an early and frequent reproduction. These results shed light on how interactions between invasive populations can unfold when their expansion ranges overlap in the wild, thereby contributing to the knowledge base on the complex population dynamics between existing and emerging invasive species. 

Keywords: Biological invasion • pet trade • animal release • species interactions • sympatry

Open access

30 April 2021

Zoobabies, 2021 edition

The Cincinatti Enquirer answers a question I’ve been wondering for a while. 


Some years ago, I noted the Cincinatti Zoo had a display of “Marbled crayfish” and listed them as Procambarus fallax. The zoo’s description mentioned nothing about asexual reproduction, so I thought they were slough crayfish from Florida or Georgia.

But a new article about the zoo says:


This baby marbled crayfish resembles a small lobster, but it will only grow to 2 to 3 inches long. All marbled crayfish are women. They don't need a partner to reproduce.

Marmorkrebs they are, then! Which makes me wonder why their reproduction wasn’t mentioned on the display.

Related posts


Zoo babies


External links


Up close with the Cincinnati Zoo's most adorable ambassadors

29 April 2021

International Conference on Aquatic Invasive Species 2022

International Conference on Aquatic Invasive Species logo

The date for the next conference on aquatic invasive species will be 18-22 April 2022 in Belgium. It will be a mix of in person and online and the focus will be on climate change. But I’m sure there will be some crayfish content!


It must be challenging to plan conferences, since COVID-19 is still out of control in some regions but maybe coming under control with vaccination and we really don’t know what will happen.

External links


22nd International Conference on Aquatic Invasive Species

22 April 2021

Ontario seeks public comment on regulating marbled crayfish

Ontario Ministry of Natural Resources

Nation Valley News reports that Ontario is moving to the next phase of a process that could result in the regulation of Marmorkrebs in the province, along with twelve other aquatic species.


The first round of consultation identified “no significant concerns” of regulating Marmorkrebs.


A ban on Marmorkrebs in Ontario would arguably be the most significant regulatory action in North America yet implemented. Ontario is Canada’s most populous province. It’s also one of the largest single jurisdictions in terms of size in North America. Currently, Marmorkrebs are routinely available in the pet trade.

Louisiana red swamp crayfish (Procambarus clarkii) are also on the list. This crayfish would get an exception for its use as food.

Comment is open until 7 June 2021.

External links


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


Seeking information on invasive species and carriers under the Ontario Invasive Species Act, 2015 (closed)


Province seeks input into wild pig strategy and updates to Invasive Species Act

19 April 2021

Scheers and colleagues 2021

BioInvasions Records cover.

Scheers K, Brys R, Abeel T, Halfmaerten D, Neyrinck S, Adriaens T. 2021. The invasive parthenogenetic marbled crayfish Procambarus virginalis Lyko, 2017 gets foothold in Belgium. BioInvasions Records 10(2): 326-340. https://doi.org/10.3391/bir.2021.10.2.11




In 2020, four populations of the marbled crayfish Procambarus virginalis, which is included on the list of Invasive Alien Species of Union concern, were discovered in northern Belgium. These records represent the first established populations of this invasive parthenogenetic species in the Benelux. The marbled crayfish seems well established at all sites where it was discovered. Genetic analysis confirmed the species’ identity with the obtained COI Folmer fragments being 100 percent identical to reference sequences of P. virginalis from Germany, Italy, Sweden and the Czech Republic. We proposed a single diagnostic nucleotide for unambiguous character-based species identification between P. virginalis and P. fallax. The finding of this new species through opportunistic surveys instigated by citizen science reports indicates considerable knowledge gaps on crayfish distribution in Belgium. Considering the regulated status of most species in Belgium, we advocated the further set-up of dedicated crayfish surveillance using passive and active monitoring including environmental DNA detection.


Keywords: invasive species, Cambaridae, non-native species, Procambarus fallax forma virginalis

Open access

Stara and colleagues 2021

Chemosphere cover

Stara A, Zuskova E, Vesely L, Kouba A, Velisek J. 2021. Single and combined effects of thiacloprid concentration, exposure duration, and water temperature on marbled crayfish Procambarus virginalis. Chemosphere 273: 128463. https://doi.org/10.1016/j.chemosphere.2020.128463


The increasing utilization of chemicals and ongoing climate change have a negative impact on aquatic ecosystems. The present study examined combined effects of water temperature, chemical concentration, and duration of exposure to the neonicotinoid thiacloprid on marbled crayfish Procambarus virginalis. Crayfish were exposed to thiacloprid at the environmental concentration of 4.50 μg L-1 and 10% 96LC50 to marbled crayfish, 64.64 μg L-1, at water temperature of 17 and 23°C for 28 days followed by a 28 day depuration period. No crayfish died during the experiment. Both thiacloprid concentrations at 23°C showed a synergistic effect with temperature on the biochemical indicators in haemolymph compared to those at 17°C. Both concentrations of thiacloprid at both temperatures were associated with significant differences from thiacloprid-free controls (P < 0.01) in haemolymph glucose, ammonia, calcium, inorganic phosphate, and lactate; haemolymph enzymes aspartate aminotransferase, alanine aminotransferase, creatine kinase, and alkaline phosphatase; antioxidant biomarkers superoxide dismutase, catalase, glutathione S-transferase, and reduced glutathione in hepatopancreas, muscle, and gill, and showed lipid peroxidation in hepatopancreas and muscle. Histological analyses revealed structural changes and damage to gill and hepatopancreas of exposed crayfish.

Keywords: neonicotinoid • insecticide • non-target organism • synergism • haemolymph • antioxidants

Grandjean and colleagues 2021

BioInvasions Records cover.

Grandjean F, Collas M, Uriarte M, Rousset M. 2021. First record of a marbled crayfish Procambarus virginalis (Lyko, 2017) population in France. BioInvasions Records 10(2): 341-347. https://doi.org/10.3391/bir.2021.10.2.12




Here we report the first record of marbled crayfish Procambarus virginalis in France. In total, 34 individuals were found in a pond close to the Moselle River, coexisting with the invasive Faxonius limosus and the native Astacus astacus. Their presence seems limited to one pond of the seven located in this area, probably due to a very recent human introduction. Molecular analyses based on COI mt gene confirmed the morphological identification of captured specimens as marbled crayfish. The risk of spread to the Moselle is very high particularly during flood periods. Management recommendations are given. 


Keywords: invasive species • parthenogenetic crayfish • coexisting crayfish species • mitochondrial DNA

Open access

18 April 2021

Ohio lists Marmorkrebs as “Injurious aquatic invasive species”

Map of United States with Ohio highlighted.

Ohio is the latest North American jurisdiction to regulate Marmorkrebs.


In a PDF dated 9 April 2021 in the file name, Marmorkrebs is designated an Injurious Aquatic Invasive Species (IAIS). The one page pamphlet notes:


Listed species are unlawful to possess, import, or sell unless dead and/or preserved.

However, the Department of Natural Resources list of injurious aquatic invasive species is on a page that says “Published on Jul 31, 2020” in the search results. So it’s possible that Marmorkrebs were already listed last year and the new document is just the start of publicizing the new regulation. Another PDF from Spring 2019 indicates that Ohio was planning to add marbled crayfish to the list. But it hadn’t happened yet.

It’s symptomatic of a recurring problem. I, as someone who actually cares about when new regulations about this species are passed, cannot find out when these things happen. What chance does a normal pet owner with a 10 gallon aquarium have?

External links


Marbled Crayfish (Marmorkrebs) Control in Ohio (PDF)

Injurious Aquatic Invasive Species


09 April 2021

New website: The Perfect Invader

The Perfect Invader logo

The Perfect Invader is a new project to examine how the introduction of Marmorkrebs in Madagascar is affecting human health. 


Part of the project is looking at how people are eating Marmorkrebs. Some of that has already been published (e.g., here and here).


A newer aspect of the project, which I’ve seen in relation to other crayfish, but not Marmorkrebs, is how the crayfish affect schistosomiasis infections.


Check it out!


External links


The Perfect Invader


17 March 2021

Okada and colleagues 2021

The Journal of Experimental Biology cover

Okada S, Hirano N, Abe T, Nagayama T. 2021. Aversive operant conditioning alters the phototactic orientation of the marbled crayfish. The Journal of Experimental Biology 224(6): jeb242180. https://doi.org/10.1242/jeb.242180




Aversive learning was applied to affect the phototactic behaviour of the marbled crayfish. Animals initially showed negative phototaxis to white light and positive taxis to blue light. Using an aversive learning paradigm, we investigated the plasticity of innate behaviour following operant conditioning. The initial rate of choosing a blue-lit exit was analysed by a dual choice experiment between blue-lit and white-lit exits in pre-test conditions. During training, electrical shocks were applied to the animals when they oriented to the blue-lit exit. Memory tests were given to analyse the orientation rate to the blue-lit exit in trials 1 h and 24 h after training and these rates were compared with the pre-test. In general, animals avoided the blue-lit exit in the memory tests. When training was done three times, the long-term memory was retained for at least 48 h, although a single bout of training was also enough to form a long-term memory. Cooling animals at 4 °C or injection of cycloheximide immediately after training altered the formation of long-term memory, but had no effect on short-term memory formation. Administration of the adenylate cyclase inhibitor SQ22536, the PKA inhibitor H89, or the CREB inhibitor KG-501 immediately after training also blocked the formation of long-term memory, but had no effect on short-term memory formation. Thus, our pharmacological behavioural analyses showed that new protein synthesis was necessary to form long-term memories and that the cAMP/PKA/CREB pathway is the main signal cascade for long-term memory formation in the marbled crayfish.


Keywords: None provided.

26 February 2021

Heroes release zeroes

The Illinois-Indiana Sea Grant has started a new campaign against invasive species. The aquatic species arm of the campaign is Release Zero.


I particularly appreciate the point that it’s hard to be a responsible pet owner when so many providers don’t know or provide scientific names. There are hundreds of species of crayfish with different invasive potential, so just selling “crayfish” is irresponsible. There is a great need for quick, high quality ways of identifying species in the pet trade.


Marmorkrebs are not featured on the main webpage, but are species of concern for the Great Lakes, as the project’s Twitter account points out.


Wild marbled crayfish populations are established across Europe and elsewhere. They have NOT been found in the Great Lakes! 🙌 Aquarium owners, anglers and others can help keep it that way.

We need way more education on this, so I hope this campaign is very successful!

External links


Release Zero website

24 February 2021

Marmorkrebs talk online, 26 February 2021

Seminar announcement poster featuring Saisupritha Talasu is presenting “Identifying various biogenic amine receptors in Procambarus virginalis”

Wolfgang Stein announced a seminar about Marmorkrebs will be held on Zoom!

Saisupritha Talasu is presenting “Identifying various biogenic amine receptors in Procambarus virginalis” at 12:00 pm (noon) Central time on Friday, 26 February 2021. The Zoom meeting ID is 630 494 073.

It will be followed by a talk on escape responses, species unknown.

19 February 2021

Invasive Species Week is coming...

 Mark your calendars for 24 May, 2021. That will be the start of Invasive Species Week.

Invasive Species Week, 24-30 May 2021.

This blog will be participating, naturally!

External links


Invasive Species Week

15 February 2021

Wen 2020

Swedish University of Agricultural Sciences logo
Wen Y. 2020. Characterization of MITF gene in crayfish and their possible role in innate immunity. Master’s thesis, Department of Animal Breeding and Genetics, Sveriges lantbruksuniversitet (Swedish University of Agricultural Sciences). http://urn.kb.se/resolve?urn=urn:nbn:se:slu:epsilon-s-16418


Microphthalmia-associated transcription factor (MITF) is a tissue-specific transcription factor (TF), with a basic helix-loop-helix leucine zipper (bHLH-LZ) domain, which binds to the canonical E-box sequence (5’-CANNTG-3’) in the promoter region of target genes. In this study, the MITF-like protein was identified in the marbled crayfish (Procambarus virginalis). The full-length cDNA coding sequence of the most similar gene to MITF from marbled crayfish is 1284bp (427 amino acids). In the secondary and tertiary structure of the deduced amino acid sequence, a conserved functional structure of bHLH-LZ was shown, which could bind to E-box. In the phylogenetic analysis, this obtained MITF-like gene showed a lager evolutionary distance to all the vertebrates and some invertebrates like lancelet (Branchiostoma belcheri), starfish (Acanthaster planci), sea urchin (Paracentrotus lividus) and (Lytechinus variegatus), but is closer than worms (Caenorhabditis elegans). The bHLH-LZ domain is located in exon 6, exon 7, exon 8, and exon 9 in the MITF gene and has a similar structure as the corresponding exons in human. Besides, in this study, a comparison of exon-intron structure of MITF between human, mouse, fruit fly and marbled crayfish was performed, it was shown that the splicing sites of the bHLH-LZ domain in MITF gene might be conserved across species. To evaluate the possible role of MITF as a TF in innate immune system regulation, a similar prophenoloxidase (proPO) DNA sequence was analysed for the presence of E-box. The proPO gene is responsible for trapping and myelinization of pathogens in invertebrate. The proPO-like gene of marbled crayfish contains eight CANNTG sequences. In addition, anti-apoptotic factor (BCL-2)-like gene was found in marbled crayfish and four CANNTG sequences were found. Our results provided evidence of the presence of MITF-like gene in crayfish species and may provide knowledge on the role of MITF in innate immune activation.

Keywords: Microphthalmia-associated transcription factor • basic Helix-Loop-Helix Leucine Zipper • crayfish • Aphanomyces astaci • immunity

12 February 2021

Marmorkrebs continue advance in Asia

Map of China showing Macao.
Marmorkrebs have been found near the mainland of the People’s Republic of China, according to the Macao Daily Times.

The news article is short on details, like how many crayfish or exactly where they were found, with the newspaper simply referring to a “leisure area” on Taipa in Macau. Taipa is technically an island, but sits so close to the mainland that it is connected by reclaimed land. 

The impact of Marmorkrebs in China could be immense. The Louisiana red swamp crayfish was embraced by the restaurant business and is now one of the most popular dishes in China, so there is clearly money to be made on crayfish.

But one of the interesting points of the article is that the concern about invasive species it lists is different than other countries. The article raises the fear that invasive will remove natives that are used for... traditional Chinese medicine.

The map of Marmorkrebs introductions has been updated.

Update: The Macau Post Daily has an article with a little more detail. It sounds like it was a single individual. It also gave a more precise location: “the ecological pond in the Camellia Garden.” Which, unfortunately, I cannot find on Google Maps yet.


There is no information up at the Municipal Affairs Bureau yet. At least not on the English site. 


More update: Ah, here’s the park with Camellia Garden. And this seems to be the person who found them.


External links

Foreign species of crayfish, hazardous to local ecology, found in Taipa

Invasive marbled crayfish found on Big Taipa Hill: IAM