28 May 2020

Velisek and colleagues 2020b

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


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

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

26 May 2020

Marmorkrebs illegal in Saskatchewan

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

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

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

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

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

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

External links

Saskatchewan remains free of zebra and quagga mussels

Sakskatchewan Ministry of Environment

Saskatchewan Gazette, 3 April 2020 (PDF)

Trying Leviathan: The Nineteenth-Century New York Court Case That Put the Whale on Trial and Challenged the Order of Nature

23 May 2020

Marmorkrebs in The Times

This a Jeopardy! style post. The answer is:

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

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

External links

The Times Saturday Quiz: May 23, 2020

15 May 2020

No Marmorkrebs in Michigan

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

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

  • Dispose of it humanely

  • Do not flush it

  • Don’t sell it to someone in another state (that’s also illegal)

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

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

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

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

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

The coverage here made me laugh:

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

Related posts

Michigan considering prohibiting Marmorkrebs

External links

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

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

Michigan adds invasive marbled crayfish to prohibited species list

Michigan bans marbled crayfish, which reproduces rapidly by genetic cloning

Michigan Outlaws Self-Cloning “Marbled Crayfish”

Self-cloning marbled crayfish banned from Michigan

Great Lakes Commission

Marbled crayfish placed on Michigan’s prohibited species list

12 May 2020

Celebrate diversity: All females, all prawns

Ars Technica has a big feature article on all female crustaceans being used for food, but it’s not Marmorkrebs.

Marmorkrebs are being used as food in Madagascar (see Andriantsoaet al. 2019, 2020) and there is interest in developing them for commercial aquaculture (Jurmalietiset et al. 2019), but there is not much of an existing market for crayfish this small.

Freshwater prawns (Macrobrachium rosenbergii) are another matter. They are widely cultivated and harvested for food in many countries. There was a challenge on The Amazing Race (American version, Season 31, Episode 3) where teams caught them from an indoor fishing center in Vietnam.

I hadn’t been paying close attention to a company called Enzootic that has created a way of making prawns all female. Unlike Marmorkrebs, which are genetically distinct, this company takes advantage of plasticity in sex determination in this species:

It starts by surgically extracting the hormone-producing organ from “donor” males, which are then broken down into individual cells. When the cells are injected into young females, the hormones they produce cause the females to develop as males, despite their chromosomes. Just like natural male prawns, they can mate normally with other females, but some of their offspring possess a unique trait. Known as “super females,” they produce offspring that will develop as females regardless of the chromosomes they carry.

Enzootic has set up the genetics of its shrimp so that these super females are relatively easy to identify, and they can be used to quickly produce large populations of nothing but females.

Some technical papers on this process are Sagi and Aflalo (2005) Mohanakumaran et al. (2006), and Levy et al. (2017).


Andriantsoa R, Jones JPG, Achimescu V, Randrianarison H, Raselimanana M, Andriatsitohaina M, Rasamy J, Lyko F. 2020. Perceived socio-economic impacts of the marbled crayfish invasion in Madagascar. PLOS ONE 15(4): e0231773. https://doi.org/10.1371/journal.pone.0231773

Andriantsoa R, Tönges S, Panteleit J, Theissinger K, Carneiro VC, Rasamy J, Lyko F. 2019. Ecological plasticity and commercial impact of invasive marbled crayfish populations in Madagascar. BMC Ecology 19(1): 8. https://doi.org/10.1186/s12898-019-0224-1

Jurmalietis R, Grickus A, Elstina A. 2019. Marbled crayfish (Procambarus virginalis) as a promising object for aquaculture industry. In: Environment. Technology. Resources. Proceedings of the 12th International Scientific and Practical Conference, Volume 1, pp. 92-95. http://dx.doi.org/10.17770/etr2019vol1.4174

Levy T, Rosen O, Eilam B, Azulay D, Zohar I, Aflalo ED, Benet A, Naor A, Shechter A, Sagi A. 2017. All-female monosex culture in the freshwater prawn Macrobrachium rosenbergii – A comparative large-scale field study. Aquaculture 479: 857-862. https://doi.org/10.1016/j.aquaculture.2017.07.039

Mohanakumaran Nair C, Salin KR, Raju MS, Sebastian M. 2006. Economic analysis of monosex culture of giant freshwater prawn (Macrobrachium rosenbergii De Man): a case study. Aquaculture Research 37(9): 949-954. https://doi.org/10.1111/j.1365-2109.2006.01521.x

Sagi A, Aflalo ED. 2005. The androgenic gland and monosex culture of freshwater prawn Macrobrachium rosenbergii (De Man): a biotechnological perspective. Aquaculture Research 36(3): 231-237. https://doi.org/10.1111/j.1365-2109.2005.01238.x

External links

Can gender-bending Israeli superprawns help feed the world?

Jurmalietis and colleagues, 2019

Jurmalietis R, Grickus A, Elstina A. 2019. Marbled crayfish (Procambarus virginalis) as a promising object for aquaculture industry. In: Environment. Technology. Resources. Proceedings of the 12th International Scientific and Practical Conference, Volume 1, pp. 92-95. http://dx.doi.org/10.17770/etr2019vol1.4174


Marbled crayfish / marmorkrebs, parthenogenetically reproducing decapod crustacean of pet aquarium origin conventionally has been recognized as an undesirable species since it a) is an invasive pest dangerous for aquatic ecosystem resources because of its hardiness, omnivorousness, fast growth, self-cloning abilities; b) has little commercial value for food industry. However, recently an idea has been introduced about marmorkrebs as a promising cheap protein source, which can help to fight world hunger. Accordingly, research performed at Liepaja University (Latvia) was focused on marbled crayfish farming system design issues. Research paper presented discusses marmorkrebs survival capacities in small-volume microcosm tanks (made from recycled material), under harsh abiotic conditions. Pilot research results obtained will be used to develop experimental project on low-input microcosmic indoor aquaculture for marmorkrebs.

Keywords: crayfish • aquaculture • ecological microcosms