Posted by: genghisprawn | August 24, 2008

Egyptian Crayfish: A Follow-Up

As I looked further into Procambarus clarkii‘s invasion of the Egyptian Nile, it became increasingly apparent that the CNN article I reviewed in my last post was little more than a jumble of hearsay and poor research.

Wizen et al. (2008), reporting on the first confirmed record of P. clarkii in Israel, look to Egypt as a cautionary tale. The 2005 overview they cite provides a likelier background story (well, no overt talk of prawn-eggs-that-weren’t) and a more definite geographic distribution:

A shrimp farmer in Al Qanater released the imported crayfish into the Nile in the 1980s after they had damaged the mud banks of his ponds. The crayfish have since spread from the Delta to Bani Swaif, 500 km to the south of Cairo, with densities as high as 0.65/m² (El Zein 2005). The crayfish damaged earth dams, irrigation canals and fish stock, and though marketed, are considered of little commercial value. El Zein (2005) admits “such an introduction is now recognized to have bad consequences on biodiversity without economical profits”.

Rosy visions of Zydeco ‘n crawfish festivals on the Nile notwithstanding, the Louisiana mudbug suffers from more than an image problem. Elmossalami and Emara (1999) raise concerns of bacterial contamination — though to what extent they’d be mitigated by common cooking methods remains unknown to me:

The average aerobic plate and Enterobacteriaceae counts/g were 1.6 × 108 and 3.5 × 105, and the coliforms and E. coli were isolated from 100% and 40% of the examined samples respectively. However, Salmonellae could not be isolated from any of the examined samples. 20% of the samples were safe for human consumption, while 33.33% were marginally acceptable and 46.67% were unacceptable.

Interestingly enough, Magdi Tawfik (professor of zoology at Ain Shams University) had in 2003 assured readers of Al-Ahram weekly that consumers had nothing to fear. Name-calling by less sympathetic Cairenes aside (“sea cockroach,” “poisonous insect”), Tawfik gave an approving nod to ecdysis:

Tawfik explained that while the crayfish “clean the Nile water from harmful pollutants, its shell is shed five to six times a year, ridding the crayfish of harmful pollutants. Hence the poisonous material absorbed into the shell does not affect the meat of the crayfish.”

How is Tawfik so sure that pollutants stay sequestered in the exoskeleton, never to befoul organ or muscle tissue? What if you catch an intermolt crayfish and, horror of all horrors, boil it shell and all? Finally, what of P. clarkii‘s customary habit of consuming its molts?

To close, some photos from blogger Khalid Baheyeldin:

Crayfish in Bahr Mouweiss, a canal in Zagazig, El Sharqeyya, Egypt.  Burrow at left.

Crayfish and crayfish burrow (see left of image) in Bahr Mouweiss, a canal in Zagazig, El Sharqeyya, Egypt.

Crayfish for sale in El Meidan market in old Alexandria. They are quite cheap, and not much in demand it seems.

"Crayfish for sale in El Meidan market in old Alexandria. They are quite cheap, and not much in demand it seems."

Resources:

Baheyeldin, Khalid. “Crayfish introduction to the Nile Delta and its effects.”
Weblog post. The Baheyeldin Dynasty. 22 Mar. 2007 <http://baheyeldin.com/writings/science/crayfish-introduction-to-the-nile-delta-and-its-effects.html>.

Elmossalami, M. K., and M. T. Emara. “Safety and quality of fresh water crayfish Procambarus clarkii in the river Nile.” Nahrung / Food 43.2 (Apr. 1999): 126 – 128. 24 Aug. 2008 <http://www3.interscience.wiley.com/journal/60500951/abstract?CRETRY=1&SRETRY=0>.

El Zein G (2005) Introduction and impact of the crayfish Procambarus clarkii in the Egyptian Nile.
L’Astaciculteur de France 84: 1-12

Mahmoud, Lina. “Not Just Ugly.” Al-Ahram Weekly 9 Oct. 2003. 24 Aug. 2008
<http://weekly.ahram.org.eg/2003/659/fe2.htm>.

Wizen, Gil, et al. “First record of red swamp crayfish, Procambarus clarkii (Girard, 1852) (Crustacea: Decapoda: Cambaridae) in Israel – too late to eradicate?” Aquatic Invasions 3.2 (June 2008): 181-185. 24 Aug. 2008
<http://www.aquaticinvasions.ru/2008/AI_2008_3_2_Wizen_etal.pdf>.

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