X-ray microanalysis (EDXMA) of cadmium-exposed eggs of Bothriocephalus acheilognathi (Cestoda: Bothriocephalidea) and the influence of this heavy metal on coracidial hatching and activity Mona Khalil a,b , David Furness a , Anthony Polwart a , Dave Hoole a, * a Institute of Science and Technology in Medicine, School of Life Sciences, Huxley Building, Keele University, Keele, Staffordshire ST5 5BG, UK b Zoology Department, Faculty of Science, Helwan University, Ain Helwan, Cairo, Egypt article info Article history: Received 12 November 2008 Received in revised form 22 January 2009 Accepted 10 February 2009 Keywords: Bothriocephalus acheilognathi Cestode Egg Coracidium Cadmium X-ray microanalysis abstract Over recent years it has been established that pollutants can have a significant impact on host-parasite systems in the aquatic environment, so much so that it has been proposed that parasite fauna may be a useful parameter to monitor water quality. Surprisingly, with perhaps the exception of trematodes and bioaccumulation in adult acanthocephalans, detailed observations on the interaction between hel- minths, particularly cestodes, and pollutants such as heavy metals, are lacking. In this study, eggs of the carp tapeworm, Bothriocephalus acheilognathi were exposed to a range of cadmium concentrations (0.1, 10, 100 and 10,000 lg/L) and coracidial hatching and survival assessed. Results indicated that the egg is highly resistant to heavy metal pollution and hatching occurs even at 10,000 lg/L. In contrast, the activity of the liberated coracidium significantly decreased after 1 h exposure to cadmium at 10 and 100 lg/L. Electron microscopic X-ray microanalysis of parasite eggs exposed to 1000 and 10,000 lg/L cadmium revealed that cadmium accumulates on the surface of the egg and does not pene- trate detectably into the enclosed coracidium. This means that the parasite eggs may be able to withstand a heavy metal pollutant incident. Ó 2009 Australian Society for Parasitology Inc. Published by Elsevier Ltd. All rights reserved. 1. Introduction The effects of pollution on the parasite fauna in aquatic host– parasite systems have become of interest over recent years not only to parasitologists but to biologists in general, following the realisation that they may serve as bioindicators of water quality. An increase in our knowledge of pollutant/parasite interactions is also fundamental to understanding the complex interactions that occur in parasite life cycles. Endohelminths are good models to monitor pollution owing to their complex life cycles and their greater biomass compared with other possible indicators such as parasitic protozoa. The effects of pollutants on endohelminths can occur at several stages within their life cycle. Most studies investigating the effects of pollution on helminths other than trematode stages such as eggs, miracidia, cercariae and metacercariae (Abd Allah et al., 1997; Morley et al., 2001a,b,c, 2002, 2003b; Pietrock et al., 2002) focus on metal accu- mulation in adult fish acanthocephalans and cestodes (Sures, 2003; Sures and Siddall, 1999; Sures et al., 1997). Parasites may serve as good biomonitors of aquatic pollution owing to their ability to take up and accumulate toxicants such as heavy metals in their tissues to a greater extent than that occurring in host organs or in water (Sures and Siddall, 2001). Studies on the interaction between cad- mium and the acanthocephalan, Pomphorhynchus laevis, have shown that the cystacanth contains lower levels of cadmium than the intermediate crustacean host, Gammarus pulex (Brown and Pascoe, 1989). In contrast, several studies carried out by Sures and co-workers have revealed that adult acanthocephalans which inhabit the intestine of their definitive fish host have the ability to take up and accumulate metals to much higher concentrations than their hosts (Sures and Taraschewski, 1995; Sures et al., 1994). In contrast to the above, very few studies have been carried out on the interaction between fish tapeworms and pollutants such as heavy metals (Pietrock and Marcogliese, 2003). Although there is no difference between lead burdens detected in the adult cestode Bothriocephalus scorpii and those present in the intestinal wall of its host, the turbot, Scophthalamus maximus, the posterior gravid proglottids of B. scorpii accumulate higher contents of lead and cadmium than the anterior, immature ones do (Sures et al., 1997). Indeed, previous studies on the somatic and reproductive tissues of Bothriocephalus acheilognathi have revealed that the par- asite accumulates selenium to a greater extent than its definitive fish host and that gravid segments of the worms contain more sele- nium than the scolex and the anterior, immature proglottids (Riggs et al., 1987). 0020-7519/$36.00 Ó 2009 Australian Society for Parasitology Inc. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijpara.2009.02.023 * Corresponding author. Tel.: +44 (0) 1782 733673; fax: +44 (0) 1782 733516. E-mail address: d.hoole@biol.keele.ac.uk (D. Hoole). International Journal for Parasitology 39 (2009) 1093–1098 Contents lists available at ScienceDirect International Journal for Parasitology journal homepage: www.elsevier.com/locate/ijpara