ABSTRACT
The sensitivity of early development stages to various pollutants has been frequently reported for many aquatic animals such as sea urchins, bivalves, corals and fi sh species (Bellas et al., 2005; Farina et al., 2008; Cao et al., 2010; Wright, 1995). Larvae have important roles in the life cycle of marine organisms as during this phase there are dramatic morphological and physiological changes that lead to the growth of adult form. Despite their importance, data concerning the toxicity of pollutants in larvae is scarce (Bellas et al., 2005; Farina et al., 2008). During this phase the organisms are less tolerant than embryos or adults to the various kinds of toxicants. The resistance of fi sh embryos and larvae to stressors depends on their taxonomic and phylogenic position. For instance, the cartilaginous fi shes are characterized by life cycle attributes that result in low intrinsic rates of increase, making their population highly sensitive to environmental impacts. These qualities include low fecundity that is expressed in the production of a relatively small number of large, heavily yolked eggs in the oviparous species, which comprise about 40% of the sharks and all skates. These embryos develop slowly following their laying in nursery grounds, commonly found in shallow coastal waters that are highly impacted due to human activity. The distribution of Chondrichthyan eggs in polluted habitats could enhance their exposure to elevated contaminant levels during this long early phase of development which is most susceptible to environmental pollutants in teleost fi sh, particularly for metals (Jeffree et al., 2008). Structural and functional characteristics of fi sh eggs demonstrated that the following attributes may contribute to high accumulation of pollutants (Knight et al., 1996; Jeffree et al., 2008):
• the indicated oxidative phenolic cross-linking of the case, in combination with bound catechol groups in the outermost layer, to facilitate the chelation of metals from seawater;
• the presence of disulphide bonds that act in the stabilization of eggcase collagen could be expected to provide strong binding sites for metalchelation, particularly of inorganic Hg and Pb;
• the high internal surface area that is created by the open meshwork structure of the collagen fi bres that make up the laminae of the egg-case layers would increase sites for the potential absorption of elements passing through the transverse channels in the wall.
