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locomotion since metabolic enzyme studies in parallel fish groups indicated that catabolic,
energy-providing mechanisms were activated (Konradt et al. 1996 quoted in Triebskorn
et al. 1997). These findings were in agreement with the liver ultrastructure showing an
increase in the number of mitochondria and a reduction of glycogen storage. As shown
by these authors, histocytological examinations can help to detect energy metabolism
impairments. Structural alterations of mitochondria may be interpreted as a disturbance
of cellular respiratory mechanisms (Ballan-Dufrançais et al. 1990; Ettajani et al. 1996).
Histochemistry clearly provides added value to histological examination, giving access to
changes in cellular or tissue energy reserves such as the depletion of glycogen discussed
above after Triebskorn et al. (1997), or the depletion and recovery of glycogen in interstitial
tissues of oysters Crassostrea gigas exposed to silver then allowed to depurate in clean water
(Berthet et al. 1990), a pattern that may be explained by the energy cost of combating envi-
ronmental contaminants (Chapter 3). Histological lesions of the digestive gland observed
in the New Zealand mudsnail Potamopyrgus antipodarum exposed to multimetal pollution
in the field, apparently explain at least partly the decrease in energy reserves (triglycerides
and proteins), juvenile growth, and adult fecundity at the most contaminated site (Gust
et al. 2011).
Early life stages of organisms are generally the most sensitive to stress. Thus, effects
on germinal cells reported above as the consequence of exposure to effluents (Ballan-
Dufrançais et al. 1990) or genotoxicants (Lewis and Galloway 2009; Lacaze et al. 2010;
Devaux et al. 2011) may be suspected to affect the success of reproduction. Embryotoxicity
(such as histological impairments and associated behavioral disturbances described by
Johnson et al. 2007) or malformations associated with other impairments of embryo-larval
development in zebrafish embryos exposed to ZnO NPs described by Bai et al. (2010) is
also a source of concern from this point of view. We have not discussed in this chapter the
histopathological impairments that occur as a consequence of pollution by endocrine dis-
ruptors, such as imposex in gastropods and intersex in fish and bivalves (Chapters 8 and
9), but they also have potential to predict ecological disturbances through altered success
of reproduction.
In conclusion, biomarkers of damage reviewed in this chapter as well as lysosomal
biomarkers (Chapter 5), biomarkers of immunotoxicity (Chapter 6), endocrine disrup-
tion (Chapters 8 and 9), and genotoxicity (Chapter 13) provide precise information on the
health status of individuals. However, in most cases, it may be difficult to extrapolate to
the population level. Between infra- and supra-individual effects, a number of mecha-
nisms can interfere to mitigate and repair damage. In particular, the ecological signifi-
cance of oxidative damage cannot be assessed independently of antioxidant defense and
repair mechanisms (Metcalfe and Alonso-Alvarez 2010). In order to have an ecological
significance and therefore value, any infra-individual biomarker must be linked to a key
process in the functioning of organisms and their progeny. Among the approaches used
to study pollutant responses in aquatic organisms, those associated with the success of
reproduction are particularly able to provide relevant toxicological as well as ecological
information. Reproduction is indeed at a crossroads of numerous processes, notably hor-
mone levels, genetic changes, energy metabolism, and behavior. Even when it has not been
established that damage will lead to population depletion or local extinction through cas-
cading events, it is nevertheless important to know the effects of environmental toxicants
before they affect higher levels of organization, and many biomarkers of damage make
this possible. It has been proposed that the “precautionary principle” could be applied as
soon as a biochemical biomarker shows a value deviating significantly from normal levels
(Lopez-Barea 1994, in Flammarion 2000).
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