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almost all species studied so far, including roach (
R. rutilus
), gudgeon (
Gobio gobio
), chub
(
Squalius cephalus
), rudd (
Scardinius erythrophthalmus
), and bream (
Abramis brama
). Species
such as flounder (
P. l e su s
) and smelt (
Osmerus eperlanus
), which are euryhaline fish spend-
ing only part of their life in the estuary and therefore may be less exposed, are nevertheless
affected. It was suggested that these effects could not be found in the sea because the dilu-
tion of the compounds would be too large, yet intersex individuals of swordfish (
Xiphias
gladius
) and red mullet
Mullus barbatus
have been found particularly in the Mediterranean
Sea (De Metrio et al. 2003; Martín-Skilton et al. 2006).
The most noticeable effects observed in fish populations studied seem to indicate that
EDCs lead to a feminization of individuals. Yet laboratory studies show that it is possible
to completely reverse the phenotypic sex (Nimrod and Benson 1998). Such effects could
possibly occur in the field. Unfortunately, there is no genetic sex marker for roach and
flounder. Despite this lack of genetic tool, and although a causal relationship between the
occurrence of intersex fish and specific EDCs in the field cannot be firmly established, it
was found that the number of males is significantly lower than those of females in the
Seine estuary. Male roach, flounder, and gobies (
Pomatoschitus minutus
) account only for
less than 40% of the fish population in the Seine estuary. These figures may be indicative
of an effect on the population level on sexual development.
Other cytological changes accompany these histological changes. The frequency of
necrosis observed in the gonads of intersex fish is twice that of normal individuals. These
alterations indicate that molecular mechanisms are disrupted in the reproductive organs
and may further reduce the reproductive capacity of the fish. Another molecular altera-
tion is often observed: numerous oocytes in intersex fish from the Seine estuary undergo
abnormal cell divisions leading to the appearance of several nuclei within a cell. Such an
effect has been reported only twice in the literature. The first time was from an experiment
conducted on rats with very high doses of a very potent EDC, diethylstilbestrol, whose
effects were dramatic in men (Igushi et al. 1990). The second time was after a major spill
of several pesticides in Lake Apopka in Florida that led to major effects in populations
of alligators (
Alligator mississippiensis
) (Guillette et al. 1994). Steroid hormone plasma con-
centrations were significantly altered, and male alligators developed only a small penis.
A decrease in the number of individuals was observed in the 10 years after the spill. The
cytological changes observed in fish gonads are the result of alterations in crucial molecu-
lar mechanisms and may be indicative of other potential effects. Indeed, EDCs could be
responsible for long-term effects by affecting the DNA. It should be noted that some EDCs
are carcinogenic; steroids, in particular, are tumor promoters and could be involved in
tumor development in vertebrates (Hankinson and Eliassen 2007).
9.2.6 Long-Term Consequences
The Seine estuary appears to be the recipient of many contaminants, some of which clearly
affect the endocrine system of fish. The most obvious effect is feminization of male fish
that produce female proteins and the testes of which show developing oocytes. The recur-
ring and important question is “What are the effects on populations in the long term?”
It may seem obvious, since reproduction is the basis of population turnover, that reduc-
tions in population number will occur. Such effects are, however, still largely speculative
in natural environments. Nevertheless, it is important to note that the observed effects
on fish in the Seine estuary are comparable to those that led to the disappearance of the
population of minnows (
Pimephales promelas
)
after 7 years of experimentation in a lake in
Ontario (Kidd et al. 2007).
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