Biology Reference
In-Depth Information
CHAPTER
7
Eel Secondary Metamorphosis:
Silvering
Karine Rousseau,
1,a
Salima Aroua
1
and
Sylvie Dufour
1,b,
*
7.1 Introduction
As mentioned before, secondary metamorphosis, which occurs in
juveniles, involves various morphological, physiological and behavioral
modifi cations that pre-adapt the animal to life in a new environment. These
modifi cations are less drastic than those observed during larval/true/fi rst
metamorphosis.
This type of metamorphosis in teleosts seems to be related
to extreme migration and complex biological cycles, as observed in salmons
(smoltifi cation) and eels (silvering).
Eels have complex migratory life cycle with the occurrence of two
metamorphoses (for reviews: Sinha and Jones, 1975; Tesch, 1977; Haro,
2003; Dufour and Rousseau, 2007; Rousseau and Dufour, 2008)(Fig. 1).
They present a typical larval (fi rst) metamorphosis, leptocephali larva being
transformed into glass eels (See Chapter 3). After this drastic transformation,
the growth phase starts in the continental waters and glass eels become
elvers and “yellow” eels. After many years in freshwater, the yellow eels
transform into “silver” eels which stop growing and start their downstream
migration towards the ocean and the area of reproduction. To allow this
transition from sedentary life in freshwater to migrant life in seawater,
eels undergo their second metamorphosis, known as silvering. Silvering
not only preadapts the eel to deep-sea conditions (Sébert, 2003), but also
prepares the sexual maturation, which will only be completed during the
1
Research Unit BOREA «Biology of Aquatic Organisms and Ecosystems» Muséum National
d'Histoire Naturelle, CNRS 7208, IRD 207, UPMC, 7 rue Cuvier, CP32, 75231 Paris Cedex 05,
France.
a
E-mail: rousse@mnhn.fr
b
E-mail: dufour@mnhn.fr
*Corresponding author
