Biology Reference
In-Depth Information
acclimatization to high pressure, appear to be already present in silver eels
before pressure exposure. They also showed that Lake Balaton eels, which
never become silver and do not migrate (Biro, 1992), have an alteration in
aerobic metabolism and muscle fi bre maximal aerobic capacities after 3 days
under pressure, suggesting lower pressure tolerance (Vettier et al., 2003).
In
vitro
studies using permeabilised red muscle fi bres of silver eels suggested
that the best conditions to optimize energy metabolism were low temperature
combined to high pressure (Scaion et al., 2008). High hydrostatic pressure
(101 ATA) improves the swimming effi ciency of European migrating silver
eel by signifi cantly lowering oxygen consumption (Sébert et al., 2009).
7.2.3 Changes linked to preparation to prolonged migration
7.2.3.1 Olfactory system
In contrast to vision, olfaction is important during the sedentary life, as a
precious system of prey detection. In female
Anguilla rostrata
, Pankhurst and
Lythgoe (1983) observed a decrease in the number of mucous cells in the
olfactory epithelium of silver eels compared to yellow eels, but the structure
of the lamellae remained the same. Moreover, in artifi cially matured eels,
they reported a degeneration of the olfactory epithelium with a change
in cell organization and a decrease in mucous cell number. Sorensen and
Pankhurst (1988) reported the same modifi cations in male
Anguilla rostrata
.
These modifi cations can be related to the fact that eel stops “hunting” and
begins to starve.
Different studies also showed the importance of olfaction in the
migration of eels. Tagged European eels were inhibited in either the visual,
magnetic or olfactory sense, and the group that had been made anosmic
by injection of elastomer into the nasal cavity showed irregular swimming
behaviour, slower speed and no common direction (Westin, 1990; Tesch et
al., 1991). Similarly, ultrasonic telemetry showed the importance of olfaction
in the estuarine migration of silver-phase American eels as the anosmic
eels with nares fi lled with petroleum jelly spent more time in the estuary,
whereas the control eels moved upstream and downstream with the tides
(Barbin, 1998).
Recently, it has been shown an androgen-dependent stimulation of brain
dopaminergic system in the olfactory bulbs of European eel, suggesting
that androgens, which increase during silvering, may enhance the central
processing of olfactory cues, essential for navigation during eel catadromous
migration toward the spawning grounds (Weltzien et al., 2006).
Olfaction is probably also necessary to pheromonal communication
during the migration and in the spawning area as suggested by a recent
