Biology Reference
In-Depth Information
7.2.2.3
Swimbladder
During the spawning migration, eels encountered two drastically different
environments, the shallow fresh water and the deep sea. Thus, some
modifi cations of swimbladder during silvering will permit the transition
from the shallow to the deep environment, preparing the eels to hydrostatic
pressure encountered in their future deep environment. First, an increase
in the crystalline guanine content of the swimbladder in silver compared
to yellow American eels was observed, permitting to reduce the gas loss
(Kleckner, 1980a). An increase in gas deposition rates was also demonstrated
(Kleckner, 1980b), which could result from the increase in length and in
luminal diameter of the
rete mirabilis
capillaries (Kleckner and Krueger,
1981).
7.2.2.4
Cellular metabolism
Exposure of FW eels to high pressure (HP; 101 ATA equivanlent to a 1,000
m depth) for some hours induces a sharp increase in oxygen consumption
and at the muscle level, a decrease in ATP and glycogen contents, in
cytochrome oxidase activity and an increase in LDH activity, fatty acids
stores and circulating lactate (for review: Sébert, 2002). Hydrostatic pressure
induces a state rsembling histotoxic hypoxia via a decraese in membrane
fluidity, thus aletring areobic metabolism (Sébert et al., 1993). When
exposure to pressure is maintained for several days or weeks, eels are able
to acclimatize to pressure effects. The pressure acclimatization process
is the « normalization » of metabolism through membrane fl uidifi cation
that allows normal functioning of the respiratory chain and oxidative
phosphorylation (for review: Sébert, 2002).
Vettier and collaborators demonstrated that the silvering process
appeared to mimic pressure acclimatization observed in yellow eels
(Simon et al., 1989), allowing silver eels to cope with pressure effects with
a minimal energy cost (Vettier et al., 2005). Indeed, the global sensitivity to
compression measured by the muscle fi bre oxygen consumption increased
by 60% between before (1 ATA) and at the end of compression after 21 days
at 101 ATA. At the end of the experiment, a signifi cant decrease in HSI and
a trend to increase GSI were observed (Vettier et al., 2005). In another paper,
they demonstrated that yellow eels exhibited a higher pressure sensitivity
(compression effects) compared to silver eels. The acclimatization period
(21 days at 10.1 MPa) of yellow eels cancelled the differences in pressure
sensitivity and in aerobic metabolism at 0.1 MPa observed between the
two stages.this capacity to cope with the membrane pressure effects was
due to the fact that silver eel exhibited higher membrane fl uidity (Vettier
et al., 2006). The mechanisms, which take place in yellow eels during
