Biology Reference
In-Depth Information
had signifi cantly less Jv than FW or SW-adapted smolts (Collie and Bern,
1982). From 2 to 4 weeks following the springtime T4 surge, Jv increased
in FW coho to a level comparable with that observed for SW wmolts; Jv
remained elevated throughout most of the summer and then decreased in
the autumn; this timing of the increase in Jv suggested a phase relationship
to the T4 surge (Collie and bern, 1982). Rate of mucosal to serosal water
movement, measured
in vitro
in non-everted midgut segments of Atlantic
salmon, increased signifi cantly during smoltifi cation, but was not changed
following transfer to SW (Usher et al., 1991). Veillette et al. (1993) reported,
in Atlantic salmon, using
in vitro
intestinal sac preparations, a functional
regionalization during smoltifi cation with the posterior intestine taking
on increased importance in osmoregulation in SW: the middle intestine of
smolting fi sh underwent a signifi cant decrease in fl uid transport during
the springtime, while posterior intestinal Jv signifi cantly decreased and
increased around the peak smolt period compared to parr. SW-adapted
smolts generally exhibited posterior Jv approximately double that of FW
cohorts. Sundell et al. (2003) demonstrated that, in Atlantic salmon, this
preadaptative elevation in Jv during smoltifi cation was at least due to
an increase in intestinal Na+,K+-ATPase activity in the anterior intestine
and a decrease of paracellular permeability (as judged by transepithelial
resistance) in the posterior intestine. Nonnotte et al. (1995) demonstrated
the infl uence of growth hormone on intestine physiology at the end of
smolting in the Atlantic salmon.
6.2.4.3 Kidney and urinary bladder
The FW teleost produces a large volume of dilute urine, while in SW urine
is sparse and relatively concentrated (for review: Boeuf, 1993). In FW, the
kidney and urinary bladder are of considerable importance, their action
consisting of eliminating excess water without losing ions; the glomerular
fi ltration rate is very high and tubular reabsorption is low. In SW, the role
of these organs is quite different. Ford (1958) showed a reduction in the
number of functional
glomeruli
in SW salmon. There is a major change in
kidney anatomy and physiology before migration in smoltifying salmonids,
A decrease in electrolyte absorption in the urinary bladder of terminal
coho smolts occurs in FW (Loretz et al., 1982), predisposing the fi sh to
SW entry. Eddy and Talbot (1985) found an increase in urine production
in silvery Atlantic salmon, which they interpreted as a consequence of
pre-adaptation to increase the water permeability of the gut of the fi sh in
FW. Mizuno et al. (2001c) demonstrated an increase in number and size of
kidney juxtaglomerular cells (thought to produce renin) in smolting masu
salmon, coincidentally with the increase in gill Na+,K+-ATPase.
