centration almost certainly result from the interaction of a large number of factors,
so that a solo role for one such hormone would be rather unexpected.
When fish are transferred from fresh water to sea-water, or from sea to fresh
water, a number of changes take place in the osmotic composition of their body
fluids . Initially the changes are usually more pronounced than are subsequently
maintained. This period of equilibration lasts for about 48 h in eels and flounder
(KEYS, 1933; LAHLOU, 1967) transferred from fresh wa ter to sea-water, but may
be as long as 170 h in the steelhead trout (H OUSTON, 1959) . Some of the changes
180
170
(15)
L
E 160
", '
"0
~ x: 150
u
o
E
11l
d
a: 140
130
120
40
2
Cl
:::::
L
E 30
",'
"0
(19)
1151
'§
:E
u
20
'"
::J
11l
11l
i=
10
0 Fresh
Water
Fig. 7.5 Changes in the plasma and muscle chloride concentrations in trout, Salmo gairdneri,
after transfer from fresh water to sea-water. (From HOUSTON, 1959; by permission of the
National Research Council of Canada).
232