30
THE BIOLOGY OF FISHES
water shes to the rivets and lakes ;— to change them suddenlyî—W
is, to condemn them to death, for their delicate gill—
membranes are so nicely‘
the outer conditions,
that a change of ' water acts like: poison.
Some shes,
however, like the Smelt, young of the Herring
(Whitebait), some of the American _Killishes (Fundülus),
'
and many more, live in brackish water, and some, like the
Bel, Stickleback (Gastrosz‘eus aculeatus) and one F undulus,
are
to s-tolerate salt or’fresh water with indierence.
_
Butthe most extraordinary thing is, that a few shes, like
'
the: Sal“rhon,_makeai practice of changing regularly from the
one “to the Other every year when they growup A few more,
_likethe Fioun‘der and Bel, spend their youth in {the freshintoÿthe}sea, ;çThiS ability to stand
su“dden—in ;the
ti—s Ïaa3 »mystery
'
!
Beyond
ï
Formerlyatvvasth0ught thatn0shesandeednolafe
mdsahgadpabtthayt Wa aaa=—
'
ljmore
expeditions.
It
the depths from which sh have
_
;1a1æïÿœcÿædedÇ Weré’the aCtual depths Where they
they might;
taken in higher layers
515_ …
in;
On the otherhand,wemaybesme
_,
”
’
,
ihäfnwreescapethesl0wm0vmgœtthanaretak0nmrc “—
:Fr0manexammaüonoftherecordsHiorthascome -f0 the
f
than "
2000 fath0ms.
__Ï . QntheirexpeditionacrosstheAtlantmm 1910,»Murrayand
’
Hj
ofshïdown to ‘d—epths _
;:Thosèèfi‘éŒ the .-d‘ee_per
’
}! mcolour (AStrdn'@thesî and; Gastrostomidsg
.
id), ‘Whîlst
bynttthm dspwbaa—m
of extraordmarys1ze—were red Butmostshes Were
'
layers,thatis,11V1ng ïpel‘ag—ieally" ,
f
;