FISHES AND THE WEB OF LIFE
299
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3; DISEASES AND ENEMIES OF FISHES
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Although shes have displayed a wonderful power of
adapting themselves—to all sorts of conditions, this is ageneral
rather than a particular power._ ; The time required to_ effect
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adaptive changes has been and is considerablc.
these have been accomplished thesh becomes speCiâlised
to a denite range of temperature, for example, and thus
more sensitive to conditions outsidethè range of the custo—
mary. It is probably for this reason that the freshWater
forms seem more Subject to illness and diseases than the
marine forms;
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'
'
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,
f
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‘The great attention devoted to the rearing of freshwater
sheS,
the introduction of many tropical and sub-.
tropical forms as aquarium shes, has revealed that shes
are not so immune to the ills of esh as was formerly thought.
They seem even to catch cold in the usual unaccount“able
way.
Sometimes whole populations are sWept away by
»
epidemics as mysterious as any that; trouble man and just
as much
_
seeminglÿ beyond"
.%inaMa—
.
_
tion JOf,the
of fc01dÎon
changes of temperature or= chemical inuences,
is“! the.» rst causefof the epidemics,‘ followed by. loss of
appetite and sluggishness, just as among human
Such ari epidemic has also occürredfon a large Scale Out at
…
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sea.
The American
‘
o‘fthe coast of New England in the warm Waters of the
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Gulf Stream, was almost
out in the year 1882.
Many millions of the sh were: killed, and it is said that
_
bodies literally covered the surface of the sea
for hundreds of square miles.”
It Was believed that ice—"[;
cold Water—, coming in the train of severe gales, had displa‘ced
the Warm Water Over” a large area" and caughtthe sh ’un—
awares.
For many yearsnot a singleTile-sh couldbefound,
but it has réapp‘eared againin its wonted haunts
and is now
as abundant:àé*formerly. ‘ïfë'Similar phenomena have been‘
noted—byHjortinthè case of the
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Similay,Î the eXtènsion of factoriès ,
works