-
A
fish
is
a
water-dwelling
vertebrate
with
gills
that
doesn't
change
form,
as amphibians do,
during its life. Most are cold-blooded, though
some
(such
as
some
species
of
tuna
and
shark)
are
warm-blooded.
There
are
over
29,000
species
of
fish,
making
them
the
most
diverse
group
of
vertebrates.
鱼用鳃是一种水生脊椎动物，不改
变形式，两栖动物，在其生命周期。大部分都
是冷血，虽然有些（如某些种类的金枪鱼和
鲨鱼）是温血动物。有超过
29,000
种鱼类，使他们最多样
化的脊椎动物。
Taxonomically, fish
are a paraphyletic group whose exact relationships
are
much
debated;
a
common
division
is
into
the
jawless
fish
(class
Agnatha,
75
species
including
lampreys
and
hagfish),
the
cartilaginous
fish
(class
Chondrichthyes, 800
species including sharks and rays), with the
remainder classed as bony fish (class
Osteichthyes).
分类学上，
鱼是一种系群，<
/p>
其备受争议的确切关系
;
一个共同的分工
是无颌鱼
（类
无颌类，
75
种，包括七鳃鳗和盲鳗），软骨鱼类（软骨鱼，
800
种，包括鲨鱼和
鳐鱼），其余归类为硬骨鱼（类硬骨鱼纲）。
Fish come in different sizes, from
the 16 m (51 ft) whale shark to a 8
mm
(just over ? of an inch) long stout infantfish.
Many types of aquatic
animals named
as jellyfish and cuttlefish, are not
even vertebrates. Other marine
creatures
that
have
in
the
past
been
considered
fish,
like
dolphins,
are
actually mammals.
鱼有不同的大小，从
16
米（
51
英尺）到
8
毫米（刚刚超过四分之一英寸）长的
粗壮的
infantfish
的鲸鲨。水生动物的许多类型的名为“鱼”不是真正的鱼，
在动物，如水母和乌贼的情况下，甚至不脊椎动物。其他海洋生物，在过去被认
为是鱼，像海豚一样，实际上是哺乳动物。