Zoo202 gdb Solution Fall 22 by getready
Fish are a class of aquatic vertebrates. The combination of gills, fins and the fact
that they live only in the water make fish different from all other animals.
All fish share two traits: they
live in water and they have a backbone—they are vertebrates. Apart from these
similarities, however, many of the species in this group differ markedly from
one another. Fin fish like salmon have gills, are covered in scales, and
reproduce by laying eggs.
Unlike mammals, fish are
cold-blooded (ectothermic). This means that they do not maintain a constant
internal body temperature; instead, their temperature is greatly influenced by
their environment. True fish have a backbone and fins. Most also breathe with
gills and have scales that cover their bodies. It is currently believed that
fish began to evolve about 480 million years ago. There are about 22,000 known
species of fish.
A fish’s fins are used for
balance and to help propel and steer through the water. Most fish have 2 types
of fins: single fins that are found along the centerline (top and bottom) of
the fish, and paired fins. The caudal fin, or tail fin, is the main fin used to
move the fish forward in the water, while the dorsal and anal fins (on the top
and bottom, respectively) help the fish balance and keep it from rolling over.
The paired fins help with steering and hovering.
Anatomy of a fish
On the outside of the skin, most
fish have scales. These overlap in rows and help protect the fish against
injuries and infection. Some species (for example, pufferfish) do not have
scales. The edges of scales are jagged and sharp in some fish and smooth and
rounded in others. Fish secrete a covering of mucus over the scales to further
protect against infection. The mucus traps and immobilizes bacteria and
viruses, keeping them from entering the fish’s body. This covering also helps
reduce friction, allowing the fish to move easily through the water.
To breathe underwater, fish have
developed special organs called gills. The gills, found on the side of the fish
just behind the head, contain thousands of capillaries, or tiny blood vessels.
Water is constantly pumped over the gills, which filter the oxygen out of the
water and directly into the fish’s blood. A gill cover, the operculum, is a
flexible bony plate that helps protect the sensitive gills. Gills are also
important for excretion of waste products, particularly ammonia, from the
fish’s bloodstream.
Fish have a unique internal organ
known as the swim bladder or air bladder. It is usually found in the abdomen,
and it helps fish move up or down in the water. By adjusting the amount of air
in the bladder, fish can adjust the depth at which they float without
continuously having to swim. In some fish, the swim bladder is also used to
produce sounds. Members of the shark and ray class (elasmobranchs) do not have
a swim bladder.
Many fish have excellent vision
and can see colors. They also have nostrils and are able to detect odors in
water. Fish may or may not have teeth, depending on the species. Another organ
of sense unique to fish is called the lateral line, located along the side of
the fish. It contains small sensory hairs that help detect underwater
vibrations and determine their source, enabling fish to navigate even in low
light or murky water.
