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Many fish have cigar-shaped bodies - this allows water to pass smoothly over the fish, helping it move through the water
with minimum effort.
They use fins and tail to propel themselves, thrusting their way through the water. However, each fish has special
adaptations that help it live in its own
niche, or place in the water. |
This diagram shows how the water moves more smoothly around the cigar-shaped figure.
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Fish anatomy
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Most sharks are predators that move quickly through water
to catch their prey. A shark's body has lots of muscles, which
help power the shark through the water. Its pointed nose and smooth outline slide through the water, reducing
drag on the shark's body.
The shark's tail (or caudal fin) provides a lot of its power,
but also helps to steer the shark so it can change direction
quickly. The other fins are spread out around the shark's body to keep it stable in the water. The
pectoral fins are used as
hydroplanes - they allow the shark to move up and down in the water
with minimal effort. They also help with turning. The upright
dorsal fin on the shark's back helps keep the shark upright, and stops
it rolling over in the water.
All of these special features help the shark hunt for prey that includes fish, seals, turtles, birds, other sharks and even
small whales and dolphins (sharks also eat carrion).
It had been thought that most sharks need to swim to stay alive - they would sink and drown unless they kept moving. However,
it is now known that many sharks regularly rest on the bottom of the sea and appear to breath normally. Sharks don't have a swim
bladder like other fish (a bag of air in their body that stops them sinking), but do have a large oily liver that helps with
buoyancy.
Not all sharks rely on speed or agility to feed. The 9m (30ft) basking shark simply swims along with its mouth open, filtering
its food, plankton, through gills in its mouth.
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Blue shark
(click image for a larger version)
© Paul Naylor
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Mackerel
(click image for a larger version)
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Like the shark the mackerel has a very streamlined, torpedo-shaped body, that helps it slide through the water. Also like the
shark the mackerel constantly cruises for prey, chasing food with short bursts of speed.
Its smooth, slimy skin reduces friction with the water, and its fins can be pulled in to give a more streamlined shape. The
mackerel also has a large forked tail that gives it great speed and agility. These features combine to make the mackerel one of
the fastest fish in the sea.
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The Monkfish, or anglerfish, doesn't need speed to chase its food - instead it uses a
lure. The monkfish uses what could almost
be called a fishing rod attached to its head, and twitches it to attract unsuspecting fish to its huge gaping jaws. Once the nosey
fish comes within range the monkfish grabs it with such speed that the prey usually won't escape.
The monkfish is quite a large fish, with a head that is almost as wide as the fish is long, and a huge gaping mouth. It is
also extremely ugly. It lies, half-buried on the sea floor waiting for a meal to pass close by.
The monkfish not only likes to eat - it is also good to eat. Monkfish was once sold as scampi but is now considered a delicacy,
especially in Japanese cuisine where it is often called Ankimo, a type of sushi.
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Monkfish
(click image for a larger version)
© Paul Naylor
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Sea horse anatomy
Sea horse
(click image for a larger version)
© Below Water
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The sea horse looks very different to the other fish in our race. It does not have a smooth, streamlined shape, nor a strong
tail fin to power it through the water. The sea horse needs none of these things to survive.
Sea horses live in coral reefs and sea-grass. They have
a prehensile tail that grabs hold of things like plants and rocks to
stop from being swept away, especially during storms.
Some fish need speed to catch their prey but not the sea horse. It eats tiny, slow-moving shrimp that drift past on the ocean
current. It has eyes on either side of its head that can move independently of each other, allowing the sea horse to spot food
(and predators). When it sees something it likes, the sea horse
will suck/grab its food with its long snout.
Other fish need speed to escape from predators, but the sea horse uses disguise and armour to avoid being eaten. The sea horse
hides itself by changing colour and drifting to look like a piece of plant. If it is attacked the sea horse's hard outer casing
(exoskeleton) will protect it from some predators.
The rigid skeleton stops the sea horse snaking its way through the water like a shark. Instead, the sea horse powers itself
using its dorsal and
pectoral fins, which flutter 30 times per second. These also help keep the fish upright in the water.
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