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FIND OUT MORE. Cnidarians 103 • Fishing 67 • Oceans 40–41

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LAMPREY 3

Although lampreys

are jawless fish, they

still have plenty of bite. Inside their

sucker-like mouth are rings of sharp, rasping teeth

for ripping into the flesh of their victims.

1 YELLOWHEAD JAWFISH

Some species of fish protect their eggs by incubating them in their

mouths. Before setting off to feed, this male yellowhead jawfish will

spit his mate’s eggs out into his burrow, to keep them safe.

BIOLUMINESCENCE

Anal fin

provides stability,

like the dorsal fin

Long snout

allows the

moorish idol to

reach morsels of

food in crevices

Powerful suction

around the mouth

4 MOORISH IDOLS

Most fish that live on tropical

coral reefs are colourful and

have striking markings. Coral

reefs are very crowded places.

Scientists think that the bright

colours and patterns may help

fish to recognize others of

their own kind.

DEEP-SEA ANGLERFISH 3

A deep-sea anglerfish glows like

an underwater light bulb. In some

species, bioluminescence is caused

by a chemical reaction in which

energy is released as light. Other

species are illuminated by glowing

bacteria in their skin, and some

have glands called photophores

which can be switched on and

off like miniature flashlights.

WHAT IS THE PURPOSE OF BIOLUMINESCENCE?

Bioluminescence has several uses. Deep-sea anglerfish

dangle a glowing lure in front of their jaws to attract

prey. Other species use light to identify mates. A few

even use it for camouflage – lights on the underside

of the body help fish blend in with the small amount of

light filtering down. Many fish nearer the surface have

light-coloured bellies for the same reason.

ARE THERE ANY PARASITIC FISH?

Lampreys are parasites. They attach themselves to

larger creatures using their sucker-like mouth and

drink their blood. Lamprey saliva contains a natural

anticoagulant, which prevents a victim’s blood from

clotting, so that the lamprey can continue to feed.

Little light from the surface reaches the

twilight zone in the ocean depths below

200 m (660 ft). However, over 1,000 species

of fish that live there are bioluminescent –

able to produce their own natural light.

HOW DO SHARKS HUNT?

Predatory sharks detect prey with the aid of keen

sensors, which can pick up tiny traces of blood from

several kilometres away. They home in on victims

using electrosensors that detect tiny charges given

off by the prey’s muscles. At close range, sharks use

their eyesight to target their quarry.

fish