Mekong Giant Catfish

Fast Facts

Type: Fish

Diet: Herbivore

Average lifespan in the wild: More than 60 years

Size: Up to 10 ft (3 m)

Weight: Up to 650 lbs (295 kg)

Group name: School

Did you know? The largest freshwater fish ever recorded was a Mekong giant catfish caught in northern Thailand in 2005. It was nearly nine feet long (2.7 meters) and weighed 646 pounds (293 kilograms).

Protection status: Endangered
Size relative to a 6-ft (2-m) man:

Stingray Profile

Stingrays are commonly found in the shallow coastal waters of temperate seas. They spend the majority of their time inactive, partially buried in sand, often moving only with the sway of the tide. The stingray's coloration commonly reflects the seafloor's shading, camouflaging it from predatory sharks and larger rays. Their flattened bodies are composed of pectoral fins joined to their head and trunk with an infamous tail trailing behind.

While the stingray's eyes peer out from its dorsal side, its mouth, nostrils, and gill slits are situated on its underbelly. Its eyes are therefore not thought by scientists to play a considerable role in hunting. Like its shark relatives, the stingray is outfitted with electrical sensors called ampullae of Lorenzini. Located around the stingray's mouth, these organs sense the natural electrical charges of potential prey. Many rays have jaw teeth to enable them to crush mollusks such as clams, oysters, and mussels.

When they are inclined to move, most stingrays swim by undulating their bodies like a wave; others flap their sides like wings. The tail may also be used to maneuver in the water, but its primary purpose is protection.

The stingray's spine, or barb, can be ominously fashioned with serrated edges and a sharp point. The underside may produce venom, which can be fatal to humans, and which can remain deadly even after the stingray's death. In Greek mythology, Odysseus, the great king of Ithaca, was killed when his son, Telegonus, struck him using a spear tipped with the spine of a stingray.

Cyanea lamarckii

Maximun diametre: 30 cm, but in scandinavian waters rarely larger than 15 cm.

Appearance: Blue or yellow tone. It has a great many stinging tentacles that hang from the underside of the jellyfish. The four mouth arms, also hanging from the underside, are large and have many wrinkles and ripples.
Compare the Cyanea lamarckii with the lion´s mane, moon och rhizostome jellyfish.

Depth: Sea-surface to unknown depth.

Environment: Pelagic.

Misc: The medusae bud and loosen from the mature polyps in much the same way as in the lifecycle of the moon jellyfish. This occurs between January and March around the British Isles and southern North Sea. It is probably from these areas that the species has drifted when seen in other areas between the Bay of Biscay to Iceland. In scandinavian waters a minor number are seen between May and September.

Classification: Cyanea lamarckii is a member of the jellyfish group under the cnidarians.

Anthomedusae

Maximum height: 4 ,5 cm.

Appearance: The mouth is situated at the top of the tubular formationen that hangs from the middle of the "umbrella´s" underside. Along the inside edge is a peripheral crease, and the tantacles hang from the outer edge of the "umbrella". The anthomedusae tentacles are few, and the "umbrella" form is relatively high. The organs that produce eggs and sperms are placed by the mouth or on the stomach. The anthomedusae are usually transparent, although the nether parts of the mouth and the thicker areas of the tentacles are distinctly pigmented - black, brown, blue, red, yellow, green or other colour tones.
Compare the anthomedusae with the leptomedusae and other jellyfish.

Depth: Sea-level to unknown depth.

Environment: Pelagic.

Misc: The anthomedusae catches and eats small organisms and suspended remains from the surrounding water. These medusae do not sting enough to cause discomfort to people. Representatives of the anthomedusae group are found globally. The medusae stage is part of a life cycle that is similar to the leptomedusae.

Classification: The specimen in the picture above is probably of the species Neoturris pileata. Anthomedusae are part of the hydroid group under the cnidarians.

Compass jellyfish

Maximum diametre: approx. 20 cm.

Appearance: The compass jellyfish has a yellow-whitish colour with characteristic brown V-shaped lines on top of the "umbrella". The relatively large tentacles are few (24), and the four mouth arms are wrinkled and noticiably long.
Compare the compass jellyfish with the lion´s mane jellyfish.

Depth: From sea-level to unkown depth.

Environment: Pelagic.

Misc: Compass jellyfish change sex: first they are male, followed after by female. The medusae live mainly off other medusae, comb jellyfish and arrow worms. This species is a rarity in scandinavian waters, but medusae occasionally drift into nordic waters from the south during the summer and autumn.

Classification: The compass jellyfish is part of the jellyfish group under the cnidarians.

Comb jelly - Bolinopsis infundibulum

Maximum length: 15 cm.

Appearance: The jelly in Bolinopsis infundibulum is completely transparent, except with some adults that can have a milkish white colour. On the exterior of the oblong body, four long and four short comb-rows are situated. These can shimmer with the colours of the rainbow. Bolinopsis infundibulum has two small tentacles that are transformed into fringes along the sides of the creature. The mouth is surrounded by two flaps; while the other end of the body is drawn out into a obtuse point. Compare with the sea-gooseberry and other comb-jellies.

Depth: From the surface to unknown depth.

Environment: Pelagic.

Misc: Bolinopsis infundibulum is very fragile and almost always breaks when handled. On the two large flaps small organisms fasten and thereafter are transported to the mouth with the small flickering hairs. Certain fish, e.g. lump suckers and other comb-jellies feed on Bolinopsis infundibulum. Individual adults produce both eggs and sperm which they release into the water where fertilization takes place. It is possible to see Bolinopsis infundibulum shine in the dark.

Classification: Bolinopsis infundibulum is a member of the comb jelly group (ctenophora).

Leptomedusae

Maximum diameter: About 20 cm, but on exceptional occasions up to 30 cm.

Appearance: The mouth is situated at the top of the tubular formation that hangs down from the underside of the "umbrella". Along the inside edge of the "umbrella" is a peripheral crease and the tentacles hang down from the "umbrellas" outer edge. The leptomedusae have many tentacles, the number of which increase with age. The "umbrella" form is rather shallow, and on the underside, the organs that produce eggs and sperms are situated. The leptomedusae are usually transparent, but on occasions can be milky white or have a light blue, brown, red or violet tone. Even with transparent medusae, the sexual organs, stomach and tentacles can be light red, greenish or light brown.
Compare the leptomedusae with the anthomedusae and the moon jellyfish.

Depth: From sea-level to unknown depth.

Environment: Pelagic.

Misc: The leptomedusae catches and eats small organisms and suspended remains from the surrounding water. These medusae do not sting enough to cause discomfort to people. Medusae representatives are found globally. The medusa stage is part of a life cycle where even an attached stage is present and the medusae build colonies.

Classification: The above photo shows a jellyfish (Tima bairdii). Leptomedusae are part of the hydroid, group under the cnidarians.

Rhizostome jellyfish

Maximum diametre:About 50 cm, but on rare occasions up to 90 cm.

Appearance: The top of the "umbrella" has a blueish colour, while down on the outer edge small round pockets with a dark blue to violet colour. The males sexual organs are blue, while the females are yellow, brown or red. The medusae have no tentacles. The mouth arms have grown together and have about the same length as the diametre of the "umbrella". The whole of the body has a relatively solid consistency.
Compare the rhizostome jellyfish with the lion´s mane jellyfish and the cyanea lamarckii.

Depth: From sea-level to unknown depth.

Environment: Pelagic.

Misc: Rhizostome jellyfish can swim relatively quickly. The mouth arms have an extensive system of canals. Through these water is pumped and particles of food filtered out. There are stinging cells on the "umbrella", but are so weak that they hardly irritate human skin.
This species is rare in scandinavian waters, but medusae have drifted into nordic waters during the late summer and autumn.
Rhizostome jellyfish have in certain European areas been used as a food source for people.

Classification: The rhizostome jellyfish is a member of the jellyfish group under the cnidarians.

Lion´s mane jellyfish

Maximum diameter: 50 cm, but in Arctic waters har examples of about 2 m been observed.
Appearance: The Lion´s mane jellyfish has pronounced red or yellow colour. It has great number of long irritating stinging tentacles, that hang down from the underside of the "umbrella". The four mouth arms, that also hang from the "umbrellas" underside, are large with many wrinkles and creases.
Compare the lion´s mane jellyfish with cyanea palmstruchi, the compass jellyfish and rhizostoma octopus.

Depth: From sea-level to unkown depth.

Enviroment: Pelagic.

Övrigt: Contrary to the moon jellyfish´s lifecycle only one ephyra-larvae buds from each polyp, and this happens mainly during the spring.
Examples of the lion´s mane jellyfish have been seen as far as the Gulf of Finland.

Classification: The lion´s mane jellyfish is part of the group jellyfish, part of the group cnidaria.

Moon jellyfish

Maximum diametre: 25 cm, but on rare occassions can measure up to 40 cm.

Appearance:Moon jellyfish are easy to recognize because of their four reproductive organs that are round or horseshoe-shaped. Along the periphery of the slightly arched "umbrella", short tentacles are attached. On the underside, four mouth arms are present. From the middle of the jellyfish, four channels run outwardly to a peripheral channel that circumferences the jellyfish. The moon jellyfish is transparent with a slightly blueish or pinkish tone. Its genitals, mouth arms, tentacles and channels have a slightly white, violet, red or yellow tone. Compare the moon jellyfish with the leptomedusae and the cyanea lamarckii.

Depth: From sea-level to unkown depth.

Environment:Pelagic.

Classification: Moon jellyfish are members of the jellyfish group under the cnidarians.

Seasparkle

Maximum diameter: Approx. 2 mm, but seldom more than 1 mm in Scandinavian waters. Compare the size with a hair.

Appearance: Seasparkle is almost completely colourless and transparent, but when driven together in large numbers the water can appear thick and have a light brown to pink colour. The cell is relatively large and round and is furnished with three protrusions. Two of the protrusions are small and vague and can easily be believed to correspond to the mobile cell outgrowths on other dinoflagellates. The third protrusion, that is unique for seasparkle and known as a tentacle, is striped and much more pronounced than the others. All the protrusions are situated in a large deep groove on the underside of the cell.
In the picture above, the picture at the top depicts seasparkle from its underside, the left-hand picture depicts the right side of seasparkle, while the right-hand picture depicts it from above.
Depth: Seasparkle is most common in the upper reaches of the sea that recieves sunlight.

Environment: Pelagic.

Misc: Seasparkle is so large because it pumps itself up with water. By regulating the amount of ions it can effect its bouyancy and towards the end of the bloom they usually congregate at the surface. In the large cells, thousands of small reproductive bodies can be formed.
With the help of its tentacle seasparkle collects its food, which can be of the same size as itself, and carry it to its mouth which is situated at the bottom of the groove. Coloured particles seen in the cell are often particles of food or small photosynthesizing organisms that live together with the seasparkle.
Seasparkle is one of those organisms that cause phosphorescence of the sea in our waters!

Classification: Sea sparkle belongs to the dinoflagellate group under the "protists". The protists as a systematic group is not well motivated or defined, as it is used to collect organismer that are not bacterias, fungi, plants or animals into a common group.

Flying Fish Profile

Flying fish can be seen jumping out of warm ocean waters worldwide. Their streamlined torpedo shape helps them gather enough underwater speed to break the surface, and their large, wing-like pectoral fins get them airborne.

Flying fish are thought to have evolved this remarkable gliding ability to escape predators, of which they have many. Their pursuers include mackerel, tuna, swordfish, marlin, and other larger fish. For their sustenance, flying fish feed on a variety of foods, including plankton.

There are about 40 known species of flying fish. Beyond their useful pectoral fins, all have unevenly forked tails, with the lower lobe longer than the upper lobe. Many species have enlarged pelvic fins as well and are known as four-winged flying fish.

The process of taking flight, or gliding, begins by gaining great velocity underwater, about 37 miles (60 kilometers) per hour. Angling upward, the four-winged flying fish breaks the surface and begins to taxi by rapidly beating its tail while it is still beneath the surface. It then takes to the air, sometimes reaching heights over 4 feet (1.2 meters) and gliding long distances, up to 655 feet (200 meters). Once it nears the surface again, it can flap its tail and taxi without fully returning to the water. Capable of continuing its flight in such a manner, flying fish have been recorded stretching out their flights with consecutive glides spanning distances up to 1,312 feet (400 meters).

Flying fish are attracted to light, like a number of sea creatures, and fishermen take advantage of this with substantial results. Canoes, filled with enough water to sustain fish, but not enough to allow them to propel themselves out, are affixed with a luring light at night to capture flying fish by the dozens. There is currently no protection status on these animals.

Parrot Fish Profile

It's hard to decide which of the colorful parrot fish's many unique characteristics is most remarkable.

There’s its diet, which consists primarily of algae extracted from chunks of coral ripped from a reef. The coral is pulverized with grinding teeth in the fishes’ throats in order to get to the algae-filled polyps inside. Much of the sand in the parrot fish's range is actually the ground-up, undigested coral they excrete.
There's its gender, which they can change repeatedly throughout their lives, and their coloration and patterns, which are a classification nightmare, varying greatly, even between the males, females, and juveniles of the same species.

Finally, there are the pajamas. Every night, certain species of parrot fish envelope themselves in a transparent cocoon made of mucous secreted from an organ on their head. Scientists think the cocoon masks their scent, making them harder for nocturnal predators, like moray eels, to find.

Close relatives of the wrasse, parrot fish are abundant in and around the tropical reefs of all the world’s oceans. There are about 80 identified species, ranging in size from less than 1 to 4 feet (30 to 120 centimeters) in length.

Their meat is rarely consumed in the United States, but is a delicacy in many other parts of the world. In Polynesia, it is served raw and was once considered "royal food," only eaten by the king.

Box Jellyfish Profile

The infamous box jellyfish developed its frighteningly powerful venom to instantly stun or kill prey, like fish and shrimp, so their struggle to escape wouldn’t damage its delicate tentacles.

Their venom is considered to be among the most deadly in the world, containing toxins that attack the heart, nervous system, and skin cells. It is so overpoweringly painful, human victims have been known to go into shock and drown or die of heart failure before even reaching shore. Survivors can experience considerable pain for weeks and often have significant scarring where the tentacles made contact.

Box jellies, also called sea wasps and marine stingers, live primarily in coastal waters off Northern Australia and throughout the Indo-Pacific. They are pale blue and transparent in color and get their name from the cube-like shape of their bell. Up to 15 tentacles grow from each corner of the bell and can reach 10 feet (3 meters) in length. Each tentacle has about 5,000 stinging cells, which are triggered not by touch but by the presence of a chemical on the outer layer of its prey.

Box jellies are highly advanced among jellyfish. They have developed the ability to move rather than just drift, jetting at up to four knots through the water. They also have eyes grouped in clusters of six on the four sides of their bell. Each cluster includes a pair of eyes with a sophisticated lens, retina, iris and cornea, although without a central nervous system, scientists aren’t sure how they process what they see.

Nurse Shark Profile

The scientific name for the nurse shark sounds like something Bilbo Baggins might have said to summon elves to his rescue: Ginglymostoma cirratum . Actually the name is a mix of Greek and Latin and means "curled, hinged mouth" to describe this shark's somewhat puckered appearance.

The origin of the name "nurse shark" is unclear. It may come from the sucking sound they make when hunting for prey in the sand, which vaguely resembles that of a nursing baby. Or it may derive from an archaic word, nusse, meaning cat shark. The most likely theory though is that the name comes from the Old English word for sea-floor shark: hurse.

Nurse sharks are slow-moving bottom-dwellers and are, for the most part, harmless to humans. However, they can be huge—up to 14 feet (4.3 meters)—and have very strong jaws filled with thousands of tiny, serrated teeth, and will bite defensively if stepped on or bothered by divers who assume they’re docile.

They use their strong jaws to crush and eat shellfish and even coral, but prefer to dine on fish, shrimp, and squid. They are gray-brown and have distinctive tail fins that can be up to one-fourth their total length. Unlike most other sharks, nurses are smooth to the touch.

Nurse sharks are found in the warm, shallow waters of the western Atlantic and eastern Pacific oceans. They are abundant throughout their range and have no special conservation status, although the closeness of their habit to human activities is putting pressure on the species.

Tiger Shark Profile

Tiger sharks are named for the dark, vertical stripes found mainly on juveniles. As these sharks mature, the lines begin to fade and almost disappear.

These large, blunt-nosed predators have a duly earned reputation as man-eaters. They are second only to great whites in attacking people. But because they have a near completely undiscerning palate, they are not likely to swim away after biting a human, as great whites frequently do.

They are consummate scavengers, with excellent senses of sight and smell and a nearly limitless menu of diet items. They have sharp, highly serrated teeth and powerful jaws that allow them to crack the shells of sea turtles and clams. The stomach contents of captured tiger sharks have included stingrays, sea snakes, seals, birds, squids, and even license plates and old tires.

Tiger sharks are common in tropical and sub-tropical waters throughout the world. Large specimens can grow to as much as 20 to 25 feet (6 to 7.5 meters) in length and weigh more than 1,900 pounds (900 kilograms).

They are heavily harvested for their fins, skin, and flesh, and their livers contain high levels of vitamin A, which is processed into vitamin oil. They have extremely low repopulation rates, and therefore may be highly susceptible to fishing pressure. They are listed as near threatened throughout their range.

Hammerhead Shark Profile

Hammerhead sharks are consummate predators that use their oddly shaped heads to improve their ability to find prey. Their wide-set eyes give them a better visual range than most other sharks. And by spreading their highly specialized sensory organs over their wide, mallet-shaped head, they can more thoroughly scan the ocean for food.

One group of sensory organs is the ampullae of Lorenzini, which allows sharks to detect, among other things, the electrical fields created by prey animals. The hammerhead's increased ampullae sensitivity allows it to find its favorite meal, stingrays, which usually bury themselves under the sand.

The great hammerhead is the largest of the nine identified species of this shark. It can grow up to 20 feet (6 meters) in length and weigh up to 1,000 pounds (450 kg), although smaller sizes are more common.

Found in temperate and tropical waters worldwide, far offshore and near shorelines, hammerheads are often seen in mass summer migrations seeking cooler water. They are gray-brown to olive-green on top with off-white undersides, and they have heavily serrated, triangular teeth. Their extra-tall, pointed dorsal fins are easily identifiable.

Most hammerhead species are fairly small and are considered harmless to humans. However, the great hammerhead's enormous size and fierceness make it potentially dangerous, though few attacks have been recorded.

Hammerhead populations are not accurately known, but appear stable worldwide, and they are not considered threatened.

Great White Shark Profile

The legendary great white shark is far more fearsome in our imaginations than in reality. As scientific research on these elusive predators increases, their image as mindless killing machines is beginning to fade.

Of the 100-plus annual shark attacks worldwide, fully one-third to one-half are attributable to great whites. However, most of these are not fatal, and new research finds that great whites, who are naturally curious, are "sample biting" then releasing their victims rather than preying on humans. It's not a terribly comforting distinction, but it does indicate that humans are not actually on the great white's menu.

Great whites are the largest predatory fish on Earth. They grow to an average of 15 feet (4.6 meters) in length, though specimens exceeding 20 feet (6 meters) and weighing up to 5,000 pounds (2,268 kilograms) have been recorded.

They have slate-gray upper bodies to blend in with the rocky coastal sea floor, but get their name from their universally white underbellies. They are streamlined, torpedo-shaped swimmers with powerful tails that can propel them through the water at speeds of up to 15 miles (24 kilometers) per hour. They can even leave the water completely, breaching like whales when attacking prey from underneath.

Highly adapted predators, their mouths are lined with up to 3,000 serrated, triangular teeth arranged in several rows, and they have an exceptional sense of smell to detect prey. They even have organs that can sense the tiny electromagnetic fields generated by animals. Their main prey items include sea lions, seals, small toothed whales, and even sea turtles, and carrion.

Found in cool, coastal waters throughout the world, there is no reliable data on the great white's population. However, scientists agree that their number are decreasing precipitously due to overfishing and accidental catching in gill nets, among other factors, and they are listed as an endangered species.

Bull Shark Profile

Bull sharks are aggressive, common, and usually live near high-population areas like tropical shorelines. They are not bothered by brackish and freshwater, and even venture far inland via rivers and tributaries.

Because of these characteristics, many experts consider bull sharks to be the most dangerous sharks in the world. Historically, they are joined by their more famous cousins, great whites and tiger sharks, as the three species most likely to attack humans.

Bull sharks get their name from their short, blunt snout, as well as their pugnacious disposition and a tendency to head-butt their prey before attacking. They are medium-size sharks, with thick, stout bodies and long pectoral fins. They are gray on top and white below, and the fins have dark tips, particularly on young bull sharks.

They are found cruising the shallow, warm waters of all the world’s oceans. Fast, agile predators, they will eat almost anything they see, including fish, dolphins, and even other sharks. Humans are not, per se, on their menus. However, they frequent the turbid waters of estuaries and bays, and often attack people inadvertently or out of curiosity.

Bull sharks currently are not threatened or endangered. However, they are fished widely for their meat, hides, and oils, and their numbers are likely shrinking. One study has found that their average lengths have declined significantly over the past few decades.

Whale Shark Profile

As the largest fish in the sea, weighing up to 60 tons (54.4 metric tons), whale sharks have an enormous menu from which to choose. Fortunately for most sea-dwellers—and us!—their favorite meal is plankton. They scoop these tiny plants and animals up, along with any small fish that happen to be around, with their colossal gaping mouths while swimming close to the water's surface.

The whale shark, like the world's second largest fish, the basking shark, is a filter feeder. In order to feed, it juts out its formidably sized jaws and sucks in everything in the vicinity. It then shuts its mouth, forcing water to filter out of its gills. Everything that remains becomes the giant shark's dinner.

The whale shark's flattened head sports a blunt snout above its mouth with short barbels protruding from its nostrils. Its back and sides are gray to brown with white spots among pale vertical and horizontal stripes, and its belly is white. Its two dorsal fins are set rearward on its body, which ends in a large dual-lobbed caudal fin (or tail).

Preferring warm waters, whale sharks populate all tropical seas. They are known to migrate every spring to the continental shelf of the central west coast of Australia. The coral spawning of the area's Ningaloo Reef provides the whale shark with an abundant supply of plankton.

Although massive, whale sharks are docile fish and sometimes allow swimmers to hitch a ride. They are currently listed as a vulnerable species; however, they continue to be hunted in parts of Asia, such as Taiwan and the Philippines.

Butterflyfish Profile

Butterflyfish, with their amazing array of colors and patterns, are among the most common sites on reefs throughout the world.

Although some species are dull-colored, most wear intricate patterns with striking backgrounds of blue, red, orange, or yellow. Many have dark bands across their eyes and round, eye-like dots on their flanks to confuse predators as to which end to strike and in which direction they're likely to flee.

There are about 114 species of butterflyfish. They have thin, disk-shaped bodies that closely resemble their equally recognizable cousins, the angelfish. They spend their days tirelessly pecking at coral and rock formations with their long, thin snouts in search of coral polyps, worms, and other small invertebrates.

Some butterflyfish species travel in small schools, although many are solitary until they find a partner, with whom they may mate for life.

Clown Anemonefish Profile

Anyone with kids and a DVD player probably thinks they know all there is to know about the clown anemonefish, or, simply, clownfish. What they may not know is that the heroes of Finding Nemo are actually called false anemonefish. True anemonefish, Amphiprion percula, are nearly identical, but have subtle differences in shape and live in different habitats.

Bright orange with three distinctive white bars, clown anemonefish are among the most recognizable of all reef-dwellers. They reach about 4.3 inches (11 centimeters) in length, and are named for the multicolored sea anemone in which they make their homes.

Clownfish perform an elaborate dance with an anemone before taking up residence, gently touching its tentacles with different parts of their bodies until they are acclimated to their host. A layer of mucus on the clownfish's skin makes it immune to the fish-eating anemone's lethal sting. In exchange for safety from predators and food scraps, the clownfish drives off intruders and preens its host, removing parasites.

There are 28 known species of anemonefish, most of which live in the shallow waters of the Indian Ocean, the Red Sea, and the western Pacific. They are not found in the Caribbean, Mediterranean or Atlantic Ocean.

Surprisingly, all clownfish are born male. They have the ability to switch their sex, but will do so only to become the dominant female of a group. The change is irreversible.

What is a Fish?

A fish is an animal which lives and breathes in water. All fish are vertebrates (have a backbone) and most breathe through gills and have fins and scales. Fish make up about half of all known vertebrate species.

What is a person who studies fish called : An ichthyologist.

How are fish identified : A combination of the number of fins and their characteristics, scale counts, general features, colour, maximum length and distribution are used.

Difference between male and female fish - In some species the males and females have different shaped bodies or different colouring; in other species there is no visible difference.

How fishes breathe: Some fish have lungs and breathe air, but most breathe through gills. Gills are made up of thin sheets of tissue richly supplied with blood vessels. As water passes over them dissolved oxygen is absorbed into the blood and waste products such as carbon dioxide pass out into the water. The gills are protected by a large bony plate called an operculum.