Look at the pictures. What adaptations do these fishes have? Why?

 

 

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Read and translate the text.

Text 1

FISH

Fishes have been in existence for more than 450, 000, 000 years, during which time they have evolved to fit into almost every type of aquatic habitat. In a sense, land vertebrates are simply highly modified fishes, for when fishes colonized the land habitat they became tetrapod (four-legged) land vertebrates.

The term fish is applied to a variety of vertebrates of several evolutionary lines. It describes a life-form rather than a taxonomic group. As members of the phylum Chordata, fish share certain features with other vertebrates. These features are gill slits at some point in the life cycle, a notochord, or skeletal supporting rod, a dorsal hollow nerve cord, and a tail. Living fishes represent some classes, which are distinct from one another. For example, the jawless fishes (Agnatha) are the only fishes that have a filter-feeding mouth, a feature that makes them dependent on an essentially parasitic way of life.

Sharks, skates, and rays are examples of cartilaginous fishes. The bony fishes are by far the largest class. Examples range from the tiny sea horse to the 450-kilogram (1, 000-pound) blue marlin. Unlike those of the cartilaginous fishes, the scales of bony fishes, when present, grow throughout life and are made up of thin, overlapping plates of bone. Bony fishes also have an operculum that covers the gill slits.

The study of fishes, the science of ichthyology, is of broad importance. Fishes are of interest to humans for many reasons, the most important being their relationship with and dependence on the environment. A more obvious reason for interest in fishes is their role as a moderate but important part of the world's food supply. This resource, once thought unlimited, is now realized to be finite and in delicate balance with the biological, chemical, and physical factors of the aquatic environment. Overfishing, pollution, and alteration of the environment are the chief enemies of proper fisheries management, both in fresh waters and in the ocean.

Another practical reason for studying fishes is their use in disease control. As predators on mosquito larvae, they help curb malaria and other mosquito-borne diseases. Fishes are valuable laboratory animals in many aspects of medical and biological research. Fishes have been especially important in the study of animal behaviour, where research on fishes has provided a broad base for the understanding of the more flexible behaviour of the higher vertebrates.

There are aesthetic and recreational reasons for an interest in fishes. Millions of people keep live fishes in home aquariums for the simple pleasure of observing the beauty and behaviour of animals otherwise unfamiliar to them. Sportfishing is another way of enjoying the natural environment, also indulged in by millions of people every year. Interest in aquarium fishes and sportfishing support multimillion-dollar industries throughout the world.

 

Answer these questions to Text 1.

1. Define the fish as a living organism.

2. What classes of fish do you know?

3. How do they breathe?

4. How do they reproduce?

5. What do you know about the feeding habits of fish?

6. Why are fish so important for humans?

 

Read the texts using your dictionary.

Retell one of the texts.

Text 2

Flying fish

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 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 1.2 meters and gliding long distances, up to 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 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. There is currently no protection status on these animals.

 

Text 3

White sharks

The large and extremely aggressive white shark, Carcharodon carcharias, is considered by most experts to be the most dangerous shark in the world. Although the total number of attacks by white sharks on swimmers, surfers, and boats is higher than that by other sharks, the rate of attack is relatively low, certainly much lower than other fatalities on the sea such as drowning.

White sharks are large, reaching a size of at least 6 meters and perhaps as much as 8 meters in length. Large individuals may weigh as much as 2, 180 kilograms. The mouth is large and located on the undersurface of the head. Large gill slits, of which there are five on each side of the head, extend onto the upper surface of the body.

The fearsome teeth of the white shark are particularly notable: large, triangular, and bladelike. These teeth, combined with the shark's powerful jaws, size, and swimming strength and speed, make the white shark a superpredator capable of exploiting a variety of prey. Its diet includes fishes and marine mammals. Young white sharks tend to favor fishes, while mature sharks appear to prefer mammals. Other sharks and invertebrates such as crabs and squid also serve as prey. Less commonly found in the stomachs of captured white sharks are sea turtles and birds such as gulls, and penguins. The remains of sheep, pigs, horses, dogs, and, rarely, humans have been found in their stomachs, as has indigestible garbage.

The white shark, like the other members of the same family, owes much of its strength and endurance to adaptations in its circulatory system that enable it to maintain a body temperature above that of the surrounding water. A series of structures called countercurrent exchangers, located near the gills, forms a thermal barrier that prevents the loss of heat from the body into the surrounding environment. The resultant increased body temperature allows for a more efficient metabolism, enabling these sharks to swim faster and with greater strength and endurance than fish that lack this adaptation.

 

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