Exercise 1
Name fresh-water (salt-water) fish.
Exercise 2
Chose the words from the topical vocabulary to match the definitions:
- a fish born in fresh water, that spends most of its life in the sea and returns to fresh water to spawn;
- the large single fin located along the back bone of a fish;
- one of the movable parts that look like wings, sticking out from the body of a fish. A fish uses its fins to swim and balance itself in the water;
- the waters from which a river begins;
- organisms living in a particular environment, such as a forest or a coral reef, and the physical parts of the environment that affect them;
- what a fish breathes with;
- paired fins located about halfway down the length of a fish along the abdomen;
- one of the hard, flat structures that cover the body of fish, snakes, and lizards.
Exercise 3
Use the words from the topical vocabulary to fill in the gaps.
1. A fish's … are the flat objects which stick out of its body and help it to swim and keep its balance.
2. He … the fish and removed the innards.
3. When fish or animals such as frogs …, they lay their eggs.
4. A … is a large sea fish with a very long upper jaw.
5. The skeleton of sharks and rays is composed of … rather than bone.
Fish
Fish are vertebrate animals that live in almost every part of the ocean, from the surface to the bottom of the deepest trenches, and even at the very edge of the sea. By 2004 over 20,000 species, including the 200 or so edible species, had been described. Since about 100 new species are being described each year, the total number of fishes may exceed 30,000 species.
About 60% of all vertebrate animals (animals with backbones) are fishes. About half the described species are marine, and approximately 75% of them live in shallow coastal waters. The types range from hagfish (Myxine spp.) to lungfish (Dipnoi), but here the discussion will centre on the bony fishes, which are by far the most diverse and species-rich group of fishes. They are distinct from the cartilaginous fishes, i.e. sharks and their relatives, by having bony rather than cartilaginous skeletons, gills covered with a flap, and mouths that are usually on the front of the head. The mouths of some fishes are armed with teeth that are used to rasp soft tissue, grind up molluscs, or scrape algae off rocks. Others, such as the seahorses, have no teeth and have tubular-shaped mouths adapted to suck up individual plankton.
The rich diversity of fishes is partly the result of their having adopted a great variety of ways of feeding. Their basic body form is spindle shaped, with dorsal fins on the back, two pairs of lateral fins, the pectorals and the pelvics, a ventral anal fin, and a large tail, or caudal fin that is usually symmetrical. The fins are composed of fine bones, or fin rays that normally are webbed. These fin rays can be developed into long sensory structures or hard spiny structures that may be armed with poison glands. The spindle shape gives a good hydrodynamic shape that slides through the water with minimum resistance when the posterior region of the body, and the tail, beats from side to side. However, this basic body shape has been greatly modified in different families of fish, especially in those families that live around the seabed. Eels have lost most of their fins and developed long sinuous bodies and a serpentine mode of movement, ideal for moving in and out of crannies in, reefs, but less effective for swimming in midwater.
The coloration of fishes is almost as diverse as their habits. Some, like flatfishes, can change their colour at will, either to blend in with different backgrounds or to flash warnings to would-be predators. In many shallow coral reef species, males display bright colours to guard their territories, but generally fishes use their coloration as camouflage. The commonest colour pattern in the fishes that swim in midwater is a countershading, with dark backs and pale bellies and flanks that may be banded with a disruptive pattern, often silvery or, in deep-sea species, lined with light organs. The brightness of light changes with depth, and its colour also changes—red light being absorbed very quickly – so the range of colours used by fish is restricted. Also, fish see only monochromatic blue-green light, which is the colour of light that penetrates furthest in water. In very deep water many fish species do not have functional eyes, since that there is almost nothing to see in the permanent darkness below about 1,000 metres (3,250 ft).
Another important sensory feature of fishes is their lateral line system. This is a chain of sense organs, similar to those in our ears, that can either be open to the water or semi-enclosed. With this system the fishes feel the water, sensing currents and the low-frequency vibrations transmitted by the movements of other animals. Many deep-sea fishes have long filamentous tails that, by extending the length of the lateral line organ, enable them to feel the direction from which any movements are coming.
Fishes' blood is about half as salty as sea water – that is why thirsty shipwrecked mariners can safely drink it to slake their thirst – so fish continually have to get rid of salt from their bodies across their gills. Although this helps to make fishes less dense, many still have systems for adjusting the density of their bodies to be much the same as the sea water, so when they stop swimming they do not sink. Above the gut of many fishes is a swim-bladder that is filled with gas. In some fishes this is filled by gulping in air at the surface, but the vast majority never approach the sea surface, so the swim-bladder is filled by a special gland that extracts dissolved gases from the blood. Some fishes that swim continuously, like tunas and marlin, have no swim-bladder. Instead, they have rigid pectoral fins that act like hydroplanes to generate lift as they swim. Swim-bladders do not occur in many deep-sea fishes, because the greater the hydrostatic pressure (i.e. depth) the greater the energy required to fill them, so at depths below about 500 metres (1,625 ft) it becomes physiologically too expensive. In these fishes either the swim-bladder is filled with oily fats, or it disappears. Deep-sea fishes tend to have very watery tissues, and their bones contain very little calcium, which reduces their density. However, some still retain gas-filled swim-bladders in very deep water which are connected by bones to sensory organs, and function as hearing organs. They also often have drumming muscles attached to them for the fish to produce sounds for communication. During the Cold War when hydrophones were deployed in deep water to listen for the movements of submarines, it was found that the deep ocean is quite noisy, especially during the breeding season for deep-sea fishes and when whales migrate.
Exercise 1
Find in the text English equivalents of the following words and word combinations:
прибрежные воды; тело вытянутой формы; изменять окраску по желанию; сливаться с фоном, окружением; подавать предупреждающие знаки потенциальным хищникам; защитная окраска; глубоководные рыбы; утолить жажду; гидростатическое давление; период размножения.
Exercise 2
Complete the sentences:
1. The total number of fishes may exceed …
2. The rich diversity of fishes is partly the result of …
3. The fins are composed of …
4. The coloration of fishes is almost as diverse as …
5. The commonest colour pattern in the fishes that swim in midwater is …
Exercise 3
Answer the questions:
1. What is fish?
2. What is the difference between bony fish and cartilaginous fish?
3. What can you tell about the body form of the fish?
4. What role does the coloration of fishes play in their life?
5. What is another important sensory feature of fishes?
6. Do all fishes have swim-bladders? What for?
classes of fish
There are three classes of fish. Fish that don't have jaws belong to the jawless fish class. Fish that have skeletons made of tough, flexible cartilage belong to the cartilage fish class. Most of the fish you're familiar with belong to the bony fish class. These fish have skeletons made of bone.
Jawless fish such as lampreys and hagfish don't look like fish. They have no jaws with which to open and close their mouths. Jawless fish have no scales and their skeletons are made of cartilage. Lampreys are parasites that live in fresh and salt water. Their round mouths are filled with small curved teeth. With these teeth lampreys cut holes inother fish's bodies. Lampreys attach themselves and suck the body liquids and blood out of the holes. Hagfish live only in the oceans. They have fewer teeth than lampreys. But hagfish do have slit-like mouths that help them cut holes in other fish. Once holes are made, the hagfish crawl inside and feed.
Like the jawless fish, the cartilage fish also has skeletons made of cartilage. Unlike the jawless fish, the cartilage fish have jaws and scales. Sharks are one example of cartilage fish. They are the fastest-swimming fish.
The mouths of the sharks are filled with rows of sharp teeth that slant backward. These teeth help sharks hold their prey. As sharks' teeth are lost or broken, other teeth move forward to replace the lost ones.
Another type of cartilage fish, the rays, has a flat body and lives on the ocean bottom. Some rays have strong jaws that crush the shells of clams and oysters. Other rays, such as the stingray, have poisonous spines near their tails. Their poison causes pain and even death to their prey.
Most fish known today belong to the class of bony fish. Bony fish are the fish you know best – bass, flounder, cod, sole, trout, and so on. Bony fish are covered with scales that are smooth and slimy. The slimy covering helps fish glide through the water. It also helps protect them from parasites. The scales of bony fish grow larger as the fish grow older.Growth rings on the scalesshow the age of the fish.
Most bony fish have an air bladder which enables them to swim at a certain depth. Gases from the blood move into the air bladder. As the bladder fills with gases, the fish rises in the water. If gases move out of the bladder, the fish will sink deeper in the water.
Many bony fish have well-developed fins which make these fish excellent swimmers. Sailfish and tuna can swim for long distances at fast speeds. Other fish have different kinds of fins. Flying fish have winglike fins that help the fish to leap above the water. The walking catfish has muscular fins that help it move on the land. Instead of separate fins, eels have fins that are continuous and joined.
Most fish reproduce by external fertilization. This means that eggs and sperm join outside the bodies of the fish. Female fish usually release their jelly-coated eggs in the water. Some species lay eggs in nests made from weeds, twigs, or mud. Male fish release sperm to fertilize the eggs. Most fish lay thousands and even millions of eggs at a time. Why aren't the waters overcrowded with fish? First, not all of the eggs are fertilized. Second, other eggs are eaten by predators before they hatch. Some of the young fish will be eaten before they become adults.
Bony fish provide food for the world's population, that is high in protein and low in fat. Some countries, such as Norway and Japan, rely on fish as their main food. Fish are also used to make animal feed and glue. Sharks' skins are used to make shoes. Oil from fish is used in making paints and varnishes and in tanning leather.
Exercise 1
Find in the text English equivalents of the following words and word combinations:
бесчелюстные рыбы; хрящевые рыбы; костные рыбы; щелевидное ротовое отверстие; удерживать добычу; быть покрытым шелухой; оплодотворение вне организма; оплодотворять яйца; с высоким содержанием белка и низким содержанием жиров.
Exercise 2
Complete the sentences:
1. Fish that don't have jaws belong to …
2. Fish that have skeletons made of tough, flexible cartilage belong to …
3. Fish that have skeletons made of bone belong to …
4. Sharks are one example of …
5. Most fish reproduce by …
Exercise 3
Answer the questions:
1. What are the major classes of fish?
2. What are the examples of jawless and cartilage fish?
3. How do bony fish look like?
4. How do most fish reproduce?
5. Where is fish used?