IV. Fill in the blanks with the words given below:

1. The fins consist of numerous … called fin rays which support the folds of thin skin.

2. Coloration of perch differs depending on the natural …

3. The organs of smell are found in the … in front of the eyes.

4. The camouflage helps the pike to … itself.

Environment, head, conceal, spines.

Text 2

Fish Evolution

About 500 million years ago, a tiny animal first appeared in the earth oceans. This strange animal had no jaws. It did have fins, but they were not like the fins of modern fish. This early fish was the first animal with a backbone, the first vertebrate.

Fish are the vertebrates that are best adapted to a life underwater. Their smooth bodies, usually covered with scales, are streamlined, allowing them to glide through the water. Most fish have fins. Some fins keep a fish upright so that it does not roll over on its side. Other fins help the fish steer and stop. The side-to-side movement of the large tail fin helps the fish move through the water.

Fish take oxygen from the water through gills. As a fish swims, water passes through the gills. Oxygen passes from the water into blood vessels in the gills. Carbon dioxide wastes also pass out of the fish through the gills. Fish have well-developed digestive, circulatory, and nervous systems.

Fish reproduce in an interesting manner. In most species female fish release jelly-coated eggs directly into the water. Then, male fish release sperm to the eggs. Because this type of fertilization occurs outside the body of the female it is called external fertilization.

Fish live in all of the earth's waters, in both fresh and salt water. But the same fish usually cannot live in both fresh and salt water. While some fish such the cod live in the cold water of the Arctic, others, such as fierce piranha, live in warm, tropical waters. Changes in fish environment can affect their body temperature. If the changes are severe, most fish will not survive. Fish have little trouble maintaining a constant body temperature as long as they remain in their native waters. This results in a saving of energy, for fish do not have to use food energy to keep warm.

Vocabulary:

the vertebrates – хребетні

oxygen – кисень

carbon oxygen – водень

gills – зябра

jaw – щелепа

blood vessel – кровоносна судина

fin – плавник

scale - луска

male duct - канал самця

digestive system - система травлення

circulatory system - система кровообігу

nervous system - нервова система

fertilize - запліднювати

maintain - підтримувати

release - випускати

reproduce – розмножуватися

I. Answer the following questions:

1. What were the early fish like?

2. What fish are considered to be best adapted to a life underwater? Why?

3. How do fish take oxygen from the water?