5th Class Science Animals Fishes

      Fishes

Fishes are our very distant ancestors. These are believed to be first veterebrates, came into being about 550 millions years ago. Those were extremely different from what we see today, those were without Jaw. They did not have bones in their mouth. During this 550 million years, they have taken many different shapes, and varied into some dangerous fishes. Some fishes developed electrical and chemical weapons, some took giant shape and some other developed strong jaw and sharp teeth. Since their origin, they have been adapting the varied conditions of the earth and in spite of extinct of Dinosaur, they have been maintained their existence successfully.

        Parts and Features of Fish Body

Fishes have fins and tails which provide movement and balance in water while swimming. A fish move forward by pushing water backwards with fins and its tails,

Fishes possess gills, a special organ to take in oxygen dissolved in water.

More than 20,000 kinds of fishes are there on the earth, because % part of the earth is covered with water, which provides accommodation to fishes.

Fishes are vertebrates that have skeleton either made up of bones or cartilage.

Poisonous fish: Puffer fish, it has poison in its internal organ. Almost all puffer fish contain tetrodotoxin. Tetrodotoxin is much more poisonous than cyanide.

Fastest swimming fish: They can swim with the speed of fast running vehicle. They have sleek, streamlined body to facilitate fast speed in water.

E.g. sailfish, marlin fish and tunas etc.

Look at the following pictures of different types of fishes:

Marlin fish                                        Pygmy goby fish                                               Shark fish  

[Note: Piranha is the most dangerous and aggressive fish in the world found in freshwater. They can even kit and eat flesh of big mammal in minutes with its sharp teeth when they attack in group]

Feeding habit: Small fishes eat plants and big fishes like shark eat other fishes.

Reproduction in fishes: Fishes reproduce by laying eggs, eggs develop into fry which after growth, changes into adult fish.

        Salinity of seawater is 3.5 %, this means that every liter of seawater contains 35 g salt. 'Fresh water fish can survive in the salty oceans and seas' the given statement is;

(a) True

(b) False

(c) Partially true

(d) Partially false

(e) None of these

Answer: (b)

Explanation

Fresh water fish has adapted to low salt condition. Salt is a desiccant, it absorbs water which leads to dehydration. So they die if kept in marine habitat. Therefore, option (B) is correct and rest of the options is incorrect.

     The Whale shark is a biggest shark. It has a huge mouth which can be up to 1.4 meter wide. The whale shark is a/an :

(a) Fish

(b) Amphibian

(c) Reptile

(d) Birds

(e) Mammal

Answer: (a)

Explanation

Whale is a mammal but whale shark is the biggest shark and biggest fish that kills small fishes for its food. Therefore, option (A) is correct and rest of the options is incorrect.

         Amphibians

The word amphibian comes from two Greek words "amphi" which means "both" and "bios" means "life". Animal that can live both on land and in water is called amphibians. E.g. Frogs, toads, newts, and salamander etc.

       Salamander                                  Tree frog                             Common toad                                  Newt      

         Features of Amphibians

Amphibians are over 300 million years old.

They usually breed in water.

They are cold blooded as they can change their body temperature according to the environment.

Amphibians undergo hibernation process in winter to avoid extreme coldness.

Gills, lungs and skin are the respiratory organs of amphibians.

More than 3,500 kinds of amphibians are there on the earth.

Frogs can breathe through its moist skin in water and through lungs on land.

Some frog has poisonous skin, which helps to protect them from enemies.

Japanese salamander is the largest amphibian of size more than 1.5 m.

Poison arrow frog is one of the most poisonous animal on the earth  

Flying frog lives on trees. To allow gliding on trees it has round sticky pad son its toes.  

       Feeding in Amphibians (Frog)

Frogs eat insects, spider and other small creatures such as crayfish. Tadpoles usually feed on small water plants.

         Reproduction in Amphibians (Frog)

The female frog lays hundreds of eggs called spawn in the water. Tadpole hatches from this egg. It has tail to swim in water and has gills to breathe in water.  

         Life Cycle of Amphibians (Frog)  

      The female frog lays hundreds of soft eggs in water is called:

(a) Ovule

(b) Spawn

(c) Prawn

(d) Fry

(e) None of these

Answer: (b)

Explanation

Eggs laid by female frog are called as spawn. Fry is the young one of fishes. Ovule is produced by human female- Prawn is a type of fish. Therefore, option (B) is correct and rest of the options is incorrect.

      Find the incorrect statement.

(a) Flaps of skin help the flying frog to glide through the air

(b) Amphibians were evolved from fishes

(c) Male frogs make their croaking calls to attract females

(d) All frogs lay their eggs in water

(e) All of these

Answer: (d)

Explanation: Some frogs carries his mate's egg on his back until they develop into frog. Therefore, option (D) is correct and rest of the options is incorrect.