Introduction Water 5. Aquarium Fish 1. Fresh water fish


Fish are cold-blooded animals, have
fins and a backbone. There are about 22,000 species of fish that began evolving
around 480 million years ago. The largemouth bass illustrated above the typical
torpedo like (fusiform) shape associated with many fishes. A fish is any member of a paraphyletic (ancestral)
group of organisms that consist of all gill-bearing aquatic craniate animals
that lack limbs with digits. Included in this definition are the living
hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct
related groups. Most fish are ectothermic (“cold-blooded”), allowing their
body temperatures to vary as ambient temperatures change, though some of the
large active swimmers like white shark and tuna can hold a higher core
temperature. Fishes are oldest aquatic vertebrates found all over
the globe. 

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Nearly 500
million years ago the first fish appeared on the earth. Today fishes make up
the largest group of vertebrates with 24,000
species. Fishes have their habitats in lakes, streams, oceans, and estuaries.
In 1991 it was estimated that 2546 species of
fish populated the
world. Out of which 969 belong to genera, 254 families, and 40 orders. Around 80% of fish population around the globe was
represented by the Indian fishes. Fishes are
capable of living in both fresh and marine water.

Types of

Depending upon the habitats and characteristics there are a
variety of fish available on the world.

1.      Fresh Water

2.      Tropical

3.      Marine

4.      Cold Water


1. Fresh
water fish

Fishes that spent most of or all time
of living in fresh water bodies such as lakes and rivers in which the salinity
is less than 0.05%. These
environments differ from marine conditions in many ways, the most obvious being
the difference in levels of salinity. To survive fresh water, the fish need a
range of physiological adaptations. 41.24%
of all known species of fish are found in fresh water.

India is rich with inland freshwater fish,
with about 940 species known from its rivers, lakes and estuaries. This
constitutes about 38% of the Indian Ichthyofauna and are of considerable
economic and scientific value. Of these about 500 species are primary
freshwater fish with around 65% endemic, cloistered in the two hot spots of
India, the Western Ghats and the North East. However, threats to these fauna
are aplenty, with urbanization, deforestation, habitat loss, pollution,
over-harvesting, and culture of exotics. 
Some of them are
Indian Major Carps- Rohu, Catla, Mrigal and bala sharks, betta fish, candiru
fish, gold fish, and oscur fish.


Marine fish                            

Fishes that are capable of living in
the sea water are known as marine fish. About 15,000 species belong to the
marine species. Tropical climate is required for most of the marine fish to
survive. Every species of the marine creature have their own appearance,
environmental needs, nutritional requirements, reproduction capability, and
compatibility. Blue whale, dolphin, cuttle fish, jelly fish, loin fish and star
fish are the major marine fish species.

Tropical fish

These fishes require warm and
tropical climate to survive. Both freshwater and saltwater species come under
this category. Because of their bright coloration they act a popular aquarium
fishes. Angel and gold fish are more famous for the aquarium environment.

Coldwater fish

Coldwater fish, in the context of
aquariums, refers to fish species that prefer cooler water temperatures than
tropical fish, typically below 20 °C (68 °F). Some examples are koi and
goldfish. These species tend to grow more slowly and live longer than fish that
live in warmer waters, and are generally felt to be easier to keep.

Aquarium fish

The fishes which keep in aquaria for
display purpose in homes, hotels, exhibitions etc. refers to aquarium fishes.
Although a fish has to be always low growing and having small size. They may be
from all of the above types of fishes e.g. Gold fish, Cat fish etc.

of Fish based on characteristics (or

Fish, the member of the Animalia
Kingdom is classified into Phylum Chordata and Vertebrata Subphylum. Fishes poses notochord, tubular
nerve chord, and paired gills, segmentation of the body parts, post anal tail,
ventral heart, and an endoskeleton to be the member of the Chordata. In order
to be a vertebrate, it poses backbone. This back bone supports and protects the
spinal cord.

All the species of the fish found in
the world are classified into the following three groups.

1.      Agnatha – jawless fish

2.      Chrondrichthyes – cartilaginous fish

3.      Osteichthyes – bony fish

a. Ray finned group

b. Lobe finned group

About 50
species of Agnatha fish, 600 species of
Chrondrichthyes fish and 30,000 species of
Osteichthyes fish
are found in the world. Most of the fishes in the bony group belong to the ray
finned group. According to the biologist there are about 70 fish orders are found in the world.

Fish Orders- Sharks and rays;
sturgeon and gars; herring-like fishes; trout and salmon; eels, minnows,
suckers, and catfish; flying fish and relatives; cod-like fish; flatfish;
seahorses and relatives; mullets, silversides, and barracuda; and mackerels and
tunas are the main group of fishes.

Agnatha- Jawless

Phylum: chordate

Subphylum: vertebrata

Agnatha are jawless fish and lack
paired fins. They also lack the internal skeleton system. They have a circular
tooth mouth (cyclostomic) by which they bore the body of their victim and suck
their blood.

Fig 1.

These are
classified in to two major types as Hagfish and Lampreys.

of Agnatha

Jaws are absent. Paired fins are
absent. Bony scales and skin plates were present in the ancient species but are
absent in the living species. Gill pouches are present. They have seven or more
pouches. Stomach is absent in the digestive system. E.g. Hagfish

Chrondrichthyes- Cartilaginous fish

Phylum: chordate

Fig 2.
Shark Fish