- The presence of gills for respiration is an important characteristic of fishes.
- Their skin is covered with scales/plates.
- They lay eggs [oviporous].
- Some fishes are ovi-viviparous.
- Presence of paired and unpaired fins.
- fertilization is internal.
- presence of air bladder act as an organ of buoyancy in some fishes.
- They obtain oxygen dissolved in water by using gills.
- The body is streamlined, and a muscular tail is used for movement.
- They are cold-blooded and their hearts have only two chambers.
- Some fish skeletons are made entirely of cartilage [Chondrichthyes], such as sharks,
- some with a skeleton made of both bone and cartilage [Osteichthyes].
- They are marine animals with streamlined bodies and have cartilaginous endoskeletons.
- The mouth is located ventrally.
- The notochord is persistent throughout life.
- Gill slits are separate and without operculum (gill cover).
- The skin is tough, containing minute placoid scales.
- Their jaws are very powerful.
- These animals are predaceous [shark].
- Due to the absence of air bladder, they have to swim constantly to avoid sinking.
- Heart is two-chambered (one auricle and one ventricle).
- Some of them have electric organs (e.g., Torpedo) and some possess poison sting (e.g., Trygon).
- They are cold-blooded (poikilothermous) animals, i.e., they lack the capacity to regulate their body temperature.
- Sexes are separate. In males pelvic fins bear claspers.
- They have internal fertilization and many of them are viviparous [give birth to young ones].
- Examples: Scoliodon (Dogfish), Pristis (Sawfish), Carchaiodon (Great white shark), and Trygon (Stingray).
- It includes both marine and freshwater fishes with bony endoskeletons.
- Their body is streamlined.
- The mouth is mostly terminal.
- They have four pairs of gills which are covered by an operculum on each side.
- Skin is covered with cycloid/ctenoid scales.
- The air bladder is present in the teleost of bony fishes which regulates buoyancy.
- The heart is two-chambered (one auricle and one ventricle).
- They are cold-blooded
- Sexes are separate.
- Fertilization is usually external.
- They are mostly oviparous and development is direct.
- Examples: Flying fish, Sea horse, Fighting fish, Angel fish etc.
ELECTIC RAY
sub-phylum Vertebrata - Notochord replaced by vertebral column or backbone,
Economic Importance of Fishes
Fish unsuitable for human consumption is often
discarded during processing. These and such species have little market
value from important raw materials for a fishery by-product
industry. Fish is a highly perishable food material because of its moisture
and nutrient contents, and spoilable begins as soon as fish dies, it is the
result of a series of complicated chemical reactions taking place in a dead
fish, mainly by enzymes and bacteria. These are either thrown back into the sea
immediately after their catch or utilized wholly or partly as manure.
Fishes are largely consumed as a source of food material all over
the world because of their nutritional value. Fishes in India are mostly consumed
fresh and some are preserved or dried for further use as food. The
major source of fish is the oceans which fulfill the need for food for the growing
population. Most of the time waste fish are thrown back into the
sea just immediately after a catch or used wholly or partly as manure. Fishes
are highly perishable food material because of the presence of moisture and
nutrients, fishes get spoil soon after death. These are unutilized for the
preparation of many byproducts of human and industrial use. It would enhance
the economy of the country by selling them.
Some of the important fish byproducts
are as follows
1. Fish
protein concentrate
2. Fish
flour
3. Fish glue
4. Fish skin
5. Fish
liver oil
6. Body Oil
7. Fish meal
8. Gelatin
9. Insulin
10. Fish
fins
11. Isinglass
12. Fish
guano
13. Fish
manure
1. Fish protein concentrate – It
is a stable protein concentrate prepared from whole fish. It is a colorless and
odorless powder with high nutritional value for human use. It
contains protein and minerals. It is also known as fish flour or edible fish
meal.
2. Fish flour - Fish flour is
a superior quality of fish meal, which is used for human intake. It can
be mixed with another foodstuff such as wheat flour for enriching the nutritive
value of bread, biscuits, cakes, etc.
3. Fish glue or adhesive - fish
glue is prepared from the skin, fins, and bones of fish. which are
washed, crushed, and cooked in large vessels for 6-10 hours with acetic acid.
The liquid is separated and concentrated to form fish glue which is used as an
adhesive for fixing wood, paper and leather. bookbinding, labels, paper boxes
etc.
4. Fish skin- the skin of a shark
is used for the preparation of polish paper which is called as shagreen used in
furniture polishing.
5. Fish liver oil – it has huge content
of vitamins A and D used to prevent deficiency or cure rickets, xerophthalmia,
impaired vision and eye defects, abnor¬malities of skin, mucous membranes, and
vertebrae in the body.
6. Body oil – It is used in
the manufacture of cosmetics, lubricants, candles and cutting oils, printing
inks, water-proof preparations, and cheaper-grade toilet soap. Body oil
is used for coating the surface of boats for longer
preservation. Body oil is used for coating the surface of boats for
longer preservation.
7. Fish meal- It is excellent poultry and
animal feed as the highly nutritive product contains all the essential amino
acids. Fish meal is good for all classes of livestock. It increases milk and
egg production. As it is rich in calcium, phosphorus, iodine, and a rich variety
of vitamins promotes the building of tissue and bones used for the healthy growth
of growing cattle. Waste fish meal mixed with rice bran and vitamins forms an
excellent feed in aquaculture.
8. Gelatin – gelatin is extracted from
bones and skin of fishes. Gelatin is a rich source of lysine and methionine. It
is used in the food industry as a gelling, stabilizing, emulsifying, dispersing
or thickening agent.
9. Insulin: Insulin is a hormone
used for correcting the condition called diabetes mellitus in humans. Fish
insulin is more stable as it is not subjected to decomposition by protein-splitting enzymes of the pancreas.
10. Fish fins –The dried
fins of sharks are exported to China where they have great demand for the
preparation of soups.
11. Isinglass: The
air bladder of some fishes such as catfish, eels, carp, seabass etc. are used
for the preparation of isinglass. Isinglass reduces the suspended
solids in beer and increases filtration. It can also be used as an adhesive
base and in the sweet product, it is used for the preparation of ink
and also used as an effective adhesive for glass, pottery, and leather.
12. Guano: is
the byproduct from body oil extraction industries. It is nothing but the dried
waste left after the extraction of body oil. fish guano is more
effective as it contains a large quantity of nitrogen and phosphoric acid. Fish
guano is also used as fish manure.
13. Fish Manure: Fish
manure and guano are the lower quality of the fish meal. It is not fit for animal
consumption. Fish ma¬nure is a by-product of the curing yards, fish glue
industries, and oil extraction plants, where waste or spoilt fish have been
used. The fishes which are spoilt and unhealthy for use as food is used for the
preparation of fish manure. Fish manure contains nitrogen and phosphates
which are useful for agricultural use.