Respiration in Fish: Introduction, Respiration, Categorized Two Types of Fishes (For CBSE, ICSE, IAS, NET, NRA 2022)

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Introduction to Fish

  • A fish is an aquatic or marine water animal.
  • It needs oxygen to breathe for cells to sustain.
  • The respiratory function is carried out by the specialized structures.
    • Helps in inhaling oxygen dissolved in water.
  • Fish belongs to Animalia Kingdom, Chordata Phylum, Olfactores Clade, Vertebrate Subphylum, Pisces Class.


It is the highest taxonomic group within which the organisms are grouped.


It includes vertebrates along with sea squirts.


Group of such animals, which have a backbone or spinal column.


This class is in the vertebrate subphylum within the Phylum Chordata.

Respiration in Fish

Fishes respire through gills.


  • These are located next to the mouth cavity of the fish.
  • These are like the lungs in humans.
  • As they are filled with, blood vessels so gills possess a red colour.
  • It is through highly vascularized gills, that the gaseous exchange in fish takes place.
  • Gills consist of lamellae (plates) .
    • Tissues like thin filaments (protein structures) .
  • Most of the oxygen and carbon dioxide exchanged is dissolved in water.
  • Gill openings are also known as gill slits.
  • There are fishes with one gill opening and multiple gill openings. For e. g. Bony, fishes have one gill opening whereas fishes like lampreys and sharks have multiple gill openings.

Types of Fishes Categorized (Breathing Techniques)

Breathing Techniques

Obligate Air Breathers

  • These fishes breathe air periodically.
  • One of the examples is that of an African lungfish.

Facultative Air Breathers

  • These fishes breathe air if they need to.
  • They can depend upon their gills for oxygen.
  • One of the examples is that of Catfish (Hypostomus Plecostomus) .

Respiration in Different Fishes

Bony Fishes

  • Oxygen rich water is taken through mouth.
  • The gill arches do not have septum.
  • The gills are present in a branchial chamber.
  • External gills are also present in some bony fishes.

Cartilaginous Fishes

  • There are five pairs of gills present.
  • Along the gill septum, lamellae are present.
  • Through spiracle, (opening) fishes breathe by sucking water.

Lampreys and Hagfish

  • In these fishes, the gill slits are absent.
  • On outside they have a circular opening.
  • These fishes have two gills in each pouch.
  • The openings are covered and form operculum.
  • There are six to fourteen pairs of pouches in Hagfish.
Movement of Water and Ion
Movement of Water and Ions

Characteristics of Fish

  • They are cold-blooded animals.
  • The body is streamlined, and spindle shaped.
  • They heart is two-chambered also known as venous heart.
  • Being unisexual, they can undergo both internal and external fertilization.
  • In most of the fishes, there are usually 4 to 7 pairs of gills.


Q 1. What are the two types of fishes categorized on their breathing techniques?


The two types of fishes categorized on their breathing techniques are:

i) Obligate Air Breathers

ii) Facultative Air Breathers

Q 2. What is Pisces?

Answer: Pisces is a class in the vertebrate subphylum within the phylum Chordata.

Q 3. What is operculum?

Answer: Gills present beside the pharynx are covered by the operculum.

Q 4. How many pairs of gills are there in Bony fishes, Cartilaginous fishes, and Jawless primitive fishes?

Answer: In Bony fishes, there are three pairs of gills; Cartilaginous fishes have five to seven pairs of gills and Jawless primitive fishes have seven pairs of gills.

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