Accessory Respiratory Organs

 

Accessory Respiratory Organs

Accessory Respiratory Organs

Accessory respiratory organs are specialized structures other than normal gills that help certain animals breathe when oxygen availability in water is low or when they temporarily live outside water. These organs supplement the main respiratory organs and are common in many fishes, amphibians, and some invertebrates.

Need for Accessory Respiratory Organs

They develop due to:

1. Low dissolved oxygen in stagnant water
2. Seasonal drying of water bodies
3. Burrowing habits
4. Temporary terrestrial life
5. High metabolic demand

Types of Accessory Respiratory Organs in Fishes

1. Cutaneous Respiration (Skin)

• Exchange of gases occurs through moist and highly vascular skin.
• Seen in eel (Anguilla) and mudskipper (Periophthalmus).

2. Buccopharyngeal Epithelium

• The lining of buccal cavity and pharynx becomes highly vascular.
• Helps in aerial respiration.
• Example: Symbranchus.

3. Intestinal Respiration

• Posterior part of intestine becomes vascular and absorbs oxygen from swallowed air.
• Example: Loach (Misgurnus fossilis).

4. Stomach Respiration

• Stomach wall becomes vascular for gaseous exchange.
• Example: Hoplosternum.

5. Air Bladder / Lungs

• Swim bladder acts as respiratory organ.
• Example: lung fishes such as Protopterus, Lepidosiren, and Neoceratodus.

6. Suprabranchial Organs

Special chambers above gills help in aerial respiration.

Examples:

• Labyrinth organ – found in Anabas
• Arborescent organ – found in Clarias
• Air sacs – found in Heteropneustes

Significance

1. Helps survival in oxygen-deficient habitats.
2. Enables migration over land.
3. Helps fishes survive drought conditions.
4. Shows adaptation from aquatic to semi-terrestrial life.

Conclusion

Accessory respiratory organs are important adaptive structures that allow animals, especially fishes, to survive in unfavorable aquatic environments by enabling them to utilize atmospheric oxygen.

MCQs on Accessory Respiratory Organ / Labyrinth Organ of Anabas testudineus

1. The labyrinth organ in Anabas testudineus is located in the:
a) Buccal cavity
b) Intestine
c) Suprabranchial chamber
d) Operculum

Answer: c) Suprabranchial chamber

2. The main function of the labyrinth organ is:
a) Digestion of food
b) Excretion of wastes
c) Aerial respiration
d) Osmoregulation

Answer: c) Aerial respiration

3. The labyrinth organ develops from:
a) Skin folds
b) Modified gill arches
c) Vertebrae
d) Swim bladder

Answer: b) Modified gill arches

4. Which fish possesses arborescent accessory respiratory organs?
a) Anabas testudineus
b) Clarias batrachus
c) Labeo rohita
d) Catla catla

Answer: b) Clarias batrachus

5. Which of the following helps in gaseous exchange in the labyrinth organ?
a) Bone marrow
b) Blood capillaries
c) Nephrons
d) Gastric glands

Answer: b) Blood capillaries

References

1. Chordate Zoology
2. A Textbook of Vertebrate Zoology
3. Modern Textbook of Zoology: Vertebrates
4. Fish and Fisheries