Respiration in fishes|Class 11 biology|Chapter no 13|Gaseous exchange|

Описание: Title: Respiration in Fishes | Detailed Explanation for Biology Students

Introduction: Welcome back to our channel! In today’s video, we’ll explore how fishes breathe underwater. Just like humans, fishes also require oxygen for survival. However, they have a different system to extract oxygen from water instead of air. This process is called aquatic respiration, and it occurs mainly through gills.


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1. Respiratory Organs in Fishes: Gills

Fishes breathe through specialized organs known as gills, which are located on either side of the head in bony fishes and in gill slits in cartilaginous fishes like sharks and rays. Gills are highly vascularized structures – meaning they have a rich supply of blood – which allows efficient gas exchange.

Types of Gills:

External gills – found in some primitive fishes and larvae.

Internal gills – found in most modern fishes, protected by a bony cover called the operculum (in bony fishes).



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2. Structure of Gills

Each gill consists of:

Gill arches: bony or cartilaginous structures that support the gills.

Gill filaments: thin projections that increase the surface area.

Gill lamellae: microscopic folds on the filaments that contain capillaries for gas exchange.



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3. Mechanism of Respiration: How Do Fishes Breathe?

Fishes use a buccal-opercular pump mechanism to ventilate their gills. Here's how it works:

Step-by-Step Process:

1. Water Intake:

The fish opens its mouth, allowing water to enter the buccal (mouth) cavity.



2. Mouth Closes and Operculum Opens:

The mouth closes, and the floor of the buccal cavity raises, pushing the water over the gills.

At the same time, the operculum opens, allowing water to exit through the gill slits.



3. Gas Exchange:

As water flows over the gill lamellae, oxygen diffuses from the water into the blood, and carbon dioxide diffuses from the blood into the water.

This occurs through a process known as counter-current exchange, where water and blood flow in opposite directions to maximize oxygen absorption.





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4. Counter-Current Exchange System

This is a key adaptation in fishes:

Water flows over the gills in one direction.

Blood flows through the gill capillaries in the opposite direction.

This maintains a gradient where the oxygen level in water is always higher than in blood, ensuring continuous diffusion of oxygen into the blood.



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5. Types of Respiration in Fishes

A. Branchial Respiration:

Respiration through gills.

Most common and efficient method in aquatic environments.


B. Accessory Respiration:

Some fishes, especially those in oxygen-poor environments (like swamps), have developed accessory respiratory organs such as:

Skin (cutaneous respiration)

Lungs (in lungfishes)

Air bladder (in some species like gar and catfish)




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6. Special Adaptations

Lungfish: Can breathe air using lungs during droughts.

Mudskippers: Live on land and use skin and mouth lining for respiration.

Betta and Gourami: Possess a labyrinth organ that allows them to gulp atmospheric air.



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7. Importance of Dissolved Oxygen

Fishes depend on dissolved oxygen (DO) in water. If the DO levels drop due to pollution or high temperature, fishes may suffocate and die.


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Conclusion

To sum up, respiration in fishes is a highly efficient process adapted for aquatic life. The gills, along with mechanisms like counter-current exchange and special adaptations in some species, allow fishes to extract oxygen from water effectively. Understanding fish respiration not only helps us appreciate their biology but also highlights the importance of clean and oxygen-rich water for aquatic ecosystems.

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