Exchange And Transport Systems: - Gas Exchange In Fish

- Gas Exchange in fish -

Fish have many different adaptation that give would give the fish large surface area for gas exchange. 

In a fish there are rows of gill filaments which are stacked like pages of a book. 

On the gill filaments there are gill lamellae which has a network of capillaries on them. This provides a larger surface area for gas exchange. 

counter-current flow 

The water enters the mouth of the fish and leaves through the gills. 

As the water passes through the gills the water passes over the filaments and over the lamellae. 

Water and blood flow over and through the lamellae in the opposite direction. // Parallel. 

When the blood first comes close to the water, water is fully saturated with oxygen and the blood has small amounts. 

This creates a steep concentration gradient // oxygen diffuses out of the water and into the blood. 

As the blood is absorbing more oxygen as it moves along the lamellae // blood reaches the end of the lamella 80% saturated with oxygen. The blood is highly saturated than it was at the beginning of the lamellae.

The concentration has continued to be maintained so it can continue to absorb oxygen from the water. 

Concurrent flow 

The water enters the mouth of the fish and leaves through the gills. 

As the water passes through the gills the water passes over the filaments and over the lamellae. 

The blood flows in same direction as the water does.

Water is slightly less saturated as it proceeds to move along the lamellae // water has still highly saturated with oxygen compared to the blood, diffusion still occurs until water and the blood have reached equal saturation. 

The steep concentration gradient continues to decrease as the diffusion of oxygen continues.