gas exchange - fish

gas exchange in fish

small SA:V therefore require a specialised gas exchange surface - gills

made up of gill filaments

at right angles to the gill filaments are gill lamellae

Identify structures labelled F and G.

F = filament
G = secondary lamellae

counter current flow

- flow of water and blood over gill lamellae in opposite directions → maximum gas exchange
- maintains diffusion gradient of oxygen
- diffusion along entire length of lamellae
- this allows about 80% of oxygen to be absorbed by the fish

why do fish require a gas exchange surface?

fish are waterproof (have a waterproof, thus gas tight, outer layer covering) and have a small SA:V (cuz they’re relatively large)

fish gill anatomy

- 4 layers of gills on both sides of the head
- gills are made up of stacks of gill filaments
- each gill filament is covered in gill lamellae, positioned at right angles to the filament
- this creates a large SA
- when fish open their mouths, water rushes in and over the gills and then out through a hole in the sides of their heads

adaptations for efficient gas exchange in fish

- large SA:V created by many gill filaments covered in many gill lamellae
- short diffusion distance due to capillary network in every lamellae and very thin gill lamellae
- maintaining concentration gradient countercurrent flow mechanism

Explain 2 ways in which the structure of fish gills is adapted for efficient gas exchange.

1. many lamellae so large surface area;
2. thin surface so short diffusion pathway;