4.2 - Gas Exchange in Fish

Question 1

What are the gas exchange surfaces of a fish?

Answer 1

Gills

Question 2

What are the structures of fish gills

Answer 2

OPERCULUM
- bony plate covering gills
- protects the gills
- aid in respiration by facilitating water flow over them

FILAMENTS
- On each gill, two rows on thin plates stacked uo
- increase the SA for gas exchange

PRIMARY LAMELLAE (GILL FILAMENTS)
- long, thin structures that extend from the gill arch
- increase the SA for more efficient gas exchange

SECONDARY LAMELLAE (GILL PLATES
- tiny, thin structures
increase the surface area
- where the counter-current exchange happens

• lamellae have a lot of blood capillaries so they have a rich blood supply a shorter diffusion pathway

Question 3

What is the counter-current exchange system?

Answer 3

• the flow of water over the gill lamellae and the flow of blood within the gill lamellae are in opposite directions
• this is important in maintaining a steep diffusion gradient to ensure efficient gas exchange
• The oxygen concentration in the water is always higher than that in the blood, so as much oxygen as possible diffuses from the water into the blood.

Question 4

How are fish gills ventilated?

Answer 4

1. the fish opens its mouth, which lowers the floor of the buccal cavity
2. as the volume of the buccal cavity increases, the pressure decreases
   - this means that water is then sucked into the cavity
3. when the fish closes its mouth, the buccal cavity is raised, and the volume decreases so the pressure increases, and the water is forced out of the cavity across the gill filaments
4. each gill is covered by a bony cap (operculum)
5. the increase in pressure forces the operculum of each side of the head to open, allowing water to leave the gills

Question 5

Key Features of the fish gas exchange

Answer 5

1. Structure of gills
2. counter-current flow
3. ventilation mechanism