Gas Exchange In Bony Fish

Question 1

Gas Exchange in Bony Fish

Answer 1

Bony fish exchange gases with the water they live in. Gills absorb O2 dissolved in the water and release CO2. The O2 concentration is lower than in the air.

Question 2

Gaseous exchange system:

Answer 2

Gills covered by the operculum (a bony plate that covers & protects gills). Gills consist of many gill filaments (primary lamellae) attached to a bony arch (gill arch) – supports gill structure. The filaments are very thin and folded into many gill plates (secondary lamellae, or just lamellae) – thin & increased SA. Blood capillaries carry deoxygenated blood close to the surface of the secondary lamellae where gas exchange occurs – good blood supply.

Question 3

Countercurrent flow:

Answer 3

Blood flows along the gill arch and along the filaments to the secondary lamellae. The blood flows through the capillaries in the opposite direction to the water flow over the lamellae (fish must swim constantly for gas exchange to occur). Countercurrent flow maintains a high concentration gradient, the concentration of O2 in the water is always higher than in the blood, allowing absorption of the maximum amount of O2.

Question 4

Ventilation:

Answer 4

Bony fish maintain water flowing over the gills by using a buccal-opercular pump.
•The buccal cavity (mouth) can change volume, the floor of the mouth moves downwards, increasing volume inside and decreasing pressure, drawing water in.
•When mouth closes, the floor of the buccal cavity moves up, decreasing pressure and increasing volume, pushing water out through the gills.
•Each gill is covered in a bony flap called the operculum (which protects them). Movements of the operculum and buccal cavity are coordinated.
•As water is forced out from the buccal cavity, the operculum moves outwards (opens), increasing volume and reducing the pressure in the opercular cavity (space under the operculum), helping water to flow through the gills.

Question 5

Practical – Dissection of fish gill:

Answer 5

Find operculum (bony covering on each side of head) and lift it with scissors to observe the gills. Cut away one operculum to view the gills (note the gill slits or spaces between gills). Cut out each gill arch through the bone at the top and bottom (note the bony support (gill arch) and gill filaments) and draw it.