Aquatic Respiration refers to the process whereby an aquatic animal obtains oxygen from the surrounding water. The level of oxygen in water is low, and can be very low.
Very small organisms can obtain sufficient oxygen through the skin (e.g. flatworms) but larger organisms must have special structures, such as gills, and must have ways of increasing water flow over those structures.
Fish have developed gills for respiration which have:
- large surface area
- High blood flow
- small/short diffusion distances
- contain 4 gill arches(bony fishes) on each side of the fish head
- each gill arch has 2 rows of gill filaments
- each gill filament has many lamellae
Fish uses a type of countercurent flow to maximize the intake of oxygen that diffuse through the gill. Countercurrent flow is when deoxygenated blood moves through gill in one direction while oxygenated water moves in the gill in the opposite direction.