Respiration in fish:
Gills are the most effective respiratory organs in water.
Temperature affects oxygen availability.
Gills: evaginations of the body surface.
Gills can be simple extensions of the body surface e.g. dermal papillae of star fish; external gills of marine worms and salamanders.
Internal gills of fish are the most efficient at extracting O2 from water, they are ventilated and protected within pharyngeal pockets.
Rich blood supply: unidirectional flow of water past filaments with counter current blood flow.
In fast-moving pelagic species, ram-jet ventilation replaces skeletal muscle pumping.
This mechanism optimises O2 diffusion from water to blood and minimises work of ventilation.
A large diffusion gradient for O2 is maintained over most of the respiratory epithelium.
Life cycle of a salmon:
Fry hatch in the spring, and grow in the strean, 1-2 years.
Fingerlings migrate downstream.
Grow to smolt and enter the ocean.
Grow to maturity in Pacific…