1. Freshwater Life (Anadromous Phase):
* Problem: Salmon in freshwater need to prevent water from entering their bodies and losing salts.
* Solution:
* Kidneys: They produce large amounts of dilute urine, eliminating excess water.
* Gills: They actively absorb salts from the water through specialized cells called chloride cells.
* Intestines: They absorb salts from food.
2. Saltwater Life (Catadromous Phase):
* Problem: Salmon in saltwater need to prevent water loss and avoid excessive salt buildup.
* Solution:
* Kidneys: They produce small amounts of concentrated urine to conserve water.
* Gills: They actively excrete excess salts through chloride cells.
* Intestines: They minimize salt absorption from food.
Physiological Adaptations:
* Chloride cells: These specialized cells in the gills play a crucial role in both absorbing and excreting salts, depending on the environment.
* Hormonal control: Hormones like cortisol and prolactin regulate the activity of chloride cells and other osmoregulatory mechanisms.
* Behavioral adaptations: Salmon may drink more water in saltwater to compensate for water loss and may also avoid highly saline areas.
The Anadromous Migration:
The ability of salmon to switch between freshwater and saltwater is crucial for their life cycle. They are born in freshwater streams, migrate to the ocean to feed and grow, and then return to freshwater to spawn. This migration involves a remarkable physiological shift in their osmoregulatory mechanisms, allowing them to survive and thrive in both environments.
Overall:
Salmon have evolved sophisticated osmoregulatory mechanisms that allow them to maintain a constant internal salt concentration despite the fluctuating salinity of their environment. This adaptation is essential for their survival and reproductive success.