1. Reduced Permeability of Skin and Gills:
Marine fish have a reduced permeability of their skin and gills, which helps to minimize water loss. Their skin may be covered in a thick mucus layer that acts as a barrier against water diffusion. Additionally, the gills of marine fish have specialized cells that help regulate ion transport and water movement.
2. Active Absorption of Ions:
Marine fish actively absorb essential ions, such as sodium (Na+) and chloride (Cl-), from the surrounding seawater through specialized ion transport mechanisms in their gills. This active absorption helps maintain a higher internal concentration of these ions, counteracting the tendency to lose water to the seawater.
3. Osmoregulation in Kidneys:
The kidneys of marine fish play a crucial role in osmoregulation by selectively excreting excess water and retaining essential ions. The renal tubules in the kidneys are responsible for reabsorbing vital ions and allowing for the elimination of excess water in the urine.
4. Excretion of Excess Ions:
In addition to selective ion absorption, marine fish also have mechanisms to excrete excess ions that they accumulate from seawater. Specialized cells in the gills and intestines help eliminate these excess ions, preventing them from building up to toxic levels.
5. Behavioral Adaptations:
Some marine fish exhibit behavioral adaptations to help manage their water balance. For example, certain fish may seek out habitats with lower salinity, such as estuaries or brackish waters, where the osmotic pressure is closer to their internal conditions.
By employing these adaptations, marine fish can maintain their internal water balance, even in the face of the constant osmotic challenge posed by the surrounding seawater. These mechanisms allow them to survive and thrive in their marine habitats.