Osmoregulation in freshwater and marine fish:
Mechanism of osmoregulation in fish enables them to maintain a stable internal environment despite the changing osmotic conditions of their surrounding water.
Osmoregulation in Freshwater Fish:
Osmoregulation in freshwater fish involves processes that allow them to regulate water and ion balance in an environment where the surrounding water has a lower salt concentration than their bodily fluids.
| Aspect | Description | Examples of Freshwater Fish |
| Environment
| · Freshwater has hypotonic surroundings having lower salt concentration compared to fish’s body fluids. | Goldfish · Exert copious amounts of dilute urine. They have well-developed gill chloride cells. · Obtain water and ions from their food. Catfish · Catfish actively excrete excess ions. · Catfish can adjust their ion-transporting cells. Trout · They also excrete dilute urine to manage their water balance. · Trout absorb ions from their diet. Carp Carp have efficient ion-transporting cells in their gills Produce dilute urine and taking in water through osmosis. |
| Specialized gill chloride cells
| · Freshwater fish have specialized cells in their gills known as chloride cells. · To maintain a proper ion balance and prevent the loss of essential electrolytes, these cells actively transport ions, including sodium (Na+) and chloride (Cl–), out of the fish’s body into the surrounding water. | |
| Water Uptake | · Freshwater fish absorb water through gills and skin by osmosis. | |
| Production of Dilute Urine | · Freshwater fish excrete large volumes of dilute urine to eliminate excess water. | |
| Limited Drinking | · Freshwater fish do not drink water actively but may ingest small amounts of it. | |
| Ion Reabsorption | · Freshwater fish actively absorb ions (Na+, Cl–) from their food to maintain proper ion balance. | |
Osmoregulation in Marine Fish:
Osmoregulation in marine fish involves processes that enable them to regulate water and ion balance in an environment where the surrounding water has a higher salt concentration than their bodily fluids.
| Aspect | Description | Examples of Marine Fish |
| Environment | · Seawater has hypertonic surrounding having higher salt concentration as compared to fish’s body fluids. | Salmon · Salmon actively absorb ions, like sodium and chloride, from the seawater. · Salmon get water and ions from their diet.
Clownfish · Clownfish drink small amounts of water. Flounder · Flounder have an impermeable skin for preventing excessive water loss through the skin. Sharks · Sharks have specialized salt glands located near their rectal glands. · These glands actively excrete excess salts from their bodies. Tuna · Tuna produce concentrated urine to save water. · They also obtain additional water and ions through their diet. Clownfish · Clownfish can adjust their osmoregulation mechanisms. |
| Specialized gill chloride cells | · Specialized cells actively transport ions (Na+ and Cl–) from the surrounding water into the fish’s body through gills. | |
| Impermeable skin | · Skin is impermeable to water to prevent excessive water loss. | |
| Drinking Small Amounts of Water | · Marine fish drink small amounts of water. | |
| Salt Gland | · Some marine fish have specialized salt glands to actively excrete excess salts from their bodies. | |
| Production of concentrated urine | · Marine fish produce small amount of concentrated urine to minimize water loss. | |
| Taking ions through Diet
| · Marine fish obtain water and ions from their food to help maintain hydration and ion balance.
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