Fresh water bony fishes maintain water balance by

Options

A. Excreting a hypotonic urine
B. Excreting salt across their gills
C. Drinking small amount of water
D. Excreting wastes in the form of uric acid

Answer

### Step-by-Step Solution:

1. **Understanding the Environment**: Freshwater bony fishes live in an environment that is predominantly water. This environment has a lower concentration of salts compared to the fishes' body fluids.

2. **Hypertonic Body Condition**: The body fluids of freshwater bony fishes are hypertonic relative to the surrounding freshwater. This means that the concentration of solutes (like salts) inside the fish is higher than that in the surrounding water.

3. **Water Movement**: Due to osmosis, water moves from an area of lower solute concentration (the freshwater) to an area of higher solute concentration (the fish's body). Therefore, water continuously enters the fish's body from the surrounding environment.

4. **Excretion of Excess Water**: To maintain water balance, freshwater bony fishes need to expel the excess water that enters their bodies. They do this by excreting a very dilute or hypotonic urine, which contains a lower concentration of solutes compared to their body fluids.

5. **Salt Absorption**: In addition to excreting dilute urine, freshwater bony fishes also need to compensate for the loss of salts that occurs during urine production. They absorb salts through their gills to maintain their internal salt concentration.

6. **Role of Kidneys**: The kidneys of freshwater bony fishes play a crucial role in this process. They have large glomeruli and capillaries that filter the blood efficiently, allowing for the production of dilute urine while retaining necessary salts.

7. **Conclusion**: Therefore, freshwater bony fishes maintain their water balance by excreting hypotonic or dilute urine and absorbing salts through their gills.

### Final Answer:
Freshwater bony fishes maintain water balance by excreting dilute or hypotonic urine.

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