How the fishes can survive in the extreme winter, when ponds and lakes are frozen?

Answer

### Step-by-Step Solution:

1. **Understanding the Property of Water**:
- Water has a unique property where its density changes with temperature. As the temperature decreases, the density of water initially increases until it reaches 4 degrees Celsius, where it is at its maximum. Below this temperature, the density starts to decrease again.

2. **Graph of Density vs. Temperature**:
- If we plot a graph with temperature on the x-axis and density on the y-axis, we observe that the density increases as the temperature decreases until it reaches 4 degrees Celsius, after which the density decreases with further cooling.

3. **Behavior of Water in a Pond**:
- In winter, as the temperature of the pond decreases, the water at the surface becomes denser and sinks. The water at 4 degrees Celsius, being the densest, will settle at the bottom of the pond.

4. **Formation of Ice**:
- When the temperature drops to 0 degrees Celsius, ice begins to form on the surface of the pond. Ice is less dense than liquid water, which is why it floats.

5. **Insulating Effect of Ice**:
- Ice is a poor conductor of heat, which means it acts as an insulator. This property minimizes the rate of heat loss from the water below the ice layer.

6. **Temperature Stability at the Bottom**:
- The water at the bottom of the pond remains at a stable temperature of 4 degrees Celsius for an extended period because the ice layer above prevents heat from escaping. This stable temperature allows fish and other aquatic life to survive during extreme winter conditions.

7. **Conclusion**:
- Therefore, fishes can survive in frozen ponds and lakes during extreme winter because the water at the bottom remains at 4 degrees Celsius, protected by the insulating layer of ice above.