Excretory substances of marine and fresh water bony fishes respectively

Options

A. `NH_(3), NH_(3)`
B. Urea, Urea
C. `NH_(3), ` Urea
D. Urea, `NH_(3)`

Answer

### Step-by-Step Solution:

1. **Understanding Excretion in Fishes**:
- Fishes excrete waste products primarily based on their habitat, which influences their osmoregulation and excretory mechanisms.

2. **Excretory Substances of Marine Bony Fishes**:
- Marine bony fishes are adapted to a saline environment. They tend to conserve water and excrete less toxic substances.
- The primary excretory substance in marine bony fishes is **urea**. This adaptation helps them manage the osmotic pressure of their environment.

3. **Excretory Substances of Freshwater Bony Fishes**:
- Freshwater bony fishes live in a low-salinity environment and are constantly gaining water through osmosis.
- To cope with this, they excrete **ammonia**, which is highly soluble in water and can be easily diluted. This process is known as ammonotelism.

4. **Conclusion**:
- Therefore, the excretory substances of marine bony fishes are **urea**, while for freshwater bony fishes, they are **ammonia**.

5. **Final Answer**:
- The correct answer is that marine bony fishes excrete **urea** and freshwater bony fishes excrete **ammonia**.