Some animals convert highly toxic `NH_(3)` into least toxic trimethylamine oxide (TMAO) and retain high concentration of TMAO and urea to minimise `H_(2)O` loss from body are
(a) Sharks and rays
(b) Fresh water bony
(c) Myxine
(d) Marine bony fishes

Options

A. Sharks and rays
B. Fresh water bony
C. Myxine
D. Marine bony fishes

Answer

To solve the question regarding which animals convert highly toxic ammonia (NH₃) into the least toxic trimethylamine oxide (TMAO) and retain high concentrations of TMAO and urea to minimize water loss, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Context**: The question is about animals that convert ammonia, a toxic waste product, into a less toxic form (TMAO) to help with osmoregulation, particularly in marine environments.

2. **Identify the Options**: The options given are:
- (a) Sharks and rays
- (b) Freshwater bony fishes
- (c) Myxine
- (d) Marine bony fishes

3. **Analyze Each Option**:
- **Sharks and Rays (Option A)**: These are known to retain high concentrations of TMAO in their bodies, which helps them osmoregulate in a marine environment where they need to minimize water loss and manage salt intake.
- **Freshwater Bony Fishes (Option B)**: These typically excrete ammonia directly into the water as they live in a low-salinity environment and do not need to retain TMAO.
- **Myxine (Option C)**: This is a type of jawless fish that does not primarily use TMAO for osmoregulation.
- **Marine Bony Fishes (Option D)**: While some marine bony fishes do excrete TMAO, the question specifically highlights sharks and rays as the primary examples.

4. **Select the Correct Answer**: Based on the analysis, the correct answer is (a) Sharks and rays. They convert ammonia into TMAO and retain it to minimize water loss.

5. **Conclusion**: The animals that convert highly toxic NH₃ into TMAO and retain it to minimize water loss are primarily sharks and rays.

### Final Answer:
(a) Sharks and rays