Assertion (A) : Cat fishes are best culturable fishes .
Reason (R) : Cat fishes survive even at high temperature and low oxygen.

Options

A. Both A and R are correct and R is the correct explanation of A
B. Both A and R are correct but R is not the correct explanation of A
C. A is true but R is false
D. A is false and R is true

Answer

To analyze the question regarding the assertion and reason provided, we will break it down step by step.

### Step-by-Step Solution:

1. **Understanding the Assertion (A)**:
- The assertion states that "Cat fishes are best culturable fishes."
- To evaluate this, we need to consider the characteristics of catfish and their suitability for aquaculture.

2. **Understanding the Reason (R)**:
- The reason states that "Cat fishes survive even at high temperature and low oxygen."
- This is a biological fact about catfish, as they are known to thrive in conditions that are not favorable for many other fish species.

3. **Evaluating the Truth of Assertion (A)**:
- While catfish can survive in challenging conditions, they are not universally considered the "best" culturable fish. In fact, in some regions, they have been banned due to their invasive nature and the threat they pose to indigenous fish species.
- Therefore, the assertion (A) is **false**.

4. **Evaluating the Truth of Reason (R)**:
- The reason (R) is true; catfish do have the ability to survive in high temperatures and low oxygen levels, which is a notable characteristic that allows them to inhabit various environments.

5. **Conclusion**:
- Since the assertion (A) is false and the reason (R) is true, we can conclude that the correct relationship is that A is false but R is true.

6. **Final Answer**:
- The correct option is D: "A is false but R is true."