Most poisonous fish is

Options

A. Clown Fish
B. Eel Fish
C. Sword Fish
D. Puffer Fish

Answer

### Step-by-Step Solution:

1. **Identify the Options**: The question presents four options for the most poisonous fish: clownfish, eelfish, swordfish, and pufferfish.

2. **Research on Poisonous Fish**: To determine which fish is the most poisonous, we need to look into the known toxicities of each option.

3. **Understanding Pufferfish**: Among the options, the pufferfish is well-known for its toxicity. It contains a potent neurotoxin called tetrodotoxin.

4. **Source of Tetrodotoxin**: It is important to note that tetrodotoxin is not produced by the pufferfish itself but is derived from bacteria that live in or on the fish.

5. **Mechanism of Tetrodotoxin**: Tetrodotoxin acts as a sodium channel blocker, which interferes with the transmission of nerve signals between the brain and muscles. This can lead to paralysis and can be extremely dangerous.

6. **Comparative Toxicity**: Tetrodotoxin is significantly more toxic than cyanide, highlighting the danger associated with pufferfish consumption.

7. **Conclusion**: Based on the information gathered, the pufferfish is indeed the most poisonous fish among the given options.

8. **Final Answer**: Therefore, the correct answer is **pufferfish** (option number 4).