In an aquatic ecosystem, maximum biomagnification is seen in

Options

A. Phytoplanktons
B. Zooplanktons
C. Large fishes
D. Fish-eating birds

Answer

To solve the question regarding maximum biomagnification in an aquatic ecosystem, we will follow these steps:

### Step-by-Step Solution:

1. **Understand Biomagnification**:
- Biomagnification refers to the process where the concentration of toxic substances increases in organisms at each successive trophic level of a food chain. These substances are often non-biodegradable pollutants.

2. **Identify the Organisms in the Options**:
- The options provided are:
- Phytoplanktons
- Zooplanktons
- Large fishes
- Fish-eating birds

3. **Analyze Each Option**:
- **Phytoplanktons**: These are the primary producers in aquatic ecosystems. They may accumulate pollutants from the water, but they are at the base of the food chain.
- **Zooplanktons**: These organisms feed on phytoplanktons. They may have higher concentrations of pollutants than phytoplanktons, but they are still lower in the food chain.
- **Large Fishes**: These fish consume zooplanktons and can accumulate pollutants, but they are still not at the top of the food chain.
- **Fish-Eating Birds**: These birds are at the top of the food chain in this ecosystem. They consume large amounts of fish, which have already accumulated pollutants from the lower trophic levels.

4. **Determine the Maximum Biomagnification**:
- As we move up the food chain, the concentration of pollutants increases. Fish-eating birds, being at the top of the food chain, will have the highest concentration of pollutants due to biomagnification.

5. **Conclusion**:
- Therefore, the correct answer to the question "In an aquatic ecosystem, maximum biomagnification is seen in" is **fish-eating birds**.

### Final Answer:
**Fish-eating birds** (Option 4)