Refer to the given food chain operating in an aquatic ecosystem.
Phytoplankton `to` Daphnia `to` Platy fish `to` Catfish `to` Shark
When a new species X was introduced into this community, the population of platy fish rose and population of catfish fell over subsequent two weeks. Species X is most likely to be

Options

A. Another herbivore like platy fish
B. A predator of Daphnia only
C. A predator of catfish only
D. A predator of platy fish and prey of shark.

Answer

To solve the question regarding the introduction of species X into the aquatic food chain, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Food Chain**: The given food chain is Phytoplankton → Daphnia → Platy fish → Catfish → Shark. Each organism plays a specific role, where the phytoplankton are the primary producers, and the others are consumers.

2. **Analyze the Changes**: When species X was introduced, the population of platy fish increased while the population of catfish decreased over two weeks. This indicates a change in the dynamics of the food chain.

3. **Identify the Relationships**: In the food chain, platy fish are preyed upon by catfish. If the population of platy fish is rising, it suggests that there is either more food available for them or less predation on them.

4. **Determine the Role of Species X**: Since the population of catfish is decreasing, it implies that species X is likely a predator of catfish. If species X is preying on catfish, this would lead to a decrease in their population.

5. **Conclude the Identity of Species X**: Given that species X is causing a decrease in catfish population while allowing the platy fish population to rise, species X is most likely a predator of catfish.

### Final Answer:
Species X is most likely a predator of catfish.

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