Key Indicator for Aquatic Ecosystem Health

Organisms that indicate the health of an ecosystem are called bioindicators. They are sensitive to environmental changes, making them useful for monitoring ecosystem health.

Analyzing Ecosystem Indicators

We need to identify which of the given options best indicates the health of an aquatic ecosystem (an ecosystem in water). Let's examine each option:

• Lichen: Primarily grow on rocks and trees and are sensitive to air pollution. They are indicators of air quality, not aquatic health.
• Fish: Aquatic organisms that live in water bodies like rivers, lakes, and oceans. Their survival, diversity, and behavior are highly dependent on water quality parameters such as dissolved oxygen, temperature, pH, and the presence of pollutants. A healthy and diverse fish population typically signifies a healthy aquatic environment.
• Cockroach: These are insects typically found in terrestrial environments and are associated with human habitats. They are not indicators of aquatic ecosystems.
• Earthworm: These are primarily soil-dwelling organisms that improve soil quality. While some species live in wet soil near water or in shallow aquatic environments, they are not the primary or most sensitive indicators of overall aquatic ecosystem health compared to fish.

Conclusion on Indicator Organism

Based on the analysis, fish are the most suitable key indicator among the choices for a healthy aquatic ecosystem because their populations directly reflect the water's condition.