Why are fish populations often used as indicators of freshwater ecosystem health?

Fish populations are considered effective indicators of freshwater ecosystem health primarily because they reflect the overall condition of the habitat. The health and diversity of fish species in a river or lake can provide insights into various environmental factors, such as water quality, availability of food, and habitat structure. Changes in fish populations can signal shifts in the ecosystem, like increased pollution, habitat degradation, or the impact of invasive species.

For instance, sensitive species may decline in numbers or disappear entirely from polluted environments, while more tolerant species may proliferate. This relationship between fish populations and environmental conditions allows researchers and ecologists to assess the integrity and sustainability of aquatic ecosystems, making them vital for monitoring ecological health.