Which is a biological indicator of a perennial stream?

A strong population of fish other than mosquitofish serves as a biological indicator of a perennial stream because the presence of diverse fish species typically requires stable water conditions, including consistent flow and adequate habitat. Perennial streams maintain a dependable flow of water throughout the year, which supports a wider range of aquatic life, including different species of fish that have specific habitat and water quality requirements.

In contrast, species such as mosquitofish are often found in more ephemeral or variable water conditions, so their presence alone does not indicate a stable perennial environment. Other indicators, like dragonfly larvae and damselflies, while they can be found in both perennial and intermittent streams, may not reflect the stability necessary for a diverse fish population. Thus, a vibrant fish community comprised of various species signifies the reliability of the stream, making it a dependable indicator of a perennial stream ecosystem.