Which one of the following is not a bioindicator of water pollution?
Stoneflies are usually associated with clean, cool flowing streams. Most stonefly taxa are sensitive to water pollution. Generally, the presence of stoneflies is a reliable indicator of excellent water quality, but because of their specific habitat requirements, their absence does not necessarily mean the waterbody is polluted.
Sewage fungus is a mass of filamentous bacteria that usually grows in response to pollution.
Sludge worms and Bloodworms contain haemoglobin that helps them transport oxygen much more efficiently and thus, they have a lower requirement for oxygen. On the other hand, Stoneflies have no haemoglobin and transport oxygen through their body through diffusion. This is more ineffecient and hence they have a higher oxygen requirement.
Since polluted water has a lower oxygen concentration due to the presence of large amounts of organic matter, bloodworms and sludge worms are more abundantly present.