Fungi rapidly colonize leaves that fall into freshwater streams. they break down the cellulose in the leaves and absorb the glucose produced. in turn, the fungi serve as food for many insect species that consume the leaf litter; these insects cannot digest cellulose themselves, but gain the nutrients from cellulose indirectly. the insects then provide vital food for stream fish. taken together, these relationships suggest that fungi

Fungi indirectly help the fishes by providing digested organic nutrients to their prey insects.

Explanation:

According to the given information, fishes are predators of insects. These insects feed on dead leaves. The insects are not able to digest the cellulose of dead leaves. Fungi breakdown the dead and decaying leaves and digest the complex molecules such as cellulose into simpler organic nutrients which in turn are consumed by insects.

If fungi do not decompose the dead leaves, insects would not be able to derive the organic nutrients from them. A shortage of food supply to insects would starve them. Unavailability of prey insects would starve fishes. Thereby, fungi indirectly benefit the fishes to obtain their nutrition from the insect.