* Detrivores are organisms that feed on dead organic matter. They play a crucial role in decomposition.

Let's look at each option:

* Fungus: Many types of fungi are decomposers. They break down dead plants, animals, and other organic matter, releasing nutrients back into the environment.

* Cat: Cats are carnivores, meaning they eat meat.

* Radish: Radishes are plants. While they decompose after they die, they are not primarily detrivores while alive.

* Cow: Cows are herbivores, meaning they eat plants.

Therefore, the only organism from the list that fits the definition of a detrivore is fungus.