* Biotic refers to living things or the parts of living things. A dead fish no longer exhibits the characteristics of life (like growth, reproduction, metabolism, etc.).
* Abiotic refers to non-living things or components of the environment. While a dead fish was once alive, its decomposition is a process driven by abiotic factors like bacteria and the environment.
Think of it this way: a dead fish is no longer contributing to the ecosystem in the same way a living fish would. It's essentially a decaying piece of organic matter.