What is a chemical specifically used to control pests in aquatic environments?

The correct answer is piscicide, which is a chemical designed specifically for controlling fish populations and managing aquatic pests. Piscicides are used in situations where it is essential to reduce or eliminate fish for various reasons, such as restoring the balance in an ecosystem, managing invasive species, or facilitating the control of diseases that can affect both fish and the surrounding aquatic environment.

In contrast, insecticides are formulated to target insects, while herbicides focus on controlling unwanted vegetation. Fungicides are used to manage fungal pathogens that can harm plants and crops. Thus, piscicides are the most appropriate choice when discussing chemicals used specifically for controlling pests in aquatic settings.