Piscicides are described as being what, requiring specific timing for application?

Piscicides, which are substances used to control fish populations, are sensitive to environmental conditions and can undergo photochemical degradation. This means that their efficacy can be reduced by exposure to sunlight, which is particularly important when considering the timing of application. Applying them when sunlight is minimal—such as during periods of low light or overcast conditions—can help ensure that the maximum amount of the piscicide remains effective in the water.

In contrast, the other terms do not accurately describe the nature of piscicides in relation to their timing of application. Biochemical stability would suggest that they remain effective over time without degradation, which does not apply here. Being thermally activated would imply that heat enhances their effectiveness, which is not a characteristic of most piscicides. Environmentally persistent suggests that the substances remain active in the environment for extended periods, which can also be counterproductive with respect to their intended control measures. Knowing that piscicides can decompose due to light exposure is crucial for effective management and timing in aquatic environments.