Aside from natural causes, what can affect fish populations negatively?

Runoff from insecticides can have a significant negative impact on fish populations. When insecticides are washed off from agricultural fields, urban areas, or landscaping into nearby water bodies, they can lead to toxicity in the aquatic environment. These chemicals can directly harm fish by affecting their physiology and behavior, leading to reduced survival rates, reproductive issues, or even death. Moreover, the presence of insecticides can disrupt food chains and ecosystems, further diminishing fish populations over time.

In contrast, while cold temperatures can influence fish behavior and habitat ranges, they do not typically result in direct harm, especially for species adapted to local conditions. Heavy fishing activity, while it can certainly deplete fish populations, is generally managed through regulations and quotas to prevent long-term detriment. Increased aeration, on the other hand, generally benefits aquatic life by improving oxygen levels in the water, which is crucial for fish survival and health.