Which option is a biological control method in aquatic pest management?

Introducing a predator species is a prime example of a biological control method in aquatic pest management. This approach involves utilizing natural predators to keep pest populations in check, promoting a balanced ecosystem. By introducing organisms that naturally prey on invasive or harmful species, it is possible to manage their population effectively without resorting to chemical methods. This method enhances ecological stability and can often lead to long-term pest management solutions by utilizing existing food chains within the aquatic environment.

The other options, while valid pest management strategies, do not fall under the category of biological control. Herbicide application involves the use of chemicals to eradicate unwanted plant species, water treatment includes various physical and chemical methods to maintain water quality, and pesticide spraying typically refers to the application of chemical agents designed to kill pests. All these techniques may provide immediate results but do not leverage the natural predator-prey dynamics as effectively as introducing a predator species.