When an object rests on a surface, such as a table, for example, the downward force it applies to the surface is counteracted by an equal but upwards force, or reaction, applied by the surface. See more at Newton's laws of motion. A response to a stimulus, such as a reflex.
Background. The northern snakehead fish (Channa argus) has been identified as an invasive aquatic fish across the country. Snakehead fish got their name because of their long, cylindrical body plan and large scales on their head that give them a snake-like appearance.
A species is invasive when it is both nonnative to the ecosystem in which it is found and capable of causing environmental, economic, or human harm. Invasive species often compete so successfully in new ecosystems that they displace native species and disrupt important ecosystem processes. Plants, fish, insects, mammals, birds, and diseases all can be invasive. The Pacific Northwest, like other regions of the country, is inhabited by a variety of invasive species.