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.
Native to parts of Asia, the northern snakehead (Channa argus) was first introduced through the live food fish trade. It has taken hold in the Potomac River and its tributaries throughout Maryland and Virginia. Reasons Snakeheads Are a Threat. 1. Theyâre voracious predators and can severely alter the feeding habits, food availability, and behaviors of other members of an ecosystem. 2. They can survive in water with very low oxygen, which other fish species often cannot do. 3.