The northern pike (Esox lucius), known simply as a pike in Britain, Ireland, most parts of the USA, or as jackfish in Canada or simply “Northern” in the Upper Midwest of the USA), is a species of carnivorous fish of the genus Esox (the pikes). They are typical of brackish and freshwaters of the northern hemisphere. Pike grow to a relatively large size; lengths of 150 centimetres (59 in) and weights of 25 kilograms (55 lb) are not unheard of. The average length is about 70–120 cm (28-47 inches). Northern pike are most often olive green, shading from yellow to white along the belly. The flank is marked with short, light bar-like spots and there are a few to many dark spots on the fins. Sometimes the fins are reddish. Younger pike have yellow stripes along a green body, later the stripes divide into light spots and the body turns from green to olive green. The lower half of the gill cover lacks scales and they have large sensory pores on their head and on the underside of the lower jaw which are part of the lateral line system. Unlike the similar-looking and closely related muskellunge, the northern pike has light markings on a dark body background and fewer than six sensory pores on the underside of each side of the lower jaw. Pike are capable of “fast start” movements, which are sudden high energy-bursts of unsteady swimming. These fast starts terminate when the pike has reached terminal velocity. During such motions, pike make S conformations while swimming at high rates. To decelerate, they, simply make a C conformation, exponentially slowing down their speed so that they can “stop”. Pike are found in sluggish streams and shallow, weedy places in lakes, as well as in cold, clear, rocky waters. Pike are typical ambush predators; they lie in wait for prey, holding perfectly still for long periods and then exhibit remarkable acceleration as they strike.