Northwest Fishing Reports

Muskellunge closely resemble other Esocids such as the northern pike and American pickerel in both appearance and behavior. Like other pikes, the body plan is typical of ambush predators with an elongate body, flat head and dorsal, pelvic and anal fins set far back on the body. Muskellunge attain lengths of 60–150 cm (2.0–4.9 ft) and weights of over 30 kg (66 lb). The fish are a light silver, brown or green with dark vertical stripes on the flank, which may tend to break up into spots. In some cases, markings may be absent altogether, especially in fish from turbid waters. This is in contrast to northern pike which have dark bodies with light markings. A sure way of distinguishing the two similar species is by counting the sensory pores on the underside of the mandible. A muskie will have seven or more per side while the northern pike never has more than six. The lobes of the caudal (tail) fin in muskellunge come to a sharper point while those of northern pike are more generally rounded. In addition, unlike pike, muskies have no scales on the lower half of the operculum.

source: http://en.wikipedia.org/wiki/Tiger_muskie

ESOX: Muskellunge, Hybrid "Tiger" Muskie and Pike:
IMHO, I think it is beneficial to keep all the Esox together.
For purposes of comparison, this chart is a perfect tool for identification of these species.
See Chart: http://nwtigermuskies.org/files/2006KTDPostr.pdf

That was all put together by Cabela's, Muskies, Inc. and Gander Mt. back in 1986. It was copyrighted, especially the artwork by Virg Beck (see his signature in details). Always like to give the credit to the author of the artwork; they get little pay and even less recognition.