hey gang, as a musky fisher-woman
I can tell you that the easiest way to determine if it's a musky or a northern is this...
light markings on a dark body = northern
dark markings on a lighter body = musky.
There are so many varients of musky now... spotted, striped, spotted-striped, clear even which is very pretty. Northerns always have the creamy white spots. Muskys also have more reddish fins. They get bigger is the norm. Northern fry grow faster and prey on musky fry. Small northern we call "hammer-handles" cuz when they're about a foot long they're so skinny. I joke that they're half tail and half mouth, goofy things will hit anything! They're fun to catch and release. Ice fishing northerns is a blast! (I pickle them). We have northern in abundance in our northern WI lakes, but the musky is still usually honored as the ultimate game fish and many practice catch and release. Some people want a trophy for the wall which is fine too... many guys fish for years and never get a trophy. There are so many hybrids now... we have two on the wall; my husbands is a 40" tiger (hybrid) musky, and mine is a true musky caught in late spring, therefore it's not a big fat sow like they are in the winter. I haven't caught a musky since, it was sheer luck that I boated this one... it is 45". I'm not sure what the weights were, but I know it tipped 20 lbs.
our fish wall (that big walleye was 30" through the ice):
my husbands 40" tiger musky:
my 45" true musky (and yep, that's the lure I caught it on!):