This will be of interest to all SFFC anglers as they will be able to tell whether they've caught a male or a female Musky. 

The sex of individual adult or juvenile muskellunge is determined by observing the width of the anal opening and its surrounding tissue relative to that of the urogenital papilla and the slit-like pit. In mature female muskellunge, the width of the urogenital papilla and the crescentric slit-like pit are approximately two times greater than the anal pore and its associated tissue. At spawning, the papilla is hemorrhagically red, as it is for female northern pike. In mature males, the urogenital papilla and the straight slit-like pit are significantly narrower than the anal opening and its surrounding tissue. 
The outline of the female urogenital region is therefore approximately pear shaped with the stem end directed anteriorly, whereas in males this region is keyhoIe-shaped with the "slot" directed posteriorly What the above is basically saying is that if you turn your fish briefly upside down, you will see one of the configurations. If you are looking at the underside of the musky "from the tail-towards the head", you will see either a "PEAR" shape (female), or a "KEYHOLE" (male). This keyhole is shaped like an old fashioned skeleton key slot found in most older house doors, hence the name. 



Pear Shaped opening (left) indicates a Female.  Key-hole Shaped opening (right) indicates a Male. 

This simple method of sexing live muskellunge is highly beneficial, since it does not require instruments, measurements, or calculations, and is not detrimental to the fish.