The most obvious difference between the two is C. celidochilus has lip spots. Its a little early for me on the west coast so I decided to just attach some photos of ones my group or I collected in Uruguay so you can see the differences. The first is a young C. vittata, second a young C. celidochilus, and third an adult female C. celidochilus.
Celidochilus males max out about 11", females about 8" or so...
Vittata aka 'gator' pike get much larger, 16" to 20". Oliver Lucanus told me a friend saw one about 24" while diving on a collecting trip. They have an elongated head (hence the name gator pike) with eye teardrops, similar coloration but differant body markings. We've had two different groups of vittata in the past, but none at the moment. Am trying to get some in this Spring/Summer....