Picture of the Indiscriminate Interval #000006b - Morone saxatilis

I can assure you this Nightmare Mode identification challenge is solvable. Okay, so maybe fish crania are rarely figured in the literature and this particular example was damaged before I could photograph it, but all the pieces are there, I swear!

Location is a major clue. The specimen was found far into Narragansett Bay in an area with a salinity of 30.0 ppt (Hicks 1959), which is right at the brackish-saline transition. Considering that this delicate structure was recovered intact, it seems probable that the fish died in the immediate vicinity. I think it's safe to conclude that the owner of the cranium was tolerant of marine and brackish conditions, which reduces the number of candidates considerably.

Then there's size. After having recently skeletonized a fish and being surprised at the comparatively puny cranium, I was startled to see a cranium around 6" (15 cm) long, when complete. Since it does not appear that any large local fish have a head less than 1/3 of the total length (yes, even American Angler and Oyster Toadfish) and since cranium ≠ head, I set a very conservative lower bounds of 50 cm (20"). This is still a massive body size and coupled with the presumed habitats, a very manageable number of candidates emerges. 

The Atlantic Sturgeon (Acipenser oxyrinchus) is anadromous and very large, however, the cranium is radically different. I cannot resist mentioning the bizarre proboscis-mouth. Atlantic Cod (Gadus morhua) are certainly large enough, however the cranium is not a match, despite being much more similar than that of the sturgeon. I have observed a large dead Tautog (Tautoga onitis) in almost the same locale, but cannot find the neurocranium illustrated anywhere. Before trying to acquire a dead Tautog and testing that hypothesis, I wondered if there was a better candidate I overlooked. I recalled seeing Striped Bass (Morone saxatilis) being caught nearby and photographs of local specimens which demonstrated that they reached colossal sizes fairly regularly. By sheer dumb luck, I stumbled across Jordan (1905) which had the cranium figured:

The supraoccipital (sagittal crest-like structure) and end of the snout strongly resembled the illustration below before being damaged.

Note that the mystery specimen still has an attached vertebrae. It seems somewhat wider than the Striped Bass cranium, but this could be due to damage, variation, or the illustration being inaccurate. 

The mystery specimen lacks the paired foramina (?) on the midline about  3/4 of the way up. Considering that the crania appear to be otherwise identical, maybe it was just weird shading or these fish are variable.

One odd difference aside, this is certainly the owner's species (being held):

From Wikipedia Commons.

The Striped Bass has some other relatives in the 'family' Moronidae and while a couple species in my area attain record lengths approaching 50 cm TL (Morone americana, M. chrysops), such sizes are apparently freakish and I doubt the crania would be large enough anyways.

My hat is off to anyone seriously working with fish skeletons. After my little tastes, I am completely and utterly traumatized. 

References:

Hicks, S. D. (1959). The Physical Oceanography of Narragansett Bay. Limnology and Oceanography 4(3), 316-327. Available.

Jordan, D. S. (1905). A Guide to the Study of Fishes. Volume 1. Henry Holt and Company: New York. Available.