I am inclined to believe it may be an engine with cowling circling the central propeller shaft. Looks like three cylinders (at 8, 12 and 2 o'clock) have been forced forward.
Here's a photo of the engine from the Purdue Archives. I thought this might be the object when I first saw it. But, the entire body of the engine would have would have to be deeply embedded in coral, or the front section somehow became separated. I don't know how the engine is assembled but I don't think it's possible for just the front end to have been sheared off of the main body. The cowling maybe, but not with the prop shaft geometry intact.
A yoke is an interesting possibility, if it could last that long underwater.
If the object is circular, there appears to be too much buildup of crud between the left side (B3-B4) and right side of the object (E3-E4). See
Rick's Grid here . I'd expect a similar amount of crud buildup on both sides.
I was fooled by the image of a tire before
(click here for explanation). The object in a video correlated almost perfectly with the Electra tire. But, when the object was viewed from a different angle it was clearly composed of three unrelated objects.
For the type of fish I'd trust the New England Aquarium.
My vote is it's interesting, probably nothing, but worth a look if you can find the object without wasting too much time.