HI
Its my experience as a former suba diver, observing fish in their natural habitat that :
The larger the fish, the more plain or draby the coloration…
Conversly, notice that the smaller fish have that highest colorations patterns of all sorts…
Therefore your primitive fish drawn here , I think, should be more uniform in color with few patterns…
( just look at Latimeria for example)
The difference in coloration between the head and the body is too strong here…
As a predator this fish could not “advertise” its presence while hunting, therefore light color such as white
should be avoided.
The “impressiveness” of this fish, I think, should be in its shear bulk and strong head plates rather than its coloration…
Also, I think that the teeth should be textured a little more ( striations…)
As for scale, maybe several other smaller “less significant” fish should be added to the scene.
Hope this helps.