The bagel with whitefish salad is the only build on the appetizing scale where the fish is not sliced and laid but flaked, bound, and dressed. Smoked whitefish is picked off the bone and folded with mayonnaise, a little onion, and often celery into a soft, spreadable salad. That single decision changes everything about the sandwich. The fish stops being a slippery layer that needs gluing down and becomes the bind itself, so the cream cheese that mortars every other version is optional here, and frequently left off entirely. The salad does both jobs at once: it is the smoky filling and the thing that holds it together.
The craft is the same boiled-then-baked bagel, paired with a filling that behaves like a spread rather than a slice. A bagel is boiled before baking, which sets a tight, chewy crumb and a glossy crust, and unlike the sliced-fish builds it can take a light toast here, because a bound salad does not depend on the raw pull of the crumb against a slippery cure and a warm, crisp crust gives the soft, cool filling something to push against. The salad is mounded thick on the cut faces so each bite is mostly fish, and the balance is set in the mixing bowl rather than on the bagel: enough mayonnaise to bind without going to paste, enough onion and celery for crunch and bite, enough acid to keep a smoky, fatty fish from reading flat. Lettuce or tomato is added for cool and structure, not flavor.
The variations are positions on a graded scale of cured and smoked fish on the same bagel. The sliced builds run from mild cold-smoked nova up through rich, oily sable to firm, premium smoked sturgeon, all of them laid rather than bound. Whitefish salad stands apart as the bound, dressed end of that scale. The carrier can shift to a softer onion bialy. Each of those sits on the same appetizing counter and deserves its own article rather than being crowded in here.