Other possibilities are sardines, boned and rolled and threaded through like rollmops.
From the guardian.co.uk
There will also be rollmops, a marinated herring served with rye bread, along with German potato salad and sauerkraut, both made by the ladies of the Delaware Saengerbund.
From the delawareonline.com
More examples
(rollmops) a pickled herring filet that has been rolled or wrapped around a pickle
Rollmops are pickled herring fillets, rolled (hence the name) into a cylindrical shape around slices of onion, pickled gherkin, or green olive with pimento. Rollmops can be served held together with one or two small wooden skewers.