Dried pollock
Air-dried Alaska pollock, usually pulled into fibrous shreds, mildly savoury and barely fishy.
Dried pollock is Alaska pollock air-dried either whole or as pulled shreds; the version that freezes and thaws repeatedly over winter is yellowish and especially fluffy. It tastes mild, salty and faintly sweet, far less fishy than other dried fish, and simmered in soup it gives a pale, slightly milky, very rounded broth. Dry it is tough and fibrous, so it is briefly soaked in water or softened by pounding with the back of a knife before cooking. You can find it whole or shredded in Asian grocery shops, especially Korean ones, and by mail order.
Substitute:
There is no truly equivalent substitute. Stockfish is related but must be soaked for days, is firmer and gives a less mellow broth; dried anchovies add savoury depth to a soup but taste much stronger and fishier and do not replace the fibrous texture.