While Alaska pollock items are often featured at US quick-service restaurants (QSRs) when the 40-day Catholic religious period of Lent rolls around, they don't always stay on the menu afterward.

Beyond the big fast food chains such as McDonald's and Burger King -- who have made a staple out of their pollock-based items -- most chains try to take advantage of Lent, then move on.

US-based White Castle -- one of the most famous hamburger chains on the US East Coast with close to 400 locations and over $700 million (€642 million) in revenue -- is one of the few QSRs bucking this trend.