The secret that was hard to keep amidst a community filled with constant chatter seems to have been kept from the ears of the two it was intended to surprise. The marching, singing, ukulele-playing flash mob gathered at 7 a.m. this past Monday morning to celebrate Betsy, Kristine and their entire Larsen’s Fish Market family’s — both biological and not — 50th anniversary. Although Big Louie and Mary are no longer with us, Betsy, Kristine and their staff carry in the tradition of smiles and customer service.