A Queens fisherman thinks he knows the best spot in NYC for fresh sushi and sashimi , and it’s not Nobu. It’s — don’t gag — The Hudson River. Gilberto Diaz Jr. enjoys eating striped bass sashimi he catches himself in the murky waters, and has been doing so for years. Gilberto Diaz Jr. enjoys eating sushi from the Hudson. J.C. Rice for NY Post He began making Hudson sushi in 2014 as a lark. “I was experimenting at first, to be honest. I know striped bass is used as sashimi; flounder and blackfish are used as sashimi. So I just started trying it and enjoyed it,” he told The Post. Diaz, 35, who manages a Manhattan parking garage when he’s not chasing monster tautog, detailed his methodical process of preparing the peculiar dish. First, he puts his catch out of its misery by stabbing it through its brain. Once the fish had moved on to the next world, Diaz will filet the fish from gill to tail, following the spine. He then flips the filet, scales down, and skins it before cutting quarter-inch sushi slices.…