FISH AIN''T A FOUR LETTER WORD: "I'm a lifelong environmentalist, but I own a sushi restaurant. This is horrible, paradoxical and ironic," explains Kristofor Lofgren, owner of Masu East, the popular Northeast 28th Avenue sushi outpost. He's talking about the fact that when it comes to fish, being sustainable is a tough business. Sushi joints rarely tell customers where their fish comes from, and, according to Lofgren, often don't know where it came from themselves, let alone how their tuna or mackerel was caught or whether its distribution is adversely affecting other species or ecosystems. Lofgren wants to change all that—so he's closing Masu East on Nov. 1. Luckily, he'll be opening what he claims is the first fully sustainable sushi restaurant in the country, Bamboo Sushi, in the same spot about a week later. The downtown outpost of Masu, owned by Lofgren's former business partner Jeff Berback, will be unaffected. How's Lofgren gonna keep Bamboo on the up and up? He's partnering with the Blue Ocean Institute and other eco-groups to make sure Bamboo's fish choices are sustainable. Plus, he's enlisted the Marine Stewardship Council to essentially "audit" his restaurant twice a year, to make sure his menu stays as "green" as he says it'll be. "We don't want to make the restaurant] doom or gloom," Lofgren says. "We want to say, "Hey, there's problems, but by eating with us, you're saying you care about this issue...and if you don't care, no problem, you're still gonna get great sushi.'" Bamboo Sushi is slated to open around Nov. 8.