It looks like the end of the line for one of Japan's best-loved summer dining rituals. Unagi (eels) are on the endangered list, with catches plummeting and prices heading skyward. The annual "unagi day" summer feeding frenzy has an uncertain future, and so too the wonderful grill-houses that serve them.

But there's an obvious alternative: anago (saltwater eels). Not that they're a like-for-like swap: The flesh is softer and sweeter, with none of the oiliness that gives unagi its rich flavor and reputation for boosting energy levels. But anago's delicate texture makes it even more versatile — especially in the hands of chef Kenichi Ishikawa.

At Kaiseki Ikku, his unpretentious little restaurant in the backstreets of Yanaka, he has built his menu and his reputation around anago. It is an unusual choice of fish for a place specializing in traditional Japanese cuisine: Most chefs prefer to serve tai (snapper), fugu (pufferfish) or that Kyoto summer staple, hamo (pike eel).