Tangy Salmon Soup with Fresh Ginger and Tamarind

A beautiful soup, delicate and nourishing, with the flavor of Thai country life. Freshwater fish are typically used, but salmon is my favorite and shrimp make a marvelous special-occasion version. To cut fresh ginger into fine threads, peel and slice it crosswise into very thin coins, stack the coins in little piles, and cut into very thin strips. If this is too much work, just mince it up and toss it in.