That sentence does not mean what you think it means. Change one particle and it becomes: 私はうなぎです - "I'll have the eel. " Which is probably what you meant in the first place. は and が. Two particles. The single hardest grammar point in all of Japanese. Not because any one rule is complicated, but because there are nine of them, and they all apply at the same time. Here is what most textbooks tell you: - は = topic marker - が = subject marker Here is what they don't tell you:

- は emphasizes the verb. が emphasizes the subject. - が introduces new info ("a man"), は marks known info ("the man") - but only with verbs. With adjectives, は introduces properties instead. - WH-words (誰, 何, どれ) always take が. Zero exceptions. - は cannot appear inside subordinate clauses. Only が. - Stative verbs (好き, 分かる, 欲しい, 必要) flip the English subject/object structure: the "object" takes が.