What is a small sturgeon (Acipenser ruthenus) found in the Caspian Sea and its rivers, and highly esteemed for its flavor. The finest caviare is made from its roe called?

sterlet — A small sturgeon (Acipenser ruthenus) found in the Caspian Sea and its rivers, and highly esteemed for its flavor. The finest caviare is made from its roe. (Webster's 1913.)

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