Tilapia fingerlings are fish that are about one inch long and weigh almost one gram, and have developed functional fins, scales, and sexual organs. They are the result of a tilapia going through several stages of development, including fry, where they are genderless and live in their mother's mouth for the first few days of their lives. After about 21 days, the tilapia's gender is determined, and if they have the necessary scales and fins, they can be considered fingerlings.