In addition to the primary sexual characteristics - the difference between the ovaries and testes - people mainly use secondary sexual characteristics (or secondary sexual characteristics) to identify the sex of fish. However, secondary sexual characteristics are usually more obvious during the reproductive season, and it is difficult to accurately distinguish them at other times.
In most cases, female fish are larger than male fish, with a swollen abdomen and a slightly protruding genital opening. Male fish often show variations in fins and snouts, such as elongated fins, and elongated and curved snouts and jaws of salmon.
Many fish undergo color variations during the reproductive season, and male fish appear bright colors. Some male fish have pearl stars on their bodies, especially on the snout and pectoral fins. Some fish also have pearl stars on many parts of the head and anal fins.
Male individuals of some fish become aggressive during the reproductive season. When male fish meet or compete for mates, they often "fight".
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