From the Greek πολύς "numerous" and γάμος "marriage".

Polygamy is a phenomenon observed among fish when one male and several females (stickleback) or one female and several males (pink salmon, grayling) take part in the spawning process.

A distinction is made between general polygamy, female polygamy and male polygamy.

General polygamy is the tendency of males and females to engage in haphazard copulation during the breeding season, which increases the probability of successful fertilization.

Female polygamy consists of males preferring a single female, while the female tends to mate with many males. This form of polygamy is found in shrimp, whose females are forced to mate with dominant males with small spermatophores. After copulation, they mate again with young males with larger spermatophores.

In male polygamy, one male fertilizes several females during the breeding season.