The testes are the male reproductive organs where spermatozoa are produced. They are paired oblong-shaped organs located in the abdominal cavity.

Testes of most fish are paired sac-like formations. The mature sex cells are discharged into the external environment through a special genital opening (in males of salmon, herring, pike and some others) or through the urogenital opening located behind the anus (in males of most bony fish).

From the inner walls of the testis, seminal tubules branch inward, converging to the vas deferens. According to the location of the tubules, the testes of bony fish are divided into two groups: cyprinoid or acinoid - in carp, herring, salmon, catfish, pike, sturgeon, cod and others. Percoid, or radial, in perch, stickleback, and others.