At the end of the incubation period, the eggs are examined for the presence or absence of the nucleus. Conclusions External appearance of brood fish has long been used to assess the stage of sexual maturity. In some species of fish, the males change in appearance during the spawning season. Milt can usually be stripped from males of most species when they are ready for spawning. However, secondary female sex characteristics are extremely subjective and can be misleading.
Several methods are available to determine the stage of development of the eggs in the fish's ovary.
These require that a sample of eggs be taken from the fish. The diameter and appearance of the egg and the position of the nucleus in the egg are visual indicators of development. The steroid assay procedure determines the physiological response of the eggs to hormones. An understanding of sperm viability and egg stage development will greatly improve the success of hormone-induced spawning of fish. The work reported in this publication was supported in part by The Southern Regional Aquaculture Center through Grant No.