Females of all glandulocaudine species are inseminated. The females produce fewer eggs per unit body weight than externally fertilizing species; this is possibly because insemination increases the efficiency of fertilization, so fewer eggs are necessary. This insemination is preceded by courtship in all species. After insemination, the female may retain the live sperm for many months in her ovaries. This allows the eggs to be laid when environmental conditions are favorable. However, there is no evidence of an intromittent organ, and the exact mechanism of insemination is unknown. Hooks on the anal fin of males may play a role, although these are also found in characins that exhibit external fertilization. It was originally believed that internal fertilization occurs in glandulocaudines. However, the exact time of fertilization is unknown and no fertilized eggs are found internally; this suggests fertilization occurs when the eggs are being laid or even outside of the body.