Partial spawning occurs when a proportion of the mature oocytes are not released from the ovary are destined to be reabsorbed by the female. It has been reported that oocytes infected with virus, such as white spot syndrome virus (WSSV), do not fully mature (Kuo and Lo 1998). Thus prevalent partial spawnings may indicate that the broodstock are infected with virus. Although infected oocytes are not ovulated, virus particles released in the ovary as the infected oocytes are reabsorbed may adhere to uninfected eggs that are ovulated. This may result in the vertical transmission of virus from mother to offspring and hence potentially produce offspring that are viral carriers. The washing of eggs from infected mothers can assist in the prevention of horizontal transmission of viruses.

Partial spawnings may also be due to other factors. Typically 300,000 to 500,000 eggs are spawned within a 2 minute period (see section below on spawning). If spawning itself is time limited then a partially blocked oviduct will slow egg release and hence not all of the fully developed eggs will be released within the spawning period. Alternatively the chemical trigger that induces ovulation, followed by spawning, may be below a critical threshold level in some of the ovarian lobes and hence eggs within these lobes are not ovulated.

The female must mate again immediately after the next molt if she is going to be capable of fertilising spawned eggs. It is therefore necessary to hold both females and males in hatchery holding tanks if successful fertilisation is to be achieved from females held for longer than 2 weeks. The average molt frequency in the 90 to 120 gram body mass range in 28 to 30ºC water in the AIMS Maturation Unit is 16 – 18 days.

Since ovarian maturation may take place entirely in the hatchery, a high quality diet is necessary for the female to optimise egg quality. The quality of the egg at the time of formation, ie vitellogenesis, and the packaging of critical molecules into the egg, is a major determinant of larval quality. The successful development of the embryo, hatching, and the 6 naupliar stages are dependent on egg quality. The larvae do not become self feeding until the zoea 1 stage, which is the first time that they become dependent on the quality of larval feeds.