The production of gametes depends on internal factors
such as age (maturity) and external factors that influence
the energy being available for reproduction. Depending on
the species, corals may reach maturity within 1 year (i.e.
the opportunistic brooderFavia fragumfollowing Petersen
et al.2007a) to several years after settlement (see Harrison
and Wallace 1990; Bariaet al.2012). It is usually difficult
to determine age based on size as a proxy for maturity
because growth rates may vary due to environmental conditions (Bariaet al.2012). External factors such as competition (algae, corals, etc.), disease, insufficient water quality,
inappropriate hydrodynamics and predation may lead to
reduced energy resources available for the production of
gametes. These negative factors may be reduced to a minimum in a coral aquaculture system, when the culture conditions are kept at an optimum. It is also not favourable to
use the same broodstock simultaneously for asexual and
sexual propagation, because fragmentation may lead to
decreased fertility (Okuboet al.2007). A clear determination whether a coral is in the process of producing gametes
can be achieved through histology (as described by Okubo
et al.2007), although it is time-consuming and invasive to
the coral. A commonly applied, although less precise, alternative to predict spawning time is the use of spawning
records if available