During spermatogenesis, the spermatogonia go through various stages until they become flagellated spermatozoa that reach sizes of up to 60 μm in length (Franco et al. 2008, Oyarzún et al. 2014 - Fig. 2). On the other hand, oogenesis follows a similar pattern to spermatogenesis in that primary oogonia are transformed by mitosis into secondary oogonia which are arrested at the prophase stage of meiosis I. The remaining meiotic stages are completed at fertilization (extracted from Gosling 2015). The oocytes then go through a period of vitellogenesis, which involves the accumulation of lipids and glycogen, important nutrients during embryogenesis (Chung 2007). During this period, the size of the oocytes increases (Fig. 3), a characteristic that fluctuates between species (e.g. ~70 μm in the Chilean mussel Mytilus chilensis or ~130 μm in the chorito maico, Perumytilus purpuratus - Oyarzún et al. 2011, 2018). At the end of vitellogenesis some oocytes can be lysed, those are called atresic oocytes. Atresia provides metabolic substrates for energy production at a time when energy stores are in short supply (Beninger & Le Pennec 2006).

Gonadal maturation is conditioned by exogenous factors such as temperature, salinity and food (quantity and quality). However, endogenous factors, such as the genetic pool and hormonal load, are also important (see Gosling 2015). Oyarzun et al. (2018) indicated that latitude does not have an effect on the development stage, but it does on the spawning date. However, there is a relationship between the reproductive cycles and temperature fluctuations. The decrease in temperature reduces the rate of development stages and, therefore, increases the reproductive cycles from semi-annual to annual, as evidenced in bivalve samples from Taltal, along a semi-decadal period (2007–2012) (see Fig. 4).

Understanding the gametogenic cycles allows making predictions about recruitment, about the time of collection of seeds for aquaculture, for the establishment of fishing ban, and for the determination of minimum catch sizes (Oyarzún et al. 2011). For this reason, reproductive information is essential for fisheries management.