Histomorphological study of ovarian atresia over the reproductive cycle of Octopus vulgaris from Galician waters (NW Spain)

Atresia has been poorly examined in cephalopods. We here provide a histological description of this process along the whole ovary development for Octopus vulgaris. Additionally, we related its occurrence to morphometric parameters, and its seasonal cycle was further analysed. Atresia occurred all year round in immature and mature females and in previtellogenic and vitellogenic oocytes. However, more mature females were more prone of being atretic. This occurred mainly in spring when females had atretic previtellogenic oocytes in mature macrostages. By contrast, vitellogenic atresia occurred mainly from spawning to post-spawning females. Furthermore, two types of phagocytic cells were identified as responsible for the reabsorption during atresia. The phagocytic follicle cells only occurred in yolk-bearing oocytes; and within the two haemocyte populations only the smaller ones seemed to be involved in engulfing atretic oocytes. Additionally, advanced atresia in post-spawning females showed yellow-brown bodies as a possible result of follicle cell apoptosis and highlighting the end of the reproductive cycle. Given the pattern of atresia, the reproductive strategy of this species is based on an asynchronic ovary development and a synchronous ovulation during spawning. We further suggest that potential fecundity for this species should be measured on late vitellogenic oocytes in pre-spawning females.