Histology in cephalopods reproductive studies
“Contrasting macroscopic maturity staging with histological characteristics of the gonads in female Octopus vulgaris” is the title of the last paper (published in Hydrobiologia) in which we have colaborated. Although we do not participate as coauthors, The Fisheries Ecology Group (CSIC) allowed the author to use image analyzer, and we also provided support in the use of the stereological method and helpful suggestions during the manuscript preparation.
Histology and stereological techniques has been generally used in fish reproductive studies for a long time; but only a few studies have used histological analysis in cephalopod species. As part of a broad maturity staging study of Octopus vulgaris, Sieiro et al. adopted and sterological approach to develop a new histological maturity index.
ABSTRACT: We contrasted histological characteristics with a macroscopic maturity scale in Octopus vulgaris. Seven histological stages of maturation were identified, and a stereological method was used to develop a new histological maturity index (HMI). This index was related to the gonadosomatic index giving the possibility to estimate the histological stage of individual octopus without sampling the gonads. However, the existing macroscopic maturity scale produced some degree of overlap along the range of HMI, suggesting that this macroscale at this moment might be just good enough to separate immature from fully mature individuals. A histological maturity criterion based on the presence of a larger proportion of folding oocytes compared to earlier microstages resulted in a size at maturity of 1.5 kg. However, using two different macroscopic criteria, size at maturity was 1.3 and 2.3 kg. The estimate of size at maturity is therefore sensitive to the maturity criteria used. The maturation cycle of female O. vulgaris was seasonal, peaking in spring months and reaching a maximum of reproductive activity in April independently of the maturation criteria used. Oogenesis was reviewed and found to be an asynchronic process. Our results suggest that there is a need to examine all these issues in other cephalopod species.