Caracterización histológica de las fases de desarrollo gonadal del calamar gigante Dosidicus gigas (d ́Orbigny, 1835) en el Pacífico ecuatoriano

Abstract

The giant squid Dosidicus gigas is an important fishing resource in the American Pacific, so many of its reproductive aspects have been widely studied. However, the histological characteristics of their reproductive organs and the changes that these suffer during maturation have been very little studied in this species of Ommastrephidae. Therefore, the aim of this study was to characterize the phases of gonadal development in D. gigas of the Ecuadorian Pacific, through macroscopic and microscopic description, as well as to propose a scale of gonadal maturity for the species. The collection of specimens of D. gigas was carried out in the Ecuadorian Pacific in September 2016 and March, May, June and July 2017. The organisms were fixed in 10% neutral formalin and translated to the CSA laboratory of the Escuela de Acuicultura y Pesquería, Universidad Técnica de Manabí, where the dorsal length of the mantle (mm) and the total weight (g) were recorded, and fragments of gonads and accessory glands were taken, which were processed by the histological technique of paraffin inclusion, cut into sections of 5-7 μm, stained with the routine stain Hematoxylin-Eosin and mounted with Entellan® resin (Humason, 1979). From a total of 224 organisms collected, 172 females and 52 males were obtained to a sexual ratio of 3.31: 1. The average size of the analized females was 226.53 ± 43.49 mm of LDM with an average weight of 367.75 ± 232.86 g, while for the males it was 200.33 ± 32.93 mm of LDM and an average weight of 223.72 ± 114.68 g. As the female matures, the ovary changes its small, translucent appearance with predominance of previtellogenic oogonies and oocytes, until reaching a prominent size in the body cavity, with a clear brown color and visible eggs. No oogonies of primary growth were observed in mature females. The nidamental glands and the oviducts showed a synchronous development with the development of the ovary, with an increase of the glandular tissue in the first and dilatation and thinning of the wall in the second. In male specimens the testicle changed its small and translucent appearance in immature organisms, due to a prominent size and opaque whitish color, with predominance of spermatozoa in mature specimens. As the males mature, the accessory glands become more visible, take on an opaque coloration and the presence of spermatophores is observed in the Needham sack and throughout the pallial cavity. We propose a maturation

scale of four phases for each sex (I- Immature, II- In maturation, III-Mature, IV- Spawning).