Aspectos estruturais da diferenciação sexual do pirarucu Arapaima gigas (Schinz, 1822) e do jundiá Rhamdia quelen (Quoy & Gaimard, 1824)

Abstract

With the stagnation of extractive fishing, producing fish protein has become a major challenge for aquaculture. This fact, coupled with the demographic explosion and the search for healthy food were the main factors driving the growth and advancement of world aquaculture. Based on the above and considering the ecological and social importance of pirarucu Arapaima gigas and jundiá Rhamdia quelen, their productive and economic potentials for the northern and southern regions of Brazil, respectively, and the current lack of knowledge regarding their reproductive physiologies. , the present work aimed to characterize the process of formation of the gonadal primordium and gonad in differentiation of these two native species, through serial histological sections, as subsidy for the development of technologies for the cultivation of species in commercial fish farms, conservation programs and still in evolutionary and climate change studies. As in most teleosts, pirarucu and jundiá show direct sexual differentiation, with the undifferentiated gonad directly originating an ovary or testis. However, in pirarucu the ovarian differentiation was a little earlier than the testicular and in jundiá the onset of ovarian and testicular differentiation occurred in fish of the same age. In pirarucu, the hallmark of ovarian differentiation (female) is the concentration of germ cells in the lateral face of the gonad, surrounded by pre-follicular somatic cells, while the epithelium changes from squamous to cubic in fish approximately 9 cm long. total. With the development of these structures, the formation of small ovigerous lamellae, which later form the ovarian fringes, which are characteristic of this species. The alleged males remain with the gonads with an undifferentiated aspect for longer, until the germ cells rearrange spatially in the organ (concentrating inside) to give rise to the testicular cords. These cords subsequently fragment into spermatogenic cysts. In jundiá, ovarian formation begins with the development of the ovarian cavity in specimens 4 weeks after hatching. This structure is formed by a small projection of the gonadal epithelium, which eventually bends and closes, leaving a cavity inside the organ. This cavity, initially closed, opens to the formation and development of the ovarian lamellae within it. In males of the same age, the undifferentiated gonad begins to show grooves that are the origin of the testicular fringes characteristic of some catfish species.