Based on the economic and ecological relevance of Brycon amazonicus, the goal of this work was to describe the diameter of oocytes and eggs of this species, as well as the chronological embryonic development. The material was provided by Buriti fish farm, Nova Mutum – MT, Brazil. Samples of both oocytes and eggs were obtained from extrusion to hatching. The material was fixed and measured under stereomicroscope, and the samples were divided for light microscopy or scanning electron microscopy (SEM) analyses. At extrusion, the oocytes were bluish green. The frequency distribution of oocytes revealed that 87.7% of them ranged from 1.11–1.30 mm in diameter. During incubation, the total diameter of the eggs increased from 1.22 ± 0.04 mm to 3.06 ± 0.46 mm in the first 60 min post fertilization (PF), and growth ceased at 180 min PF. Between 10–30 s PF, most eggs were fertilized and fertilization cones were observed from 10 s onwards after gamete activation. The main fertilization events took place asynchronically and spermatozoa were visualized in the micropyle vestibule up to 90 s PF. The first cell was formed in the centre of the blastodisc 20 min PF. The morula stage was identified 2 h PF and, 3 h later, 70% of the yolk was covered by the blastoderm; the blastopore was almost entirely closed at 6 h PF. The cephalic and caudal regions of the embryo could be defined 8 h PF and hatching occurred after 13 h of embryonic development. The larvae hatched with undifferentiated organic systems and with a large yolk sac, free from swimming abilities or visual acuity.

The aim of this study was to evaluate the oocytes, post-fertilization events and embryonic development in Brycon insignis, under both scanning electron microscopy and stereomicroscopy. Oocytes and embryos were sampled from spawning up to hatching. Stripped oocytes were spherical, non-adhesive, greenish-brown, possessed a single micropyle, pore-canals and had a mean diameter of 1.46 mm. In 63% of oocytes the germinal vesicle was peripheric. The main post-fertilization events were the fertilization cone formation (20 s), micropyle closure (100–180 s) and agglutination of supernumerary spermatozoa (100–180 s). Embryonic development lasted 30 h at ~24 °C and was characterized by seven stages. Zygote, cleavage, blastula and gastrula stages were first observed at 0.25, 1, 3 and 6 h post-fertilization, respectively. Fertilization rate was determined at the moment of blastopore closure, 10–11 h post-fertilization. The segmentation stage began at 11 h post-fertilization and comprised the development of somites, notochord, optic, otic and Kupffer's vesicles, neural tube, primitive intestine, and development and release of the tail. The larval stage began 21 h post-fertilization and was characterized by the presence of somites, growth and elongation of the larvae. At the hatching stage, embryos presented vigorous contractions of the tail and body leading to chorion rupture (30 h). The morphological characteristics described for B. insignis were similar to that described for other teleost species, and such knowledge is important for a better understanding of reproductive features of a species and useful for ecological and conservational studies.

Brycon gouldingi is an endemic species from Tocantins-Araguaia basin, used as a food source by riverine communities and relevant to aquaculture. Information about the initial morphology of B. gouldingi, a recently described species, is absent. In the present study, we analysed the fertilization and the embryonic development of this species based on light and scanning electron microscopy. After collection of adult specimens in Mortes River – Mato Grosso, Brazil, adaptation to captivity and induced spawning at Buriti Fishculture, Nova Mutum – Mato Grosso, Brazil, in December 2007 and January 2008, samples were collected at pre-defined periods from egg extrusion up to larval hatching, which occurred at 13.9 ± 0.06 h post-fertilization (hpf) in average. At the moment of extrusion, the eggs were slightly ovoid bearing a single micropyle per oocyte with a funnel-shaped micropyle canal and vestibule covered with longitudinal folds, typical of the genus Brycon. The embryonic development of B. gouldingi was characterized by six stages with distinct features: zygote (from fertilization up to formation of egg-cell); cleavage (cell divisions resulting in blastomeres, including the morula phase); blastula (several embryonic cells in a cup shape, without distinction of cell boundaries); gastrula (cell movement); histogenesis/organogenesis (formation of tissues and organs); and hatching (larval chorion rupture). Right after hatching, the larvae presented neither swimming abilities nor visual accuracy, and the digestive trait was undifferentiated. The present study is the first report on biological features of embryogenesis in B. gouldingi, providing relevant information to several approaches, mainly related to taxonomy, ecology, conservation and captive rearing of this new Brycon species.