Oocyte adhesiveness and embryonic development of Astyanax bimaculatus (Linnaeus, 1758) (Pisces: Characidae).
This study shows for the first time the presence of a jelly coat on oocytes of neotropical Characiformes fish. This structure could be responsible for the adhesiveness of Astyanax bimaculatus oocytes, a species widely distributed in South America including in the São Francisco River basin in Brazil. Adult specimens of A. bimaculatus were submitted to artificial reproduction in order to analyse the egg morphology and embryonic development. The eggs were fertilised and kept in incubators with a water temperature of 24°C so that embryogenesis could be monitored. Ovulated and unfertilised oocytes were also collected and submitted to routine histological techniques. Astyanax bimaculatus oocytes were found to be spherical, yellowish, and covered by a thin jelly coat with a slightly adhesive surface. The mean oocyte diameter was 1.03 ± 0.03 mm, the perivitelline space was 0.21 ± 0.02 mm and the jelly coat's thickness was 0.04 ± 0.01 mm. Positive periodic acid-Schiff (PAS) stain and Alcian blue stain pH 2.5 indicated the presence of neutral glycoproteins, and carboxylated acid glycoconjugates on the jelly coat that formed mucosubstances that may be associated with egg adhesiveness. At a water temperature of 24°C, blastopore closure and hatching occurred at 5 h and 17 h after fertilisation, respectively. The results of this study provide essential information for phylogenetic studies and for a better understanding of the reproductive strategy of A. bimaculatus, currently included in the incertae sedis group of the Characidae family due to the lack of monophyly among the families of the group.
Programa de Pós-graduação em Zoologia de Vertebrados, Pontifícia Universidade Católica de Minas Gerais, Av. Dom José Gaspar, 500, CEP: 30535-610, Belo Horizonte, MG, Brasil.
André Alberto
AA
Weber
Fábio Pereira
FP
Arantes
Yoshimi
Y
Sato
Elizete
E
Rizzo
Nilo
N
Bazzoli
D000268:Adhesiveness; D000818:Animals; D047108:Embryonic Development; D005306:Fertilization; D005399:Fishes; D009865:Oocytes / Q000166:cytology* / Q000502:physiology*; D010060:Ovulation / Q000502:physiology*; D045483:Rivers