Abstract
The chorion is an acellular envelope that surrounds fish oocytes and embryos, playing a crucial role in protection against environmental factors until hatching. In salmonids, several chorion malformations have been documented, including white-spotted (disc-like) chorion. This study focused on investigating the ultrastructural modifications of the chorion with discs and their possible influence on embryonic viability in Atlantic salmon. A total of 136 females were included in the study. The incidence of disc chorion was evaluated at 130 °h and in pigmented eye embryos at 280 ATU (accumulated thermal units). Scanning electron microscopy (SEM) was used for this ultrastructural characterization. The results revealed that 3.17% of females had embryos with discs in the chorion at 130 °h, with a mean of 1.21 ± 7.24% of affected embryos per female. At 280 ATU, 15% of the females had embryos with discs in the chorion, with a mean of 0.45 ± 2.17% per female. Females with this malformation were observed to have a slightly higher fertilization rate (75 ± 21.21%) compared to females without this malformation (74.2 ± 23.7%). Embryonic survival at 280 ATU for both groups was 70.1 ± 20.6% and 71.6 ± 21.0%, respectively. Although a clear origin for the chorion with disc malformation is not known, the possibility is raised that it may be due to pathological conditions specific to the female and that it probably occurs in a similar way to nephrocalcinosis, by bioaccumulation of elements in the chorion during its synthesis. Further studies are needed to better understand this malformation to help refine economic projections in salmon farms dedicated to embryo production.