Embryonic mortality is one of the main causes of losses in the early stages of development of Atlantic salmon (Salmo salar), although due to its early presentation its economic impact is lower compared to losses in advanced stages of development.
This situation can also occur at any stage of embryo development, from fertilization to the moment of hatching, although there is no consensus, it is possible to classify it according to the stage of development in which it occurs.
This loss of specimens occurs between fertilization and ova with eye, the intermediate occurs between the ova with eye stage and close to hatching and finally late, which occurs from the start of hatching to the complete hatching of the batch.
Thus, the affected eggs normally turn white, which, depending on the cultivation and handling conditions, quickly become infected with fungi belonging to the genus Saprolegnia sp. In this way, late embryonic mortality occurs during hatching, being called in some cases as “abortion or embryonic abortion”.
Likewise, the percentages of mortality are variable and have been associated with management conditions, water quality and, less frequently, infectious causes.
Among the probable causes to consider are the culture conditions (handling, temperature, gas supersaturation, etc.) during hatching. Additionally, the development of weak, deformed fingerlings and causes related to the chorion should be considered.
This embryonic abortion is also characterized by a significant increase in partially hatched fingerlings, due to the incomplete hatching process.
Source: Doctor Marcos Godoy, Pathology in aquaculture, 2022. Embryonic mortality (“embryonic abortion”) in Atlantic salmon (Salmo salar): macroscopic pathology. https://bit.ly/3UmYYi0.