The absence of magnetic fields can affect fish embryogenesis. The influence of hypomagnetic field on the survival of roach (Rutilus rutilus) embryos was estimated. Delayed consequences of R. rutilus embryos and prelarvae exposure to these magnetic conditions were also studied. Hypomagnetic field during embryogenesis led to an increased mortality of embryos. The juveniles developed from the exposed embryos were characterised by reduced vertebral phenotypic diversity. The influence of hypomagnetic field on roach prelarvae led to changes in the size–mass indices of juvenile fish. Present results differ from those that were previously obtained in experiments with simulated geomagnetic storms and artificial low-frequency magnetic fields and emphasise the importance of the magnetic environment for the fish embryogenesis. Possible mechanisms of the described effects are discussed.