MacDonald-type jars for the incubation of eggs of several marine and freshwater species. Robust and long-lasting, the upwelling water flow excludes the formation of anoxic zones, while ensuring the continuous rotation of the eggs within the water column. Transparent jars for accurate monitoring of the incubation process. Water inlet and concave base provide optimum flow conditions, precluding ova aggregation and fungal growth. The water outlet  allows for the passage of larvae into rearing tanks without manual handling, minimizing hatching stress. Fitted with an overflow sieve to retain hatching debris.