Size at maturity Salzwedel (1979) reported the smallest specimen with recognizable sex to be 7.7 mm long, but that typically the gonads were not fully developed until shell length had reached 10 mm.
Feeding Fabulina fabula is capable of both suspension feeding and deposit feeding. Salzwedel (1979) observed feeding behaviour in the laboratory. While suspension feeding, the inhalant siphon is held a few mm above the sediment surface and sucks in suspended particles. While deposit feeding, the inhalant siphon is bent over toward the sediment surface, sucking up detritus and sand grains more or less unselectively. Salzwedel (1979) made the suggestion that Fabulina fabula is solely a suspension feeder up until the age of 1.5 yr., after which it changes between feeding methods according to environmental conditions. Whilst in the laboratory, the species was fed on a mixed culture of the unicellular green alga Dunaliella marina and the diatom Phaeodactylum tricornutum.