How do free-floating clupeiform eggs stay suspended in water?

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clupeiform A young common herring (*Clupea harengus*).

Most clupeiform fishes produce pelagic, or free-floating, eggs that remain suspended in the water column due to a specific structural adaptation: a large, swollen space located between the egg itself and its outer membrane.1

While these eggs are designed to float in surface or bottom water layers, other clupeiform species—particularly freshwater and anadromous varieties—produce eggs that are slightly denser than water and would naturally sink. These eggs rely on environmental factors, such as water turbulence, wave action, and currents, to remain lifted and suspended above the bottom.1