Busch, A.: Transition from endogenous to exogenous nutrition: larval size parameters determining the start of external feeding and size of prey ingested by Ruegen spring herring Clupea harengus. Marine Ecology Progress Series, 130: 39-46, 1996.
and the width of the eaten prey was between 0.5 and 1.4, it varied between 1.4 and 7.4 for the corresponding mouth size parameters and the prey width. The results of this investigation show that external feeding starts when the yolk is exhausted sufficiently to allow the oesophagus to open so that prey organisms can pass through it. Thus, external feeding can be prevented, especially for young larvae, not only by prey limitation, but also by a restriction of the oesophagus opening - even if sufficient prey is available.