Food and feeding of young herring larvae of Norwegian spring spawners
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The gut contents of young herring larvae sampled each hour from 4 to 9 April 1967 around a floating drogue at three depth intervals were examined to study their feeding. Copepod eggs constituated more than 90% of the food items. Feeding started shortly after sunrise within the same hour in the depth intervals 25-5 m, 30-50 m and 75-55 m. Mean length increased with diminishing yolk-sac until absorbtion when mean length decreased. The latter could indicated lack of suitable food. The mean gut content of feeding larvae did not increase until after absoption of the yolk-sac. Larvae from the deepest strata had less gut contents than the others, probably because a lower percentage of them had absorbed yolk-sacs. A high percentage of larvae feeding during day-time contradicts total defecation due to capture. No correlation was found between number of Calanus eggs in the guts and in plankton. Larvae containing Calanus nauplii had more assorted gut contents than larvae containing Calanus eggs. The critical period concept is discussed.