GROWTH AND MORTALITY IN YOUNG LARVAL HERRING (CLUPEA-HARENGUS) - EFFECTS OF REPETITIVE CHANGES IN FOOD AVAILABILITY

Following yolk resorption, laboratory-reared larval Baltic herring (Clupea harengus L.) were exposed to two sequences of food restriction for 5d and re-alimentation for 10d. Comparisons regarding larval growth (standard length and content of water-soluble protein), mortality and content of the sum of trypsin and trypsinogen were made with larvae at a continuous high ration. Larvae exposed to varying prey abundance grew less in length than the control, and during the second high-ration period (Day 22 to 32) growth in length ceased. From the first low-ration period onwards, the content of water-soluble protein in these larvae was lower than that of the control larvae, and the survival rate of the low-high ration group was 59% compared to 77% in the larvae at a continuous high ration. In contrast, the effects of varying food availability were minor on larval content of trypsin and trypsinogen. Results are compared with previous findings in larval Clyde herring, and the effects of larval stock and timing and duration of food restriction on larval growth performance are discussed.