Effects of a transitory,low food supply in the early life of larval herring (Clupea harengus) on mortality,growth and digestive capacity

In order to assess possible effects of a transitory, low food supply on later development, three groups of Clyde herring larvae (Clupea harengus L.) were exposed in 1989 to different feeding regimes immediately after yolk resorption. Group 1 received a high daily ration of 80 copepods larvae^–1 for 31 d, Group 2 a low daily ration of 15 copepods larva^–1 for 10 d followed by a high ration (80 copepods larva^–1) for 21 d and Group 3 a low ration of 15 to 20 copepods larva^–1 for 31 d. After 31 d of feeding, digestive capacity, expressed as the sum of trypsin and trypsinogen, was markedly reduced in Group 2 compared to Group 1, while Group 3 had an even lower digestive capacity. After the switch from low to high ration Group 2 exhibited compensatory growth and caught up with Group 1 both in standard length and content of soluble protein. Group 3 had the lowest growth rates. Mortality was equal in Groups 1 and 2, while Group 3 showed an excess mortality of 40% of the start population. Although Group 2 larvae had caught up with Group 1 in growth at the end of the study, content of trypsin and trypsinogen in Group 2 was only half of that found in Group 1. Thus, comparing effects of a short period of food limitation on future growth, mortality and content of digestive enzymes, the study indicates content of trypsin and trypsinogen to be the most sensitive variable for detection of food limitation in the early stages of exogenous feeding.