Diet composition influences the growth of the pelagic mysid shrimp, Mysis mixta (Mysidacea)

We studied the growth, feeding, and elemental composition of Mysis mixta from June to September 1997 in the northern Baltic Sea. In June the juvenile population had a unimodal size distribution (mean length ~6 mm), but in July–August, the population was divided into two cohorts. A stomach content analysis showed that the mysids in the larger and faster growing cohort fed significantly more on crustacean zooplankton and pelagic material than the smaller one: the mean ratios of zooplankton:phytoplankton and pelagic:benthic particles in July–August were respectively 0.27 and 0.11 for the small cohort, and 0.54 and 0.36 for the large cohort. This suggests that food quality and its energy content are important in influencing the growth of pelagic mysids in the northern Baltic. The C:N ratio of the two cohorts did not vary much, which shows that ingestion of food items with varying elemental content is not necessarily reflected in the elemental composition of consumers.