Feeding and assimilation kinetics of Artemia franciscana fed Isochrysis galbana (clone T. Iso)

Artemia franciscana was grown on Isochrysis galbana Green (clone T. Iso) at saturated food concentrations (13 to 20 mg C l(-1)]) for 11 d at 26 to 28 degrees C, and 34 ppt salinity. Three groups of brine shrimp were used in t he feeding experiments: metanauplius III and IV (Group 1), post-metanaupliu s II and III(Group 2) and post-metanauplius VIII (Group 3), corresponding t o 4-, 7- and 11-d-old animals, respectively. The ingestion rate, clearance rate and carbon balance were estimated for these stages at different concen trations of C-14-labeled I. galbana ranging from 0.05 to 30 mg C l(-1) The handling time of algae was determined for all three groups. The ingestion r ate (I, ng C ind(-1) h(-1)) increased as a function of animal size and food concentration. In all three groups, the ingestion rate increased to a maxi mum level (I-max) and remained constant at food concentrations greater than or equal to 10 mg C l(-1) (saturated food concentrations). The clearance r ate (CR, mu l ind(-1) h(-1)) increased with increasing food concentration u p to a maximum rate (CRmax), after which it decreased for even higher food concentrations. The functional response of A. franciscana was most consiste nt with Welling's Type 3 functional response curve (sigmoidal model), which for the two oldest groups (Group 2 and 3) differed significantly from a Ty pe 2 response (p < 0.05). The gut passage time for the three groups of A. f ranciscana, feeding on saturated food concentration (20 mg C l(-1)), varied between 24 and 29 min. As the nauplii developed to pre-adult stage the han dling time of the algae increased as a function of animal size. The assimil ation rate (ng C ind(-1) h(-1)) in the youngest stages (Group 1 and 2) incr eased with increasing food concentrations, reaching a maximum level close t o 10 mg C 1(-1). At higher food concentrations the assimilation rate decrea sed, and the proportions of defecated carbon increased, reaching 60 to 68% in the post-metanauplius stages (Group 3). The assimilation efficiency (%) was high at the lowest food concentrations in all three groups (89 to 64%). At higher concentrations, the assimilation efficiency decreased, reaching 56 to 38% at the highest concentrations.