On the Nutritive Significance of Dissolved Free Amino Acid Uptake for the Cosmopolitan OligochaeteNais elinguisMüller (Naididae)

Uptake of dissolved free amino acids (DFAA) byNais elinguisMüller from a brackish water lagoon has been confirmed by autoradiographic studies, liquid scintillation counting of animals incubated with labelled DFAA, and by HPLC analysis of the incubation water. Net uptake was shown to occur at ambient DFAA concentrations. The results indicate that most of the absorbed DFAA were respired, and only a minor portion was incorporated into proteins. Parallel determination of respiration and DFAA uptake in a flow-through system allowed a calculation of the contribution of uptake to the maintainance metabolism ofN. elinguis. The average weight-specific uptake rate of mixed DFAA was 1•4 μmol g−1h−1at a salinity of 6 and 4•1 μmol g−1h−1at a salinity of 12 (temperature 20 °C). Assuming that 10 μmol of mixed amino acids (average mol wt. 100) require 44•64 μmol O2for complete oxidation, the nutritional profit of DFAA absorption at a salinity of 6 accounted for 7% of the total oxidative needs and for 24% at a salinity of 12. The results demonstrate that DFAA uptake can provide an important nutritional input.