ON THE NUTRITIVE SIGNIFICANCE OF DISSOLVED FREE AMINO-ACID-UPTAKE FORTHE COSMOPOLITAN OLIGOCHAETE NAIS-ELINGUIS MULLER (NAIDIDAE)

Uptake of dissolved free amino acids (DFAA) by Nais elinguis Muller fr om a brackish water lagoon has been confirmed by autoradiographic stud ies, liquid scintillation counting of animals incubated with labelled DFAA, and by HPLC analysis of the incubation water. Net uptake was sho wn 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 cont ribution of uptake to the maintainance metabolism of N. elinguis. The average weight-specific uptake rate of mixed DFAA was 1.4 mu mol g(-1) h(-1) at a salinity of 6 and 4.1 mu mol g(-1) h(-1) at a salinity of 12 (temperature 20 degrees C). Assuming that 10 mu mol of mixed amino acids (average mol wt. 100) require 44.64 mu mol O-2 for complete oxid ation, the nutritional profit of DFAA absorption at a salinity of 6 ac counted for 7% of the total oxidative needs and for 24% at a salinity of 12. The results demonstrate that DFAA uptake can provide an importa nt nutritional input. (C) 1998 Academic Press Limited.