The Use of Enriched 15N as an Indicator of the Assimilation of Individual Protein Sources from Compound Diets for Juvenile Penaeus Monodon

Abstract

We examined the potential of using an enriched stable isotope (15N) to trace the assimilation of individual protein sources from compound aquaculture diets by juvenile Penaeus monodon. We used the marine diatom Chaetoceros muelleri as a source of plant protein and the brine shrimp (Artemia) as a source of animal protein. The diatoms were labelled by replacing 5% of the nitrogen in their culture nutrient media with 15N enriched KNO3. The Artemia were labelled by feeding them 15N enriched diatoms. The 15N enriched diatoms and Artemia were each incorporated into a standard compound pelleted diet. The pellets were fed to juvenile P. monodon (weight range 2 to 5 g) in the laboratory and in enclosures at a local prawn farm. Analysis of the percentage 15N in the abdominal muscle of juvenile prawns demonstrated rapid assimilation of the enriched isotope from diatoms and Artemia. There was a progressive increase in the percentage 15N in the abdominal muscle during the 4-week experiment. Application of a simple mixing model showed that the relative assimilation rate of enriched nitrogen from Artemia was approximately 4.3 times that of the diatoms after 2 weeks and approximately 3.6 times that of diatoms after 4 weeks. The results demonstrated that enriched stable isotope tracers can provide rapid and direct information about the assimilation and retention of nitrogen from individual protein sources in compound diets for shrimp.