Changes in the plasma free amino acid profile of the Norway lobster Nephrops norvegicus at different stages of infection by a parasitic dinoflagellate (genus Hematodinium)

The haemolymph free amino acid (FAA) composition of Norway lobsters Nephrop s norvegicus from the Clyde estuary, Scotland, UK, at different stages of i nfection by the parasitic dinoflagellate Hematodinium sp. was determined by reverse phase high performance Liquid chromatography (HPLC). In uninfected lobsters the total detected haemolymph FAA concentration was 3.79 mu mol m l(-1). Collectively, glycine, histidine/glutamine, alanine, serine, taurine and asparagine constituted 80% of the total. The concentrations of several FAAs, notably serine, were reduced in early infections (Stage 1), while at later stages (2-4) several FAAs were increased in concentration. The most significant change was in taurine, which had increased 13-fold (from 0.22 t o 2.56 mu mol ml(-1)) in the final infection stage, when its relative contr ibution to the total FAA was 41.6%. Possible causes of these changes in the lobster haemolymph FAAs are the breakdown of host tissues including the he patopancreas and muscle, haemocyte lysis, a host stress response and releas e of FAAs from the parasite cells. Results indicate that the taurine:serine ratio in the haemolymph provides a sensitive diagnostic measure of patent Hematodinium infections. Implications of these FAA alterations for Hematodi nium-infected N. norvegicus are discussed.