Free amino acid and protein contents of start-feeding larvae of turbot (Scophthalmus maximus) at three temperatures

The contents of free amino acids (FAA) and total protein, together with gro wth and gut-content, of turbot (Scophthalmus maximus L.) larvae reared at 1 4, 18 and 22 degrees C were studied from first-feeding to approximately 140 effective day-degrees post hatch (D(eff)degrees). Artemia franciscana naup lii and two species of rotifers were used as prey. Protein content accounte d for about 42 and 26% of dry body mass in the A. franciscana nauplii and t he rotifers, respectively. The FAA pool constituted 5.6 and 4.8% of the tot al amino acids in the same animals. The dry body mass of turbot larvae was exponentially related to D(eff)degrees. Protein and FAA contents were linea rly related to dry body mass, and were independent of rearing temperature b etween 14 and 18 degrees C. At the end of the experiment, however, turbot l arvae at 22 degrees C had lower gut content values, retarded growth rates, and decreased FAA contents and concentrations. Thus, at this high temperatu re, turbot larvae seem unable to catch and ingest sufficient prey, or to su stain an amino acid assimilation rate from the intestine sufficient to meet metabolic demands.