Variability of the total free amino acid (TFAA) pool in Mytilus galloprovincialis cultured on a raft system. Effect of body size

Variability of total free amino acid (TFAA) pool in Mytilus galloprovincialis was analysed following raft culture of growing mussels. With the aim to ensure the actual effect of animal’s size, a mussel population was sampled in laboratory covering the field size (15‐ to 60‐mm shell length). TFAA showed a constant profile regardless size increase of individuals in both field and laboratory experiments. Environmental salinity and temperature varied within a relatively narrow range in the field (34–35 g L^?1 and 14–19 °C, respectively). Despite the narrow variability of TFAA, significant differences were reported for the most representative amino acids. Specifically, taurine content significantly dropped with soft tissues increase in both field and laboratory experiments. Up to 40% of taurine drop in growing individuals was counterbalanced by the increase in alanine as main protein free amino acid (PFAA), whereas glycine showed high variability and inconsistency. PFAA increased linearly with the endogenous condition of individuals and were inversely correlated with protein content. In summary, TFAA pool of M. galloprovincialis remained unchanged with animal’s size, which might ensure optimal protein turnover rates during growth and establish a significant link between energetic status (condition) and PFAA, values that are equilibrated by a significant drop of the most abundant taurine.