MEPS 361:227-238 (2008)  -  DOI: https://doi.org/10.3354/meps07443

ABSTRACT: Growth and condition of larval Engraulis encrasicolus larvae in the Bay of Biscay were analysed relative to their biochemical composition. Protein, carbohydrate, lipid, DNA and RNA contents of larvae were quantified during larval ontogeny to analyse changes associated with growth. Proteins were the main organic component of E. encrasicolus at every larval stage, followed by lipids and carbohydrates. The increase in relative protein content in terms of protein percentage (P%) and the decrease in lipid relative content (L%) of the total organic matter (OM) with size observed are consistent with the definition of Type 1 larvae. Protein relative content increased until the P% in larvae reached ~71%, whereas L% and carbohydrate relative content (CH%) declined, exhibiting minimum values of ~20, and ~6%, respectively. In general terms, the feeding condition of larvae, as defined by their RNA/DNA ratio, was good. Food did not seem to be a major factor limiting larval growth in the study area throughout late spring and early summer. The RNA/DNA ratio was size-related and increased during larval growth up to an asymptotic optimal value of ~3.6 in postflexion larvae in relative protein content, in terms of protein percentage (P%). The ‘actual’ RNA/DNA ratios found in a given larval population when compared with the ‘starving’ RNA/DNA ratio, and using an ‘absolutely optimal’ value as complementary information, could be used to determine the overall status of the population. Parental effect of low egg quality is a possible explanation of delayed ontogenetical development of larvae from July 2000.

KEY WORDS: Engraulis encrasicolus · Larvae · Condition · Biochemical composition · RNA/DNA · Protein/DNA · Growth · Ontogeny