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.

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The growth strategies of pelagic larvae of 3 fish species from the Bay of Biscay belonging to 2 different shape groups, the eel-like anchovy Engraulis encrasicolus and sardine Sardina pilchardus, and the tadpole-like horse mackerel Trachurus trachurus, are compared in terms of changes in their biochemical composition and energy allocation. In anchovy and sardine, the relative amount of protein increased and relative amounts of carbohydrates and lipids decreased throughout their growth. The biochemical composition in horse mackerel did not change significantly during growth. Differences between the 2 shape groups could be associated with the various energy allocation patterns related to dissimilar growth strategies. Although the patterns of change in biochemical composition during growth are different in the 2 shape groups, they show a very similar biochemical composition at the notochord flexion stage, indicating convergences in life-history patterns of the different species.

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