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The otoliths of juveniles and adults of European anchovy Engraulis encrasicolus held in aquaria were marked by immersion in oxytetracycline hydrochloride (OTC) at concentrations between 350 and 410 mg l−1 for 12 h. Counts of microincrements between fluorescent bands validated the daily otolith increment formation. The otolith increments were easily readable at ×400 with average increment widths of c. 1·1 µm. Validation was successfully demonstrated in juveniles and adults maintained for short periods in the aquaria in the summer. For European anchovy captured as juvenile and reared to adults, however, increment formation appeared less than daily. The daily periodicity of the otoliths in juvenile European anchovy implies that counting of microincrements can be used to study their birth dates. The application of this technique to adults, however, may lead to the underestimation of actual age and further research needs to be done to clarify the reasons for the apparent loss of the daily rhythm over long periods.

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The early development, growth and morphological changes of mackerel Scomber scombrus were investigated at different incubation temperatures (8, 10, 13, 15 and 18°C). Details on the early life history are illustrated with special reference to morphological transformations. Culture techniques to rear larval mackerel stages are described using laboratory cultured foods. Artificially fertilized eggs were hatched after 80Á6 h at 18Á4°C and 256Á8 h at 8Á7°C. The standard length (L S ) of the individuals at first feeding was 4Á71 AE 0Á18 mm. Four mortality critical periods and cannibalistic behaviour were identified. A maximum average larval size of 37Á5 AE 4Á41 mm L S was attained 30 days post-hatch (dph) at 18Á4°C. Development and growth were affected significantly by temperature during both endogenous and exogenous feeding periods. Larvae grew more rapidly at high, than at low temperatures. Daily specific growth rate (in mass) ranged from 2Á4% at 10Á6°C to 16Á9% at 18Á4°C. Likewise, average growth rate (in length) ranged from 0Á05 mm day ÿ1 at 8Á4°C to 0Á37 mm day ÿ1 at 18Á4°C. The allometric relationship of L S , with several body measurements was not affected by temperature. Comparison with larvae collected in the Bay of Biscay did not show any significant difference in the dry mass and L S relationship; conversely, the growth rate in length differed significantly between both laboratory and field conditions. The trends observed in the laboratory are described in relation to some aspects of the year-class strength regulation.

Experiments were conducted during the summer of 2008 and 2009 to study the growth of early post yolk-sac European anchovy (Engraulis encrasicolus, Linnaeus, 1758) larvae reared under different food regimes. The fatty acid composition was used to assess nutritional condition of the larvae. Prey items used in the experiments were Gymnodinium sanguineum, Brachionus plicatilis and nauplii of the copepods Acartia grani and Euterpina acutifrons. Food type and concentration affected the growth of the larvae. Mixed diets composed of rotifers and copepod nauplii at high concentration resulted in higher anchovy larvae growth rates in comparison with single-prey diets using either rotifers or copepod nauplii. The addition of the dinoflagellate G. sanguineum (25-50 cells ml −1 ) to the prey offered did not enhance significantly larval growth. Highest growth rates of anchovy larvae (0.28 mm d −1 ) were obtained using high concentrations of a mixed diet, particularly the combination of rotifers and A. grani nauplii. Fatty acid composition at hatch was similar to the composition observed in the field, but during larvae ontogeny there was a marked decrease in the contribution of polyunsaturated fatty acids such as EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid). Such difference reflects the high requirements of these PUFA for larvae development, and suggests that the food offered failed to fulfill the larvae nutritional requirements. The growth rates obtained in our experiments were, overall, in the lower range of those observed in natural conditions. Taking into considerations the fact that larvae in the field are expected to encounter lower prey concentrations, we discuss the reasons for such disagreement.