Larval development and growth of the European hake Merluccius merluccius in the northwestern Mediterranean

The larval growth and development of the European hake, Merluccius merluccius, was studied from field larvae. Larvae were collected in the northwestern Mediterranean on three cruises carried out during the peak spawning months (November 1998, September 1999 and November 1999). Like other species of the genus, these larvae are characterised by a well-developed anterior part of the body, head and trunk region. Nevertheless, yolk sac larvae are much more slender than larvae at notochordal flexion stages. In the present study we analysed the allometric relationships between several body measurements and body length. This is the first attempt to infer larval growth of Merluccius merluccius by means of sagittal otolith analysis. Our results show the change in the otolith shape from a lenticular otolith in early larvae to an almond-shaped otolith in larger larvae. Otolith diameter showed a power relation with larval size, with no significant differences between seasons. In spite of the sea surface temperature differences between the three periods of larval collection, the early growth estimates showed no significant differences. This was explained by the similarity in the temperature at the depths at which the larvae are located. Absolute growth rates in length were estimated by relating daily growth increments in otoliths and larval size (standard length). When using the whole larval size range the values obtained were similar to those found for other Merluccius species. Nevertheless, the present data evidenced that growth for larvae younger than 12 days is very low, showing a significant increase thereafter. This indicates that length is probably not the best parameter for describing the growth of hake larvae in the first days of life, as allometric analysis suggested.