Nutritional condition of metamorphosing sole: spatial and temporal analyses
Sole Solea solea larvae were collected during five cruises in the Bay of Biscay in 1992 and 1993. The larval growth rate, triacylgycerol (TAG) and sterol (ST) content, and the width of the marginal otolith increments were determined on the same individual larva as indicators of nutritional condition. The TAG content increased during the ontogenetic larval development up to an elevated value corresponding to the end of metamorphosis. During metamorphosis, sole larvae continued to accumulate TAG and to increase in length. Seasonal and yearly variations of growth and nutritional condition of sole larvae at the onset of metamorphosis were more important than spatial variations. Analysis of larval growth showed that, during each cruise, the faster growing larvae were generally those with the highest TAG content (and TAG : ST ratio). In 1993, larvae began to metamorphose earlier and their growth (both larval growth and recent growth) were significantly higher than in 1992. Their relatively low nutritional condition, however, seemed to be the result of a low accumulation of TAG. Sole metamorphosis occurs without growth arrest and the majority of the larvae during this phase are judged to be in good nutritional condition (TAG : ST ratio > 1). In the Bay of Biscay, metamorphosis does not seem to be a critical period in the life cycle of the sole. It is suggested that larvae originating from different cohorts probably have the same chance of survival during or just after metamorphosis when they enter the benthic environment.
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