| Summary: | National audience The evolution of pigment stages was monitored on six glass eel samples collected in the Vilaine estuary, and kept in cages in the freshwater and in the estuary. In each location, one sample was kept for reference to assess the effect of handling procedure on pigment development. It was pulled out the water only to monitor and retrieve mortality. The other sample was anaesthetised and analysed for pigment developmental stages three times a week. The analysis of 9 920 glass eels showed first that the anaesthesia and the reading of pigment stages did not modify the pigmentation process. The second result, in accordance with other published results, was to show that temperature is the main factor controlling the pigmentation dynamics. In freshwater, the duration to reach from 88-99% of young stages VB and VIA0 to 86-99% of old stages VIA2 VIA3 and VIA4 varied from 6 days at 18°C to 45 days at 8°C. We finally confirmed that the salinity acts as a secondary factor slowing down the pigmentation. The samples kept in the estuary were less pigmented than the samples kept in freshwater, except during flood periods when there was a differential mortality of young stages in the estuary. This result was in accordance with most of published and unpublished results re-analysed in the paper. L`évolution pigmentaire des civelles est analysée à partir de six échantillons de civelles prélevés en estuaire de Vilaine, et placés dans des cages en estuaire et en eau douce. Les stades pigmentaires des civelles sont lus trois fois par semaine. L`effet de la manipulation sur le vieillissement est contrôlé à l`aide de lots témoins qui sont laissés dans le milieu et analysés en fin d`expérimentation. L'analyse de 9 920 civelles montre que la température est le principal facteur de la cinétique de pigmentation. La durée nécessaire pour passer de 88 à 99 % de jeunes stades (VB et VIA0) à 86 à 99 % de stades plus avancés (VIA2, VIA3 et VIA4) varie de 6 jours à 18 °C à 45 jours à 8°C. La salinité agit comme facteur ...
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