European anchovy recruitment to the Guadalquivir estuary mainly occurs when the
environmental conditions show more stability. Unusual changes in the environmental conditions of
this estuary negatively impacted on key preys of anchovy and therefore on its nursery function. In
this way, nutritional condition should determine strongly the physiological state of this species in
estuaries and thus its survival and recruitment. RNA:DNA ratio has been applied with success as
indicator of nutritional condition and growth in marine organisms. We study RNA:DNA ratio in
anchovies of the coupled system Guadalquivir estuary-coastal influenced area in the Gulf of Cádiz in
order to evaluate the condition seasonal variability of this species along this spatial gradient. Spatial
differences in the size distribution of anchovy and high values of RNA:DNA in the Guadalquivir
estuary compared to its influence coastal area suggest that anchovies migrate to the estuary and
they acquire a very good condition. We conclude that RNA:DNA is an useful tool to understand the
ecological mechanisms by which the coupled system Guadalquivir estuary-coastal influenced area in
the Gulf of Cádiz control the success or failure of the recruitment of this important fishery resource
in the region
