Every winter, young-of-the-year herring and sprat migrate to North Sea estuaries and become the dominant member of the estuarine fish assemblage, both by numbers and by biomass. These winter migrations have been related to abiotic factors (temperature and salinity), estuarine productivity and the reduced predation pressure in turbid brackish water areas. During estuarine residency, herring and sprat mainly feed on calanoid copepods. We have estimated the food consumption of zooplankton (g C m-3 day-1) by herring and sprat which overwinter in the Scheldt estuary using two models of feeding in fish: a bioenergetic model based on physiological parameters and a model based on the change in stomach contents over time. To assess the impact of fish on the copepod biomass of the brackish part of the estuary, we have developed a simple copepod biomass model and included food consumption by fish as a biomass sink. In general, the consumption of zooplankton by fish is too low to represent a major source of copepod mortality. The low impact of fish predation may be a function of the low fish biomass in spring at a time when copepod production increases.