The purpose of this study is to create awareness about the species of mosquito fishes (Gambusia holbrooki Girard, 1859) both vectors and ways of introduction to new aquatic habitats. Because the species creates risks, especially for the circumstance of the native and endemic fish fauna, studies about introduction stories of the species are quite important to prevent the risk. In the current report, mosquitofishes which are known as a highly invasive species were found in the crop content of a hen mallard duck (Anas platyrhynchos L., 1758) in an estuarine area, the Gediz River Basin (İzmir, Turkey). This report is the first record of a duck consuming mosquitofish. Although nevertheless, it is known that mallard duck feeding behaviour does not predominantly contain fish (they mainly feed on plant seeds), according to this observation, mosquitofish might be added to the prey list of mallards as a new type of food. Therewith, this feeding behavior also indicates that ducks might be a potential vector for the transport of invasive mosquitofishes.