Although fish, particularly freshwater coarse fishes, are regarded as being "fish-like" from hatching to adulthood, during the first month of free existence they develop through a number of stages that are difficult for aquatic biologists (and most ichthyologists) to recognise. This has led to considerable neglect of these early stages and their impact on the surrounding biota, as predators, competitors and prey. Until recently, studies on recruitment in these early stages were also few and far between. This key, or complex of keys, provides a most necessary tool to assist such studies.