An investigation of fishermen€™s knowledge of fish occurrence patterns on various spatio-temporal scales has been realized in the Fatala Estuary (Guinea, West Africa), accompanied by a one-year survey with standardized gill-net sets. Seventy one fishermen distributed in four zones corresponding to gill-net sampling sites were questioned about seasonal variations of species€™ relative abundances. Longitudinal and seasonal patterns of fish relative abundances were described with correspondence analysis and ANOVA for both approaches. Comparison of results showed a good coherence between fishermen€™s answers and gill-net sampling results. Thus, it is proposed that investigation of fishermen€™s ecological knowledge should be used as a preliminary study to help defining fish sampling designs in tropical rivers and estuaries.