We assessed the quality of fishermen's local ecological knowledge, or LEK, as a potential source of information about coastal ecosystem functioning in the Republic of Guinea. Interviews were conducted by means of partial immersion or repeated surveys at six landing sites. In each site and for each topic, discussions were conducted with 3 to 15 individual fishermen and 1 to 10 groups of fishermen. Knowledge was obtained about habitats, substrate preferences, the location of nurseries, reproductive cycles, fish diet, and the trophic network of the Sciaenid community, the major resource for fisheries in this area. We systematically compared the reliability of the information collected with that of scientific information collected in parallel surveys or published data. The contribution of LEK should be considered on a case-by-case basis. Indeed, LEK could be used as (i) a supplementary source of scientific studies (seabed description), (ii) a basis for new scientific investigation (species reproductive cycle), (iii) the only possibility to obtain information (nursery location), (iv) a surrogate to scientific surveys providing an identical level of validity (fish diets) or a satisfactory proxy (trophic network) in a context of limited resources and data in which wide-ranging knowledge relating to the entire coast must be obtained.