Abstract: The contributions of environmental and haematological factors to the distributions and estimations of Eustrongylides africanus larvae densities in Clarias gariepinus and C. anguillaris from Bida floodplain of Nigeria were investigated. The environmental factors making the most important contributions to the distributions of E. africanus larvae infection in Clarias species are rainfall, soil pH, water conductivity, sunshine and silt-clay; in descending order of magnitude; having the manifestation for the months of January, March and June by the year being closely related. The haematological factors making the most important contributions to the distributions of E. africanus larvae infections in the two species are Mean Corpuscular Haemoglobin Concentration (MCHC), Mean Corpuscular Haemoglobin (MCH), Mean Corpuscular Volume (MCV) and neutrophils count, in descending order of magnitude; having the manifestations for the months of January, March, September and December of the year being closely related. Six and five environmental (sand, silt-clay, soil pH, water turbidity, dissolved oxygen and total phosphate content) and haematological (neutrophils, lymphocytes and eosinophils counts; MCH and MCV) factors, respectively, having positive or negative correlation coefficient (r) between 0.50 and 0.85 contributed to the estimations of E. africanus larvae densities in the wild population of Clarias species in Bida floodplain. The relevance of these results in quick estimations of the distribution and density of parasites in fish is discussed.