Introduction: One of the most commonly used methods of waste management is landfilling, which has been a major environmental concern. Objective: To examine the effect of leachate on Clarias gariepinus. Methods: We tested Clarias gariepinus (n=700) with varying concentrations of leachate (0, 10, 15, 20 and 25%) from the Amoyo dumpsite, Ilorin, Nigeria. After 28-day exposure, haematological, biochemical, bacteriological and histopathological assays were carried out. Results: pH ranged from 7,78 to 13,97; cadmium, iron, lead, manganese and zinc were 178-, 134-, 6248-, 400-and 3-fold, respectively, higher than the regulatory limits for waterbodies, while copper fell within the limits. Values of red blood cell, haemoglobin, packed cell volume, mean cell volume, mean cell haemoglobin, mean cell haemoglobin concentration, lymphocytes and monocytes were significantly lower than the control. Conversely, white blood cell, neutrophils and eosinophils increased in a concentration-dependent manner. There were tissue-specific differences in the responses of all biochemical parameters investigated except for protein that significantly decreased in all the tissues. 27 bacterial isolates classified into seven genera including Bacillus, Klebsiella, Pseudomonas, Staphylococcus, Acinetobacter, Escherichia and Micrococcus were recorded from the leachate and selected organs of C. gariepinus. The total bacterial, viable coliform and total counts in the leachate were 4,2×10 6 CFU/mL, 3,8×10 8 CFU/mL, 3,6× 10 6 CFU/mL and 2,7×10 8 CFU/mL, respectively. The highest counts were recorded in the gills (14,2×10 6 CFU/mL) and lowest in the muscle (2,7×10 6 CFU/mL) at the highest and least concentration of the leachate, respectively. Most of the bacteria isolated from the leachate were also recovered from the fish organs. Escherichia coli had the highest frequency of occurrence (26%). Conclusion: This study revealed that toxic constituents of the leachate elicited deleterious changes in the bacteriology and physiology of C. gariepinus. RESUMEN: "Perfil fisiológico y bacteriológico del pez Clarias gariepinus (Siluriformes: Clariidae) expuesto crónicamente a diferentes concentraciones de lixiviados de residuos municipales en Nigeria". Introducción: Uno de los métodos más utilizados para el manejo de residuos es el relleno sanitario, que ha sido una preocupación ambiental importante. Objetivo: Examinar el efecto del lixiviado sobre Clarias gariepinus. Métodos: Analizamos especímenes de Clarias gariepinus (n=700) con concentraciones variables de lixiviado (0, 10, 15, 20 y 25%) en el vertedero de Amoyo, Ilorin, Nigeria. Después de 28 días de exposición, se realizaron ensayos hematológicos, bioquímicos, bacteriológicos e histopatológicos. Resultados: El pH varió de 7,78 a 13,97; cadmio, hierro, plomo, manganeso y zinc fueron 178, 134, 6 248, 400 y 3 veces, respectivamente, más altos que los límites regulatorios para cuerpos de agua, mientras que el cobre cayó dentro de los límites. Los valores de glóbulos rojos, hemoglobina, volumen de células empaqu...