The indiscriminate use of plant-derived piscicides in artisanal fisheries has raised concerns regarding their potential adverse effects on non-target aquatic organisms. This study evaluated the effects of sublethal concentrations of aqueous crude bark extract of Albizia gummifera on water-quality parameters and oxidative stress biomarkers in Clarias gariepinus juveniles. A total of 80 acclimatised juveniles (mean weight 20.66 ± 1.64 g; mean length 13.96 ± 0.38 cm) were randomly assigned to four treatment groups exposed to 0.00 (control), 0.10, 0.20 and 0.30 g L⁻¹ of the extract under a static-renewal bioassay. Water-quality parameters, including temperature, pH, electrical conductivity, total dissolved solids, salinity, alkalinity, general hardness and dissolved carbon dioxide, were monitored throughout the exposure period. Oxidative stress biomarkers comprising superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), reduced glutathione (GSH) and malondialdehyde (MDA) were analysed in the liver, gills, testes and ovaries. Data were analysed using one-way analysis of variance (ANOVA) at a significance level of P < 0.05. Among the measured water-quality variables, only alkalinity differed significantly (P < 0.05) among treatments, whereas temperature, pH, salinity, electrical conductivity, total dissolved solids, general hardness and dissolved carbon dioxide remained statistically comparable with the control. Exposure to A. gummifera crude bark extract elicited tissue-specific antioxidant responses. In the liver, GPx and CAT activities increased with increasing extract concentration, while MDA generally declined, suggesting activation of antioxidant defense mechanisms. Gill tissues exhibited variable antioxidant responses, reflecting their direct exposure to dissolved phytochemicals. Marked increases in SOD and CAT activities were observed in the testes at higher exposure concentrations, indicating enhanced oxidative stress responses. In the ovaries, elevated MDA concentrations and reduced CAT activity at the highest concentration suggested increased lipid peroxidation and oxidative challenge. Overall, antioxidant biomarkers responded more sensitively to the extract than conventional water-quality parameters. The study demonstrates that sublethal exposure to aqueous crude bark extract of Albizia gummifera disrupts redox homeostasis and induces tissue-specific oxidative stress in Clarias gariepinus juveniles despite causing minimal changes in general water chemistry. These findings highlight the potential ecological risks associated with the indiscriminate use of A. gummifera as a traditional piscicide and support the use of oxidative stress biomarkers as sensitive indicators for monitoring sublethal toxicity in freshwater ecosystems.