The relative acute toxicity and sub-lethal effects of two surfactants; Faab liquid soap (FLS) and Morning Fresh liquid soap (MFLS) were evaluated for the Poecilia reticulata in laboratory bioassays. The acute toxicity was evaluated for 96 h while the sub-lethal effects of the two surfactants on the biochemical parameters of P. reticulata were investigated for a 6–day exposure period. The derived toxicity indices showed that the FLS (96hLC
50= 0.062ml/L) was 1.37 times more toxic than the MFLS (96hLC
50= 0.085ml/L) against P. reticulata. Analysis of variance (ANOVA) showed significant difference (p<0.05) in the quantal response of P. reticulata to different concentrations of FLS and MFLS at 24, 48, 72 and
96 h of exposure. The mean tissue protein, triglyceride, glucose and cholesterol ranged from (21.04 - 48.54 and 18.06 - 58.54mg/dl), (87.43 - 154.95 and 85.63 - 144.28mg/dl), (33.95 - 55.03 and 32.76 - 53.15mg/dl) and (37.30 - 65.38 and 37.12 - 58.11mg/dl) for FLS and MFLS respectively. ANOVA showed significant difference (p<0.05) in the biochemical response of P. reticulata to FLS and MFLS. The implications of these findings are highlighted.