Moringa oleifera is an indigenous tree growing in Southwestern Nigeria for food and medicinal property. Therefore this study evaluates the preliminary toxicological screening of ichthyotoxic compounds in Moringa oleifera to freshwater fish, Oreochromis niloticus fingerlings. The morphological parts such as leaf, seed, stem-bark, pod (fruit), root-wood and root-bark were subjected to standard phytochemical screening method of plant metabolites. Screening done was just only to identify their presences and not quantify as limited to the current research. The Fresh Root-bark Hot Ethanolic Extract (FRBHEE) was toxicologically tested on fish fingerlings for-1 96hours.Acute toxicity concentrations obtained were 0, 10,17,31,56,100 where 0mgl served as control. The Median Lethal Concentration (LC) for Oreochromis niloticus fingerlings obtained 50-1-1 was 43.09 mgl with 95% upper and lower limit confidence interval between 74.78-28.65 mgl-1 respectively. High mortality was obtained at 100mgl of FRBHEE where fish behavioural changes such as rolling upward, backward swimming, sudden mucus secretion, haemorrhages, stiff fin rays and erratic collision on wall of the tank attested to ichthyotoxic property of FRBHEE. Therefore, ichthyotoxic compounds found in M.oleifera could further be quantified to know the exact grammes it's contained. FRBHEE could serve as organic piscicides in aquaculture pond management to wipe out predators prior to stocking of fish pond with desirable fish species.