Phytochemical Composition and Acute Toxicity of Aqueous Stem Bark Extract of Adenium obesum in African Catfish (Clarias gariepinus)
Keywords:
Adenium obesum, phytochemical screening, African CatFish, Acute toxicity, Behavioural responsesAbstract
The continued use of botanical piscicides for artisanal fishing has generated increasing concern regarding their potential impacts on non-target aquatic organisms. Adenium obesum (Forssk.) Roem. & Schult. is a well-known indigenous piscicidal plant in many parts of Africa due to its rich phytochemical composition. However, scientific information linking its phytochemical constituents with its acute toxicity in economically important freshwater fish remains limited. This study investigated the phytochemical composition and acute toxicity of the aqueous stem bark extract of A. obesum in juvenile of Clarias gariepinus. Fresh stem bark of A. obesum was collected, processed, and extracted using distilled water. Qualitative phytochemical screening was conducted using standard analytical methods to identify the major secondary metabolites present in the extract. Acute toxicity was evaluated using a 96-hour static bioassay in which juvenile C. gariepinus were exposed to six concentrations (0.0, 6.5, 8.0, 9.5, 11.0, and 12.5 mg/L) of the aqueous stem bark extract of A. obesum. Behavioural responses and mortality were recorded throughout the exposure period, and the 96-hour median lethal concentration (LC₅₀) was estimated by probit analysis. Proximate analysis showed that the stem bark contained predominantly nitrogen-free extract (54.62%), followed by crude fibre (21.34%), crude protein (9.10%), ash (7.75%), moisture (5.65%), and crude lipid (1.54%). Qualitative phytochemical screening revealed the presence of alkaloids, saponins, steroids, flavonoids, terpenes, and tannins, indicating that the extract is rich in biologically active secondary metabolites. Fish exposed to the extract exhibited concentration-dependent behavioural alterations, including erratic swimming, increased opercular movement, excessive mucus secretion, loss of equilibrium, air gulping, reduced swimming activity, and respiratory distress. Mortality increased progressively with increasing extract concentration, while no mortality was observed in the control group. The estimated 96-hour LC₅₀ was 6.31 mg/L, indicating that the aqueous stem bark extract possesses high acute toxicity toward juvenile C. gariepinus. The aqueous stem bark extract of A. obesum contains diverse bioactive phytochemicals that are likely responsible for its pronounced ichthyotoxic activity. The concentration-dependent behavioural abnormalities and relatively low 96-hour LC₅₀ demonstrate that the extract is highly toxic to juvenile African catfish. These findings provide scientific evidence supporting the traditional use of A. obesum as a botanical piscicide while highlighting the potential ecological risks associated with its indiscriminate use in freshwater ecosystems. The study contributes valuable baseline information for environmental risk assessment and the sustainable management of inland fisheries.
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