Phytochemical Composition, Toxicity, and effects of Sphenostylis marginata Aqueous Root Extract on Oxygen Consumption Rate in Oreochromis niloticus Fingerlings

Abstract

Introduction: Sphenostylis marginata is a plant in the family Fabaceae and native to many parts of Africa. It is used as a wild vegetable, in folk medicine, as a fetish plant, food additive, and for harvesting fish. Small-scale fishermen in selected parts of Zambia use the crushed roots of this plant to harvest fish for consumption. Published data suggests that phytochemicals present in fish toxins and the lethal concentration have a major role to play in the ability of fish to utilize dissolved oxygen. Phytochemical screening and lethal concentration (LC50) of fish toxins are the initial tests required to discover their bioactive profile and short-term poisoning potential. S. marginata may not only be toxic to fish but other aquatic organisms and possibly humans who consume the fish killed with this toxin. Reports have indicated human deaths due to consumption of fish contaminated with fish toxins around Lake Victoria prompting authorities in affected countries to act against the use of poisons to catch fish, therefore, there is need to investigate the phytochemicals present in this plant as well as its lethal concentration and to inform on the impact of this toxins on the ecosystem and consumers. Objective: To determine the effects of S. marginata on dissolved oxygen consumption rate on Oreochromis niloticus fingerlings. Materials and Methods: An interventional approach was used to determine the effects of different concentrations of the aqueous root extract of S. marginata on dissolved oxygen consumption rate (DOCR) in Oreochromis niloticus fingerlings. The fresh root of S. marginata was collected from the Muchinga escarpment in Mpika district of Zambia while the crude stem methanol extract of the positive control Albizia versicolor was collected from the University of Zambia’s Biology department. The studied plant was examined, identified, extracted, and concentrated using Yamato DC401/801 Neo Cool freeze drier. Phytochemical screening was carried out and toxicity studies were performed to establish the LC50. Dissolved oxygen was measured using a calibrated 86031 AZ waterproof IP67 combo water quality tester for O. niloticus fingerlings in the presence of S. marginata and the positive control. Dissolved oxygen results were used to calculate dissolved oxygen consumption rates. Comparisons of dissolved oxygen consumption rate results between the study plant and the positive control were made using a two-sample t-test for unequal variances in IBM SPSS statistics version 20. Analysis of variance (ANOVA) of temperature, salinity, and pH for both plants were performed. P values less than 0.05 were considered statistically significant. The Least Significant Difference (LSD) was used as a post hoc test to determine where the differences lie in statistically significant results. Results and Conclusion: Phytochemical screening of S. marginata revealed the presence of alkaloids, saponins, sterols, flavonoids, tannins, and glycosides. From experimental results, 200 mg/L of S. marginata was required to cause mortality in 50% of O. niloticus in 3 hours (LC50). Calculations from the arithmetic method of Karber showed the LC50 of 210 mg/L while graphical approximations using RS statistical software estimated a lethal concentration of 221.6 mg/L at ± 15.4 standard error with lower and upper limit of 186.1 and 257.2 respectively. Fingerlings mortality increased with the increase in concentration of the extract accompanied by induced behavioral changes like rapid swimming, gasping for oxygen, vertical swimming, and loss of balance. The study plant affected the ability of O. niloticus fingerlings to utilize dissolved oxygen in a concentration-dependent response and the mean dissolved oxygen consumption rate of S. marginata was significantly lower than the positive control A. versicolor (-0.7075 mg/L/hr. and -0.2675 mg/L/hr. respectively). Both plants did not affect the solution parameters pH, temperature, and salinity.