Distribution of trace elements in muscle and organs of Tilapia, Oreochromis niloticus, from lakes Awassa and Ziway, Ethiopia

Abstract

Samples of Tilapia, Oreochromis niloticus, were collected from Lakes Awassa and Ziway during December 2002–March 2003. The moisture content of freeze-dried organs (muscle, bone, gill and liver) collected from six sites ranged between 76.0 and 80.7% (m/m). An optimal procedure required 12 mL of tertiary mixture consisting of HNO₃, HClO₄, and H₂O₂ to mineralize powdered samples in open refluxed digestion vessels: 1.0 g bone or muscle, 0.5 g gill or liver. The concentrations of 8 elements in muscle, bone, gill and liver determined by flame atomic absorption spectrophotometer varied, respectively, (mg element/kg dry mass): Cd 0.44–1.43, 4.58–4.93, 2.20–2.85, and 1.08–1.90; Co 2.47–3.59, 17.1–18.9, 8.28–10.1, and 10.2–13.0; Cu 1.68–4.95, 6.65–7.58, 7.08–8.58, and 602–797; Fe 18.7–53.0, 81.9–94.3, 120–196, and 635–7139; Mn 1.03–6.78, 23.1–146, 26.1–107, and 8.80–24.5; Ni 7.80–15.9, 64.1–71.0, 34.8–42.4, and 14.1–21.3; Pb 1.65–2.69, 39.5–42.3, 17.1–23.1, and 2.20–3.37; Zn 34.6–38.6, 61.9–78.8, 82.3–97.1, and 85.6–115.9. Results revealed organ specific distribution of trace metals in Tilapia, which has been discussed in terms of physiological role in fish and/or the likely influence of anthropogenic origin on lakes. Application of the statistical t-test on trace elements data further showed significant difference between the two lakes, which could be attributed to anthropogenic influences.

KEY WORDS: Tilapia, Oreochromis niloticus, Distribution of trace elements in fish, Water pollution, Lake Awassa, Lake Ziway

Bull. Chem. Soc. Ethiop. 2004, 18(2), 119-130.