<b>Distribution of trace elements in muscle and organs of Tilapia, <i>Oreochromis niloticus</i>, from lakes Awassa and Ziway, Ethiopia</b>

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.