Seasonal Levels of Essential Metals in Fresh and Fried Marine Shrimp and Fishes from Lagos Lagoon, Nigeria

Transition metals are essential for health, forming integral components of proteins involved in all aspects of biological function. However, in excess these metals are potentially toxic, and to maintain metal homeostasis organisms must tightly coordinate metal acquisition and excretion. The diet is the main source for essential metals, but in aquatic organisms an alternative uptake route is available from the water. The levels of Zinc, Iron and Manganese accumulation in marine fish, shrimp and water were investigated in this study to cover the two major seasons in Nigeria. Water and samples of fish and shrimps were pooled weekly for five weeks between November and December 2007 during the dry season and repeated in April 2008 during the rainy season and analyzed using standard methods. The results obtained showed that the levels of bioconcentration of Zinc, Iron and Manganese in shrimp and fish were significantly higher than the levels of accumulation in water. The result also revealed temporal differences, with higher bioconcentration values observed during the rainy season. The highest bioconcentration of trace metal detected was Zinc, in fried fish (15.7 mg/l) and fried shrimp (11.1 mg/l). However, the value of Zinc is lower than the FAO recommended limits (30 mg/kg), although its relatively high level suggests a high bioavailability of the heavy metals in the studied water body.