Heavy metal analyses and nutritional composition of raw and smoked fishes from Ologe and Lagos Lagoon, Lagos, Nigeria

Abstract

This study was conducted to evaluate nutritional composition and heavy metals concentration of smoked and raw edible fish species from Ologe lagoon (freshwater) and Lagos lagoon (marine). The fish species from Ologe include: Chrysichthys nigrodigitatus (Catfish), Monodactylus sebae (African moony), Pomadasys jubelini (Buro), Sphyraena barracuda (Great barracuda), and Pseudotolithus elongatus (Croaker), while that of Lagos lagoon include Chrysichthys nigrodigitatus (Catfish), Caranx hippos (Crevalle jack), Liza falcipinnis (Sicklefin mullet), Pomadasys jubelini (Buro), and Monodactylus sebae (African moony). The nutritional composition ranged in the following trend moisture (43.24 - 76.79 %) > carbohydrate (3.16 – 63.45 %) > protein (0.80 - 31.55 %) > fibre (1.07 – 2.8 %) > ash (0.81 – 1.88 %) > fat (0.40 – 1.30 %). In this study, these fishes are generally low in fats (lean fish), and fish smoking tend to reduces their nutritional composition. Heavy metals concentration trend thus Zn (2.4 – 7.75 mg/kg) > Ni (0.80 – 1.925 mg/kg) > Cr (0.20 – 0.550 mg/kg) > Pb (0.025 – 0.50 mg/kg). In all the samples, all the metals of interest were detected except cadmium which was not found in any of the samples analysed. Pb (0.025 - 0.5 mg/kg) values in the fishes were lower than the maximum standard level reported to be 0.5 mg/kg dry weight by FAO except in the raw Pomadasys jubelini where the value is 0.5mg/kg. The fresh water fishes showed higher concentration of heavy metals than marine water fishes but not statistically significant (p>0.05). Although, smoked fishes showed higher concentration of heavy metals than the raw fishes, it was only significant for zinc (p<0.05). In view of this study and the importance of fish in human diet, it is recommended that biological monitoring of fishes meant for consumption from these two water bodies be carried out regularly to ensure human safety.

Keywords: Nutritional composition, heavy metals, fresh water fishes, marine water fishes, lagoons