Variability of Selected Mineral Contents in Marine Fish from Local Markets in Tanzania

Abstract

Mineral contents (K, Na, Ca and Mg) in selected marine fish species (Alectis ciliaris, Lethrinus harak, Rastrelliger kanagurta and Siganus canaliculatus) from local fish markets were analysed in wet and dry seasons. The processing methods (frying and boiling) were also assessed for their influence on the mineral contents. Samples were randomly collected from Tanga, Bagamoyo, Dar es Salaam and Mtwara seaports, analysed using established methods and determined by Graphite Furnace Atomic Absorption Spectrometry. Mean mineral contents in individual and all analysed fish species were high during dry season compared to wet season except Ca and the difference was statistically significant (p < 0.05). Mean K, Na and Mg contents in all fish were decreasing after processing (raw > fried > boiled), while those of Ca were similar. Mineral contents in all fish species between raw and frying as well as between raw and boiling processing methods varied significantly for K only. Variation of mineral contents in all fish species between frying and boiling was not significant. Pearson correlations and Principal component analyses have indicated significant close relationships between minerals (except Ca) and seasonal variations. In addition, significant relationship between processing methods and K mineral only was observed. Derived models have accurately predicted variations of mineral contents due to seasons and variations of K content due to processing methods. Further research is required to determine effects of using steaming and microwaving on mineral contents and what factors control variations of Ca, Na and Mg using frying and boiling in these fish species.

Keywords: Marine fish; wet season; processing methods; Siganus canaliculatus; frying