Mineral content of muscle tissue of rainbow trout (Oncorhynchus mykiss Walbaum)

Fish are most often considered as a rich source of valuable fat, although sometimes the high quality of fish meat protein is also emphasized, but there is comparably little information on the mineral composition of fish meat. Chemical composition, caloric value and health safety of fish as food depend on many factors, of which the rearing conditions are most influential. Aside from environmental conditions, production technology is a major determinant of the quality and nutritional value of trout. In this study, the influence of a farming technology on the content of minerals in the muscle tissue of rainbow trout (Oncorhynchus mykiss Walbaum) netted in various Polish regions has been assessed. Fish were caught in autumn 2010 and 2011 and spring 2011, at 3 farms with a water flow-through system and 3 farms with water recirculation. The trout muscle tissue contained: 188.4 - 518.4 mg kg-1 of calcium, 306.9 - 338.1 mg kg-1 of magnesium, 464.0 - 718.2 mg kg-1 of sodium, 4.5 - 6.9 mg kg-1 of zinc, 2485.7 - 2823.6 mg kg-1 of phosphorous, 4261.2 - 4615.4 mg kg-1 of potassium, 3.0 - 9.4 mg kg-1 of iron and 0.09 – 11.74 mg kg-1 of copper. The farming technology influenced the content of calcium, sodium, zinc, iron and copper but had no effect on the content of magnesium, phosphorous and potassium in rainbow trout muscle tissue. Trout farmed in water recirculation systems contained higher amounts of most elements than the fish reared in water flow-through systems. The season of sample collection (date of netting) also affected the content of sodium, zinc, phosphorus, iron and copper. The fish farming site (localization of the farm) determined the content of most of the minerals except magnesium. Rainbow trout is a good source of phosphorous and potassium in a human diet, significantly covering the daily demand for the elements.