Levels of total mercury in the muscle (29 samples) and liver tissue (15 samples) of bluefin tuna (<i>Thunnus thynnus</i>) weighing 100&minus;300 kg were determined by cold vapour atomic absorption (AA) spectroscopy. Tunas were previously captured in the waters of Malta, towed to the farm in the Adriatic Sea and fattened with defrosted herring and sardine for the period of 6 to 7 months. The purpose of the investigation was to determine the magnitude of mercury contamination and to ascertain whether the concentrations in muscle tissue exceeded the maximum level defined by the European Commission Decision (1 &mu;g/g wet weight). Total mercury concentrations in the muscle tissue of tunas ranged from 0.49 to 1.809 (median 0.899 &mu;g/g wet weight) while in the liver tissue it was from 0.324 to 3.248 (median 1.165 &mu;g/g wet weight). Total mercury concentrations in six samples of sardine ranged from 0.050 to 0.072 &mu;g/g wet weight while two samples of herring contained 0.020 and 0.053 &mu;g/g wet weight. Twelve out of 29 (41%) muscle samples of tuna contained mercury above the maximum level defined by the European Commission Decision. It is generally believed that mercury levels in Mediterranean fish are higher than those of the other seas or oceans due to numerous deposits of mercury ores and metallic mercury in surrounding countries.

The concentrations of cadmium, lead and zinc were determined in the soft tissue of oysters (<i>Ostrea edulis</i> L.) from three locations in the Mali Ston Bay on the south-eastern coast of the Adriatic Sea. The sampling was performed during two periods of breeding cycle, in summer (age ~1 year) and winter (age ~20 months, consumption size). The concentrations of cadmium, lead and zinc measured in the oyster soft tissue showed considerable spatiotemporal variations that could be attributed to seasonal differences in the freshwater inflow which varied between the study locations. Median concentrations measured at different locations and in different time periods ranged from 0.303 to 0.969, 0.13 to 0.32 and 208.9 to 650.0 µg/g wet weight for cadmium, lead and zinc, respectively. Although metal concentrations do not exceed the maximal legally approved limits according to the legislation of the Republic of Croatia and EU, more knowledge of their spatiotemporal distribution – of cadmium in particular – would contribute to the sustainable future development of oyster farming in Croatian waters.

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