Trace metal concentrations in deep sea fish from the North Atlantic

Specimens of six species of continental slope fish (17 orange roughy Hoplostethus atlanticus, 84 roundnose grenadier Coryphenoides rupestris, 37 roughhead grenadier Macrourus berglax, 27 Mediterranean grenadier Coryphenoides [Chalinura]mediterranea, 25 spear-snouted grenadier Coelorhyncus labiatus and five armed grenadier Coryphenoides [Nematonurus] armatus), were collected between 1987 and 1995, and their muscle tissue subsequently analysed for mercury, lead, cadmium, copper and zinc. The early samples were collected in the Rockall Trough area by the research vessel Challenger. The 1995 samples were obtained from commercial landings at Lochinver fishing port by fishing vessels which had been operating on the Hebridean Continental Slope, in ICES areas 43E0, 44E0, 45E0, 46E1, 47E3 and 48E3. Sub-samples of the muscle tissue of individual fish whose ages ranged from 3 to > 70 y, were analysed for the above trace metals using atomic absorption spectrophotometry, following nitric acid digestion. The mean mercury concentrations in all species were below 0.5 mg/kg, ranging from a mean value of 0.06 mg/kg in roundnose grenadier to 0.42 mg/kg in orange roughy. However, individuals from three of the six species were found to have concentrations greater than 0.5 mg/kg but less than 1.0 mg/kg (orange roughy up to 0.86 mg/kg, roughhead grenadier 0.89 mg/kg and armed grenadier 0.65 mg/kg). In all species, concentrations of mercury were found to increase with both age and length. Mean concentrations in shallow water commercial fish species are normally less than 0.1 mg/kg, although some long-lived fish predators can contain 1 mg/kg or more. The ranges of mean concentrations of zinc (2.2–6.7 mg/kg), copper (0.01–0.47 mg/kg) and cadmium (0.002–0.02 mg/kg) for all species were similar to those observed in commercially exploited shallow water marine fish landed at Scottish ports, although some of the lead concentrations (means 0.004–0.72 mg/kg) were rather higher. In Mediterranean grenadier, the concentrations of copper, zinc, cadmium and lead decreased with increasing length/age offish. Although this was also observed in orange roughy, the relationships were not as significant as those in the Mediterranean grenadier.