Can the movements of barramundi in the Fly River region, Papua New Guinea be traced in their otoliths?

To determine whether the concentrations of heavy metals in fish otoliths co uld be used to infer the fish's movement into water contaminated by heavy m etals, we collected barramundi Lates calcarifer from two sites below the ou tfall from a large copper mine. It was first demonstrated that otolith Sr c oncentration could be used to separate the marine and freshwater life phase s. Twelve elements were then examined (in particular Cu, Mn, Zn, Cd and Pb) in the otoliths by laser-ablation inductively coupled plasma mass spectrom etry (LA-ICPMS). Cadmium concentrations were rarely above the detection lev el of the instrument. There were low concentrations of Cu in the otoliths o f most fish during the freshwater phase of their life history. Three fish o ut of 10 had higher levels of Cu at some ablations, coinciding with higher concentrations of both Zn and Pb. However, further analysis found no correl ation between the Cu concentration of replicate ablations in the same growt h zone to those with initially higher Cu values. Copper concentration in th e otoliths did not rise during the period the fish were in freshwater, desp ite the concentration of dissolved Cu in the water being several times grea ter than in the lower estuary and adjacent coast. These results and other data from recent studies of heavy metals in fish ti ssues suggest that very little of the dissolved Cu in the Fly River is in t he form of free ions that can be adsorbed across the gills and into the blo od and the otoliths. It can be concluded that otoliths are not a good indic ator of the history of barramundi movements into water contaminated with he avy metals. Our data support recent studies that suggest that the concentra tion of many elements, such as Cu, may vary in the endolymph around the oto lith and thus may be attached to the calcium-binding proteins that form the matrix around the aragonite. Hence, high concentrations of heavy metals in some ablations may be related to the relative amount of aragonite and prot ein in each ablation rather than reflect environmental differences.