Sources and uptake of trace metals in otoliths of juvenile barramundi (Lates calcarifer)

We conducted an experiment to determine if the concentrations of three trac e metals (Cu, Sr, and Ph) in the otoliths of juvenile barramundi (Lates cal carifer) were related to their concentrations in the water or diet. Fish we re kept in freshwater aquaria for 22 days and either fed diet enhanced with 10 mug g(-1) Cu, Sr or Pb, or had 10 mg l(-1) (Sr and Pb) or 0.5 mg l(-1) Cu added to the water. A control group were then transferred to seawater an d maintained for a further 83 days. The otoliths were initially ablated for five trace metals (Li, Cu, Sr, Ba and Ph) with LA-ICPMS. Ablation interval s corresponded to between 7 and 11 days of growth. There was no detectable increase in the otolith concentration of any metal for the fish in the enha nced-diet treatments. There was significant uptake of the three metals adde d to the water (Cu, Sr and Pb). Three (Sr and Pb) or six fish (Cu) were rea nalysed with the ICPMS in high-sensitivity mode enabling 5 mum wide ablatio ns to be made at intervals equal to every day or second day during the expe riment. These analyses showed that there was considerable variation in upta ke rate among individual fish and that the concentration fluctuated widely before an equilibrium concentration was reached after about two weeks expos ure. Analysis of the otoliths of the control group of fish that were transf erred to seawater showed that the concentration of Li, Sr and Ba in the oto liths varied between the periods of fresh and seawater residency. These var iations were related to changes in the concentration of these metals in the water. The fluctuations in Sr concentration were similar to those seen in wild diadromous fish and not as great as those measured in the fish kept in Sr-enhanced water. Sr concentration in the otoliths was strongly negativel y correlated with Ba concentration in the experimental fish, but not in wil d fish that migrate from the sea into freshwater. Sr/Ca, Ba/Ca and Cu/Ca ra tios in the otoliths were positively correlated with water ratios. The part ition coefficients of Sr and Ba were similar to published values for marine fish. The concentrations of Li and Pb in the water were below the detectio n limit in some treatments so no comparisons could be made for these metals . When taken in conjunction with the results of other recent studies of tra ce metal uptake in otoliths. our data indicate that under experimental cond itions, otolith concentrations of several trace metals are related to water concentrations. However, these patterns do not simply extrapolate to the n atural environment where the mechanisms involved appear to be more complex. (C) 2001 Elsevier Science B.V. All rights reserved.