Life on the bottom: the chemical and morphological asymmetry of winter flounder ( Pseudopleuronectes americanus) sagittae.

We observed that paired winter flounder ( Pseudopleuronectes americanus) sagittae are not morphologically or chemically identical. Statistically significant ( p < 0.05) chemical asymmetry was detected between the sagittae in five of eight elements (with three other elements, Sr, I, and Sn not statistically different). The blind-side otolith exhibited higher mean concentrations of Ba, Mn, Mg, Cu, and Zn trace elements than the eyed-side otolith. These asymmetries may be due to blind-side otoliths absorbing higher concentrations of transitional elements, partly as a result of environmental heterogeneity caused by redox reactions emanating from the sediments. Metamorphic transformation and the subsequent shift to the benthos by fully formed fish may also account for element concentration levels that were significantly different between juveniles and both sub-adults and adults. Our results also suggest that chemical uptake in a pair of winter flounder sagittae is an asynchronous event, and that each otolith potentially records the chemical history of its environment independent of the other. The physiological pathway for entry into winter flounder otoliths is uncertain and warrants further testing. Overall, our results have implications for other flatfish genera as well, and demonstrate the need for standardization of methodology when conducting otolith chemistry on flatfishes. [ABSTRACT FROM AUTHOR]