Comparison of intracellular trace element distributions in the liver and gills of the invasive freshwater fish species, Prussian carp (Carassius gibelio Bloch, 1782)

Prussian carp (Carassius gibelio) is an invasive freshwater fish known for its high tolerance to aquatic pollution. Our aim was to try to clarify its tolerance to increased exposure to metals/nonmetals, by determining their cytosolic distributions among peptides/proteins of different molecular masses (MM), which form a part of the fish protective mechanisms. The applied approach consisted of fractionation of gill and hepatic cytosols of Prussian carp from the Croatian river Ilova by size-exclusion high performance liquid chromatography, whereas Cd, Cu, Zn, Fe, Mo, and Se analyses were done by high resolution inductively coupled plasma mass spectrometry. The results indicated high detoxification of Cd by its binding to metallothioneins (MTs) in both fish organs. In addition, binding to MTs was observed for Cu in both organs and for Zn in the liver, whereas clear Zn binding to MTs in the gills was not recorded. Zinc in the gills was predominantly bound to proteins of higher MM (50–250 kDa) and to biomolecules of MM below 2 kDa. Predominant Fe binding to proteins of MM of ~400 kDa (presumably storage protein ferritin) was observed in the liver, whereas in the gills Fe was mainly associated to proteins of MM of ~15–65 kDa (presumably hemoglobin oligomers). Maximum Mo and Se elutions in the liver were noted at 235 kDa and 141 kDa, respectively, and in the gills below 10 kDa. The striking difference was observed between two organs of Prussian carp, with predominant metal/nonmetal binding to high MM proteins (e.g., enzymes, storage proteins) in the liver, and to very low MM biomolecules (<10 kDa) in the gills (e.g., antioxidants, metallochaperones, nonprotein cofactors). Such metal/nonmetal distributions within the gills, as the first site of defense, as well as association of several metals to MTs, indicated highly developed defense mechanisms in some organs of Prussian carp.