Assimilation and retention of metals in teleost and elasmobranch fishes following dietary exposure

In a radiotracer study designed to evaluate the fate of metals from fish prey to predator fish, we measured the trophic transfer of 7 trace elements (Am, Cd, Co, Cr, Cs, Mn, Zn) from juvenile Mediterranean sea bream Sparus auratus to 3 predator species, the teleosts Psetta maxima and Sparus auratus, and the elasmobranch Scyliorhinus canicula. Prey S. auratus were labeled by exposure to metal radioisotopes in solution for a period of 3 wk and were then fed to predators, after which the metal retention in the predator was assessed. Mean assimilation efficiencies (AEs) of ingested metals in the predator fishes ranged from 6 to 15% for Am, to 63 to 74% for Cs; significant differences in AEs were noted between species for Co and Mn only. Efflux rate constants (k_e) of assimilated metal did not differ consistently among predators for any metals. The mean k_e ranged from 0.003 d^-1 for Mn in S. canicula to 0.02 d^-1 for Cd and Cs in all 3 species and for Co in S. canicula. Trophic transfer factors (TTF) for each metal were determined in predator fishes to assess the potential for metal biomagnification. TTF, calculated by dividing the product of metal AE and ingestion rate (IR) by k_e, exceeded 1 only for Mn, Zn and Cs. For most likely scenarios of IR and AE, TTF was <1 for these metals, suggesting that these metals will not biomagnify in piscivorous fishes.