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

Abstract

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.

Intraspecific comparisons of metal bioaccumulation in the juvenile Atlantic silverside Menidia menidia

“…Zn tissue partitioning was split mainly between the head and body after an aqueous exposure, and primarily associated with the head after a dietary exposure. Our tissue distribution data is consistent with other studies looking at either aqueous or dietary uptake of Zn (Baines et al 2002, Mathews et al 2008. Zn is a borderline metal (Nieboer & Richardson 1980) with some association for both the mineral and protein phase, and therefore could be expected to bind to both bone in the head region and protein within body tissue.…”

“…Our k ew values for Am, Cd, Hg(II), MeHg, and Zn are similar to those determined in other studies (Wang & Wong 2003, Pickhardt et al 2006, Mathews et al 2008). However, our values for Am, Cd, and Zn are higher than those for turbot (Jeffree et al 2006).…”

“…Except for Hg(II) after dietary exposure, and Cd after aqueous exposure, the tissue partitioning of each metal did not vary between the 2 populations after either aqueous or dietary exposure, indicating that both populations physiologically processed metal in the same way. After aqueous exposure, Am was mainly associated with the head (64 to 69%), consistent with what has been observed in other studies (Jeffree et al 2006, Mathews et al 2008. Am is a Class A metal (Nieboer & Richardson 1980), with a strong binding preference to the mineral phase within organisms.…”

“…Wang & Wong (2003) noted that during the first 7 d of metal loss in fish, Hg(II) efflux rates were higher after both dietary and aqueous exposures, and decreased significantly between 9 and 28 d of metal loss (k ef decreased from 0.096 to 0.055 d ). Our Cd and Zn efflux rates were higher than those noted for larger, more mature sea bream and turbot fed fish prey (Mathews et al 2008), suggesting that size influences the loss of assimilated metal. This is consistent with the findings of Baines et al (2002) …”

“…After aqueous exposure, the highest percentage of Cd was associated with the viscera in Nova Scotia silversides, and the body in South Carolina silversides, but the highest Cd concentration was in the viscera for both populations. Other studies have also noted a high percentage of Cd associated with the viscera in marine fish (Jeffree et al 2006, Mathews et al 2008, but this percentage decreases throughout depuration indicating a redistribution of Cd over time. Marine fish actively drink seawater to osmoregulate, and a study has shown that even though aqueous Cd accumulation decreases with an increase in salinity, the percentage body burden of Cd associated with the viscera increases with salinity, suggesting drinking is an uptake mechanism for Cd in marine fish (authors' unpubl.…”