RETENTION OF ELEMENTS ABSORBED BY JUVENILE FISH (MENIDIA-MENIDIA, MENIDIA-BERYLLINA) FROM ZOOPLANKTON PREY

Radiolabeled copepods (Acartia spp.) were fed to juvenile silversides (Menidia menidia and Menidia beryllina) to study element absorption in the fish. Copepods were reared from nauplii in the presence of different radiotracers (C-14, Cd-109, Co-57, P-32, S-35, Se-75, or Zn-65) and were analyzed for relative concentrations of these elements in their tissue fractions. Copepod exoskeletons contained nearly all of the trace metals (>97%), 60% of the Se, and less than half of the C, P, and S accumulated by the copepods. Within the nonexoskeleton tissues of the copepods, nonpolar (CHCl3 extractable) material contained 34 and 24% of the total C and P, but only 8 and 2% of the total S and Se Absorption efficiencies of trace metals in juvenile silversides (2.7% for Cd, 2.1% for Co, 6.2% for Zn) were an order of magnitude lower than those for nonmetals (29% for Se, 50% for S and C, 60% for P). The absorption efficiencies in the juvenile silversides of all seven elements studied were directly related to the percent of each element in the nonexoskeleton fraction of the copepod prey, indicating that the fish absorbed the soft tissues of the copepods and egested the chitinous exoskeleton and its associated elements.