Transfer of Cd, Cr and Zn from zooplankton prey to mudskipper Periophthalmus cantonensis and glassy Ambassis urotaenia fishes

Assimilation efficiency (AE) of metals from ingested food is critical for u nderstanding trace metal accumulation and trophic transfer in aquatic anima ls. Most recent measurements of metal AEs have been on aquatic invertebrate s. whereas relatively few studies have examined metal assimilation in fishe s. In this study we determined the AEs of Cd, Cr and Zn in 2 fishes (pelagi c glassy Ambassis urotaenia, Ambassidae, and the intertidal mudskipper Peri ophthalmus cantonensis, Gobiidae) feeding on 2 zooplankton prey (brine shri mp Artemia larvae and copepods). Zooplankton were radiolabeled either by fe eding on radiolabeled phytoplankton or by direct exposure to radiotracers i n the dissolved phase. Fishes were then fed with radiolabeled zooplankton p rey for <1 h, and the retention of ingested metals in the fishes was follow ed for 2 d. The measured AEs of Cd, Cr and Zn were 14 to 33, 4 to 12, and 5 to 17 % in glassy fish, and 10 to 26, 4 to 19, and 11 to 31 % in mudskippe r, respectively. Routes of radiolabeling in copepod prey did not affect met al AEs in either mudskipper or glassy, whereas metal AEs differed by up to 10-fold in glassy fish feeding on Artemia larvae labeled from different rou tes. There was little difference in the gut passage time of metals for diff erent food types and metals or between fishes. AE was not significantly rel ated to metal gut passage time or metal distribution in the soft tissues of zooplankton prey, for each metal. However, AE in mudskippers was significa ntly correlated with metal distribution in the prey's soft tissues when all 3 metals were considered. Our study demonstrated that marine fishes can ap preciably assimilate trace metals. and trophic transfer should be considere d as a source for metal accumulation in fishes.