Comparative study of trophic transfer of the essential metals Co and Zn in two tropical fish: a radiotracer approach

The trophic transfer of two essential metals (Co and Zn)was investigated in twotropical euryhalinefish species (Monodactylus argenteus and Scatophagusargus), at both the adult and juvenilestages, using the pulse-chase feeding method and radiotracers ( 57 Co and 65 Zn).The food selected wasbrine shrimp (Artemiasalina) previously exposed to dissolved radiotracers. Depuration kinetics of both elements were followed for 45d. During this period, 57 Co and 65 Zn distribution was also determined at different time intervals among 15 different body compartments. Results showed that, in juveniles, the ingested Co was poorly assimilated by both species (AE <6%), whereas S. argus assimilated 65 Zn more efficiently than M. argenteus(AE= 24% vs. 15%). In terms of bodydistribution of these essential elements, the trends were similar between adults and juveniles of both species:Co was concentrated and mainly distributed in the liver in S.argus,highlighting the role of this organ in the storage of Co. Conversely, in both species, ingested Zn was more diffusely distributed throughout the body.The differences observed between species could be related toa difference inthe digestive enzymatic system ineach studied species,which in turn is relatedto their slightly different feeding habits in the natural environment.