Zinc flux in Palaemon elegans (Crustacea: Decapoda): moulting, individual variation and tissue distribution

Abstract

Zinc flux has been followed through individual shrimp Palaemon elegans using Zn-65 as a tracer. Rates of uptake and loss of labelled zinc varied widely between individuals but could not be attributed to differences in size (dry wt), sex, nor stage in the moult cycle, indicating genetic variation. Rapid zinc flux into the shrimp occurs immediately after moulting and subsequently flux rates are enhanced for several days. The first moult in non-labelled media results in losses of up to 20 % of the previously accumulated labelled zinc burden. Subsequent moults cause insignificant losses of labelled zinc. Moulting under high external zinc levels may cause a small increase (= 10 %) in the total body zinc concentration, the increase being restricted to the cuticle. Zinc is unevenly distributed between individual tissues of P. elegans, the highest concentrations being in the eye (215 pg Zn g-' dry wt), hepatopancreas (178) and gill (136), the lowest in the muscle (49.6). Individual tissues show different rates of zinc flux, 2.41 pg Zn g-' d-' in the hepatopancreas to 0.13 pg Zn g-' d-' in the muscle, and also vary in the size of fast and slow exchanging pools of zinc. Zinc in the cuticle is absorbed into internal tissues prior to moulting. Cast moults take up zinc from the surrounding medium.