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

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Abstract
Zn flux was followed through individual shrimp P. elegans using Zn-65 as a tracer. Rates of uptake and loss of labeled Zn varied widely between individuals but could not be attributed to differences in size (dry wt), sex, nor stage in the molt cycle, indicating genetic variation. Rapid Zn flux into the shrimp occurs immediately after molting and subsequently flux rates are enhanced for several days. The 1st molt in non-labeled media results in losses of up to 20% of the previously accumulated labeled Zn burden. Subsequent molts cause insignificant losses of labeled Zn. Molting under high external Zn levels may cause a small increase (.simeq. 10%) in the total body Zn concentration, the increase being restricted to the cuticle. Zn is unevenly distributed between individual tissues of P. elegans, the highest concentrations being in the eye (215 .mu.g Zn g-1 dry wt), hepatopancreas (178) and gill (136), the lowest in the muscle (49.6). Individual tissues show different rates of Zn flux, 2.41 .mu.g Zn g-1 d-1 [day-1] in the hepatopancreas to 0.13 .mu.g Zn g-1 d-1 in the muscle, and also vary in the size of fast and slow exchanging pools of Zn. Zn in the cuticle is absorbed into internal tissues prior to molting. Cast molts take up Zn from the surrounding medium.