Iron Deposits Turn Blue Shrimp Gills To Orange

In the grow-out ponds of the blue shrimp (Litopenaeus stylirostris) farms of New Caledonia, animals with orange gills (OG) have been observed over the last ten years, with up to 70% of the shrimp in a given pond being affected. During the processing and marketing of the product, this coloring leads to reduced quality and selling prices, resulting in lower income for the producers concerned. Individual observations and transfer experiments led us to conclude that gill coloration intensity varies according to the intermolt stages, ranging from white in the postmolt stage to a deep orange in the premolt stage, which then disappeared after molting. Histological, biochemical studies and a semi-quantitative analysis by scanning electronic microscopy (SEM + EDX) showed that the coloration is due to layers of iron which settle on the gill tissue surface in a heterogeneous way. Because Cr and Co showed an increase in their concentrations on the whole orange gills but not at their surface, it is possible that elements were mobilized and transported (translocated) from the exoskeleton to the tissue. Animals kept out of contact with sediment show a decrease in OG intensity, suggesting a link with the sediment biogeochemistry. In grow-out ponds, orange gills first appeared in shrimp populations between 10 and 13 weeks after stocking and reached a maximum after 15 weeks. These findings are discussed with a view to identifying the environmental processes that lead to metal accumulation on gills.