Tag performance and physiological responses of juvenile mud crabs Scylla paramamosain tagged with visible implant elastomer

► We successful apply six unreported sites to tag very small crabs with VIE tag. ► We evaluate the tagging effects with a series of methods. ► After three molts, the retention and identification of tag is very high and distinct. ► The results of survival, molt frequency, carapace width show that the damage is negligible. ► The result of enzymatic assay further confirms that the damage is very little. Juvenile crabs are small, frail and frequently molt, which poses a great challenge to individual identification. This study evaluated the use of single and double visible implant elastomer marks in juvenile mud crabs Scylla paramamosain (1.57–2.50 cm carapace width). Elastomer was injected ventrally in body sites adjacent to the second, third and fourth pair of pereiopods. After eight weeks, the untagged, single-tagged and double-tagged treatments showed no differences in survival, development or growth. For the three treatments, there were also no differences in the amylase, trypsinase and SOD (superoxide dismutase) activities in the hepatopancreas. However, the lactate dehydrogenase, adenosine triphosphatase and SOD levels in crab muscle where elastomer was implanted were higher than respective muscle in untagged crabs. Although most crabs had gone through three ecdyses, all surviving crabs in the tag treatments retained visible elastomer material. Except for elastomer implanted ventrally adjacent to the fourth, left pereiopod, elastomer at the other five sites were mostly clear and intact during cultivation with no difference between single-tagged and double-tagged treatments. Finally, dissection revealed that tags mainly migrated to the surface of the gill with the degree of tag migration dependent on the depth of injection.