J. Appl. Ichthyol. 2016; 32: 1161–1170 wileyonlinelibrary.com/journal/jai | 1161 © 2016 Blackwell Verlag GmbH Received: 4 April 2016 | Accepted: 17 June 2016 DOI: 10.1111/jai.13191 Summary The purpose of this study was to mark endangered sterlet (Acipenser ruthenus) with visible implant elastomer (VIE) in order to assess mortality, compability, retenon, persistence and histological reacons resulng from this tagging technique. It was hy- pothesized there would be only minor effects on the fishes’ health, and assumed that acute effects would be more pronounced than long-term effects. On 11 September 2013, 20 specimens were tagged ventrally with visible implant elastomer, 20 received a subcutaneous injecon with 0.9% NaCl soluon, and another 20 served as untreated control. Mean total length was 28.0 ± 1.8 cm and mean body mass 64.1 ± 12.0 g. The sterlets were kept in four 4,000-L tanks filled with 2,400-L water. Acute effects were monitored for 95 days, where fish were held at temperatures between 2.4°C and 15.2°C, reflecng outdoor condions. Chronic effects were examined 282 days post- tagging through histological secons of the tagging region in five sterlets. During the first 95 days of observaon, tag retenon was 100%. No signs of incompability were detected. Body mass did not significantly differ between VIE-tagged fish and controls. At day 282 post-tagging, however, disnct ssue reacons were visible at the tagging sites of nine fish. Histological examinaon of five fish revealed a variable degree of infiltraon with leukocytes in the areas around the elastomer, which did not necessar- ily correspond with the externally visible degree of inflammaon. Aſter medical treat- ment, the lesions healed without complicaons, whereas the retenon rate of the VIE tags was 5%. According to the findings, the tag locaon rather than the tag itself was responsible for the externally visible irritaons, indicang that the ventral subcus of sterlet is not a suitable site, even for small VIE tags in long-term studies. The results of this study also suggest that VIE marking should in general be crically evaluated be- fore applicaon in field studies. 1 Bezirk Oberpfalz, Fachberatung für Fischerei, Teichwirtschaſtlicher Beispielsbetrieb Wöllershof, Störnstein, Germany 2 Tiergesundheitsdienst Bayern e. V., Fachabteilung Fischgesundheitsdienst, Geschäſtsstelle Schwandorf, Almesbach, Weiden, Germany 3 Bezirk Oberpfalz, Fachberatung für Fischerei, Regensburg, Germany 4 Bayerische Landesanstalt für Landwirtschaſt, Instut für Fischerei, Starnberg, Germany 5 Technical University of Munich, Chair of Aquac Systems Biology, Freising, Germany Correspondence Juergen Geist, Aquac Systems Biology Unit, Technical University of Munich, School of Life Sciences Weihenstephan, Mühlenweg 22, D-85354 Freising, Germany. Email: geist@tum.de ORIGINAL ARTICLE Subcutaneous injecon of visible implant elastomer in sterlet (Acipenser ruthenus Linnaeus, 1758): a study on compability and retenon A. Nastoll 1 | B. Feneis 2 | T. Ring 3 | M. Schubert 4 | H. Wedekind 4 | J. Geist 5 1 | INTRODUCTION Depending on the technique used, marking fish provides a wide range of important informaon about a species. Mark-recapture studies allow assessments of links between subpopulaons, and esma- ons of populaon size (Coggins et al., 2006). Also, monitoring the movement of individual fish is crucial in idenfying behavioural traits including the use of disnct habitat types (Bonnot et al., 2011; Cunjak et al., 2005; Young & Scarnecchia, 2005; Zeller, 1997). Criteria for suitable tagging methods are biocompability, tag visibility and retenon, easy recognion, and cost. Furthermore, methods requiring special scienfic skills or equipment, such as im- mersion baths in chemicals that induce colouring of otoliths or the use of genec markers, are mostly not suitable in projects depending