IsoMark

Chemical environmental information is to a certain degree stored in soft and hard tissues of fish and other living organisms, although being influenced by physiological processes. Consequently site- and species specific microchemical patterns stored in hard parts of fish can be used as natural chemical tags for studying the spatial behaviour of fish for answering important ecological questions like the origin of fish, stock identification or dispersal and other migratory patterns (homing of fish to natal birthplaces, individual and group life histories or habitat use). Although mainly otoliths have been studied so far, scales and fin rays bare the potential for non-lethal sampling, especially needed when studying endangered species. On the other hand eye lenses could be sampled easily, which is of special relevance when large numbers of fish are investigated. Therefore the "IsoMark" project focuses for the first time on the comprehensive investigation of microchemical information (elemental fingerprint of Ca, Sr, Na, Ba, Mg; isotopic fingerprint of Sr and Ca) in different hard parts of typical European freshwater fish species like brown trout (Salmo trutta f.f., L.), European grayling (Thymallus thymallus, L.), nase (Chondrostoma nasus, L.) and the Danube salmon (Hucho hucho, L.). Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) will be used as major technique for direct and simultaneous in situ high precision analysis of trace elements and isotope ratios of hard parts. Fish from ten fish farms will be analyzed for their microchemical signatures in different hard parts as fish farm specific signatures would make expensive artificial tagging, e.g. to track farmed fish in natural rivers after stocking, nonessential. As a reliable interpretation of the chemical patterns in different hard parts requires an understanding of the relationship between environmental conditions and the uptake of elements and isotopes, controlled field experiments will be conducted for two species (brown trout and nase) at different life stages. Additionally adult and juvenile individuals of brown trout and nase from natural rivers with different environmental chemistry will be sampled to assess the influence of geological formations, ontogeny and temperature on microchemical patterns in hard parts. The stability of the chemical fingerprints of rivers as a pre-requisite for a clear interpretation of microchemical patterns in hard parts will be assessed as well. Trans- generational marking via injecting enriched isotopes into gravid females will be tested offering an amazing opportunity to mark large numbers of larvae in the field since the environmental information experienced by adult females is passed over to the primordial core of the otolith. The project will be run as collaboration between the Division of Analytical Chemistry (Department of Chemistry) and the Institute of Hydrobiology and Aquatic Ecosystem Management (Department of Water, Atmosphere & Environment) at the BOKU, University of Natural Resources and Applied Life Sciences, Vienna, together with the Institute for Water Ecology, Fisheries and Lake Research at Mondsee/Scharfling (Federal Agency for Water Management), and is directly related to the research of the START-project "VIRIS" (Vienna Isotope Research Investigation and Survey, FWF 267-N11).

The comprehensive assessment of the elements and isotopes in hard parts of freshwater fish by laser-ablation-(multicollector)-inductively coupled plasma mass spectrometry (LA-(MC)-ICPMS) within the IsoMARK project significantly contributed to the understanding which microchemical information is stored in all incrementally growing tissues of freshwater fish in a time resolved manner. The main focus was on otoliths, vertebrae, scales, fin rays and eye lenses. The knowledge gained is especially relevant for applications in ecology, aquaculture and freshwater management, where the reconstruction of origin and migration pathways of fish is needed. It was possible to clearly distinguish fish from different chemical environments by the microchemical information stored in their hard parts, and to relate them to their origin. Furthermore the time resolved analysis of the chemical information in different hard parts helped to determine the potential of this information to reconstruct the habitat use over whole life time of a fish. This potential mainly depends on the growth and dimension of the hard part itself and the spatial resolution that can potentially achieved by laser ablation. Fin rays as well as scales proved to be important non-lethal sampling alternatives to otoliths, as they contain similar information.The analysis of the chemical signatures of the water in different fish farms and in rivers along the Austrian Danube resulted in different isoszones characterized by significantly different isotopic and elemental composition. It proved to be possible that fish movements between these different isozones along the Austrian Danube can be tracked by the chemical patterns stored in the different hard tissues of fish. Transgenerational marking using natural and non-toxic Sr isotopes was successfully tested for brown trout Salmo trutta f.f. and European carp Cyprinus carpio. Transgenerational marking offers the unique possibility to mark all offspring of individual female by just one injection of an enriched isotopic spike, which is applied to the female spawners. This maternal chemical information is then passed over to the central otolith regions of the offspring. The method is especially important for applications in aquaculture, ecological research and management where individual-specific marking and tracking of high numbers of offspring is needed. C. carpio served as model species for other cyprinids with small eggs inhabiting lowland river systems like the Danube, brown trout as a salmonid species with large eggs inhabiting headwaters.The knowledge gained within this project has been already applied for practical questions, like the determination of the origin of fish from Austrian aquaculture. By the time resolved analysis of otoliths it was possible to trace back fish to individual fish farms by 100 % accuracy. These results gained public interest already during the time of the project.