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Otolith analysis to investigate variation in early life of the gilthead sea bream, Sparus aurata in the eastern Adriatic Sea

Shallow coastal areas are used as nursery habitats by many fish species as they are highly productive environments. Their role as nurseries for early life stages of many species, as well as foraging and spawning grounds, has been clearly documented in number of previous studies across globe. Studies of fish otolith geochemistry have contributed to the understanding of the early life history and nursery identification of different fish species. Otoliths are paired calcified structures located in the inner ear of teleost fishes. They have been widely used in marine ecology and fishery research to describe population age structure, assess connectivity between fish stocks and study individual migration patterns. The aim of this study is to investigate differences in otolith composition among juvenile of gilthead sea bream, Sparus aurata captured in different habitats. Juvenile fish of S. aurata were collected by beach seine net in three estuarine locations (Ploče, Pantan and Prosika), in the eastern Adriatic, during March and May 2018. Upon collection, fish were kept frozen and transported to the lab for further preparations. Three similar sized specimens were selected for subsequent analysis. The otoliths have been extracted, cleaned and prepared for transverse sections through the otolith core with a low-speed saw. Further sample preparation was done at the Johannes Gutenberg University (JGU ; Mainz, Germany) where the concentrations of Li, Na, Mg, Ca, Mn, Zn, Sr, Mo, Pb i U were determined by means of LA-ICP-MS in line scan mode along maximum growth rates. Concentration of Ba:Ca and Sr:Ca in otolith core varied within otoliths from same location as well as between otoliths from different locations. Obtained concertation were compared to salinity. Higher concentrations of Pb, Mn and Zn were found in the estuary of river Neretva which can be related to an anthropogenic effect from surrounding agricultural area that contribute to the increase of these elements. The otolith core Mg:Ca ratio was highest for the estuary of river Pantan. These preliminary investigations serve as a basis for future research to investigate connectivity between juvenile and adult’s individuals within Nursefish project.

Otolith microchemistry, Gilthead sea bream (Sparus aurata L.), Nursery grounds, Adriatic, LA ICP MS analysis

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