How old is a fish? Age validation studies on wild fish


Ein mit Tetracyclin makierter Dorschotolith im Querschnitt (c) Thuenen-Institut/Aisha Degen-Smyrek
Ein mit Tetracyclin makierter Dorschotolith im Querschnitt (© Thuenen-Institut/Aisha Degen-Smyrek)

DCF (Data Collection Framework): Age validation studies on Baltic round- and flatfishes

We would like to know the age of a fish as precisely and accurately as possible. Since fish do not swim around with an identification card, we have to use the partly imprecise interpretation of ring structures in their ear stones (otoliths). To verify the relationship between structures in ring formation and true fish age, we carry out age validation experiments on wild fish.

Background and Objective

Age validation is a central pillar for the understanding of the biology of fish stocks. Presently, the age determination of many fish stocks is subject to significant levels of uncertainty despite numerous efforts in the past. Accordingly, the predictions of the stock assessment are uncertain.

Therefore, we initiated catch-release experiments. Thereby we want to validate the age of abundant Baltic roundfish species like cod and whiting as well as flatfishes such as plaice, flounder or turbot. We analyse the ring structures the fish has produced between release and recapture. Thus, in the future we can improve the age determination for these fish species and the quality of input data to populations models and of ecological studies.


In a pilot study we identified tetracycline as the most appropriate chemical to mark the otoliths for an age validation study. We are catching live fish to mark them internally (with tetracycline as a time tag inside the otoliths) and externally (with a numbered so-called spaghetti tag for the detection by fishers and anglers upon recapture). Then we hope and wait that the marked fish are recaptured and returned as whole fish for further analysis. A reward is paid for each recaptured fish when the whole individual fish is returned.


Involved Thünen-Partners


9.2013 - 12.2027

More Information

Projekt type:
Project status: ongoing


hits: 7

  1. Plonus R, McQueen K, Günther C, Funk S, Temming A, Krumme U (2021) Is analysis of otolith microstructure a valid method for investigating early life history of Western Baltic cod? Mar Biol 168:30, DOI:10.1007/s00227-021-03834-x
    pdf document (limited accessibility) 1841 kb
  2. Carbonara P, Coad Davies J, Damme CJG van, Aanestad Godiksen J, Allegaert W, Beier U, Bekaert K, Canha A, Farias I, Follesa MC, Gault M, Gillespie-Mules R, Haase S, Hilvarsson A, Hüssy K, Korta M, Krüger-Johnsen M, Krumme U, Stransky C, Ulleweit J, et al (2020) Working Group on Biological Parameters (WGBIOP). Copenhagen: ICES, 150 p, ICES Sci Rep 2(117), DOI:10.17895/
  3. McQueen K, Hrabowski J, Krumme U (2019) Age validation of juvenile cod in the western Baltic Sea. ICES J Mar Sci 76(2):430–441, DOI:10.1093/icesjms/fsy175
  4. McQueen K, Paige Eveson J, Dolk B, Lorenz T, Mohr T, Schade FM, Krumme U (2019) Growth of cod (Gadus morhua) in the western Baltic Sea: estimating improved growth parameters from tag-recapture data. Can J Fish Aquat Sci 76(8):1326-1337, DOI:10.1139/cjfas-2018-0081
  5. Stötera S, Degen-Smyrek AK, Krumme U, Stepputtis D, Bauer Robert, Limmer B, Hammer C (2019) Marking otoliths of Baltic cod (Gadus morhua Linnaeus, 1758) with tetracycline and strontium chloride. J Appl Ichthyol 35(2):427-435, DOI:10.1111/jai.13829
  6. Krumme U, Bingel F (2016) Tetracycline marks visible in Baltic cod Gadus morhua otoliths stored for 40 years. J Fish Biol 89(4):2189-2194, DOI:10.1111/jfb.13108
  7. Stötera S, Krumme U (2016) Use of otolith quality flags to assess distributional dynamics in Baltic cod stocks. Mar Freshwater Res 67(7):980-991, DOI:10.1071/MF15048