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  • 1 Szent István University Faculty of Agricultural and Environmental Sciences H-2100 Gödöllő Hungary
  • | 2 Kaposvár University Faculty of Animal Science H-7400 Kaposvár Hungary
  • | 3 Hokkaido University Nanae Freshwater Laboratory, Field Science Center for Northern Biosphere Kameda, Hokkaido 0411105 Japan
  • | 4 Pannon University Georgikon Faculty H-8360 Keszthely Hungary
  • | 5 Hungarian Academy of Sciences Balaton Limnological Research Institute H-8237 Tihany Hungary
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The present study aimed in vivo tracking of maturation of male eel by computed tomography (CT). Additionally, individually monitored testes sizes were correlated with the conventionally used external maturity indicators (i.e. eye and nose indexes) in order to test and improve their usefulness at individual level. Testes could be clearly identified with the CT from the end of the third week of hCG administration routinely used to induce maturation in fish. The volume of testes increased exponentially during hormone treatment, and by the end of the sixth week of maturation procedure all males produced motilable spermatozoa. Present results prove that testes size can noninvasively be monitored with CT from maturity level where testes size rich 3000 mm3 volume. Eye and nose indexes are in close correlation with testes volume and thus can also be effectively used to monitor maturaty level of male eel, but preferably only at stock level. However, due to their high individual variability, these indexes can be applied only with caution at individual level and should be supplemented with other noninvasive techniques such as CT.

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