This research was conducted on 22 red-eared sliders during hibernation and after arousal. The material came from Poznan Zoo (Poland). Species affiliation was established on the basis of the Turtles of the World key. The examined sliders were of a similar age. The histological, histochemical and ultrastructural studies were conducted during hibernation and after arousal. Additionally analysis of liver elemental composition (C, O , Na, Ca, Al, P, Mg and S) was performed. The results showed morphological and ultrastructural liver changes, related to hibernation process concerning shape and size of hepatocytes as well as morphology and location of cell organelles. The conducted elemental analyses revealed during hibernation the reduction of the phosphorus levels up to70–80% while after arousal there was distinct increase of oxygen, sodium and aluminum concentration noticed.

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