Metodické problémy při určování stáří hlodavců na základě hmotnosti očních čoček [Methodical problems in the age identification of rodents on the base of the eye lens weight]
Josef Bryja, Marta Heroldová, Eva Jánová, Emil Tkadlec
Determination of age based on eye lens mass is a commonly applied method in small mammals. Published papers are focused mostly on removing eyes from freshly killed animals. In practice, animals are usually frozen first and the removal of lenses, followed by fixation, is postponed to be done later according to time conditions. The aim of this paper is to describe some methodological problems in age identification using the eye lens weight in the cases when lenses were frozen before dissection and when the lens weight was affected by the fixative. Another question was sex dependence of the eye lens weight. It was found that when using frozen eye lens, the slope of calibration curve was statistically significant, therefore, this method is available for age determination. A faster growth of lens was recorded in males than in females. The weight of lens, especially the dry one, correlated with body measures, most strongly with body length. Differences in weight between the two lenses were low, so it was possible to use one lens weight multiplied by two in the model. Both frozen and unfrozen lenses lost their weight (9.21% on average) after fixation in 10% formalin. The length of fixation had no effect on lens weight. In frozen lenses, fluctuations in weight during the whole process were similar to those recorded in lenses which were processed immediately after killing. As a conclusion, authors using this method are advised to appoint their own calibration curve established from the population under study. All material used within one study should be processed under the same conditions, especially as to the length of storage in fridge, the length of fixation and temperature of drying.