While many authors are working at attracting public attention to crayfi sh protection, management and conservation (a very precious intent), the authors of this chapter would like to stress the importance of crayfi sh in protecting human wellbeing. In fact, crayfi sh are known to be characteristic representatives among the keystone species in freshwater ecosystems (Reynolds and Souty-Grosset 2012), which enables us to rely on crayfi sh indices while estimating the ambient status of their natural habitats and those carefully simulated in laboratories. The latter is done to imitate various water conditions, thus screening and predicting crayfi sh reactions to changes in those specifi c conditions, should they happen in nature. At fi rst, it may sound irrational to move crayfi sh from their natural homes to simulated ‘close-to-natural’ laboratory conditions, but by exposing them to stress, their reactions can be tested. The elucidative point is that the ethophysiological responses in crayfi sh, studied during stress, are functions of their environmental adaptation (Burmistrov and Shuranova 1996). For us, it means an opportunity to observe, study and forecast, as far into the future as possible, how they would behave on ethological and physiological levels in common environments if certain conditions, pretested in vitro, occurred.