Influence of the water heating rate upon thermal tolerance in common carp (Cyprinus carpio L.) during different seasons

For the first time, the dependence of the upper lethal temperature (ULT) level upon the water heating rate was determined in young common carp (Cyprinus carpio) during different seasons and within the wide range of heating rates. The highest ULT values were revealed by using the chronic lethal impact method, with a water heating rate of 1°C/day (or 0.04°C/h). At such a rate, fish can successfully acclimate to a temperature increase. The ULT values determined by that method characterize the fish maximal thermal tolerance. During different seasons these values were differing from each other within a 3°C range. The data on the common carp ULT, along with data on crucian carp (Carassius auratus), evidences that this species belongs to the group of the most thermophilic fish, not only among cyprinids, but also compared to the representatives of other families. Obtained experimental data characterizing the upper thermal limits for fish vital functions may be used for the development of ecological safety criteria near the zones of discharge of heated waters from heating and nuclear power plants, as well as for the forecasting of the potential consequences of global warming.