Unusual Thermoregulatory Behaviour of Anadromous and Residential Formsof the Larvae of the River Lamprey Lampetra fluviatilis (Petromyzontidae)
The thermal tolerance and thermoregulatory behavior of the river lamprey larvae Lampetra fluviatilis are presented. The upper lethal temperatures recorded at water heating rate ~8°C/h<sup>–1</sup> and acclimation temperature 18°C did not differ in individuals which descendants of producers of anadromous and resident life forms – 34.3 and 34.5°C, respectively (p > 0.05). There are also no significant differences in the temperatures chosen by larvae from populations where different types of life strategies are implemented. The studied individuals did not show a distinct thermopreferendum reaction, and were spreading out over the entire thermogradient field provided to them. The average values of the selected temperature in each of the three days of the experiment were 18.3, 19.3 and 19.8°C.