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Ectoine (ECT) is an amino acid produced and accumulated by halophilic bacteria in stressful conditions in order to prevent the loss of water from the cell. There is a lack of knowledge on the effects of ECT in heat-stressed aquatic animals. The purpose of our study was to determine the influence of ECT on Daphnia magna subjected to heat stress with two temperature gradients: 1 and 0.1 °C/min in the range of 23–42 °C. Time to immobilisation, survival during recovery, swimming performance, heart rate, thoracic limb movement and the levels of heat shock protein 70 kDa 1A (HSP70 1A), catalase (CAT) and nitric oxide species (NOx) were determined in ECT-exposed and unexposed daphnids; we showed protective effects of ECT on Daphnia magna subjected to heat stress. Time to immobilisation of daphnids exposed to ECT was longer when compared to the unexposed animals. Also, survival rate during the recovery of daphnids previously treated with ECT was higher. ECT significantly attenuated a rapid increase of mean swimming velocity which was elevated in the unexposed daphnids. Moreover, we observed elevation of thoracic limb movement and modulation of heart rate in ECT-exposed animals. HSP70 1A and CAT levels were reduced in the presence of ECT. On the other hand, NOx level was slightly elevated in both ECT-treated and unexposed daphnids, however slightly higher NOx level was found in ECT-treated animals. We conclude that the exposure to ectoine has thermoprotective effects on Daphnia magna, however their mechanisms are not associated with the induction of HSP70 1A.

Ectoine (ECT) is an osmoprotectant produced and accumulated by halophilic bateria under hyperosmotic stress. There is a lack of knowledge on the effect induced by this amino acid during subchronic animal exposure to ECT in vivo. Therefore, the aim the present study was to determine influence of ECT on survival, motility, physiological activity (heart rate, thoracic limb activity, and mandible movement rate), growth rate and moulting of unfed and fed with normal diet Daphnia magna exposed for 10 days to 2.5, 4, 20 and 25 mg/L ECT. The results showed that survival of unfed animals exposed to 25 mgL ECT was decreased; however it was increased at lower concentrations of the amino acid when compared to the control. 20 and 25 mg/L of ECT significantly decreased swimming velocity, heart rate and thoracic limb activity and mandible movement rate. On the other hand, the osmoprotectant did’nt cause mortality of fed daphnids at any concentration but stimulated swimming velocity and the physiological parameters, however no differences were found in mandible movement rate. We found that ECT increased growth rate both in starving and fed daphnids, however the stimulatory effect was not concentation-dependent. The most significant increase of growth rate both in unfed and fed dapnids was found at 4 mg/L ECT. Moulting frequency was increases only in unfed daphnids exposed to the highest concentrations of ECT. Fed daphnids showed slighlty elevated moulting frequency only at 25 mg/L ECT. Our results indicate ECT is a stimulator of growth rate and physiological indices in fed Daphnia magna, however the elucidation of its mechanisms requires further studies.