Potential impact of climate change on the reproductive success of grayling ( <scp> <i>Thymallus thymallus</i> </scp> )

The European grayling is a salmonid species experiencing a sharp population decline, and conservation measures have been initiated through artificial propagation. As the species is not commonly cultivated in aquaculture, there is little information on their optimal reproduction conditions. Therefore, this study has combined a two-pronged approach of examining the temperature of the natural spawning area during the spawning season, while also experimentally testing four different incubation temperatures under standardized aquaculture conditions. Nine egg clutches from pond-reared females were fertilized with a sperm mix from 10 wild grayling. Eggs were divided into four treatment groups and incubated at 6, 8, 10 and 12°C. Hatched larvae were then collected and examined for body weight, yolk-sac weight and length. Both the temperature of the natural habitat and the physiological parameters of the larvae indicate that 6 and 8°C are the optimal hatching temperatures for grayling reproduction. The hatching rate was highest at 8 and 6°C, at 80.35 ± 6.30% and 76.87 ± 8.01%, respectively, although it gradually decreased with increasing temperature. The impact of warmer water temperatures hindered survival rates, resulting in a significant decrease in hatching rates at 10°C (68.46 ± 13.85%) and 12°C (45.54 ± 27.14%).