Characterizing egg transport of Chondrostoma nasus (L.): a combined laboratory and field experiment

Population recruitment of endangered rheophilic fish species strongly depends on the survival of critical egg and larvae life stages. However, the transportation and fate of eggs after spawning is not well understood. This study analyzed the egg transport and settling patterns of the endangered European nase (Chondrostoma nasus L.), testing the transferability of physical modelling approaches for simple solid sphere surrogates to the eggs of lithophilic fish species. This model approach was validated in both laboratory and field experiments, where wetted millet corns were used as surrogates excluding deformability and stickiness of natural nase eggs. The transport and settling patterns of the surrogate accurately modelled the transportation of C. nasus eggs. Results further indicate that transport processes of eggs are small-scaled in the range of less than 3 m. These findings provide helpful information for restoration planning of C. nasus spawning grounds. They also highlight the importance of the interstitial zone regarding the egg settling process, which conforms to the ecological relevance of this habitat for egg and larval development. While the surrogate was suitable for this model approach, further investigations are necessary to confirm transferability to other species.