Negative impact of the invasive topmouth gudgeon (Pseudorasbora parva) on population growth of a native fish species, the sunbleak (Leucaspius delineatus)
Biotic interactions of invasive and native species are one of the main drivers of declining freshwater biodiversity. The recent population declines of sunbleak (Leucaspius delineatus) in its native range have been attributed to the spread of the rosette agent (Sphaerothecum destruens) carried by the invasive topmouth gudgeon (Pseudorasbora parva). However, both fish species highly overlap in their habitat preferences and omnivorous feeding strategy and their interspecific interactions may have contributed to the decline of sunbleak populations. To test this hypothesis, we carried out two experiments in small (0.8 m3 water volume) and large (8 m3 water volume) outdoor mesocosms and followed their population and individual responses over one growing season in single-species and syntopy treatments. In each experiment, both species reached similar final abundance, final biomass and biomass-based population growth rate in the single-species treatment. However, the final biomass and biomass-based population growth rate of sunbleak were much lower than those of topmouth gudgeon in the syntopy treatment in both experiments. That is, the biomass-based population growth rate of topmouth gudgeon was not affected by interspecific interactions, while that of sunbleak significantly declined. These disparate population-level responses of both species to syntopy were not reflected in the individual-level responses. At the end of each experiment, topmouth gudgeon individuals were heavier than sunbleak individuals of the same size and individuals in the large mesocosms were heavier than conspecific individuals of the same size in the small mesocosms, but we found no difference between the single-species and syntopy treatments. Taken together, these results suggest that the presence of topmouth gudgeon in the small waterbodies can significantly impact sunbleak populations. More broadly, it underscores the need to mitigate invasive species’ effects on native fish through proactive conservation and management strategies. Graphical abstract
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