Predation on fish larvae by black-striped pipefish (Syngnathus abaster) during the breeding season in invaded fresh waters of the Dnieper River basin

The black-striped pipefish Syngnathus abaster, which naturally inhabits brackish waters, invaded a variety of fresh waters of the Black Sea basin. Although this species penetrated fresh waters a long time ago and is known to prey on fish larvae, its habits and effects in these habitats were not studied sufficiently. The aim of this study was to investigate S. abaster predation on other fishes in invaded fresh waters in detail. The material for the study was collected between 2015 and 2020 in the Stugna River and Kaniv Reservoir (Dnieper River basin) during the breeding period of the majority of local fishes. The gut content analysis showed the presence of 44 prey taxa in the diet of S. abaster. The most important and frequently encountered prey were copepods. Fish larvae contributed 6.5–55.2 % of the total food items, while their relative importance in the diet ranged from 0.03 %IRI (percent index of relative importance) up to 14.36 % IRI. Four groups of fish prey were identified: Gobiidae, Cyprinidae, Perccottus glenii, and S. abaster juveniles. Fish were more frequently encountered and more abundant in the digestive tract of females than in males of S. abaster. Overall, the level of predation of this species on fish larvae was low and temporally associated with the massive spawning of co-occurring fishes inhabiting macrophytes. Previous studies suggest high to moderate probability of establishment of this species in the Laurentian Great Lakes if introduced, but the present study suggests relatively little effect on native fishes.