Relationship between the environment and the occurrence of invasive pumpkinseed Lepomis gibbosus in lotic and lentic habitats.

The pumpkinseed Lepomis gibbosus is a freshwater fish species native to North America. It has been introduced to Europe, where it is recognized as one of the worst aquatic invaders due to its high adaptability and invasive potential. This study aimed to determine the presence of L. gibbosus in small to medium-sized water bodies, both lotic and lentic, across the Sava River Basin in continental Croatia and identify the environmental variables associated with its occurrence. Lepomis gibbosus was recorded at 22 out of 111 lotic sites and 16 out of 29 lentic sites. The best-fitting Bernoulli generalized linear model on lotic data indicated that L. gibbosus occurrence was significantly and positively associated with the maximum depth of the sampling site and its distance from agricultural areas; the best-fitting lentic model showed that species occurrence was positively correlated with the pH and surface area of the water body. The lotic model was more robust, whereas the lentic model was interpreted with caution due to the smaller sample size. The species' presence in isolated larger ponds, usually more attractive to anglers, indicates that human introduction as a bait fish could be a primary driver of its dispersion. The findings of this study provide a first step in understanding the ecological habitat preferences of L. gibbosus in this region and could serve as a starting point for future research, monitoring and management of this invasive species.