Seasonal Effects on Health Status and Parasitological Traits of an Invasive Minnow in Iberian Waters.

Simple Summary: Assessments of invasive species are of particular relevance in the Iberian Peninsula, where the endemic fish fauna is highly important for conservation. Parasites of invasive fish can vary substantially because of the seasonal variability in freshwater habitats. The study species was the invasive Languedoc minnow, native to France. Fish organs and parasites were assessed across seasons in a Mediterranean stream, which has a wide range of habitat variability throughout the year. Autumn was the most 'benign' season in the study area, with minnows displaying a better health status and a lower parasite burden. This information is relevant to understanding the effects of seasonal variation on parasites of invasive fish. Also, these data could assist environmental managers in controlling the spread of this non-native fish in Mediterranean streams. Biological invasions are of special conservation concern in the Iberian Peninsula and other regions with high levels of endemism. Environmental variability, such as the seasonal fluctuations of Mediterranean streams, is a key factor that affects the spread of aquatic species in novel habitats. Fish parasites have a great potential to reflect such changes in the habitat features of freshwater ecosystems. The aim of this study consisted of seasonally analysing the health status and parasitological traits of non-native fish in Iberian waters. In particular, a strongly invasive population of Languedoc minnow Phoxinus septimaniae (leuciscid species native to south-east France) was assessed in Tordera Stream (north-eastern Iberian Peninsula, Mediterranean conditions). Fish were sampled in April, July, and October 2023 by electrofishing. Health status (external/internal organs) was significantly better in autumn (HAI = 28.8) than spring (HAI = 35.6). Life-cycle complexity was higher in spring (LCI = 1.98), whereas parasite abundance and Shannon diversity were significantly lower in autumn (TA = 19.6 and H' = 2.15, respectively). In October (more 'benign' environmental conditions in Iberian streams), minnows could display elevated foraging activity, with fish increasing their health condition and level of parasite resistance/tolerance. Overall results showed a particular seasonal profile of health and parasite infra-communities that allow this minnow species to thrive under highly fluctuating habitat conditions. This information could help environmental managers to control non-native fish in Mediterranean streams. [ABSTRACT FROM AUTHOR]