One Year Monitoring of Ecological Interaction of Silurus glanis in a Novel Invaded Oligotrophic Deep Lake (Lake Maggiore)

Caterina M Antognazza,Tommaso Costantini,Serena Zaccara,Monica Campagnolo

doi:10.3390/w14010105

Abstract

The European catfish (Silurus glanis) was introduced in Italy during the last century for aquaculture purposes, and now it is well-established. S. glanis is an invasive species and a top predator that can deplete prey supply in the surrounding habitat, leading to changes in the aquatic food web. Consequently, its presence is considered a threat to native fish populations. Its presence in the Lake Maggiore (Northern Italy) is recent and there is a lack of knowledge about its ability to completely exploit this new ecosystem throughout the year. This study corroborated the ability of European catfish to exploit both pelagic and littoral habitats, promoting trophic interactions in both habitats. Over 2019, multiple sampling approaches have been applied by collecting S. glanis and analysing its stomach contents with the aim of inferring interactions with the freshwater community. Its diet was mainly based on crayfish (Orconectes limosus), followed by six prey fish and the genus Corbicula; two fish species (Padogobius bonelli and Salaria fluviatilis) were added to the list of known prey fish. Notably and alarmingly for the early potential top-down pressure towards all trophic levels, young individuals were proved to also feed on fish and crayfish. S. glanis showed the ability to hunt at deep depths (>60 m) and a high growth rate, despite Lake Maggiore being oligotrophic.

Highlights

The introduction of non-native fish into the freshwater system has a long history acrossEurope [1], the successful introduction of the European catfish (Silurus glanis, L., 1758)being one of the most widespread [2]
This study corroborated the ability of S. glanis to exploit both pelagic and littoral habitats in the Lake Maggiore, and its capability to hunt in the deep area of the lake
Due to fishing law restrictions, it was not possible to catch S. glanis in the littoral habitat during springtime, the presence of S. glanis in the pelagic habitat was preponderant towards that time (Supplementary Table S4), and the presence of A. agone in the stomach confirmed its interaction at the pelagic trophic level

Summary

Introduction

The introduction of non-native fish into the freshwater system has a long history acrossEurope [1], the successful introduction of the European catfish (Silurus glanis, L., 1758)being one of the most widespread [2]. Its introduction in Italy was for aquaculture purposes in the early 20th century, but was introduced in ponds of private fishing reserves, and subsequently reported in rivers since the 1930s onward [3,4]. From the 1980s, the presence of S. glanis can be considered common and continuous in the Po valley, artificial channels included [5], and nowadays it is well-established in the eutrophic sub-alpine lakes, such as. The first reports of its presence in the oligotrophic and deep Lake Maggiore dated back to the early 1990s [8], which is successfully colonised by S. glanis, demonstrating its remarkable ecological plasticity. S. glanis can adapt its diet to novel and available resources, including developing new feeding behaviour [13]; its presence in a newly invaded habitat is considered a potential threat.

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