Trophic consequences of an invasive, small-bodied non-native fish, sunbleak Leucaspius delineatus, for native pond fishes

Evaluating the Feasibility and Effectiveness of Removing the Globally Invasive Eastern Mosquitofish Gambusia holbrooki from Lotic Environments

Effective control measures for small-bodied invasive alien species (IAS) in lotic environments are essential for preserving native biodiversity and ecosystem health. This study integrates modeling and field-based removal data to assess the efficacy of electrofishing in controlling populations of the globally invasive Eastern mosquitofish Gambusia holbrooki across four lowland headwater streams in southern Greece over a one-year period. Results indicated significant reductions in mosquitofish post-removal abundance, although natural recruitment persisted, leading to population suppression rather than eradication. Indeed, our pre-removal population viability analysis suggested a temporary suppression of mosquitofish populations, influenced by factors such as the species' life history and reproductive traits. Furthermore, our study suggests modifications of physical control methods expected to enhance effectiveness. Specifically, the narrow implementation timeframe of the removal actions highlights the need for multiple removal campaigns in consecutive years and for long-term population monitoring, thus aligning with past research. The timing of removal efforts is also critical as it must exploit seasonal variability in fish eradication susceptibility, by its implementation within the best "window of opportunity". Finally, addressing knowledge gaps in the ecological impacts of IAS control methods as well as exploration of novel control and monitoring technologies, are also vital for informed management strategies. This study, by proposing modifications to fish removal planning and methodology, contributes to ongoing efforts for optimal IAS control, particularly in regions where such management approaches are underutilized.

Understanding feeding competition under laboratory conditions: Rohu (Labeo rohita) versus Amazon sailfin catfish (Pterygoplichthys spp.)

Competitive interactions between species is widely prevalent within the animal world. In this manuscript, we attempted to understand feeding competitions between the Amazon sailfin catfish, an invasive species introduced globally, and rohu, a keystone species native to several countries within southeast Asia. We used two different size classes of each species, large-size having total length (TL, from snout tip to caudal fin) of 15-20 cm and fingerling having TL<6 cm, and feeding duration was used as a proxy to understand competition. Our results demonstrated that feeding durations of large-size rohu were either similar or significantly (P<0.05) higher in presence of catfish when compared to trials in presence of conspecifics, indicating that large-size rohu is not a weak competitor. However, feeding durations of fingerling rohu was significantly (P<0.05) reduced in presence of both large-size and fingerling catfish, when compared to trials in presence of conspecifics. Moreover, fingerling rohu also displayed freeze (alarm) behavior in presence of the catfish. Interestingly, presence of rohu had no significant (P>0.05) impact on feeding durations of catfish. Overall, the study demonstrated that invasive catfish may behaviorally outcompete fingerling rohu, thus, threatening the sustenance of a species that is native to several freshwaters around the globe.

An integrative approach to assess the impact of disturbance on native fish in lakes

Freshwater fish are in a perilous state with more than 30% of species considered critically endangered. Yet significant ecological and methodological complexities constrain our ability to determine how disturbances are impacting native fish communities. We review current methods used to assess the responses of fish communities, especially native fish, to disturbances, with a focus on lakes. These methods include contemporary population surveys, manipulative experimental approaches, paleolimnological approaches and Indigenous Knowledge and social histories. We identify knowledge gaps, such as a lack of baseline data for native fish, an inability to assess the impact of historical disturbances, stressor response dynamics in contemporary multi-stressor environments, and natural disturbance regimes. Our assessment of the current methods highlights challenges to filling these knowledge gaps using the reviewed methods. We advocate strongly for the implementation of an integrative approach that combines emerging technologies (i.e. molecular-based techniques in contemporary surveys and paleolimnology) and underutilised knowledge streams (i.e. Indigenous Knowledge and social histories) which should be used in concert with conventional methods. This integrative approach will allow researchers to determine the key drivers of decline and the degree of change, which will enable more informed and successful management actions.

Trophic Niches, Trophic Positions, and Niche Overlaps between Non-Native and Native Fish Species in a Subalpine Lake

In the last century, Italian freshwater ecosystems have been invaded by several non-native fish species. In the subalpine Lake Mergozzo (northern Italy), several recently introduced non-native species dramatically expanded their populations. We used carbon and nitrogen stable isotopes to describe the isotopic niches and trophic positions of native and non-native fish species in Lake Mergozzo. We evaluated their trophic niches, trophic diversity, trophic redundancy and trophic evenness utilizing isotopic niche metrics, and estimated asymmetrical niche overlaps. The trophic traits of non-native fish species and Perca fluviatilis clearly define them as trophic generalists, in terms of among-individual variability of their isotopic niches. The historical increase in abundance of fish non-native species in this lake, their dominance by numbers and biomass within the assemblage, and their broad asymmetrical niche overlaps suggest that their higher degree of trophic generalism might have been one of the key factors that have promoted the invasion of the recipient community.