Trophic interactions of two Ponto-Caspian gobies in the Turkish part of their native range

Several Ponto-Caspian gobiids have expanded from their native distribution ranges to Europe and North America. As knowledge on their bio-ecological features in their native range is still limited, the trophic ecology of monkey goby Neogobius fluviatilis and Western tubenose goby Proterorhinus semilunaris was studied in three natural lakes in the Marmara Region of NW Turkey using the stable isotopes of δ13C and δ15N. In two of the lakes, the trophic niches (as the isotopic niche) of the gobies were highly divergent with co-existing native fishes, with no overlap. Moreover, mixing models suggests considerable inter-specific dietary differences. In all lakes, the trophic niches of gobies were never significantly larger than those of co-existing fishes. These results suggest that when introduced outside of their natural range, the gobies might integrate into new fish communities via exploiting resources that are underexploited by native fishes or will initially share resources with these species before their niches diverge, perhaps through competitive displacement

Origin and invasion of the emerging infectious pathogen Sphaerothecum destruens

Non-native species are often linked with the introduction of novel pathogens with detrimental effects to native biodiversity. Since the first discovery of Sphaerothecum destruens as a fish pathogen in the UK, it has been identified as a potential threat to European fish biodiversity. Despite this parasite’s emergence and associated disease risk there is still a poor understanding of its origin in Europe. Here, we provide the first evidence supporting the hypothesis that S. destruens has been accidentally introduced to Europe from China along with its reservoir host Pseudorasbora parva via the aquaculture trade. This is the first study to confirm the presence of S. destruens in China and has expanded the confirmed range of S. destruens to more locations in Europe. The demographic analysis of S. destruens and its host P. parva in their native and invasive range further supported the close association of both species. The work has direct significance and management implications for S. destruens in Europe as a non-native parasite

Promoting the use of non-lethal sample collection for analysing the trophic relationships of inshore flatfish populations using stable isotope analysis

Trophic studies on inshore flatfish populations usually rely on stomach content analyses and/or stable isotope analysis (SIA) of dorsal white muscle that involves the collection of samples from euthanised fishes. To promote the use of non-lethal sampling methods in inshore flatfish populations of relatively high intrinsic angling and/or ecological value, the applicability of using fin tissue and/or epidermal mucus as non-lethal alternatives to muscle in SIA studies was assessed for European flounder Platichthys flesus, plaice Pleuronectes platessa and common sole Solea solea. In all species, the results indicated that there were significant differences in the δ13C and δ15N values of dorsal muscle versus their fin and mucus samples. These significant differences were, however, predictable by linear regression, with regression coefficients produced for converting fin and mucus SI values to the equivalent muscle SI values. The use of combined data across the species also provided regression coefficients for converting fin and mucus SI to equivalent muscle values for flatfish populations more generally. These results indicated that there are tissue alternatives to dorsal muscle that can be applied to the SIA of flatfish populations, with these tissues able to be collected using non-lethal sampling methods

Inter-tissue variability in the stable isotope values of European perch (Perca fluviatilis) and pumpkinseed (Lepomis gibbosus)

Ecological studies on native and invasive populations of European perch Perca fluviatilis and pumpkinseed Lepomis gibbosus are often based on stable isotope (SI) analysis based on dorsal muscle, where samples are usually taken from sacrificed fishes. However, other tissues, such as scale and fin tissue, can be used as non-lethal alternatives, where their SI values can be standardised to dorsal muscle values for comparative purposes. In both perch and pumpkinseed, there was a pattern of δ13C enrichment and δ15N depletion from muscle to fin and scale. As comparative studies must account for these inter-tissue differences prior to analyses, conversion equations for SI data from scale and fin tissue to standardised muscle values are provided

Evidence of threat to European economy and biodiversity following the introduction of an alien pathogen on the fungal–animal boundary

Recent years have seen a global and rapid resurgence of fungal diseases with direct impact on biodiversity and local extinctions of amphibian, coral, or bat populations. Despite similar evidence of population extinction in European fish populations and the associated risk of food aquaculture due to the emerging rosette agent Sphaerothecum destruens, an emerging infectious eukaryotic intracellular pathogen on the fungal–animal boundary, our understanding of current threats remained limited. Long-term monitoring of population decline for the 8-year post-introduction of the fungal pathogen was coupled with seasonal molecular analyses of the 18S rDNA and histological work of native fish species organs. A phylogenetic relationship between the existing EU and US strains using the ribosomal internal transcribed spacer sequences was also carried out. Here, we provide evidence that this emerging parasite has now been introduced via Pseudorasbora parva to sea bass farms, an industry that represents over 400 M€ annually in a Mediterranean region that is already economically vulnerable. We also provide for the first time evidence linking S. destruens to disease and severe declines in International Union for Conservation of Nature threatened European endemic freshwater fishes (i.e. 80% to 90 % mortalities). Our findings are thus of major economic and conservation importance

Resolving the issues of translocated species in freshwater invasions

Biological invasions, driven by human-mediated species movements, pose significant threats to global ecosystems and economies. The classification of non-native species is a complex issue intertwining ecological considerations and ethical concerns. The need for nuanced and less ambiguous terminology is emphasised, considering biogeographic, evolutionary, and ecological principles. In-country translocations of native species into ecosystems in which they do not naturally occur, are often overlooked and are the least regulated among species movements, despite being increasingly common in conservation. Our case studies, spanning various ecosystems and taxa, illustrate the diverse impacts of translocations on native species and ecosystems. The challenges associated with translocated species underscore the urgency for robust risk management strategies and rigorous monitoring. A comprehensive and adaptable management framework that considers translocated species for evidence-based management decisions is critical for navigating the complexities of translocations effectively, ensuring the conservation of biodiversity and ecosystem sustainability

A posterior epidural mass causing paraparesis in a 20-year-old healthy individual

We present a case of a posterior epidural abscess at the thoracic vertebral level causing paraparesia in a young, healthy individual with no otherwise predisposing factors, with normal laboratory findings, as diagnosed using fat-suppressed MR imaging. Spinal epidural abscess is a rare condition, encountered mostly in the midthoracic or lower lumbar vertebral levels of elderly patients, that has a high mortality and morbidity (18-31%) when diagnosis and treatment is delayed. It is rarely spontaneous and is usually accompanied by spinal osteomyelitis. Diagnosis is rather easy in cases of vertebral osteomyelitis or when classical clinical, laboratory and imaging findings are present. However, cases of spontaneous development, with no predisposing factors, and lack of abscess suggesting clinical and laboratory findings may be a diagnostic challenge. In such cases, other posterior epidural masses such as schwannoma, neurofibroma, meningioma and hematoma should be considered in the differential diagnosis. Both the clinician and the radiology physician should have a high suspicion of epidural abscesses, because their early diagnosis and treatment is important. In addition to routine MR images, fat-suppressed MR images prove helpful in the diagnosis of spontaneous epidural abscesses by showing the inflammatory changes in the paraspinal area

Trophic relationships of translocated and indigenous chub Squalius cephalus populations with trophically analogous fishes

The translocation of non-indigenous fishes into lowland rives can result in invasive populations establishing and dispersing. Because non-indigenous fishes can cause ecological harm, it is important to understand their trophic relationships and the effects they may have on native fishes. We assessed the trophic ecology of a translocated chub Squalius cephalus population in the River Frome, a lowland chalk stream in Southern England, using bulk stable isotope (δ13C, δ15N) metrics, and compared the results with those derived from indigenous chub populations. The isotopic niche sizes of all fishes in the River Frome were substantially larger in the tidal versus non-tidal site, with the δ13C values suggesting some fish were foraging further downstream of their sampling point in areas that had greater tidal and salinity influences. Inter-specific comparisons of isotopic niches revealed a consistent pattern of similar niche size and overlap between chub and the trophically analogous dace Leuciscus leuciscus. These isotopic relationships between chub and dace were then also apparent in the indigenous populations of these fishes. These results suggest that the colonisation of this lowland river by translocated chub is being facilitated by their isotopic relationships with other fishes that are similar to those observed in their native range

Interactions of invasive pumpkinseed with a riverine endemic fish indicate trophic overlap but minimal consequences for somatic growth and condition

The North American invasive fish pumpkinseed Lepomis gibbosus has been associated with some detrimental ecological consequences in some parts of its invasive range. Here, we tested the trophic interactions of pumpkinseed with the endemic stream fish Aegean chub Squalius fellowesii ('chub') in a Mediterranean-type water course in SW Anatolia, Turkey, using a bulk stable isotope approach (d13C, d15N). Seven sampling sites were able to be grouped as chub in pumpkinseed presence (n=2) and absence (n=3), and pumpkinseed in chub absence (n=2). Across these groups, stable isotope metrics revealed that chub trophic (isotopic) niche size was similar in pumpkinseed presence/absence, but pumpkinseed had a larger niche in chub presence. In sites where they are co-habited, their niches showed some convergence, but with no apparent consequences for their growth or body condition, suggesting there were minimal ecological consequences of this sharing of food resources. These results suggest that the trophic consequences of this riverine invasion of pumpkinseed on this endemic chub was minimal

Exploring invasiveness and versatility of used microhabitats of the globally invasive Gambusia holbrooki.

Introductions of non-native species can lead to severe impacts, including the decline of ecosystem function through deleterious impacts on species diversity. The successful establishment of non-native species in new environments is the first barrier a species must overcome, ultimately depending on its ability to either cope with or adapt to local site-specific conditions. Despite the widespread distribution and ecological consequences of many freshwater invaders, site-specific and climatic preferences are often unknown, as in the case of the Eastern mosquitofish Gambusia holbrooki, a global invader considered as a pervasive threat to endemic species. Here, we determined the ecological features and preferred site-specific conditions of G. holbrooki in Türkiye, which spans a wide range of diverse biogeographically distinct ecosystems, by surveying populations from 130 localities in 2016 and 2017. Gambusia holbrooki were detected by hand-net in 48 of these sites (19 lotic, 29 lentic). It showed a preference for shallow waters with medium sized rocks, and abundances differed spatially across a latitudinal gradient and was influenced predominantly by variations in pH. The only other factors predicting its presence were low current velocities and gravel substrate, highlighting its ecological versatility in utilising a wide range of microhabitats. Bioclimatic models suggest that G. holbrooki is found in areas with an average annual temperature ranging from 10 to 20 °C, but with temperature not being a limiting factor to its invasion. Gambusia holbrooki shows a preference for xeric freshwater ecosystems and endorheic basins, as well as temperate coastal rivers, temperate upland rivers, temperate floodplain rivers and wetlands, and tropical and subtropical coastal rivers. These results, particularly the wide occurrence with only few limiting factors, emphasise the invasion potential of mosquitofish and should substantiate the need for localised invasive species management and conservation efforts, particularly in smaller or insular areas where mosquitofish and endemic fish species co-exist