Western Mosquitofish Gambusia Affinis Research Articles

Fishes move to transient local refuges, not persistent landscape refuges during river drying experiment

Abstract Anthropogenically driven flow intermittency is increasing in freshwater streams, with important implications for the management and conservation of aquatic ecosystems. Because most freshwater fishes are mobile, they are expected to emigrate from intermittent reaches, but this may not be true in streams transitioning from perennial to intermittent. Here, we attempt to determine if riverine fishes vacate drying reaches before intermittency or remain in local refuges. We implemented a controlled, in situ experimental flow reduction resulting in intermittency, reducing flows from ~1.0 to 0 m3/s over a 3‐week period. We monitored fish and fish‐habitat changes over a 5‐week period before, during and after flow reductions. During flow reductions, total wetted habitat was ultimately reduced by 91%. Habitat loss over time was not equal among habitat types: pool habitat increased slightly as run habit was lost, and backwater and isolated pool habitats were not strongly related to discharge. Likewise, water depth in run habitats decreased faster than other habitats. Only the river carpsucker Carpiodes carpio appeared to move upstream during flow recession; seven other species remained within drying sites. Habitat loss negatively affected fish populations, but at a lower rate than that at which habitat was lost, until sites dried completely. Overall, two species, red shiner Cyprinella lutrensis and western mosquitofish Gambusia affinis, had increased population growth during the study, whereas the remaining species had population declines. Fishes were able to find transient local refuges during flow reductions but did not vacate sites before intermittent conditions. Accounting for lack of emigration from anthropogenic flow‐intermittent reaches will be important for designing conservation actions for fishes threatened by increasing flow intermittency. Creation of refuge habitats may not be effective for widely dispersed species that do not actively seek refuge habitats, unless those habitats support enough individuals to maintain resilience following the intermittent conditions.

Transfer of Se from sediments to the western mosquitofish Gambusia affinis: Tissue distribution, accumulation, and effects on the antioxidant physiology

Selenium (Se) has been shown to cause various toxicities in predatory species (i.e., fish and birds) in Se-contaminated aquatic environments. However, trophic transfer of Se from abiotic environments to freshwater fish has been relatively less addressed. In this study, 2-month-old mosquitofish (Gambusia affinis) were fed Se-enriched oligochaete (Lumbriculus variegatus, exposed to different concentrations of Se(IV) at 0.0, 3.0, 10.0, and 30.0 µg/g dry weight for 7 days) for 45 days. Tissue distribution, Se speciation, and effects on the antioxidant physiology in G. affinis were assessed. The results showed Se was rapidly accumulated in the oligochaete, with 6.30 ± 1.20, 16.20 ± 2.10, and 34.50 ± 2.40 µg/g dw of total Se levels in the worms exposed to 3.0, 10.0, and 30.0 µg/g of Se(IV), respectively. Total Se levels were increased in a dose-dependent manner in fish tissues and Se(IV) from sediments was maternally transferred to the fish embryos. Se-Met-and Se-Cys-were the predominant Se species in the worm and fish tissues, accounting for a minimum of 91.01% of the total Se. Furthermore, increased lipid peroxidation and altered the activities of antioxidant enzymes and levels of GSH were noticed in G. affinis fed the Se-enriched L. variegatus. This study has demonstrated that Se(IV) is transferred from an abiotic vector to freshwater organisms, disturbing the antioxidant physiology in G. affinis and potentially their offspring. This study highlights the importance of dietary exposure on the accumulation and toxicity of Se in aquatic organisms.

Activation of Henneguya ictaluri Actinospores by Nonictalurid Fish Species, with Implications for Management of Proliferative Gill Disease in Catfish Aquaculture

AbstractProliferative gill disease (PGD), caused by the myxozoan Henneguya ictaluri, is an important parasitic disease in U.S. catfish aquaculture. Continuous exposure of Channel Catfish Ictalurus punctatus to the actinospore stage of H. ictaluri results in a severe inflammatory response at the gills, leading to morbidity and death. Previous work indicates that the chemical cues in fish mucus that are recognized by myxozoan actinospores are not host specific. Building on these findings, the potential decoy effects of nonictalurid fish to actinospores of H. ictaluri were evaluated. Exposure of actinospores to gill mucus from multiple nonictalurid fishes resulted in actinospore activation for all fish species tested. Based on these findings, experimental transmission trials with potential interceptor fish were conducted. Individual Channel Catfish were co‐stocked with Western Mosquitofish Gambusia affinis at 0, 10, 25, or 50% of mean Channel Catfish biomass and exposed to 3,000 actinospores of H. ictaluri. Gill tissues were sampled at 24 h postchallenge, and parasite burden was estimated by H. ictaluri‐specific quantitative PCR. Results revealed that Western Mosquitofish stocked at 25% and 50% of catfish biomass reduced H. ictaluri DNA in Channel Catfish gills more than threefold. In a second study, catfish were exposed to pond water collected from an active PGD outbreak in the presence of Western Mosquitofish stocked at 25% of catfish biomass. Channel Catfish were sampled at 24 h and at 7 d after the last pond water exposure. At 24 h postexposure, catfish that were co‐stocked with Western Mosquitofish showed significantly lower H. ictaluri DNA than catfish stocked alone. This treatment effect was absent at 7 d postexposure, as parasite quantities within tissues had increased over 1,000×, with marked variability. Still, results indicate that the chemical cues that activate H. ictaluri actinospores are not specific to Channel Catfish. This work evinces a potential benefit of nonictalurid fish in combating H. ictaluri, suggesting that the presence of nonictalurid interceptor fish in catfish ponds may minimize PGD severity.

Behavioral Interactions between a Native and an Invasive Fish Species in a Thermally Heterogeneous Experimental Chamber

Mechanisms of the displacement of native fish by nonnative fish can include agonistic behaviors that push native fish species out of their preferred habitat, including their thermal optima. To examine these interactions, we built an experimental thermal preference chamber to evaluate: (1) the thermal preference of native, glacial relict northern redbelly dace Chrosomus eos; (2) if the thermal preference and movement changed in the presence of the invasive western mosquitofish Gambusia affinis; and (3) the direction of agonistic interactions. We hypothesized that G. affinis would express agonistic behavior toward C. eos, because G. affinis is widely recognized as an aggressive invader. Given the temperature range of the experimental chamber, i.e., 20–30 °C, C. eos selected an average of 24.3 °C as its thermal preference. After G. affinis’ introduction, the thermal preference of C. eos increased by 1.7 °C and the movement, given by distance (cm) travelled, increased by 21%. Contrary to our prediction, more agonistic interactions were observed in C. eos toward G. affinis. These results indicate that agonistic behavior of G. affinis toward native fish species may be species- and condition-specific, and may not always be the primary mechanism of native species’ displacement. Biological invasions are a global issue and altered thermal regimes are expected to continue. This study provided the novel approach using of a thermally heterogeneous thermal chamber to examine thermal preferences and aggressive interactions between a native and an invasive species. Future research should examine other life history traits that may be conveying the competitive advantage to G. affinis.

Synonymous single nucleotide polymorphism in arsenic (+3) methyltransferase of the Western mosquitofish (Gambusia affinis) and its gene expression among field populations

Naturally occurring arsenic is toxic at extremely low concentrations, yet some species persist even in high arsenic environments. We wanted to test if these species show evidence of evolution associated with arsenic exposure. To do this, we compared allelic variation across 872 coding nucleotides of arsenic (+3) methyltransferase (as3mt) and whole fish as3mt gene expression from three field populations of Gambusia affinis, from water sources containing low (1.9 ppb), medium-low (3.3 ppb), and high (15.7 ppb) levels of arsenic. The high arsenic site exceeds the US EPA’s Maximum Contamination Level for drinking water. Medium-low and high populations exhibited homozygosity, and no sequence variation across all animals sampled. Eleven of 24 fish examined (45.8%) in the low arsenic population harbored synonymous single nucleotide polymorphisms (SNPs) in exons 4 and/or 10. SNP presence in the low arsenic population was not associated with differences in as3mt transcript levels compared to fish from the medium-low site, where SNPs were noted; however, as3mt expression in fish from the high arsenic concentration site was significantly lower than the other two sites. Low sequence variation in fish populations from sites with medium-low and high arsenic concentrations suggests greater selective pressure on this allele, while higher variation in the low population suggests a relaxed selection. Our results suggest gene regulation associated with arsenic detoxification may play a more crucial role in influencing responses to arsenic than polymorphic gene sequence. Understanding microevolutionary processes to various contaminants require the evaluation of multiple populations across a wide range of pollution exposures.

Influence of the presence of invasive mosquitofish and submerged vegetation on oviposition site selection by gray treefrogs (Hyla versicolor)

Amphibians often select oviposition sites based on a variety of cues that indicate the level of risk in the oviposition habitat. Surprisingly, the role of aquatic vegetation or habitat structure/complexity in anuran oviposition site selection has not been extensively studied even though it might affect perceived risk. We examined the effects of free-ranging invasive western mosquitofish (Gambusia affinis) and artificial vegetation/habitat structure on colonisation of experimental pools by gray treefrogs (Hyla versicolor). Hyla versicolor avoided ovipositing in mesocosms with G. affinis. The presence of artificial vegetation/habitat structure had no effect on oviposition site selection by H. versicolor, whether alone or in interaction with G. affinis. Our experiment provides evidence for the avoidance of fish, and more specifically G. affinis, by ovipositing H. versicolor; but provides no evidence for a role of vegetation/habitat structure.

Identifying threats from introduced and translocated non-native freshwater fishes in Croatia and Slovenia under current and future climatic conditions

Introduced and translocated non-native species are a major threat to biodiversity, especially in aquatic habitats. Efforts aimed at the mitigation of impacts and the implementation of preventative measures for the conservation of native biota must rely upon an accurate evaluation of the risks posed by non-native invasive species and are expected to be strengthened by international collaboration. In this study, 76 non-native freshwater fish species of which 48 extant (both introduced and translocated) and 28 horizon were screened for their risk of invasiveness in the neighbouring countries of Croatia and Slovenia under current and future climatic conditions. Using the Aquatic Species Invasiveness Screening Kit (AS-ISK), threshold scores for the Basic Risk Assessment (BRA) and for the combined BRA and Climate Change Assessment (BRA + CCA) allowed to distinguish with a high level of accuracy between low-, medium- and high-risk species – the latter representing ≈70% of the screened species. Brown bullhead Ameiurus nebulosus, round goby Neogobius melanostomus, topmouth gudgeon Pseudorasbora parva and Wels catfish Silurus glanis were the highest-scoring species for Croatia, and Ameiurus nebulosus, snakehead Channa argus and Pseudorasbora parva for Slovenia. There were discrepancies in medium- and high-risk rankings between Croatia and Slovenia for 12 species. Upon comparison of the BRA outcomes with those based on the Freshwater Fish Invasiveness Screening Kit (the predecessor of the AS-ISK), the risk changed for six species in Croatia and five in Slovenia. After accounting for predicted climate change conditions, the BRA + CCA risk scores increased for ≈50% of the species, with western mosquitofish Gambusia affinis, channel catfish Ictalurus punctatus and black carp Mylopharyngodon piceus achieving the highest score increment for Croatia, and round goby Neogobius melanostomus and Chinese (Amur) sleeper Perccottus glenii for Slovenia. The present outcomes will assist decision-makers in the implementation of appropriate measures for the management of extant non-native species and the potential introduction of horizon species. This is important for the regulation of pet trade and aquaculture as well as for management strategies aimed at the conservation of native biodiversity, which in the case of neighbouring countries/jurisdictions will benefit from joint efforts relying on a full risk assessment for the species classified at higher risk of invasiveness.

Feeding Ecology of Age‐0 Gar at Texoma Reservoir Inferred from Analysis of Stable Isotopes

AbstractConservation and restoration of gar (Lepisosteidae) populations in North America are increasingly of interest to fisheries managers. Alligator Gar Atractosteus spatula are being stocked as age‐0 fish in efforts to re‐establish extirpated populations. However, gars are known to be highly cannibalistic in hatcheries, suggesting that age‐0 Alligator Gar introduced into natural habitats may face predation pressures from other gar species, limiting the likelihood of released fish recruiting to the population. Furthermore, introduced age‐0 gar may not have the proper prey resources for rapid growth that would facilitate recruitment to adulthood. Texoma Reservoir, located on the Oklahoma–Texas border, hosts four native gar species, including the Alligator Gar, whose population is supported by supplemental stocking of age‐0 fingerlings. We investigated feeding by age‐0 gar to obtain a baseline level of trophic ecology for this group of fishes, including the potential for poststocking cannibalism. Food webs were reconstructed via analysis of carbon (δ13C) and nitrogen (δ15N) isotopes using Bayesian mixing model approaches. Isotopic values for age‐0 fish of all four gar species were similar. Invertebrates represented a large fraction of the diet for all gars, followed by Common Carp Cyprinus carpio and Grass Carp Ctenopharyngodon idella. Competitive interactions among Bluegill Lepomis macrochirus, White Bass Morone chrysops, White Crappie Pomoxis annularis, and young gar may occur for invertebrates, shads Dorosoma spp., and Western Mosquitofish Gambusia affinis but are likely short‐lived due to the rapid growth of age‐0 gar after their transition to piscivory. Trophic position of age‐0 Alligator Gar, Longnose Gar Lepisosteus osseus, and Spotted Gar Lepisosteus oculatus was positively related to TL, but this relationship was not observed for Shortnose Gar Lepisosteus platostomus. In Texoma Reservoir, the four native gar species, including stocked Alligator Gar, appear to have adequate food resources for recruitment, with little indication of within‐family or interspecific predation. This suggests that stocked Alligator Gar quickly acclimated to their new environment.

Transcriptomic changes in western mosquitofish (Gambusia affinis) liver following benzo[a]pyrene exposure.

Widely distributed western mosquitofish (Gambusia affinis) has been used as a new model species for hazard assessment of environmental stressors such as polycyclic aromatic hydrocarbons (PAHs). However, most of the PAH studies using G. affinis rely on targeted biomarker-based analysis, and thus may not adequately address the complexity of the toxic mechanisms of the stressors. In the present study, the whole transcriptional sequencing of G. affinis liver after exposure to a PAH model, benzo[a]pyrene (BaP) (100μg/L), for 20days was performed by using the HiSeq XTen sequencers. In total, 58,156,233 and 51,825,467 clean nucleotide reads were obtained in the control and BaP-exposed libraries, respectively, with average N50 lengths of 1419bp. In addition, after G. affinis was exposed for 20days, 169 genes were upregulated, and 176 genes were downregulated in liver. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses were applied to all the genes to determine the genes' biological functions and processes. The results clearly showed that the differentially expressed genes were mainly related to immune pathways and metabolic correlation pathways. Interestingly, almost all the pathways related with the immunity were upregulated, while the metabolism pathways were downregulated. Lastly, quantitative real-time PCR (qRT-PCR) was performed to measure expressional levels of twelve genes confirmed through the DGE analysis. These results demonstrate that BaP damages immunity and enhances the consumption of all available energy storage to activate mechanisms of the detoxification in G. affinis. Up until now, the present study is the first time that a whole transcriptome sequencing analysis in the liver of G. affinis exposed to BaP has been reported.

Impacts of non-native fishes under a seasonal temperature gradient are forecasted using functional responses and abundances

Developing predictive methods to forecast the impacts of existing and emerging invasive species is of critical importance to biodiversity conservation. However, invader impacts are context-dependent, making reliable and robust predictions challenging. In particular, it is unclear how temporal variabilities in relation to temperature regime shifts influence invader ecological impacts. In the present study, we quantify the functional responses of three coexisting freshwater fishes: the native freshwater River Goby Glossogobiuscallidus, and the non-native Mozambique Tilapia Oreochromismossambicus and Western Mosquitofish Gambusiaaffinis, under two temperature treatments using chironomid larvae as prey. This was used along with fish abundance data to determine temporal differences in ecological impacts of each fish species between seasons (i.e. at two corresponding temperatures). All three fish species exhibited potentially population-destabilizing Type II functional responses. Their maximum feeding rates were consistently higher in the warm temperature treatment, whereas attack rates tended to be reduced. Non-native Mozambique Tilapia had the highest maximum feeding rate under both temperature treatments (18 °C and 25 °C), followed by the non-native Western Mosquitofish and lastly the native River Goby, suggesting greater per capita impacts on native prey by non-native fishes. The predatory fish abundances differed significantly according to season, with native River Goby and non-native Mozambique Tilapia generally more abundant than non-native Western Mosquitofish. By multiplying functional response maximum feeding rates with abundances of each fish species across the seasonal gradient, the relative impact potential of non-native Mozambique Tilapia was consistently higher compared to that of native gobies. Western Mosquitofish impacts were less apparent, owing to their low abundances. We demonstrate how seasonal temperature fluctuations affect the relative impact capacities of introduced species and the utility of consumer functional response and the relative impact potential metric in impact forecasting.

Inter‐specific differences in invader and native fish functional responses illustrate neutral effects on prey but superior invader competitive ability

Abstract Inter‐specific interactions are key factors in the structuring and functioning of ecological communities. Therefore, it is necessary to assess species interactions, such as predator–prey dynamics and competitive exclusion, within the context of continuing global species introductions. The aim of the present study was to assess ecological impacts and competitive exclusion dynamics involving co‐occurring introduced and native fish species, using the multiple predator functional response (FR) approach. We use comparative FR analysis (resource uptake as a function of resource density) to assess inter‐specific interactions between the invasive western mosquitofish Gambusia affinis and the native freshwater river goby Glossogobius callidus towards chironomid larvae. The FR was derived for each fish species as individuals and when in heterospecific pairings. Data from single individuals were used to predict the expected FR of individuals when in heterospecific multiple predator combinations. Expected FRs were then compared to the observed FRs of each predator in combination trials, enumerated using prey items in their gut contents. Both fish species displayed Type II FRs, however, in single fish trials, invasive mosquitofish had significantly higher FRs (curve asymptotes; i.e. shorter handling times and higher maximum feeding rates) than native river gobies. Heterospecific mosquitofish‐river goby combinations revealed that the FR of the river goby was reduced (i.e. longer handling times and lower maximum feeding rates) by the presence of mosquitofish, whereas this combination greatly enhanced mosquitofish FR magnitudes (i.e. shorter handling times and higher maximum feeding rates). The heterospecific treatments resulted in neutral impacts on prey and there were clear inter‐species interference in favour of the non‐native mosquitofish. This study demonstrates how multiple predators can alter the shape of individual FRs, with neutral effects on prey but superior invader competitive ability. This has implications for predicting the naturalisation success of invasive predators, as predatory and competitive interactions with native predators and prey may facilitate rather than impede establishment.

Immobilization Threshold and Fish Conductivity of Two Small Fishes

AbstractPower transfer theory (PTT), a useful paradigm in electrofishing, asserts that the threshold power density (Dt, μW/cm3) transferred from water to fish for immobilization is dependent on the conductivity (μS/cm) of the water (σw) and of the fish (σf). Larger differences between the two conductivities require higher applied power densities and may make capture more difficult. Over a range of water conductivities, Dt as a function of σw will form a U‐shaped curve, and the minimum provides an estimate of σf and Dm (the lowest value of Dt that occurs when σw and σf are equal). Studies have demonstrated a narrow range of σf (56–160 μS/cm) relative to the conductivity of natural waters (10–5,000 μS/cm). However, these σf values are for larger species. Electrofishing may also be directed at the capture of smaller species or diverse communities. In an experimental tank, we estimated Dm and σf for a small cyprinid, the Red Shiner Cyprinella lutrensis (TL = 35–64 mm) and a smaller poeciliid, the Western Mosquitofish Gambusia affinis (TL = 23–46 mm). We estimated Dm and σf to be 120 μW/cm3 and 23 μS/cm, respectively, for Red Shiners (n = 72) and 143 μW/cm3 and 23 μS/cm, respectively, for Western Mosquitofish (n = 23). These values for σf are less than half the minimum of previously reported values, and our Dm estimates are less than those that have been reported for game species of similar length (200–300 μW/cm3). Our results serve to explain why smaller species require higher applied power densities and are more difficult to capture from an assemblage of various species and sizes.

Endocrine disrupting effects in western mosquitofish Gambusia affinis in two rivers impacted by untreated rural domestic wastewaters

Domestic wastewaters are an important source of endocrine disrupting chemicals in the receiving aquatic environment. Most rural domestic wastewaters (RDWs) in China have been directly discharged into the aquatic environment without any treatment. Here we studied the effects of RDWs on the western mosquitofish (Gambusia affinis) from two rural rivers receiving untreated RDWs. Mosquitofish samples were collected at 5 sampling sites along two rivers during dry and wet seasons. Sex ratios, secondary sex characteristics and transcriptional levels of target genes related to the endocrine system in adult females and males were determined. In parallel, various pollutants including steroid hormones, phenolic compounds, pesticides, polycyclic aromatic hydrocarbons (PAHs) and heavy metals were measured in the water samples at all sites. The results showed that the androgenic effects in the fish were evidenced by significant increase in male to female ratio in fish populations at two sampling sites and by the presence of modified hemal spines in females at four sampling sites when compared to the reference site. The males from the two rivers had increased Vtg mRNA expressions with a maximal 6.2-fold increase relative to the reference site and a delayed development of hemal spines. The redundancy analysis (RDA) showed that some physiological parameters were related to steroid hormones, phenolic compounds and PAHs. The findings from this study suggest that RDWs can lead to masculinization in females and feminization in males.

First detection of Erysipelothrix sp. infection in western mosquitofish Gambusia affinis inhabiting catfish aquaculture ponds in Mississippi, USA.

Native and introduced fish can serve as reservoirs for pathogens of cultured fish species. In the current study, 351 archived western mosquitofish Gambusia affinis collected from experimental catfish production ponds in Mississippi, USA, were surveyed histologically to evaluate their potential as vectors for fish pathogens. In addition to epitheliocystis and multiple metazoan parasites, 8 fish had widespread basophilic colonies of small Gram-positive rods associated primarily with stroma supporting the skeletal muscle and bone, as well as connective tissue components of other tissues and organ systems, such as perivascular adventitia and basement membranes. These findings were consistent with spaC-type Erysipelothrix sp. infections in ornamental fish cultured in the USA. The 16S rRNA, gyrase B (gyrB), and surface protective antigen (spa) genes were amplified and sequenced from bacterial colonies excised from paraffin-embedded tissue sections using laser capture microdissection. Molecular data confirmed the identity of a spaC-type Erysipelothrix sp., which grouped phylogenetically with spaC-type Erysipelothrix sp. from diseased ornamental fish. Given the significance of commercial catfish aquaculture in the southeastern USA and the widespread distribution of mosquitofish in catfish ponds throughout the region, infectivity trials with channel catfish Ictalurus punctatus were conducted. Catfish fingerlings were exposed to a spaC-type Erysipelothrix sp. isolate by intracoelomic injection and gavage. No mortality was observed in catfish exposed by either route, and surviving fish demonstrated no significant histopathologic lesions, suggesting channel catfish have low susceptibility to the bacteria. Further research is warranted to investigate the susceptibility of other cultured fish species to this emergent fish pathogen.

Predator-induced changes of male and female mating preferences: innate and learned components.

While many mating preferences have a genetic basis, the question remains as to whether and how learning/experience can modify individual mate choice decisions. We used wild-caught (predator-experienced) and F1 laboratory-reared (predator-naïve) invasive Western mosquitofish Gambusia affinis from China to test whether mating preferences (assessed in a first mate choice test) would change under immediate predation threat. The same individuals were tested in a second mate choice test during which 1 of 3 types of animated predators was presented: 1) a co-occurring predator, 2) a co-evolved but not currently co-occurring predator, and 3) a non-piscivorous species as control. We compared preference scores derived from both mate choice tests to separate innate from experiential effects of predation. We also asked whether predator-induced changes in mating preferences would differ between sexes or depend on the choosing individual’s personality type and/or body size. Wild-caught fish altered their mate choice decisions most when exposed to the co-occurring predator whereas laboratory-reared individuals responded most to the co-evolved predator, suggesting that both innate mechanisms and learning effects are involved. This behavior likely reduces individuals’ risk of falling victim to predation by temporarily moving away from high-quality (i.e., conspicuous) mating partners. Accordingly, effects were stronger in bolder than shyer, large- compared with small-bodied, and female compared with male focal individuals, likely because those phenotypes face an increased predation risk overall. Our study adds to the growing body of literature appreciating the complexity of the mate choice process, where an array of intrinsic and extrinsic factors interacts during decision-making.

Effect of the exposure to Mn-doped ZnS nanoparticles on biomarkers in the freshwater western mosquitofish Gambusia affinis

ABSTRACTSynthesized Mn-doped ZnS nanoparticles, with 10% of Mn dopant, were used to investigate their environmental toxicity. Mn-doped ZnS quantum dots (QDs) stabilized by 3-mercaptopropionic acid (MPA) were synthesized in a basic aqueous solution using the nucleation doping. The optical properties and structure of the obtained Mn (10%):ZnS QDs have been characterized by X-ray diffraction, UV–vis, photoluminescence spectroscopies and transmission electron microscopy. The brain, gills and liver stained sections from Gambusia affinis were dissected. Antioxidant enzyme activities (acetylcholinesterase and catalase), as well as malondialdehyde and H2O2 levels, were determined after exposure (94 h) to 14 and 28 mg/L of nanoparticles. The obtained nearly monodisperse Mn(10%):ZnS@MPA QDs have an average diameter of ca. 2.8 nm and a zinc-blende crystal structure. Mn-doped ZnS acts differently on the activities of the biomarkers in a dose-dependent manner. The recorded alterations varied between organs. Such findings provide information on the biological target of nanoparticles and their behaviour within the environment.

Invasiveness screening of non‐native fishes for the middle reach of the Yarlung Zangbo River, Tibetan Plateau, China

AbstractThe aim of this study was to identify potentially invasive non‐native freshwater fishes in the middle reach of the Yarlung Zangbo River, Tibetan Plateau (China), using the Aquatic Species Invasiveness Screening Kit (AS‐ISK), as decision‐support tool. Based on independent evaluations of 24 non‐native freshwater fishes, receiver operating curve analysis identified a threshold score of ≥29 for distinguishing species likely to pose a high risk of becoming invasive from species likely to pose low‐to‐medium risk (<29) in the risk assessment area. Nine species were categorized as “high risk”: goldfish Carassius auratus, topmouth gudgeon Pseudorasbora parva, brook trout Salvelinus fontinalis, Oriental weatherfish (a.k.a. dojo gudgeon) Misgurnus anguillicaudatus, Siberian taimen Hucho taimen, common carp Cyprinus carpio, peled Coregonus peled, western mosquitofish Gambusia affinis, and Chinese rice fish Oryzias sinensis. The three lowest scoring species were Arctic cisco Coregonus autumnalis, Wuchang bream Megalobrama amblycephala, and Chinese ice fish Neosalanx taihuensis, which are unlikely to be invasive because they are unable to complete their life cycle in the risk assessment area. Climate change assessments scores increased or remained the same for warm‐water species and decreased for coldwater species. This study was the first application of AS‐ISK in western China, and the results suggest that AS‐ISK is a useful and valid tool for identifying potentially invasive risk aquatic species in China.

Sensory Biology as a Risk Factor for Invasion Success and Native Fish Decline

AbstractNative freshwater fish populations are among the world's most threatened taxa due to the combined effects of habitat degradation and invasive alien species. Habitat degradation negatively impacts native species, whereas invasive species tend to possess adaptations, such as thermal and salinity tolerance, that are more suited to the degraded environment. Sensory ecology may also be a contributing factor. Most threatened native species are visual feeders, whereas invasive species found in degraded systems often have nonvisual specializations. Behavioral and distributional characteristics of the invasive Western Mosquitofish Gambusia affinis and the New Zealand native Inanga Galaxias maculatus illustrate the potential for sensory biology to influence foraging success, distribution, and species interaction between degraded and clear habitats. Behavioral trials measured the change in feeding rate in clear (0 NTU) and turbid (100 NTU) water over 30 min for Inanga and Western Mosquitofish feeding on brine shrimp Artemia salina nauplii. These experiments showed that Western Mosquitofish maintained similar feeding rates between clear and turbid water, whereas the native species exhibited a marked decline in feeding efficiency in turbid water. Across a strong natural turbidity boundary, the alien species was found to dominate turbid habitat less than 1 m from clear water, where both species were found. Accounting for sensory biology as a potential contributing factor in the establishment of invasive fish species in degraded habitat may help to identify invasive species risk and to shape strategies for rehabilitating native species.

Characterizing a novel predator\u2013prey relationship between native Diplonychus esakii (Heteroptera: Belostomatidae) and invasive Gambusia affinis (Teleostei: Poeciliidae) in central China

A considerable body of the literature considers the potential impact of exotic predators on native prey organisms, while comparatively, few studies have asked whether and how native predators include novel prey types into their diet spectrum. Here, we asked whether the native aquatic heteropteran Diplonychus esakii preys on the highly invasive western mosquitofish (Gambusia affinis), which has been introduced to southern China and threatens native fish species through competition and predation on their fry. We conducted 48-h prey choice experiments under semi-natural conditions. In a ‘no-choice’ experiment (one predator and one potential prey; n = 200), we found the heteropterans to prey more on large-bodied fish, a pattern that was also described for other belostomatids, while prey sex had no effect on capture rates. Moreover, large-bodied heteropterans caught more fish than small-bodied individuals. However, overall capture rates in our study were low (11.5–30%) compared to studies on other belostomatids, which explains why subsequent binary prey choice experiments using one predator and two prey—either large and small females or male and female (with smaller sample sizes of n = 20 and 30, respectively)—did not confirm the results of our first experiment. Our study exemplifies how a pattern of body size-dependent predation can arise in a novel (not coevolved) predator–prey interaction. We tentatively argue that the observed pattern could be driven by intrinsic features of the predator, namely, altered prey preferences with increasing age coupled with a general preference for large-bodied prey, or changing nutritional needs at different developmental stages.

Molecular and morphometric evidence for the widespread introduction of Western mosquitofish Gambusia affinis (Baird and Girard, 1853) into freshwaters of mainland China

Molecular and morphometric evidence for the widespread introduction of Western mosquitofish Gambusia affinis (Baird and Girard, 1853) into freshwaters of mainland China