# Paradise under threat: the successful invasion of the freshwater shrimp Neocaridina davidi (Bouvier, 1904) and its microsporidian parasites on La Réunion Island

Sebastian Prati, Laetitia Faivre, Valentin de Mazancourt, Bernd Sures, Pierre Valade

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## To cite this version:

Sebastian Prati, Laetitia Faivre, Valentin de Mazancourt, Bernd Sures, Pierre Valade. Paradise under threat: the successful invasion of the freshwater shrimp Neocaridina davidi (Bouvier, 1904) and its microsporidian parasites on La Réunion Island. BioInvasions Records, 2025, 14 (2), pp.403 - 419. 10.3391/bir.2025.14.2.08 . hal-05214330

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Research Article

# Paradise under threat: the successful invasion of the freshwater shrimp *Neocaridina davidi* (Bouvier, 1904) and its microsporidian parasites on La Réunion Island

Sebastian Prati<fnref n="1" />,<fnref n="2" />, Laetitia Faivre<fnref n="3" />, Valentin de Mazancourt<fnref n="4" />, Bernd Sures<fnref n="1" />,<fnref n="2" />,<fnref n="5" /> and Pierre Valade<fnref n="3" />

Corresponding author: Sebastian Prati (sebastian.prati@uni-due.de)

**Citation:** Prati S, Faivre L, de Mazancourt V, Sures B, Valade P (2025) Paradise under threat: the successful invasion of the freshwater shrimp *Neocaridina davidi* (Bouvier, 1904) and its microsporidian parasites on La Réunion Island. *BioInvasions Records* 14(2): 403–419, https://doi.org/10.3391/bir.2025.14.2.08

**Received:** 9 August 2024

**Accepted:** 9 March 2025

**Published:** 21 May 2025

**Handling editor:** Michal Grabowski

**Thematic editor:** Kenneth A. Hayes

**Copyright:** © Prati et al.

This is an open access article distributed under terms of the Creative Commons Attribution License (Attribution 4.0 International - CC BY 4.0).

OPEN ACCESS

## Abstract

Invasive species are one of the major threats to global biodiversity, particularly in hotspots of endemic species, such as oceanic insular ecosystems. Tropical and subtropical islands are particularly vulnerable to biological invasions, with freshwater ecosystems expected to experience the most severe impacts. This is especially true if the insular freshwater fauna comprises a large set of near-threatened to critically endangered species. This study assesses the establishment of the pet-traded shrimp *Neocaridina davidi* and its parasites on the island of La Réunion, a biodiversity hotspot within the Malagasy region. We confirm the establishment of feral *N. davidi* in two river catchments. Moreover, we confirm the presence of the microsporidian *Ecytonucleospora hepatopenaei*, an economically and ecologically relevant parasite that might impact a wide range of native species, including those living in brackish and marine environments. Three other microsporidians, two of which are unknown, have also been detected for the first time in *N. davidi*, raising concerns over possible spillover-spillback events. Therefore, we recommend timely actions to curb the spread of *N. davidi* and its parasites in an effort to preserve the already endangered native freshwater fauna.

**Key words:** Atyidae, DNA barcoding, *Ecytonucleospora hepatopenaei*, invasive species, Microsporidia, pet-trade, Decapoda

## Introduction

Due to their negative impact on recipient environments, invasive species are increasingly becoming one of the major threats to global biodiversity (Simberloff et al. 2013; Gallardo et al. 2016; Pyšek et al. 2020). This is especially true for hotspots of endemic species, such as oceanic insular ecosystems, where the impact of invasive species is disproportionally higher than that experienced on continents, mostly due to simplified food webs without top predators and small population sizes (Velmurugan 2008; Keppel et al. 2014; Russell et al. 2017; Lenzner et al. 2020). Tropical and subtropical islands

<footnote n="1">¹Aquatic Ecology, University of Duisburg-Essen, Universitätsstr. 5, 45141 Essen, Germany</footnote>

<footnote n="2">²Centre for Water and Environmental Research, University of Duisburg-Essen, Universitätsstr. 2, 45141 Essen, Germany</footnote>

<footnote n="3">³OCEA Consult, 97432 Ravine des Cabris, La Réunion, France</footnote>

<footnote n="4">⁴Laboratoire de Biologie des Organismes et Écosystèmes Aquatiques (BOREA), Muséum national d'Histoire naturelle, CNRS-8067, IRD-207, Sorbonne Université, UCN, UA, Equipe Biodiversité, Plasticité, Adaptation et Conservation, 75005, Paris, France</footnote>

<footnote n="5">⁵Research Center One Health Ruhr of the University Alliance Ruhr, University of Duisburg-Essen, Universitätsstraße 5, 45141 Essen, Germany</footnote>
are particularly vulnerable to biological invasions due to food-webs erosion bolstered by increased anthropogenic pressures and the introduction of non-native and eventually invasive species (Velmurugan 2008; Barlow et al. 2018; Moser et al. 2018). The largest impact of non-native species on oceanic islands is expected in terrestrial and freshwater ecosystems (Lenzner et al. 2020). Here, introduced non-native species often lead to strong predator-prey dynamics and competition, rapidly reducing the abundance of native species or leading to local extinctions (Russell et al. 2017). Freshwater ecosystems are generally more prone to experience biological invasion than their terrestrial counterpart due to habitat degradation and a soaring number of introduced non-native species linked to biological control, recreational angling, aquaculture, or pet trade (Cambray 2003; Savini et al. 2010; Patoka et al. 2018; Bernery et al. 2022). Even if introduced non-native species fail to establish, they might still negatively affect the recipient ecosystems by transmitting pathogens that can persist in the system even after the original host's disappearance (Simberloff et al. 2013; Yonvitner et al. 2020).

The oceanic island of La Réunion (French overseas territory), a biodiversity hotspot within the Malagasy region (Myers et al. 2000), is increasingly threatened by invasive species, including parasites introduced alongside their non-native hosts (Sasal et al. 2008; Soubeyran et al. 2015; Fenouillas et al. 2021). While the impact of invasive species on the island's terrestrial ecosystem is relatively well-studied, information is lacking for the freshwater counterpart. Several of the 29 native fish and the vast majority of the 10 decapod species present on the island are considered near-threatened to critically endangered at a regional level (Keith et al. 2006; Fricke et al. 2009; IUCN 2010; Froese and Pauly 2024). A situation that may worsen with the introduction of non-native species. Currently, successfully introduced non-native species on the island number eight fish and three decapods (Keith et al. 2006; Fricke et al. 2009; IUCN 2010; Leoville 2012; Froese and Pauly 2024). However, observations of additional species, mostly originating from the pet trade, suggest that the number of established non-native species is likely to increase. Several of the successfully introduced species on the island, e.g., *Amatitlania nigrofasciata* (Günther, 1867), *Cherax quadricarinatus* (von Martens, 1868), *Poecilia reticulata* (Peters, 1859), and *Xiphophorus helleri* (Heckel, 1848), have also established feral populations worldwide mostly due to pet-trade releases (Magalhães and Jacobi 2017; Seebens et al. 2017; Baudry et al. 2020; Haubrock et al. 2021). Among pet-traded crustaceans not yet confirmed to be established on La Réunion, and thus not included in the aforementioned list, is the atyid shrimp, *Neocaridina davidi* (Bouvier, 1904) (syn. *Cardina davidi*, *C. denticulata sinesis*, *N. denticulata davidi*, *N. denticulata sinensis*, *N. heteropoda*, *N. heteropoda heteropoda*).

The shrimp was presumably observed on the island in 2017 by an employee of Hydrô Réunion, who signaled it to GEIR (Group Espèces Invasives de La Réunion). Volunteers of the latter, a group constituted by associations
and professionals and local institutions, promptly engaged in an eradication
action (Groupe Espèces Invasives de La Réunion 2017). Since then, a
ministerial decree (28 June 2021) prohibits the import, sale, and possession
(except for animals already owned before July 28, 2021) of exotic animal
species (including *N. davidi* and other pet-traded decapods) in La Réunion.
Exotic animals owned prior to the decree can be kept if owners declare them,
prevent escapes and reproduction, and do not sell or give them away. While
these measures might have reduced the number of *N. davidi* traded on the
island, the shrimps continue to be sold among aquarium hobbyists and the
whereabouts of the feral *N. davidi* population remain unknown.

*Neocardina davidi*, a shrimp of Southeast Asian origins widely available in the global pet trade, displays high environmental plasticity and fecundity, which allow them to rapidly adapt to local conditions becoming invasive (Klotz et al. 2013; Prati et al. 2024). Established feral populations of *N. davidi* have been reported worldwide, including in Canada, Germany, Hungary, Israel, Metropolitan France, Japan, Poland, Slovakia, and the USA (Klotz et al. 2013; Jabłońska et al. 2018; deBruyn 2019; Levitt-Barmats et al. 2019; Weiperth et al. 2019; Prati et al. 2024; Jamonneau et al. 2025). The ecological impacts of introduced *N. davidi* include the replacement of native shrimps with similar ecological niches (Onuki and Fuke 2022), alteration of meiofaunal assemblages (Weber and Traunspurger 2016), changes in leaf-litter breakdown in invaded areas (Schoolmann and Arndt 2017), and possible parasite exchange with native and invasive species (Patoka et al. 2016; Prati et al. 2024).

*Neocaridina davidi* hosts a wide range of commensals and parasites (Ohtaka et al. 2012; Liao et al. 2018; Bauer et al. 2021; Maciaszek et al. 2023; Prati et al. 2024), some of which have been co-introduced outside their native range (Niwa and Ohtaka 2006; Maciaszek et al. 2021; Kakui and Komai 2022; Prati et al. 2024). Among them is also the ecologically and economically relevant microsporidian parasite *Ecytonucleospora (=Enterocytozoon) hepatopenai* (EHP) (Tourtip et al., 2009) (Wang et al. 2023), which has first been molecularly detected in a feral population of *N. davidi* inhabiting a German stream (Schneider et al. 2022). This parasite was later detected both molecularly and histologically in other European feral populations and animals sold in the pet trade (Prati et al. 2024). EHP is a host generalist parasite known to infect cultured penaeid shrimps in coastal and marine environments (Chaijarasphong et al. 2021) but also a wide range of freshwater, brackish, and marine invertebrates, including the freshwater prawn *Macrobrachium rosenbergii* (De Man, 1879) and insects such as dragonflies (Karthikeyan and Sudhakaran 2020; Krishnan et al. 2021; Jang et al. 2022; Munkongwongsiri et al. 2022; Dewangan et al. 2023; Wan Sajiri et al. 2023). However, EHP's infectivity is reduced in low-salinity environments (Aranguren Caro et al. 2021).
Native freshwater decapods, most of which are considered vulnerable, comprise several amphidromous species belonging to the genera *Atyoida*, *Caridina*, *Macrobrachium*, and *Palaemon* (Keith et al. 2006). These might be impacted by introduced *N. davidi* and its parasites. If present, infected *N. davidi* individuals might transmit infectious pathogens to native species. In the case of EHP, the parasite might also indirectly impact other macroinvertebrates, including those living in brackish and marine environments. Therefore, this study aims to confirm the presence of feral *N. davidi* on the island and conduct a parasitological screening aimed at detecting microsporidian parasites.

## Materials and methods

### *Sampling sites*

Shrimps were sampled on 15 April 2024, in three sites along two river catchments with perennial water on the island's eastern side: the Mat (n = 2) and the Saint-Jean (n = 1). The Mat, with 145 km², is the largest catchment on the island. Its water sources, fed by regular rainfall, originate from the volcanic cirque of Salazie and flow eastwards toward the Indian Ocean. In the lower part of the river, a seemingly large population of shrimps, presumably *N. davidi*, was observed for the first time in 2017 by a group of citizen conservationists (PM 2017).

Successively, riverine ecological monitoring campaigns conducted by OCEA Consult revealed a widespread presence of shrimps in the Mat catchment. These monitoring campaigns also included other areas, revealing the shrimp's presence in the lower part of the nearby Saint-Jean catchment (Figure 1). We, therefore, collected shrimps in the upper part of the Mat River from a right-side creek outflowing from the Mare à Poule d'Eau, a pond located in Salazie, from the Bras Citronnier, a left-side tributary of the Mat River located further downstream, and from the Ravine Sèche, a right-side tributary of the Saint-Jean River (Figures 1, 2; Table 1). At the Ravine Sèche site, presumed *N. davidi* co-occurred with the native *Caridina typus*.

### *Sampling collection and processing*

Shrimps were collected using hand nets and immediately preserved in 96% ethanol. All individuals were morphologically and molecularly identified, measured, dissected in the laboratory, and visually screened for internal parasites. The morphological identification of presumed *N. davidi*, followed (Bouvier 1904; Englund and Cai 1999; Klotz et al. 2013). However, its taxonomy remains somewhat unclear, particularly when it comes to distinctions between *N. davidi* and *N. denticulata* (De Haan, 1844) (Onuki and Fuke 2022). Therefore, we relied on the sexual dimorphism in the third pereiopods and the distinctly shorter appendix interna of the male second pleopods, as suggested by Shih et al. (2024), and molecular analyses.
<figure><img src="image_3.png" /><figcaption>**Figure 1.** Map of the sampling areas where *Neocaridina davidi* individuals were collected. Black dots indicate sites where shrimp were collected in the present study, and white dots indicate additional sites where *N. davidi* was observed during monitoring campaigns conducted by OCEA Consult. The map was generated using QGIS.</figcaption></figure>

A small portion of shrimp, including muscles and hepatopancreatic tissue, was used for molecular analyses of hosts and microsporidian parasites. Epibionts were not analyzed as their preservation in ethanol is generally poor.

*Molecular analyses*

DNA was isolated from hosts using a modified salt precipitation protocol described by Grabner et al. (2015). Shrimps were identified using the universal eukaryotic primers LCO1490 (5'-GGTCAACAAATCATAAAG ATATTGG-3') and HCO2198 (5'-TAAACTTCAGGGTGACCAAAAAA TCA-3') (Folmer et al. 1994) targeting the COI region and microsporidians with the universal microsporidian primer V1F (5'-CACCAGGTTGATTC TGCCTGAC-3') (Zhu et al. 1993) and 1342R (5'-ACGGGCGGTGTGTAC AAAGAACAG-3') (McClymont et al. 2005) targeting the small subunit ribosomal RNA gene (SSU rRNA). PCR reactions for shrimps consisted of 20 µL assay with 10 µL of Dream-TaqTM Hot Start Green PCR Master Mix (Thermo Fisher Scientific, Waltham, MA, USA), 1.6 µL (5 µM) of each primer, 4.8 µL of nuclease-free water and 2 µL of DNA template per reaction. Those for microsporidians consisted of 20 µL composed of 10 µL of 2x AccuStart II PCR ToughMix (Quantabio), 1 µL of each primer (0.5 µM), 0.35 µL of 50x GelTrack Loading Dye (Quantabio), 6.65 µL MilliQ water and
<figure><img src="image_4.png" /><figcaption>**Figure 2.** Sites in which *Neocaridina davidi* were collected: A: Creek near Salazie, B: Bras Citronnier, C: Ravine Sèche, and D: feral *Neocaridina davidi* photographed underwater. Photos by Sebastian Prati.</figcaption></figure>

<table><caption>**Table 1.** Sampling sites in which *N. davidi* were collected, including elevation, temperature, and conductivity measured at the collection date (15/04/2024).</caption><thead><tr><th>Catchment</th><th>Sampling sites</th><th>Coordinates</th><th>Elevation m.s.l.</th><th>Temperature [°C]</th><th>Conductivity [µs/cm]</th></tr></thead><tbody><tr><td rowspan="2">Mat</td><td>Creek near Salazie</td><td>-21.0418, 55.5295</td><td>526</td><td>24.5</td><td>268</td></tr><tr><td>Bras Citronnier</td><td>-20.9881, 55.6191</td><td>171</td><td>24.5</td><td>132</td></tr><tr><td>Saint-Jean</td><td>Ravine Sèche</td><td>-20.9680, 55.6460</td><td>120</td><td>26.2</td><td>76</td></tr></tbody></table>

1 µL of DNA template. The PCR setting used for the primer pair LCO1490-HCO2198 followed those employed by Prati et al. 2024), while those used for the primer pair V1F-1342R were the following: initial denaturation for 5 min at 94 °C, followed by 35 cycles of denaturation for 40 s at 94 °C, 40 s of annealing at 60 °C and 55 s of elongation at 68 °C, and a final elongation step for 5 min at 68 °C. PCR products were sent unpurified to Microsynth Seqlab (Germany) for Sanger sequencing.

Raw sequences were quality-checked and edited using Geneious Prime v2024.0.5 (Biomatters, Ltd., New Zealand) and then compared against GenBank records using the blastn algorithm (https://blast.ncbi.nlm.nih.gov).
Shrimps and parasite sequences were separately aligned using the MAFFT v7.490 algorithm with standard settings (Katoh et al. 2019) and Maximum likelihood phylogenetic trees (1000 replicate bootstrap values) were produced in IQ-Tree 2.2.2.6 (Minh et al. 2020). The substitution models chosen based on the Bayesian Information Criterion were TPM2u+F+I for shrimps and TIM3+F+G4 for microsporidians, and the outgroups *Neocaridina palmata* (Shen, 1948) (NCBI GenBank accession number MN701612) and *Triwangia caridinae* (Wang et al., 2013) (JQ268567). Sequences generated in this study were submitted to NCBI GenBank (accession number PQ069719 for *N. davidii* and PQ096043-47 for microsporidians).

## Statistical analyses

Differences in the carapax length among *N. davidii* collected at different sampling sites were investigated with linear regression, accounting for size differences related to sex. The model included carapax length as the dependent variable and sampling sites and sex (females and males) as interacting independent variables. The results were summarized using the Anova type 3 function from the r package car (Fox and Weisberg 2018). The prevalence of microsporidian parasites was too low for direct comparisons between shrimp populations or shrimp sex. However, we used the exact binomial probability estimation with a 95% confidence interval to estimate the infection rate of background populations at each site using the R package exactici (Fay 2023). Statistical and descriptive analyses were performed with the open-source software R (version 4.4.1, R Core Team 2024) via the RStudio GUI (version 2024.04.2, RStudio Inc.).

## Results

A total of 120 presumed *N. davidii* individuals were collected. The sexual dimorphism in the third pereiopods and appendix interna of the male second pleopods was consistent with that of *N. davidii*. Moreover, the shrimps showed a bright red coloration typically displayed in the pet-traded *N. davidii* sold under the commercial names red cherry and red fire (Figure 2D). Morphological identification was corroborated by molecular identification. Irrespective of sampling location, a single *N. davidii* haplotype based on COI sequences was detected. This showed 100% similarity and 97.04–100% coverage with the haplotype Ndh2 (see Prati et al. 2024) of feral and pet-traded individuals previously found in Brazil (PP718677), Canada (MG319788), Germany, Hungary, Poland, and Slovakia (MG816764–65 and OR610863), and wild individuals from Taiwan (MG734262) (Figure 3).

Among the collected *N. davidii*, 24 were females (four of whom were ovigerous), 56 males, and 40 immatures. Overall, the size of sexed *N. davidii* varied greatly between genders ($F(1, 74) = 5.1, p = 0.026$), with females having
<figure><img src="image_5.png" /><figcaption>**Figure 3.** A: Maximum likelihood phylogenetic tree of feral *Neocaridina davidi* and B: microsporidians identified in this study. Grey dots represent bootstrap support values above 90%. Sequences obtained in this study are indicated in bold. The substitution models used are TPM2u+F+I for shrimps and TIM3+F+G4 for microsporidians, and the outgroups are represented by *Neocaridina palmata* and *Triwangia caridinae*. The names and circumscriptions of microsporidian clades follow Bojko et al. (2022).</figcaption></figure>

a larger carapax length than males and between sampling sites (F (2, 74) = 16.14, p < 0.001) mostly due to the large size of individuals of both sexes collected at Ravine Sèche. However, such differences were also influenced by differing sex ratios across sampling sites (F (2, 74) = 4.31, p = 0.017). Namely, the
<table><caption>**Table 2.** Prevalence of microsporidians in *Neocaridina davidi* for every sampling site (All = all, F = females, M = males, and I = immatures individuals), with a 95% confidence interval for background population prevalence based on binomial probability estimation. Note that the 95% confidence interval is calculated for the overall prevalence and that of each microsporidium based on all individuals (n = 40) collected at each sampling site.</caption><thead><tr><th>Sampling sites</th><th>N</th><th>Sex</th><th>Size</th><th>Prevalence in %</th><th>95% CI in %</th><th>Microsporidians</th></tr></thead><tbody><tr><td rowspan="4">Creek near Salazie</td><td>40</td><td>All</td><td>3.19 ± 0.91</td><td>5 (2/40)</td><td>0.61–16.92</td><td>All</td></tr><tr><td>7</td><td>F</td><td>4.23 ± 0.61</td><td>0 (0/7)</td><td>—</td><td>—</td></tr><tr><td>17</td><td>M</td><td>3.66 ± 0.26</td><td>0 (0/17)</td><td>—</td><td>—</td></tr><tr><td>16</td><td>I</td><td>2.23 ± 0.44</td><td>12.5 (2/14)</td><td>0.61–16.92</td><td>Orthosomella lipae</td></tr><tr><td rowspan="5">Bras Citronnier</td><td>40</td><td>All</td><td>3.07 ± 0.88</td><td>7.5% (3/40)</td><td>1.57–20.39</td><td>All</td></tr><tr><td>8</td><td>F</td><td>4.05 ± 0.48</td><td>0 (0/8)</td><td>—</td><td>—</td></tr><tr><td>14</td><td>M</td><td>3.57 ± 0.29</td><td>7.14 (1/14)</td><td>0.06–13.16</td><td>Microsporodium sp. SRE01</td></tr><tr><td>18</td><td>I</td><td>2.24 ± 0.46</td><td>5.56 (1/18)</td><td>0.06–13.16</td><td>Ecytonucleospora hepatopenaei</td></tr><tr><td></td><td></td><td></td><td>5.56 (1/18)</td><td>0.06–13.16</td><td>Microsporidium sp. SRE02</td></tr><tr><td rowspan="4">Ravine Sèche</td><td>40</td><td>All</td><td></td><td>0 (0/40)</td><td>0.00–8.81</td><td>All</td></tr><tr><td>9</td><td>F</td><td>5.27 ± 0.77</td><td>0 (0/9)</td><td>—</td><td>—</td></tr><tr><td>25</td><td>M</td><td>4.04 ± 0.50</td><td>0 (0/25)</td><td>—</td><td>—</td></tr><tr><td>6</td><td>I</td><td>2.62 ± 0.36</td><td>0 (0/6)</td><td>—</td><td>—</td></tr></tbody></table>

highest proportion of females was found in the Bras Citronnier (36.36%) and the lowest at the ravine Ravine Sèche site (26.47%). The overall prevalence of microsporidians in the shrimp investigated was 4.16% and between 1.36 and 9.46% for background populations. Four isolates were detected, three of which were found in the Bras Citronnier population (Table 2). Immature *N. davidi* individuals had the highest diversity of microsporidians, albeit with low prevalences. No females but a single male was infected (Table 2).

*Neocaridina davidi* individuals were infected with EHP isolated from the prawn *Penaeus vannamei* (Boone, 1931) (99.9% similarity and 100% coverage to KX981865), *Orthosomella lipae* (Ovcharenko et al., 2013) isolated from the coleopteran *Liophloeus lentus* (Germar, 1823) (100% similarity and 99.5% coverage to JF960137), and two undescribed microsporidian isolates here named *Microsporidium* sp. SRE01 and *Microsporidium* sp. SRE02. The most similar isolate to *Microsporidium* sp. SRE01 was *Microsporidium* sp. EM.L-11 isolated from the amphipod *Eulimnogammarus verrucosus* (Gerstfeldt, 1858) (87% similarity and 84.2% coverage to KT956059), and the closest described species was *Enteroppectra longa* (Zhang & Felix, 2016) isolated from the nematode *Oscheius* sp. (85.3% similarity and 84.5% coverage, to KX36014). The most similar isolate to *Microsporidium* sp. SRE02 was *Orthosomella* sp. KMI-3 isolated from the moth *Conistra vaccinii* (Linnaeus, 1761) (98.2% similarity and 100% coverage to GU299512), and the closest described species was *Orthosomella operophterae* (Canning, 1960) isolated from the moth *Operophtera brumata* (Linnaeus, 1758) (97.9% similarity and 100% coverage to AJ302316). All detected microsporidians belonged to the *Enterocytozoonida* clade sensu Bojko et al. (2022).

Discussion

Insular freshwater ecosystems are increasingly threatened by invasive species, including those of pet-traded origin (Velmurugan 2008; Moser et al. 2018; Baudry et al. 2020; Lenzner et al. 2020). The establishment of *N. davidi* and associated parasites in the Mat and the Saint-Jean catchments on the
island of La Réunion is one such example. Commercially successful pets like *N. davidi* are inexpensive, widely available, prolific, and adaptable to a wide range of environmental variables. These are features that favor their establishment in novel locations (Lipták and Vitázková 2015; Bláha et al. 2022; Prati et al. 2024). Their commercial success depends on mass production, which creates an ideal environment for the proliferation of pathogens, including parasites (Maciaszek et al. 2023; Prati et al. 2024). Due to a lack of stringent biosecurity measures along the supply chain, these might end up in private aquaria (Patoka et al. 2016, 2018; Maciaszek et al. 2021; Prati et al. 2024). Consequently, releasing ornamental pets and associated parasites into novel environments might pose severe risks to native biota (Sures 2011; Svoboda et al. 2017; Patoka et al. 2018; Putra et al. 2018). Therefore, deepening the knowledge of invading hosts and parasites is paramount, especially in insular systems.

Feral *N. davidi* populations have been present in Europe since 2003 when a population established itself in Poland (Jabłońska et al. 2018). Afterward, more established populations were discovered in Germany, Hungary, metropolitan France, and Slovakia (Klotz et al. 2013; Weiperth et al. 2019; Prati et al. 2024; Jamonneau et al. 2025). The present study expands this list to two river catchments in the French overseas territory of La Réunion, increasing the number of confirmed established non-native decapod species on the island to three. The presence of *N. davidi* haplotype Ndh2 on the island is unsurprising, as this is the most common haplotype found in feral and pet-traded individuals (Prati et al. 2024). The occurrence of a single haplotype suggests that the collected individuals stem from a single source population, which might have been translocated across river catchments. This lack of genetic diversity compared to other feral populations likely reflects the remoteness of the island and the difficult access to a larger variety of pet-traded *N. davidi*.

Surprisingly, all shrimps displayed a bright red coloration, similar to that displayed by a feral population in Canada (deBruyn 2019). This is rather uncommon, as feral *N. davidi*, similarly to other crustaceans (Duarte et al. 2017), rely on camouflage to avoid predation, thus reverting to nearly translucent to brown coloration typically found in wild populations (Englund and Cai 1999; Levitt-Barmats et al. 2019). Accordingly, flashy colorations, which are more accentuated in females, likely result in increased predation pressures by visual feeders such as fish (Prati et al. 2024). Indeed, intense predation by both native and non-native species upon feral *N. davidi* has been recorded in a German stream (Schoolmann and Arndt 2018). This might not be the case on the island's freshwater ecosystems, where top predators are lacking. On the island of La Réunion, the only top predator in freshwater ecosystems is the non-native *Oncorhynchus mykiss* (Walbaum, 1792), which is found in the colder water of rivers located at higher elevations (Keith 2002; Keith et al. 2006).
Native fish species, e.g., *Anguilla* spp., *Awaous commersoni* (Schneider, 1801), *Cotylopus acutipinnis* (Guichenot, 1863), *Eleotris* sp., and *Kuhlia rupestris* (Lacepède, 1802) might potentially prey on *N. davidi* and are present in the lower and middle stretches of the two investigated catchments (Biotope 2021). However, their abundance is dwindling, with all the abovementioned species being classified as near-threatened, vulnerable, or critically endangered at a regional level (IUCN 2010). Moreover, the presence of impoundments along the rivers might further limit their occurrence and movement. Thus, the predation pressure asserted by native species on *N. davidi* is nearly nonexistent. Predation from non-native species also seems negligible. Non-native fish species, such as *P. reticulata*, are commonly found co-occurring with *N. davidi*. However, their small mouth allows only for a short window in which the predation of, i.e., newly hatched shrimp, can occur.

This lack of predation is also evidenced by the sex ratio of collected *N. davidi* individuals. In *N. davidi*, the sex ratio is temperature dependent, with females accounting for about 20% of the population at 26 °C and just over 50% at 23 °C under laboratory conditions (Serezli et al. 2017). Females, which are larger and more colorful than males, are more likely to be targeted by visual predators like fish; therefore, in their presence, a lower proportion of females than what can be predicted at a certain water temperature is expected. Based on the water temperature at the sampling sites, the sex ratio among the collected individuals reflected what was expected in the absence of predators. Therefore, without effective top-down control, *N. davidi* will continue to proliferate undisturbed on the island rivers.

The further proliferation of *N. davidi* on the island's rivers could potentially pose a severe threat to native decapods, particularly amphidromous shrimp with similar niches such as *Atyoida serrata* (Spence Bate, 1888), *Caridina natalensis* (De Man, 1908), and *Caridina typus* (Milne Edwards, 1837). Two of these species are classified as either near threatened or vulnerable at a regional level (IUCN 2010) but of least concern globally (IUCN 2024). In the present study, only a few *C. typus* individuals were observed co-occurring with *N. davidi* at the Ravine Sèche site. This situation underscores the potential impact of *N. davidi* on native decapods, emphasizing the severity of the issue. Due to its high feeding rate, which is estimated to be over half of its body weight per day, *N. davidi* might outcompete and replace less efficient native crustaceans who rely on the same resources (Schoolmann and Arndt 2017; Onuki and Fuke 2022).

Trophic niche aside, *N. davidi* possesses a major competitive advantage over the native shrimps due to high reproduction rates and a direct development unfolding entirely in freshwater (Tropea and Greco 2015). Female *N. davidi* can produce up to 60 eggs which hatch after an incubation period of 16-19 days at 25 °C (Pantaleão et al. 2017). Newly hatched shrimps can reach sexual maturity within 3 months (Pantaleão et al. 2017).
On the other hand, all native species are amphidromous, meaning their
freshly hatched larvae must reach marine environments to complete their
development. However, anthropogenic interference on the island, such as
river discharge alteration and occasional dewatering of river mouths, can
considerably impact larvae drift toward the ocean (Hoarau et al. 2019).
Moreover, the adult stages of native species are considered a local delicacy
and subject to overfishing (Hoarau et al. 2019). Another aspect that may
impact native species and should be considered is the possible transmission
introduction of parasites alongside *N. davidi*.

The investigated *N. davidi* were infected with four different microsporidians, three of which were recorded for the first time in this host, increasing the number of its endoparasites to seven. Among them is the microsporidian parasite EHP, which was previously reported from pet-traded and feral populations (Schneider et al. 2022; Prati et al. 2024). This parasite, which is tolerant to a wider range of salinity (up to 40 ppt) has been reported from a variety of invertebrate hosts (Karthikeyan and Sudhakaran 2020; Aranguren Caro et al. 2021; Krishnan et al. 2021; Munkongwongsiri et al. 2022; Wan Sajiri et al. 2023). Its presence on the island is concerning, as the parasite might spread to native biota via predation, e.g., in the case of dragonflies, or via spore ingestions in shrimps or other macroinvertebrates feeding on contaminated organic matter (Dewangan et al. 2023). Moreover, spores might be transported by water flow and end up in brackish and marine environments, where they are more infective (Aranguren Caro et al. 2021). *Neocaridina davidi*'s tolerance to salinity is unknown, but the recent finding in Brazil of a single individual in seawater (Bochini et al. 2024) may open novel possibilities for the spread of this non-native species and its parasites. Fortunately, the observed prevalence of EHP remains low, likely due to the lotic nature of the environments inhabited by *N. davidi*, which may contribute to a dilution of infective spores. Nevertheless, the current background population prevalence might be as high as 13.6%. Thus, the situation should be closely monitored, as the consequences of a possible outbreak among native species are unpredictable.

Parasites that are transmitted from introduced to native host species may
have greater pathogenic effects in native hosts as they lack a coevolutionary
history (Mastitsky et al. 2010). However, non-native species might also
acquire local parasites, amplifying or diluting their prevalence in native
species (Strauss et al. 2012; Telfer and Bown 2012). This might be the case
for the other three microsporidians detected in the present study. It is not
known if these microsporidians are present in native species, but until
now, they have never been detected in feral or pet-traded *N. davidi*, which
suggests local origin. Members of the genus *Orthosomella*, to which two of
our sequences belong, are parasites of insects, but undescribed isolates have
also been detected in gastropods suggesting possible switching between hosts
that share similar habitats (Ovcharenko et al. 2013). Unfortunately, the study of parasites co-introduced and acquired by introduced species and the consequences for local environments are often neglected in biological invasion studies. Therefore, we recommend timely actions such as eradication campaigns with the support of local citizens and stakeholders to curb the spread of *N. davidi* and its parasites on the island in an effort to preserve the already endangered native freshwater fauna.

## Authors' contribution

Sebastian Prati, Laetitia Faivre, Valentin de Mazancourt, Bernd Sures, and Pierre Valade conceived the study. Pierre Valade supervised the project. Sebastian Prati and Pierre Valade carried out the sampling. Sebastian Prati carried out laboratory analyses and data analyses. Sebastian Prati wrote the first draft of the manuscript, and all authors contributed critically to the final draft. All authors read and approved the final manuscript.

## Authors' ORCIDs

Sebastian Prati: 0000-0001-9878-3848; Valentin de Mazancourt 0000-0003-3739-603X; Bernd Sures: 0000-0001-6865-6186; Pierre Valade 0000-0001-9744-6153.

## Acknowledgments

We are grateful for the support from the Open Access Publication Fund of the University of Duisburg-Essen and for the anonymous reviewers' extremely valuable suggestions, which have helped substantially improve the quality of our manuscript.

## Funding declaration

This study was performed within the Collaborative Research Center (CRC) RESIST (A09) and funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) – CRC 1439/1 – project number: 426547801. We acknowledge support from the Open Access Publication Fund of the University of Duisburg-Essen.

## Ethics and permits

French authority waived ethical approval for this study under order No. 23-05/DEAL/SEB/UPEMA, authorizing Pierre Valade to capture and transport fish and macrocrustaceans for ecological purposes as part of his mission as head of the GEIR network.

## Data availability

The reported nucleotide sequence data are available in the GenBank database under the accession numbers PQ069719 for *N. davidi* and PQ096043-47 for microsporidians.

## References

* Aranguren Caro LF, Alghamdi F, De Belder K, Lin J, Mai HN, Millabas J, Alrehaili Y, Alazwari A, Algetham S, Dhar AK (2021) The effect of salinity on *Enterocytozoon hepatopenaei* infection in *Penaeus vannamei* under experimental conditions. *BMC Veterinary Research* 17: 65, https://doi.org/10.1186/s12917-021-02778-0

* Barlow J, França F, Gardner TA, Hicks CC, Lennox GD, Berenguer E, Castello L, Economo EP, Ferreira J, Guénard B, Gontijo Leal C, Isaac V, Lees AC, Parr CL, Wilson SK, Young PJ, Graham NAJ (2018) The future of hyperdiverse tropical ecosystems. *Nature* 559: 517–526, https://doi.org/10.1038/s41586-018-0301-1

* Baudry T, Becking T, Goût J-P, Arqué A, Gan HM, Austin CM, Delaunay C, Smith-Ravin J, Roques JAC. Grandjean F (2020) Invasion and distribution of the redclaw crayfish, *Cherax quadricarinatus*, in Martinique. *Knowledge & Management of Aquatic Ecosystems* 421: 50, https://doi.org/10.1051/kmae/2020041

* Bauer J, Jung-Schroers V, Teitge F, Adamek M, Steinhagen D (2021) Association of the alga *Cladogonium* sp. with a multifactorial disease outbreak in dwarf shrimp (*Neocaridina davidi*). *Diseases of Aquatic Organisms* 146: 107–115, https://doi.org/10.3354/dao03625
Bernery C, Bellard C, Courchamp F, Brosse S, Gozlan RE, Jarić I, Teletchea F, Leroy B (2022) Freshwater fish invasions: a comprehensive review. *Annual Review of Ecology, Evolution, and Systematics* 53: 427–456, https://doi.org/10.1146/annurev-ecolsys-032522-015551

Biotope (2021) Suivi des éléments biologiques "Poissons et Macrocrustacés" des rivières du bassin Réunion - Campagne 2020. Maîtrise d'ouvrage Office de l'Éau de la Réunion, 185 pp

Bláha M, Weiperth A, Patoka J, Szajbert B, Balogh ER, Staszny Á, Ferincz Á, Lente V, Maciaszek R, Kouba A (2022) The pet trade as a source of non-native decapods: the case of crayfish and shrimps in a thermal waterbody in Hungary. *Environmental Monitoring and Assessment* 194: 795, https://doi.org/10.1007/s10661-022-10361-9

Bochini GL, Rios A dos S, Teles JN, Zara FJ, Mantelatto FL (2024) Confirmed by integrative taxonomy first and unusual occurrence of the exotic shrimp *Neocaridina davidi* (Caridea: Atyidae) in Brazil. *Boletim do Instituto de Pesca* 50: e849, https://doi.org/10.20950/1678-2305/bip.2024.50.e849

Bojko J, Reinke AW, Stentiford GD, Williams B, Rogers MSJ, Bass D (2022) Microsporidia: a new taxonomic, evolutionary, and ecological synthesis. *Trends in Parasitology* 38: 642–659, https://doi.org/10.1016/j.pt.2022.05.007

Bouvier EL (1904) Crevettes de la famille des Atyidés: espèces qui font partie des collections du Muséum d'Histoire Naturelle. *Bulletin du Muséum d'Histoire naturelle* 10: 129–138

Cambray JA (2003) Impact on indigenous species biodiversity caused by the globalisation of alien recreational freshwater fisheries. *Hydrobiologia* 500: 217–230, https://doi.org/10.1023/A:1024648719995

Chaijarasphong T, Munkongwongsiri N, Stentiford GD, Aldama-Cano DJ, Thansa K, Flegel TW, Sritunyalucksana K, Itsathitphaisarn O (2021) The shrimp microsporidian *Enterocytozoon hepatopenaei* (EHP): Biology, pathology, diagnostics and control. *Journal of Invertebrate Pathology* 186: 107458, https://doi.org/10.1016/j.jip.2020.107458

deBruyn A (2019) Conservation ecology of a unique population of lake chub (Cyprinidae: *Couesius plumbeus*): population size, movement ecology, habitat use and potential interactions with the exotic cherry shrimp (*Neocaridina davidi* var. red). Master thesis. University of British Columbia (Vancouver), https://doi.org/10.14288/1.0380902

Dewangan NK, Pang J, Zhao C, Cao C, Yin B, Weng S, He J (2023) Host and transmission route of *Enterocytozoon hepatopenaei* (EHP) between dragonfly and shrimp. *Aquaculture* 574: 739642, https://doi.org/10.1016/j.aquaculture.2023.739642

Duarte RC, Flores AAV, Stevens M (2017) Camouflage through colour change: mechanisms, adaptive value and ecological significance. *Philosophical Transactions of the Royal Society B: Biological Sciences* 372: 20160342, https://doi.org/10.1098/rstb.2016.0342

Englund RA, Cai Y (1999) The occurrence and description of *Neocaridina denticulata sinensis* (Kemp, 1918) (Crustacea: Decapoda: Atyidae), a new introduction to the Hawaiian Islands. *Bishop Museum Occasional Paper* 58: 58–65

Fenouillas P, Ah-Peng C, Amy E, Bracco I, Dafreville S, Gosset M, Ingrassia F, Lavergne C, Lequette B, Notter J-C, Pausé J-M, Payet G, Payet N, Picot F, Poungavanon N, Strasberg D, Thomas H, Triolo J, Turquet V, Rouget M (2021) Quantifying invasion degree by alien plants species in Reunion Island. *Austral Ecology* 46: 1025–1037, https://doi.org/10.1111/aec.13048

Folmer O, Black M, Hoeh W, Lutz R, Vrijenhoek R (1994) DNA primers for amplification of mitochondrial cytochrome *c* oxidase subunit I from diverse metazoan invertebrates. *Molecular Marine Biology and Biotechnology* 3: 294–299

Fox J, Weisberg S (2018) An R companion to applied regression. Sage publications, 608 pp

Fricke R, Mulochau T, Durville P, Chabanet P, Tessier E, Letourneur Y (2009) Annotated checklist of the fish species (Pisces) of La Réunion. Including a Red List of threatened and declining species. *Stuttgarter Beiträge zur Naturkunde A (Neue Serie)* 2: 1–168, https://www.biodiversity library.org/page/61172121

Gallardo B, Clavero M, Sánchez MI, Vilà M (2016) Global ecological impacts of invasive species in aquatic ecosystems. *Global Change Biology* 22: 151–163, https://doi.org/10.1111/gcb.13004

Grabner DS, Weigand AM, Leese F, Winking C, Hering D, Tollrian R, Sures B (2015) Invaders, natives and their enemies: distribution patterns of amphipods and their microsporidian parasites in the Ruhr Metropolis, Germany. *Parasites & Vectors* 8: 419, https://doi.org/10.1186/s13071-015-1036-6

Haubrock PJ, Oficialdegui FJ, Zeng Y, Patoka J, Yeo DC, Kouba A (2021) The redclaw crayfish: A prominent aquaculture species with invasive potential in tropical and subtropical biodiversity hotspots. *Reviews in Aquaculture* 13: 1488–1530, https://doi.org/10.1111/raq.12531

Hoarau PE, Courtecuisse E, Treilhes CR, Lagarde R, Teichert N, Valade PB (2019) Reproductive biology of a small amphidromous shrimp *Atyoida serrata* on Reunion Island, south-west Indian Ocean. *Limnologica* 76: 41–47, https://doi.org/10.1016/j.limno.2019.03.005

Jabłońska A, Mamos T, Gruszka P, Szlauer-Łukaszewska A, Grabowski M (2018) First record and DNA barcodes of the aquarium shrimp, *Neocaridina davidi*, in Central Europe from thermally polluted River Oder canal, Poland. *Knowledge & Management of Aquatic Ecosystems* 419: 14, https://doi.org/10.1051/kmae/2018004

Jamonneau T, Camargo AR, Halima IB, Prati S, Denys GP (2025) Evidence of an established population of *Poecilia reticulata* and *Neocaridina davidi* in metropolitan France. *Cybium*, https://doi.org/10.26028/CYBIUM/2024-034

Jang G-I, Kim S-M, Oh Y-K, Lee S-J, Hong S-Y, Lee H-E, Kwon M-G, Kim B-S (2022) First report of *Enterocytozoon hepatopenaei* infection in giant freshwater prawn (*Macrobrachium*
rosenbergii de Man) cultured in the Republic of Korea. *Animals* 12: 3149, https://doi.org/10.3390/ani12223149

Kakui K, Komai T (2022) First record of *Scutariella japonica* (Platyhelminthes: Rhabdocoela) from Hokkaido, Japan, and notes on its host shrimp *Neocaridina* sp. aff. *davidi* (Decapoda: Caridea: Atyidae). *Aquatic Animals* 2022: AA2022-1, https://doi.org/10.34394/aquaticanimals.2022.0-AA2022-1

Karthikeyan K, Sudhakaran R (2020) Exploring the potentiality of *Artemia salina* to act as a reservoir for microsporidian *Enterocytozoon hepatopenaei* of penaeid shrimp. *Biocatalysis and Agricultural Biotechnology* 25: 101607, https://doi.org/10.1016/j.bcab.2020.101607

Katoh K, Rozewicki J, Yamada KD (2019) MAFFT online service: multiple sequence alignment, interactive sequence choice and visualization. *Briefings in Bioinformatics* 20: 1160–1166, https://doi.org/10.1093/bib/bbx108

Keith P (2002) Freshwater fish and decapod crustacean populations on Réunion island, with an assessment of species introductions. *Bulletin Français de la Pêche et de la Pisciculture* 364: 97–107, https://doi.org/10.1051/kmae:2002005

Keith P, Marquet G, Valade P, Bosc P, Vigneux É (2006) Atlas des poissons et des crustacés d'eau douces des Comores, Mascareignes et Seychelles. Publications scientifiques du Muséum national d'Histoire naturelle, Paris, 250 pp

Keppel G, Morrison C, Meyer J-Y, Boehmer HJ (2014) Isolated and vulnerable: the history and future of Pacific Island terrestrial biodiversity. *Pacific Conservation Biology* 20: 136–145, https://doi.org/10.1071/pc140136

Klotz W, Miesen FW, Hüllen S, Herder F (2013) Two Asian fresh water shrimp species found in a thermally polluted stream system in North Rhine-Westphalia, Germany. *Aquatic Invasions* 8: 333–339, https://doi.org/10.3391/ai.2013.8.3.09

Krishnan AN, Kannappan S, Aneesh PT, Praveena PE, Jithendran KP (2021) Polychaete worm - a passive carrier for *Enterocytozoon hepatopenaei* in shrimp. *Aquaculture* 545: 737187, https://doi.org/10.1016/j.aquaculture.2021.737187

Lenzner B, Latombe G, Capinha C, Bellard C, Courchamp F, Diagne C, Dullinger S, Golivets M, Irl SDH, Kühn I, Leung B, Liu C, Moser D, Roura-Pascual N, Seebens H, Turbelin A, Weigelt P, Essl F (2020) What will the future bring for biological invasions on islands? An expert-based assessment. *Frontiers in Ecology and Evolution* 8: 280, https://doi.org/10.3389/fevo.2020.00280

Leoville A (2012) Etude des peuplements de macro crustacés décapodes amphidromes de l'Etang de Saint-Paul. Etat d'expansion de l'écrevreis exotique *Cherax quadricarinatus* (Von Martens, 1868). Master thesis. University of la Réunion (Le Tampon).

Levitt-Barmats Y, Yanai Z, Cohen T, Shenkar N (2019) Life-history traits and ecological characteristics of the ornamental shrimp *Neocaridina denticulata* (De Haan, 1844), recently introduced into the freshwater systems of Israel. *Aquatic Invasions* 14: 684–702, https://doi.org/10.3391/ai.2019.14.4.08

Liao C-C, Shin J, Chen L-R, Huang LLH, Lin W-C (2018) First molecular identification of *Vorticella* sp. from freshwater shrimps in Tainan, Taiwan. *International Journal for Parasitology: Parasites and Wildlife* 7: 415–422, https://doi.org/10.1016/j.ijppaw.2018.10.002

Lipták B, Vitázková B (2015) Beautiful, but also potentially invasive. *Ekológia (Bratislava)* 34: 155–162, https://doi.org/10.1515/eko-2015-0016

Maciaszek R, Świderek W, Kaliszewicz A, Karaban K, Szpakowski B (2021) First report of *Scutariella japonica* (Matjašič, 1990), a temnocephalid epibiont from South-East Asia, found on introduced ornamental freshwater shrimp in European waters. *Knowledge & Management of Aquatic Ecosystems* 422: 19, https://doi.org/10.1051/kmae/2021018

Maciaszek R, Świderek W, Prati S, Huang C-Y, Karaban K, Kaliszewicz A, Jabłońska A (2023) Epibiont cohabitation in freshwater shrimp *Neocaridina davidii* with the description of two species new to science, *Cladogonium kumaki* sp. nov. and *Monodiscus kumaki* sp. nov., and redescription of *Scutariella japonica* and *Holtodrilus truncatus*. *Animals* 13: 1616, https://doi.org/10.3390/ani13101616

Magalhães ALB, Jacobi CM (2017) Colorful invasion in permissive Neotropical ecosystems: establishment of ornamental non-native poeciliids of the genera *Poecilia/Xiphophorus* (Cyprinodontiformes: Poeciliidae) and management alternatives. *Neotropical Ichthyology* 15: e160094, https://doi.org/10.1590/1982-0224-20160094

Mastitsky SE, Karatayev AY, Burlakova LE, Molloy DP (2010) Parasites of exotic species in invaded areas: does lower diversity mean lower epizootic impact? *Diversity and Distributions* 16: 798–803, https://doi.org/10.1111/j.1472-4642.2010.00693.x

McClymont HE, Dunn AM, Terry RS, Rollinson D, Littlewood DTJ, Smith JE (2005) Molecular data suggest that microsporidian parasites in freshwater snails are diverse. *International Journal for Parasitology* 35: 1071–1078, https://doi.org/10.1016/j.ijpara.2005.05.008

Minh BQ, Schmidt HA, Chernomor O, Schrempf D, Woodhams MD, von Haeseler A, Lanfear R (2020) IQ-TREE 2: New models and efficient methods for phylogenetic inference in the genomic era. *Molecular Biology and Evolution* 37: 1530–1534, https://doi.org/10.1093/molbev/msa015

Moser D, Lenzner B, Weigelt P, Dawson W, Kreft H, Pergl J, Pyšek P, van Kleunen M, Winter M, Capinha C, Cassey P, Dullinger S, Economo EP, García-Díaz P, Guénard B, Hofhansl F, Mang T, Seebens H, Essl F (2018) Remoteness promotes biological invasions on islands worldwide. *Proceedings of the National Academy of Sciences* 115: 9270–9275, https://doi.org/10.1073/pnas.1804179115

Munkongwongsiri N, Thepmanee O, Lertsiri K, Vanichviriyakit R, Itsathitphaisarn O, Sritunyalucksana K (2022) False mussels (*Mytilopsis leucophaeata*) can be mechanical carriers of the shrimp
microsporidian *Enterocytozoon hepatopenaei* (EHP). *Journal of Invertebrate Pathology* 187: 107690, https://doi.org/10.1016/j.jip.2021.107690

Myers N, Mittermeier RA, Mittermeier CG, Da Fonseca GA, Kent J (2000) Biodiversity hotspots for conservation priorities. *Nature* 403: 853–858, https://doi.org/10.1038/35002501

Niwa N, Ohtaka A (2006) Accidental introduction of symbionts with imported freshwater shrimps. In: Koike F, Clout MN, Kawamichi M, De Poorter M, Iwatsuki K (eds), Assessment and control of biological invasion risks. Shoukadoh Book Sellers and World Conservation Union, Kyoto and Gland, pp 182–186

Ohtaka A, Gelder SR, Nishino M, Ikeda M, Toyama H, Cui Y-D, He X-B, Wang H-Z, Chen R-B, Wang Z-Y (2012) Distributions of two ectosymbionts, branchiobdellidans (Annelida: Clitellata) and scutariellids (Platyhelminthes: "Turbellaria": Temnocephalida), on atyid shrimp (Arthropoda: Crustacea) in southeast China. *Journal of Natural History* 46: 1547–1556, https://doi.org/10.1080/00222933.2012.692826

Onuki K, Fuke Y (2022) Rediscovery of a native freshwater shrimp, *Neocaridina denticulata*, and expansion of an invasive species in and around Lake Biwa, Japan: genetic and morphological approach. *Conservation Genetics* 23: 967–980, https://doi.org/10.1007/s10592-022-01467-1

Ovcharenko M, Świątek P, Ironside J, Skalski T (2013) *Orthosomella lipae* sp. n. (Microsporidia) a parasite of the weevil, *Liophloeus lentus* Germar, 1824 (Coleoptera: Curculionidae). *Journal of Invertebrate Pathology* 112: 33–40, https://doi.org/10.1016/j.jip.2012.10.007

Pantaleão JAF, Gregati RA, da Costa RC, López-Greco LS, Negreiros-Fransozo ML (2017) Post-hatching development of the ornamental ‘Red Cherry Shrimp’ *Neocaridina davidi* (Bouvier, 1904) (Crustacea, Caridea, Atyidae) under laboratorial conditions. *Aquaculture Research* 48: 553–569, https://doi.org/10.1111/are.12903

Patoka J, Bláha M, Devetter M, Rylková K, Čadková Z, Kalous L (2016) Aquarium hitchhikers: attached commensals imported with freshwater shrimps via the pet trade. *Biological Invasions* 18: 457–461, https://doi.org/10.1007/s10530-015-1018-9

Patoka J, Magalhães ALB, Kouba A, Faulkes Z, Jerikho R, Vitule JRS (2018) Invasive aquatic pets: failed policies increase risks of harmful invasions. *Biodiversity and Conservation* 27: 3037–3046, https://doi.org/10.1007/s10531-018-1581-3

Prati S, Grabner DS, Hupało K, Weipert A, Maciaszek R, Lipták B, Bojko J, Bérces F, Sures B (2024) Invisible invaders: range expansion of feral *Neocaridina davidi* offers new opportunities for generalist intracellular parasites. *Biological Invasions* 26: 2499–2523, https://doi.org/10.1007/s10530-024-03324-3

Putra MD, Bláha M, Wardiatno Y, Krisanti M, Yonvitner Y, Jerikho R, Kamal MM, Mojžišová M, Bystřický PK, Kouba A, Kalous L, Petrusek A, Patoka J (2018) *Procambarus clarkii* (Girard, 1852) and crayfish plague as new threats for biodiversity in Indonesia. *Aquatic Conservation: Marine and Freshwater Ecosystems* 28: 1434–1440, https://doi.org/10.1002/aqc.2970

Pyšek P, Hulme PE, Simberloff D, Bacher S, Blackburn TM, Carlton JT, Dawson W, Essl F, Foxcroft LC, Genovesi P, Jeschke JM, Kühn I, Liebhold AM, Mandrak NE, Meyerson LA, Pauchard A, Pergl J, Roy ER, Seebens H, van Kleunen M, Vilà M, Wingfield MJ, Richardson DM (2020) Scientists’ warning on invasive alien species. *Biological Reviews* 95: 1511–1534, https://doi.org/10.1111/brv.12627

Russell JC, Meyer J-Y, Holmes ND, Pagad S (2017) Invasive alien species on islands: impacts, distribution, interactions and management. *Environmental Conservation* 44: 359–370, https://doi.org/10.1017/S0376892917000297

Sasal P, Taraschewski H, Valade P, Grondin H, Wielgoss S, Moravec F (2008) Parasite communities in eels of the Island of Reunion (Indian Ocean): a lesson in parasite introduction. *Parasitology Research* 102: 1343–1350, https://doi.org/10.1007/s00436-008-0916-5

Savini D, Occhipinti-Ambrogi A, Marchini A, Tricarico E, Gherardi F, Olenin S, Gollasch S (2010) The top 27 animal alien species introduced into Europe for aquaculture and related activities. *Journal of Applied Ichthyology* 26: 1–7, https://doi.org/10.1111/j.1439-0426.2010.01503.x

Schneider R, Prati S, Grabner D, Sures B (2022) First report of microsporidians in the non-native shrimp *Neocaridina davidi* from a temperate European stream. *Diseases of Aquatic Organisms* 150: 125–130, https://doi.org/10.3354/dao03681

Schoolmann G, Arndt H (2017) Leaf-litter preferences of the introduced freshwater shrimps *Atyaephyra desmarestii* and *Neocaridina davidi*. *Crustaceana* 90: 1715–1730, https://doi.org/10.1163/15685403-00003736

Schoolmann G, Arndt H (2018) Population dynamics of the invasive freshwater shrimp *Neocaridina davidi* in the thermally polluted Gillbach stream (North Rhine-Westphalia, Germany). *Limnologica* 71: 1–7, https://doi.org/10.1016/j.limno.2018.05.001

Seebens H, Blackburn TM, Dyer EE, Genovesi P, Hulme PE, Jeschke JM, Pagad S, Pyšek P, Winter M, Arianoutsou M, Bacher S, Blasius B, Brundu G, Capinha C, Celesti-Grapow L, Dawson W, Dullinger S, Fuentes N, Jäger H, Kartesz J, Kenis M, Kreft H, Kühn I, Lenzner B, Liebhold A, Mosena A, Moser D, Nishino M, Pearman D, Pergl J, Rabitsch W, Rojas-Sandoval J, Roques A, Rorke S, Rossinelli S, Roy HE, Scalera R, Schindler S, Štajerová K, Tokarska-Guzik B, van Kleunen M, Walker K, Weigelt P, Yamanaka T, Essl F (2017) No saturation in the accumulation of alien species worldwide. *Nature Communications* 8: 14435, https://doi.org/10.1038/ncomms14435

Serezli R, Atalar MS, Hamzacebi S, Kurtoglu IZ, Yandi I (2017) To what extent does temperature affect sex ratio in red cherry shrimp, *Neocaridina davidi*? The scenario global warming to offspring sex ratio. *Fresenius Environmental Bulletin* 26: 7575–7579
Shih H-T, Cai Y, Niwa N, Yoshigou H, Nakahara Y (2024) Integrative taxonomy reveals freshwater shrimp diversity (Decapoda: Atyidae: Neocaridina) from Kyushu and southern Honshu of Japan, with a discussion on introduced species. *Zoological Studies*, https://doi.org/10.6620/ZS.2024.63-18

Simberloff D, Martin J-L, Genovesi P, Maris V, Wardle DA, Aronson J, Courchamp F, Galil B, García-Berthou E, Pascal M, Pyšek P, Sousa R, Tabacchi E, Vilà M (2013) Impacts of biological invasions: what's what and the way forward. *Trends in Ecology & Evolution* 28: 58–66, https://doi.org/10.1016/j.tree.2012.07.013

Soubeyran Y, Meyer J-Y, Lebouvier M, De Thoisy B, Lavergne C, Urtizberea F, Kirchner F (2015) Dealing with invasive alien species in the French overseas territories: results and benefits of a 7-year Initiative. *Biological Invasions* 17: 545–554, https://doi.org/10.1007/s10530-014-0766-2

Strauss A, White A, Boots M (2012) Invading with biological weapons: the importance of disease-mediated invasions. *Functional Ecology* 26: 1249–1261, https://doi.org/10.1111/1365-2435.12011

Sures B (2011) Parasites of animals. In: Simberloff D, Rejmánek M (eds), Encyclopedia of Biological Invasions. University of California Press, Berkely and Los Angeles, pp 500–503

Svoboda J, Mrugała A, Kozubíková-Balcarová E, Petrusek A (2017) Hosts and transmission of the crayfish plague pathogen *Aphanomyces astaci*: a review. *Journal of Fish Diseases* 40: 127–140, https://doi.org/10.1111/jfd.12472

Telfer S, Bown K (2012) The effects of invasion on parasite dynamics and communities. *Functional Ecology* 26: 1288–1299, https://doi.org/10.1111/j.1365-2435.2012.02049.x

Tropea C, Greco LSL (2015) Female growth and offspring quality over successive spawnings in a caridean shrimp *Neocaridina davidi* (Decapoda, Atyidae) with direct development. *The Biological Bulletin* 229: 243–254, https://doi.org/10.1086/BBLv229n3p243

Velmurugan A (2008) Chapter 1 - The Nature and Characters of Tropical Islands. In: Sivaperuman C, Velmurugan A, Singh AK, Jaisankar I (eds), Biodiversity and climate change adaptation in tropical islands. Academic Press, pp 3–30, https://doi.org/10.1016/B978-0-12-813064-3.00001-6

Wan Sajiri WMH, Kua BC, Borkhanuddin MH (2023) Detection of *Enterocytozoon hepatopenaei* (EHP) (Microsporidia) in several species of potential macrofauna-carriers from shrimp (*Penaeus vannamei*) ponds in Malaysia. *Journal of Invertebrate Pathology* 198: 107910, https://doi.org/10.1016/j.jip.2023.107910

Wang Y, Chen J, Na Y, Li X, Zhou J, Fang W, Tan H (2023) *Ecytonucleospora hepatopenaei* n. gen. et comb. (Microsporidia: Enterocytozoonidae): A redescription of the *Enterocytozoon hepatopenaei* (Tourtip et al., 2009), a microsporidian infecting the widely cultivated shrimp *Penaeus vannamei*. *Journal of Invertebrate Pathology* 201: 107988, https://doi.org/10.1016/j.jip.2023.107988

Weber S, Traunspurger W (2016) Influence of the ornamental red cherry shrimp *Neocaridina davidi* (Bouvier, 1904) on freshwater meiofaunal assemblages. *Limnologica* 59: 155–161, https://doi.org/10.1016/j.limno.2016.06.001

Weiperth A, Gábris V, Danyik T, Farkas A, Kuříková P, Kouba A, Patoka J (2019) Occurrence of non-native red cherry shrimp in European temperate waterbodies: a case study from Hungary. *Knowledge & Management of Aquatic Ecosystems* 420: 9, https://doi.org/10.1051/kmae/2019002

Yonvitner Y, Patoka J, Yuliana E, Bohatá L, Tricarico E, Karella T, Kouba A, Reynolds JD (2020) Enigmatic hotspot of crayfish diversity at risk: Invasive potential of non-indigenous crayfish if introduced to New Guinea. *Aquatic Conservation: Marine and Freshwater Ecosystems* 30: 219–224, https://doi.org/10.1002/aqc.3276

Zhu X, Wittmer T, Tanowitz HB, Kotler D, Cali A, Weiss LM (1993) Small Subunit rRNA sequence of *Enterocytozoon bieneusi* and its potential diagnostic role with use of the Polymerase Chain Reaction. *The Journal of Infectious Diseases* 168: 1570–1575, https://doi.org/10.1093/infdis/168.6.1570

## Web sites, online databases and software

Fay MP (2023) exactci: Exact p-values and matching confidence intervals for simple discrete parametric cases. https://cran.r-project.org/web/packages/exactci/index.html (accessed 3 May 2024)

Froese R, Pauly D (2024) FishBase. https://www.fishbase.se (accessed 3 May 2024)

Groupe Espèces Invasives de La Réunion (2017) Une invasion de crevettes “d’aquarium” dans la riviere du Mât. https://www.especesinvasives.re/une-invasion-de-crevettes-d-aquarium-dans-la-riviere-du-mat/ (accessed 11 January 2024)

IUCN (2010) La liste rouge des espèces menacées en France–Faune de La Réunion. Paris, France. https://uicn.fr/wp-content/uploads/2010/07/Liste_rouge_France_Faune_de_La_Reunion.pdf (accessed 11 January 2024)

IUCN (2024) The IUCN red list of threatened species. Version 2024-2. https://www.iucnredlist.org (accessed 11 January 2024)