Gill Parasites Research Articles

Assessment of the Genetic Diversity of the Monogenean Gill Parasite Lamellodiscus echeneis (Monogenea) Infecting Wild and Cage-Reared Populations of Sparus aurata (Teleostei) from the Mediterranean Sea.

The diplectanid monogenean Lamellodiscus echeneis (Wagener, 1857) is a specific and common gill parasite of the gilthead seabream Sparus aurata Linnaeus, 1758, in the Mediterranean Sea. Few isolated molecular studies of this monogenean have been conducted, and its population structure and genetic diversity are poorly understood. This study represents the first analysis of the population genetics of L. echeneis, isolated from wild and cage-reared gilthead seabream from fifteen localities in both the Southern (Tunisia) and Northern (Italy and Spain) regions of the Mediterranean Sea, using nuclear ITS rDNA markers and a partial fragment of the mitochondrial gene cytochrome oxidase subunit I (COI). The phylogenetic trees based on the newly obtained dataset and the previously published sequences of L. echeneis corroborated the spread of only a single species throughout the Mediterranean Sea. The star-like haplotypes network, inferred by COI sequences, suggested a recent population expansion of L. echeneis. This is supported by the observed high haplotype diversity (Hd = 0.918) and low nucleotide diversity (Pi = 0.01595). Population structure-based AMOVA for two groups (the Adriatic Sea and the rest of the Mediterranean Sea) attributed 35.39% of the total variation to differences within populations, 16.63% to differences among populations within groups, and 47.99% to differences among groups. Fixation indices were significant, with a high FST value (0.64612), likely related to the divergence of the parasite populations from the Adriatic Sea and other Mediterranean regions. Phylogenetic analyses grouped all samples into the main clade corresponding to L. echeneis from several localities. This study provides insight into the genetic variation between L. echeneis populations, and did not show a clear genetic structure between populations of L. echeneis throughout Tunisian, Italian, and Spanish localities, which can be attributed to the considerable gene flow between the populations favoured by the potential for host dispersion within the Mediterranean Sea. Finally, haplotypes shared between wild and cage-reared hosts provided evidence for the potential for cross-infection between wild and farmed hosts in the Mediterranean Sea.

Proposal of Troglocephalinae n. subfam. (Monogenea: Monocotylidae) to accommodate existing and two new monocotylids from the gills of rhinopristiform shovelnose rays

Troglocephalinae n. subfam. is proposed for Spinuris Doran, 1953, Neoheterocotyle Hargis, 1955, Anoplocotyloides Young, 1967, Troglocephalus rhinobatidis Young, 1967 (previously incertae sedis), Nonacotyle pristis Ogawa, 1991, Mehracotyle insolita Neifar, Euzet & Ben Hassine, 2002, Scuticotyle cairaen. gen. et sp., and Brancheocotyle imbricatan. gen. et sp. All members of the proposed new subfamily are gill parasites of shovelnose rays of the order Rhinopristiformes. The subfamilies Heterocotylinae Chisholm, Wheeler & Beverley-Burton, 1995, and Dasybatotreminae Bychowsky, 1957, are amended to exclude Spinuris, Nonacotyle, Neoheterocotyle, and Anoplocotyloides and Mehracotyle, respectively. Heterocotylinae includes gill parasites of members of the orders Myliobatiformes and Torpediniformes. Dasybatotreminae includes parasites of the gills and pharyngeal cavity of members of the orders Myliobatiformes and Rajiformes. A revised phylogeny of the Monocotylidae Taschenberg, 1879 is presented and discussed, based on 28S rDNA sequences, including new sequences for Myliocotyle pteromylaei Neifer, Euzet & Ben Hassine, 1999, Heterocotyle tokoloshei Vaughan & Chisholm, 2010, Neoheterocotyle robii Vaughan & Chisholm, 2010, and the two newly proposed species and genera. Additional locality records are also provided for Monocotylidae from off South Africa.

Influence of Water Quality on the Seasonal Infestation of the Nile Tilapia with Gill Parasites in Different Localities Along Rosetta Branch, the River Nile

Influence of Water Quality on the Seasonal Infestation of the Nile Tilapia with Gill Parasites in Different Localities Along Rosetta Branch, the River Nile

Insights into the phylogenetic position of genus Synodontella (Monopisthocotylea) among some other Dactylogyridea gill parasites of African catfishes and the importance of haptoral elements

This work provides new molecular data on seven species representing three genera (Protoancylodiscoides, Schilbetrema and Synodontella) in the order Dactylogyridea. The results help to explain the origin of Synodontella spp. and to elucidate the phylogenetic position of Synodontella in relation to the other genera. The findings also highlight the importance of the haptoral elements in determing phylogenetic relationships between and within Dactylogyridea taxa, which are monogenean parasites of mostly cyprinid fishes in fresh water. A total of 36 catfish specimens representing five species in three genera (Synodontis, Schilbe and Chrysichthys) were collected from two rivers in Cameroon: the Sanaga River (at Edéa and Nachtigal, in the Littoral and Cental regions, respectively) and Boumba River (at Mang-kaka, East Region), and examined for gill parasites. The novel 28S rDNA sequences of seven species belonging to Dactylogyridea were obtained and their phylogenetic relationships inferred. Synodontella resulted as a monophyletic lineage; the samples obtained from the catfish in Cameroon were well-differentiated into two groups. Synodontella appears to be more closely related to Schilbetrema than to the other Dactylogyridea species investigated here. The shape of the ventral bar should be considered an important feature for distinguishing among Dactylogyridea genera. The existence of two or more lineages within the genus Synodontella, as suggested by previous morphological studies, is here molecularly confirmed, indicating speciation as likely an outcome of ecological influences or the phylogenetic relationships among parasites and/or hosts.

Two new dactylogyrid species (Dactylogyroidea: Dactylogyridae), gill parasites of freshwater fishes from the Peruvian Amazon, including the proposal of Peruanella n. gen.

A new genus of dactylogyrid, Peruanella n. gen., is proposed to accommodate Peruanella madredediosensis n. sp. from Brachyplatystoma tigrinum (Britski) (Siluriformes: Pimelodidae) from the Madre de Dios River, in Puerto Maldonado City, Madre de Dios region, Peru. The new genus differs from Neotropical dactylogyrids by possessing a combination of the following features: (1) tandem gonads, (2) a tubular J-shaped MCO, (3) an accessory piece connected to the base of the MCO via a filament, (4) a midventral vaginal aperture, (5) anchors similar in shape, each with short roots, (6) straight and robust bars, and (7) equal hook, each with undilated shanks and a depressed thumb. A previously described species, Demidospermus aureagarciae Morey, Rojas, Dávila, Chu & De Pina, 2023 exhibits characteristics that are compatible with the diagnosis of the new genus; therefore, this species is transferred to the Peruanella n. gen. In addition, Jainus peruensis n. sp. is described from Brycon amazonicus (Spix & Agassiz) (Characiformes: Bryconidae). This new species, which is the first species of the genus described in Peru and the third species infecting a bryconid host, can be differentiated from all congeneric species due to: (1) a slender MCO forming a counterclockwise loop at the proximal end, (2) an unarticulated accessory piece with a scythe-shaped distal end, (3) a rod-shaped ventral bar with a medial projection, and (4) a V-shaped and grooved dorsal bar.

An inside out journey: biogenesis, ultrastructure and proteomic characterisation of the ectoparasitic flatworm Sparicotyle chrysophrii extracellular vesicles

BackgroundHelminth extracellular vesicles (EVs) are known to have a three-way communication function among parasitic helminths, their host and the host-associated microbiota. They are considered biological containers that may carry virulence factors, being therefore appealing as therapeutic and prophylactic target candidates. This study aims to describe and characterise EVs secreted by Sparicotyle chrysophrii (Polyopisthocotyla: Microcotylidae), a blood-feeding gill parasite of gilthead seabream (Sparus aurata), causing significant economic losses in Mediterranean aquaculture.MethodsTo identify proteins involved in extracellular vesicle biogenesis, genomic datasets from S. chrysophrii were mined in silico using known protein sequences from Clonorchis spp., Echinococcus spp., Fasciola spp., Fasciolopsis spp., Opisthorchis spp., Paragonimus spp. and Schistosoma spp. The location and ultrastructure of EVs were visualised by transmission electron microscopy after fixing adult S. chrysophrii specimens by high-pressure freezing and freeze substitution. EVs were isolated and purified from adult S. chrysophrii (n = 200) using a newly developed ultracentrifugation-size-exclusion chromatography protocol for Polyopisthocotyla, and EVs were characterised via nanoparticle tracking analysis and tandem mass spectrometry.ResultsFifty-nine proteins involved in EV biogenesis were identified in S. chrysophrii, and EVs compatible with ectosomes were observed in the syncytial layer of the haptoral region lining the clamps. The isolated and purified nanoparticles had a mean size of 251.8 nm and yielded 1.71 × 108 particles · mL−1. The protein composition analysis identified proteins related to peptide hydrolases, GTPases, EF-hand domain proteins, aerobic energy metabolism, anticoagulant/lipid-binding, haem detoxification, iron transport, EV biogenesis-related, vesicle-trafficking and other cytoskeletal-related proteins. Several identified proteins, such as leucyl and alanyl aminopeptidases, calpain, ferritin, dynein light chain, 14–3–3, heat shock protein 70, annexin, tubulin, glutathione S-transferase, superoxide dismutase, enolase and fructose-bisphosphate aldolase, have already been proposed as target candidates for therapeutic or prophylactic purposes.ConclusionsWe have unambiguously demonstrated for the first time to our knowledge the secretion of EVs by an ectoparasitic flatworm, inferring their biogenesis machinery at a genomic and transcriptomic level, and by identifying their location and protein composition. The identification of multiple therapeutic targets among EVs' protein repertoire provides opportunities for target-based drug discovery and vaccine development for the first time in Polyopisthocotyla (sensu Monogenea), and in a fish-ectoparasite model.Graphical

Parasitism and branchitis in various fish species from 4 Cook County, Illinois inland freshwater lakes, 5-year survey, 2017-2021.

We investigated disease trends of concern for fish or public health in a 5-y (2017-2021) prospective survey of fish in Cook County, IL, inland lakes. Lesions were assessed in relation to fish species, lake type and location, season and collection year, and lake water chemistry parameters. Fish included bullheads (n = 98), common carp (n = 99), bluegill (n = 114), and largemouth bass (n = 118). Annually, fish collection and point-source water sampling were conducted in spring, summer, and fall from both seepage and impoundment lakes. Examinations included autopsy, wet-mount cytologic assessment for ectoparasites, and histopathology. No lesions of public health concern were detected. The most common abnormalities were branchitis (261 of 429; 60.8%) and endoparasitism (312 of 429; 72.7%). Branchitis was mild in most cases (189 of 261; 72.4%) and concurrent with branchial parasitism in 175 of 261 (67%) cases. Monogeneans were the most common gill parasites but did not influence branchitis severity (Kruskal-Wallis, p = 0.484). Using generalized ordered logistic regression, predictors of branchitis severity included fish species (p < 0.001), the interaction of lake or location and alkalinity (p < 0.001), and water temperature or season (p < 0.001). Endoparasites included tissue larval trematodes (metacercaria), nematodes, and cestodes (plerocercoids), enteric acanthocephalans, gastric trematodes, renal myxosporidia, biliary and gall bladder myxosporidia, enteric cestodes, and tissue microsporidia. Using generalized ordered logistic regression, variables influencing endoparasitism severity included species (p < 0.001), year (p < 0.001), chloride level (p = 0.009), and the interaction of year and chloride level (p < 0.001). Our results suggested overall good health of fish in sampled Cook County inland lakes and provide a foundation for continued monitoring of ecosystem and public health in the urban environment.

A host choosy gill parasite (Dactylogyrus spp.) in fish: an insight into host-parasite interaction for developing control strategies

A host choosy gill parasite (Dactylogyrus spp.) in fish: an insight into host-parasite interaction for developing control strategies

Phylogenetic position inferred on SSU rDNA sequence gene and description of a new parasitic cnidarian (Endocnidozoa: Myxobolidae) infecting Markiana nigripinnis (Teleostei: Stevardiinae) from a small marginal lake floodplain, Brazil.

Herein, a detailed molecular phylogeny analysis was developed to determine the phylogenetic position of a new freshwater histozoic myxosporean cnidarian, Henneguya markiana sp. nov. from the world's largest tropical wetland area, Pantanal, Brazil. The new species is described using an integrative taxonomy approach including morphology, biological traits and molecular data. Phylogenetic analysis inferred by Maximum Likehood method showed the new Henneguya species in a well-supported clade of myxosporean gill parasites of South American characids fishes. In this same clade, the new Henneguya described appeared in a sub-clade clustering with H. lacustris and H. chydadea. Nevertheless, the sequences of the new species and H. lacustris and H. chydadea have a large genetic divergence of 10.4% (148 nucleotides-nt) and 10.5% (147 nt) respectively. To the best of our knowledge, this is the first report of a cnidarian myxosporean species parasitizing a fish from Stevardiinae from South America. In the light of the differences observed from the integrative taxonomy, we are confident that this isolate is a new species of Henneguya, increasing the knowledge of diversity of this enigmatic group of cnidarians.

The efficacy of salt treatment for Dactylogyrus extensus (Monogenea) infection in Carp (Cyprinus carpio)

Salt is widely recommended as a cost-effective and readily available compound against freshwater fish parasites in aquaculture; however, a limited number of studies provide scientific evidence regarding the efficacy of salt use despite its frequent use as an anti-parasitic in fish culture. Dactylogyrus is a severe gill parasite, causing considerable losses in freshwater aquaculture. The current study aimed to evaluate the anti-parasitic efficacy of salt against Dactylogyrus extensus in Cyprinus carpio. In vitro, mortality of D. extensus showed time- and concentration-dependent patterns. In vivo, the anti-parasitic effectiveness of salt to D. extensus was assessed at 23.56% after exposure to salt at a concentration of 1.25 g/L for 10 min. Anti-parasitic efficacy of salt in short-term application in carp can be categorised between slight and mild against monogenean, D. extensus.

Distribution of the gill parasite Discocotyle sagittata (Monogenea: Polyopisthocotylea) in parr of Atlantic salmon Salmo salar and sea trout S. trutta in Norwegian rivers

The monogenean gill parasite Discocotyle sagittata is reported from parr of Atlantic salmon Salmo salar and sea trout S. trutta in the anadromous part of 86 out of 223 Norwegian rivers. The prevalence in each river varied from 1.5% to 88.9%. This study has significantly increased our knowledge about the occurrence of this salmonid parasite in Norway. Most likely, D. sagittata has a much wider distribution all over the country and probably also occur in numerous inland lakes, rivers and streams.

Support for a radiation of free-living flatworms in the African Great Lakes region and the description of five new Macrostomum species

BackgroundThe African Great Lakes have long been recognized as an excellent location to study speciation. Most famously, cichlid fishes have radiated in Lake Tanganyika and subsequently spread into Lake Malawi and Lake Victoria, where they again radiated. Other taxa have diversified in these lakes, such as catfish, ostracods, gastropods, and Monegenean gill parasites of cichlids. However, these radiations have received less attention, and the process leading to their speciation in this unique region remains to be further explored. Here I present evidence that suggests a radiation of Macrostomum flatworms has occurred in the African Great Lakes region, offering a good opportunity for such investigations.ResultsRecent field work has revealed a monophyletic clade of 16 Macrostomum flatworms that have, to date, only been collected from Lake Tanganyika. Additionally, a species collected from Lake Malawi was found nested within this clade. Molecular phylogenetic analysis, largely based on transcriptome data, suggests that this clade underwent rapid speciation, possibly due to a large habitat diversity in the lake. I also observed significant differences in the sperm morphology of these flatworms compared to those of species found outside Lake Tanganyika and Lake Malawi. These included the elongation of an anterior structure, a reduction in the size of the lateral sperm bristles, and changes in relative proportions. I propose functional hypotheses for these changes in sperm design, and formally describe Macrostomum gracilistylum sp. nov from Lake Malawi and its sister species Macrostomum crassum sp. nov., Macrostomum pellitum sp. nov., Macrostomum longispermatum sp. nov., and Macrostomum schareri sp. nov., from Lake Tanganyika.ConclusionsThe available evidence is consistent with the hypothesis that Macrostomum flatworms have radiated in Lake Tanganyika and subsequently spread to Lake Malawi. However, whether this represents a bona fide adaptive radiation still needs to be determined. Therefore, the African Great Lakes are promising targets for further research into flatworm diversity and speciation.

Transcriptome Profile Analyses of Head Kidney in Roach (Rutilus rutilus), Common Bream (Abramis brama) and Their Hybrids: Does Infection by Monogenean Parasites in Freshwater Fish Reveal Differences in Fish Vigour among Parental Species and Their Hybrids?

Hybrid generations usually face either a heterosis advantage or a breakdown, that can be expressed by the level of parasite infection in hybrid hosts. Hybrids are less infected by parasites than parental species (especially F1 generations) or more infected than parental species (especially post-F1 generations). We performed the experiment with blood-feeding gill parasite Paradiplozoon homoion (Monogenea) infecting leuciscid species, Abramis brama and Rutilus rutilus, their F1 generation and two backcross generations. Backcross generations tended to be more parasitized than parental lines and the F1 generation. The number of differentially expressed genes (DEGs) was lower in F1 hybrids and higher in backcross hybrids when compared to each of the parental lines. The main groups of DEGs were shared among lines; however, A. brama and R. rutilus differed in some of the top gene ontology (GO) terms. DEG analyses revealed the role of heme binding and erythrocyte differentiation after infection by blood-feeding P. homoion. Two backcross generations shared some of the top GO terms, representing mostly downregulated genes associated with P. homoion infection. KEGG analysis revealed the importance of disease-associated pathways; the majority of them were shared by two backcross generations. Our study revealed the most pronounced DEGs associated with blood-feeding monogeneans in backcross hybrids, potentially (but not exclusively) explainable by hybrid breakdown. The lower DEGs reported in F1 hybrids being less parasitized than backcross hybrids is in line with the hybrid advantage.

PRESENCE OF METACERCARIAE OF Opisthorchis sp. BLANCHARD, 1895 (TREMATODA: OPISTHORCHIIDAE) IN NEW HOST Macrobrachium amazonicum (HELLER, 1862), FROM THE NORTHERN BRAZIL: AN EMERGING RISK TO HUMANS BY THE SHRIMP CONSUMPTION

Herein, we report the first observation of the metacercaria Opisthorchis sp. Blanchard, 1895 recovered from a new intermediate host Macrobrachium amazonicum (Heller, 1862), an important food resource from northern Brazil, emphasising the risk of contamination from inappropriate human consumption. The shrimp specimens of M. amazonicum were collected during June 2023, using a local trap called matapi in the Guamá River (01°27’54.2”S; 048°26’02.6”W), which supplies the city of Belém, showing a characteristic of an eutrophicated river. The collected specimens were sexed, measured, weighted and dissected in the carapace region, to observe the presence of parasites in gills, hepatopancreas and gonads. We observed 56 specimens of M. amazonicum (20 males, 32 females and 4 ovigerous females), of which thirteen individuals (23.21% of total sampled) showed encysted metacercariae of Opisthorchis sp. only in gonadal tissues, with high preference in females (66.6%), when compared with males (33.4%). The observation of metacercaria in Amazon river prawn is a risk to human health, due to the parasite's life cycle being completed in humans, leading to several health problems such as hepatic and biliary degradation, diarrhoea, vomiting and respiratory problems. Additionally, the eutrophication process observed in the Guamá River may favour parasite proliferation, and dissemination to other hosts and regions, possibly increasing the cases of people infected with parasites in Belém metropolitan area. Based on that, this work is an alert to the authorities for the risk of contamination of the population due to inadequate consumption of (molluscs, crustaceans and fishes) from the eutrophic waters of the Guamá River and adjacent waters.

Variation in parasite infection between replicates of speciation in Lake Victoria cichlid fish.

Because of potentially strong eco-evolutionary interactions with their hosts, parasites may initiate or enhance host diversification. The adaptive radiation of cichlid fish in Lake Victoria provides a good system to study the role of parasites at different stages of host speciation. We analyzed the macroparasite infection of four replicates of sympatric blue and red Pundamilia species pairs that vary in their age and extent of differentiation. Sympatric host species differed in parasite community composition and in the infection levels of some of these parasite taxa. Most infection differences were consistent between sampling years, indicating temporal consistency in parasite-mediated divergent selection between species. Infection differentiation increased linearly with genetic differentiation. However, significant infection differences between sympatric species were only found in the oldest, most strongly differentiated Pundamilia species pair. This is inconsistent with parasite-driven speciation. Next, we identified five distinct species of Cichlidogyrus, a genus of highly specific gill parasites that has radiated elsewhere in Africa. Infection profiles of species of Cichlidogyrus differed between sympatric cichlid species only in the oldest and most differentiated pair, again inconsistent with parasite-mediated speciation. To conclude, parasites may contribute to host differentiation after speciation, but do not initiate host speciation.

A Monogenean Gill Parasite within the Genus Haliotrema (Ancyrocephalidae) Infecting Argyrops filamentosus Fish: Morphology and Molecular Studies

Due to the presence of different parasite taxa and other disease-causing agents, all fish species are extremely prone to dangers. As a result, the current study focused on some of the monogenean parasites that infect one of the economically important fish species, the soldier bream Argyrops filamentosus, from the Red Sea coast of Jeddah, Saudi Arabia. Following that, thirty A. filamentosus fish specimens were examined for monogenean parasites. The parasitic species were isolated and morphologically and molecularly studied. The presence of one monogenean species of Haliotrema susanae (F: Ancyrocephalidae) infecting gills was observed in 50% of the investigated fish species. The ancyrocephalid species Haliotrema susanae is characterized by having all generic features within the genus Haliotrema. It could be distinguished from other species within this genus by the male copulatory organ including a copulatory tube with no accessory piece and a haptor made up of two pairs of anchors, two bars, and seven pairs of marginal hooks. As ectoparasitic taxa of the investigated sparid fish, the current study of Haliotrema species constitutes the first report of this genus. A molecular phylogenetic analysis based on the partial 28S rRNA gene region was analyzed to investigate the phylogenetic affinity of this parasite with the genus Haliotrema belonging to Ancyrocephalidae. This study considers the addition of a new genetic sequence for this parasite species.

Gill Parasites of the Cypress Minnow, Hybognathus hayi Jordan (Cypriniformes: Leuciscidae), in South Arkansas

A survey of gill parasites was conducted in July 2019 on a small sample of cypress minnow, Hybognathus hayi Jordan, from Calion Lake, Union County, Arkansas (Ouachita River drainage). Six of 9 (67%) specimens harbored parasites, including ciliates Ichthyophthirius multifiliis Fouquet, 1876, and an undetermined Trichodina sp., a myxozoan, Myxobolus sp., and a monogenean, Dactylogyrus nuchalis Wood and Mizelle, 1957, in 2 (22%). Dactylogyrus hankinsoni Hanek, Molnar, and Fernando, 1975, was found in 3 (33%) of the host specimens. All 5 taxa of these gill-inhabiting parasites are reported for the first time from H. hayi, and the monogeneans are documented as new geographic distribution records in Arkansas.

Species depauperate communities and low abundances of monogenean gill parasites at the edge of the natural distribution range of their cichlid hosts in northern Africa

Species depauperate communities and low abundances of monogenean gill parasites at the edge of the natural distribution range of their cichlid hosts in northern Africa

Antibacterial and Antiparasitic Activity of Propyl-Propane-Thiosulfinate (PTS) and Propyl-Propane-Thiosulfonate (PTSO) from Allium cepa against Gilthead Sea Bream Pathogens in In Vitro and In Vivo Studies.

The use of phytogenic extracts is considered a sustainable strategy for the prevention of fish diseases, including Alliaceae as a potential option due to their variety of bioactive compounds. In this study, we analyzed the antibacterial and antiparasitic potential of propyl-propane-thiosulfinate (PTS) and propyl-propane-thiosulfonate (PTSO) from onions. The in vitro activity against Pseudomonas anguilliseptica, Tenacibaculum maritimum, and Photobacterium damselae of both compounds was tested. In addition, the viability of Sparicotyle chrysophrii larvae was evaluated. Moreover, a diet that consisted of a blend of PTS/PTSO (ALLIUM) was used. A total of 90 gilthead sea bream juveniles were tested against P. damselae subsp. Piscicida after 12 weeks of dietary administration. Furthermore, 150 fish with a rate of 10–15 parasites/fish were fed for 21 days and the number of gill parasites was recorded. All strains were sensitive to both compounds. PTSO showed the highest inhibitory effect against all target strains, while PTS showed higher effectiveness against S. chrysophrii. Fish from ALLIUM group presented the highest probability of survival, increasing up to 91.1%, whereas in the control group, the probability of survival was 66.7%. The number of parasites in the gilthead sea bream decreased in the ALLIUM group over time. These results suggest the inclusion of PTS and PTSO in feed as a natural strategy to prevent antibacterial and antiparasitic fish diseases.

Co-introduction of Dolicirroplectanum lacustre, a monogenean gill parasite of the invasive Nile perch Lates niloticus: intraspecific diversification and mitonuclear discordance in native versus introduced areas

The Nile perch (Lates niloticus) is a notorious invasive species. The introductions of Nile perch into several lakes and rivers in the Lake Victoria region led to the impoverishment of trophic food webs, particularly well documented in Lake Victoria. Additionally, its parasites were co-introduced, including Dolicirroplectanum lacustre (Monogenea, Diplectanidae). Dolicirroplectanum lacustre is the single monogenean gill parasite of latid fishes (Lates spp.) inhabiting several major African freshwater systems. We examined the intra-specific diversification of D. lacustre from Lates niloticus in Lake Albert, Uganda (native range) and Lake Victoria (introduced range) by assessing morphological and genetic differentiation, and microhabitat preference. We expected reduced morphological and genetic diversity for D. lacustre in Lake Victoria compared with Lake Albert, as a result of the historical introductions. We found that D. lacustre displayed high morphological variability within and between African freshwaters, with two morphotypes identified, as in former studies. The single shared morphotype between Lake Albert and Lake Victoria displayed similar levels of haplotype and nucleotide diversity between the lakes. Mitonuclear discordance within the morphotypes of D. lacustre indicates an incomplete reproductive barrier between the morphotypes. The diversification in the mitochondrial gene portion is directly linked with the morphotypes, while the nuclear gene portions indicate conspecificity. Based on our results, we reported reduced genetic and morphological diversity, potentially being a result of a founder effect in Lake Victoria.