Host Gill Research Articles

TAXES OF DICYEMIDS (PHYLUM DICYEMIDA).

Dicyemids (Phylum Dicyemida) are endosymbionts present in the kidneys of benthic cephalopods. They usually consist of 10 to 40 cells and are characterized by 2 distinct body types: vermiform individuals and infusoriform larvae. Vermiform individuals remain attached to the internal surface of the host's renal appendages, while infusoriform larvae leave the renal sac to search for a new host. To investigate how dicyemids respond to various host and environmental cues, we evaluated phototaxis, chemotaxis, thigmotaxis, and rheotaxis responses of vermiform individuals and infusoriform larvae of 2 dicyemid species in a laboratory setting. Vermiform individuals did not exhibit phototaxis and chemotaxis to the major components of the host: urine, tissue fluids, or extracts of the host gills. However, they showed positive thigmotaxis and positive rheotaxis to slow water flow, probably contributing to enabling attachment to the renal appendages and remaining in the renal sac, respectively. The infusoriform larvae exhibited negative chemotaxis to host blood and negative thigmotaxis, but there was no evidence of phototaxis and rheotaxis. Negative thigmotaxis may facilitate the release of infusoriform embryos from the renal appendages. Negative chemotaxis to the host blood suggests that the infusoriform larvae do not enter through the vascular system to gain access to the renal sac, so the process by which infusoriform larvae enter the cephalopod host is yet to be determined.

Complete mitochondrial genomes of Dactylogyrus crucifer and Dactylogyrus zandti reveal distinct patterns of codon usage within Dactylogyrus

Monogeneans of the genus Dactylogyrus Diesing, 1850, the largest genus in the family Dactylogyridae, mostly parasitize the gills of cyprinoid hosts; however, only 3 Dactylogyrus’ mitochondrial genomes (mitogenomes) are studied so far. The aim of this research is to extend our understanding of the mitogenomes of Dactylogyrus. We sequenced the mitogenomes of D. crucifer and D. zandti isolated from Rutilus rutilus and Abramis brama orientalis in northwest China, and then we compared these mitogenomes with other monogeneans. We used Illumina NovaSeq to sequence the entire mitochondrial genomes of D. crucifer and D. zandti and characterized the mitogenomes to understand the gene structure, gene identity, the secondary structures of the 22 tRNA genes, and relative synonymous codon usage. We used the analytic Bayesian Information and Maximum Likelihood methods to determine their associated phylogenetic trees. The mitogenomes of D. crucifer and D. zandti were 14,403 and 18,584 bp, respectively. Organization and positioning of these genes were in accordance with Dactylogyrus lamellatus and Dactylogyrus tuba. The nucleotide composition of Dactylogyridae was different from other families of Monogenea, and the A+T count of genus Dactylogyrus (54 – 58.4 %) was lower than other genus species of the family Dactylogyridea (63.9 – 78.4 %) in protein-coding genes. Dactylogyrus members displayed a codon usage bias. The relative synonymous codon used by Dactylogyrus was not conserved and was lower than other monogeneans. The codon use patterns of closely-related species isolated from closely-related hosts were identical. Phylogenetic analyses using mitogenomic dataset produced Dactylogyrus isolated from host subfamily Leuciscinae formed a sister-group. Our results contributed significantly to an increased database of mitogenomes, more than 50 %, for Dactylogyrus that may help future studies of mitochondrial genes and codon uses for the analysis of monogenean phylogenetics.

Reproductive Strategies and Embryonic Development of Autumn-Spawning Bitterling (Acheilognathus rhombeus) within the Mussel Host.

We investigated the reproductive strategies and embryonic development of Acheilognathus rhombeus (a bitterling species that spawns in autumn) within its freshwater mussel host in the Bongseo Stream, South Korea. By focusing on survival mechanisms during critical stages of embryonic development, the selective use of mussel gill demibranchs by the bitterlings and associated adaptive traits were observed over 1 year. A significant diapause phase occurs at developmental stage D, which lasts for approximately 7 months, allowing embryos to survive winter. Development resumes when the temperature exceeds 10 °C. Minute tubercles on the embryos (crucial for anchoring within the host gill demibranchs and preventing premature ejection) exhibit the largest height during diapause, and the height decreases when developmental stage E is reached, when growth resumes. Acheilognathus rhombeus embryos were observed in 30.5% of the mussels, mostly within the inner gills, thereby maximizing spatial use and oxygen access to enhance survival. These results highlight the intricate relationship between A. rhombeus and its mussel hosts, demonstrating the evolutionary adaptations that enhance reproductive success and survival. This study provides valuable insights into the ecological dynamics and conservation requirements of such symbiotic relationships.

Network-based integration of omics, physiological and environmental data in real-world Elbe estuarine Zander

Coastal and estuarine environments are under endogenic and exogenic pressures jeopardizing survival and diversity of inhabiting biota. Information of possible synergistic effects of multiple (a)biotic stressors and holobiont interaction are largely missing in estuaries like the Elbe but are of importance to estimate unforeseen effects on animals' physiology. Here, we seek to leverage host-transcriptional RNA-seq and gill mucus microbial 16S rRNA metabarcoding data coupled with physiological and abiotic measurements in a network analysis approach to decipher the impact of multiple stressors on the health of juvenile Sander lucioperca along one of the largest European estuaries. We find mesohaline areas characterized by gill tissue specific transcriptional responses matching osmosensing and tissue remodeling. Liver transcriptomes instead emphasized that zander from highly turbid areas were undergoing starvation which was supported by compromised body condition. Potential pathogenic bacteria, including Shewanella, Acinetobacter, Aeromonas and Chryseobacterium, dominated the gill microbiome along the freshwater transition and oxygen minimum zone. Their occurrence coincided with a strong adaptive and innate transcriptional immune response in host gill and enhanced energy demand in liver tissue supporting their potential pathogenicity. Taken together, we show physiological responses of a fish species and its microbiome to abiotic factors whose impact is expected to increase with consequences of climate change. We further present a method for the close-meshed detection of the main stressors and bacterial species with disease potential in a highly productive ecosystem.

A newly discovered trematode parasite infecting the bay scallop, Argopecten irradians

A novel parasite infecting the gill tissue of bay scallops (Argopecten irradians) was first observed in North Carolina in 2012 and has also been found infecting bay scallop populations along the Gulf Coast of Florida. Because the parasite infects a host of great fisheries interest and is extremely conspicuous to the naked eye, and yet was not observed before 2012, it is likely an introduced species. Preliminary morphological analyses indicate that this parasite is a trematode in the superfamily Hemiuroidea and that it uses the bay scallop as a first intermediate host. All other hosts are currently unknown. Phylogenetic analyses show that this novel parasite belongs to family Didymozoidae and forms a strongly supported clade with a recently described trematode from Australia, Saccularina magnacetabula. Histological analysis indicates that Saccularina sp. sporocysts inhabit and greatly expand the afferent vessels of the host's gills. Prevalence monitoring of Saccularina sp. in caged and wild bay scallop populations in North Carolina shows a strong pattern of seasonality that is consistent across sites, but no latitudinal gradient was found, suggesting that prevalence is likely driven by final host distribution in time and space. This research provides important baseline information on the basic biology of Saccularina sp. and impacts on its economically important host, the bay scallop.

Avaliação histopatológica do dourado Acanthopagrus bifasciatus Forsskål, 1775 (Sparidae) infectado por Bivagina pagrosomi (Microcotylidae)

ABSTRACT Fish, like all other species, can be impacted by a variety of environmental conditions, including parasitic infections. Although there are several parasitological researche on ectoparasitic monogeneans, few are published on those that infect sparid fish. Forty samples of Acanthopagrus bifasciatus were collected during this study from coastal regions along the Arabian Gulf (Saudi Arabia). Gills from all fish were isolated and examined to identify monogeneans. The parasites were studied morphologically using light microscopy. Overall prevalence and mean intensity were 20% and 9, respectively. Eight out of 40 (20%) fish samples were found to be naturally infected with a monogenetic species, namely, Bivagina pagrosomi (Murray, 1931) Dillon and Hargis, 1965 belonging to Microcotylidae (order Mazocraeidea). This parasite is characterized by the presence of haptor provided 43-47 clamps of microcotylid-type that deeply penetrated the gill lamellae and caused severe pathological impacts including hyperplasia, telangiectasis, and deformity of the respiratory epithelial cells Our finding indicates that this is the first report of A. bifasciatus being infected with B. pagrosomi from Saudi marine waters as well as the research of its deleterious effects on its host gills. More research is needed to confirm the parasite species’ taxonomic status at the molecular level.

In Vivo Challenge Trials with Dietary Antiparasitics Reveal New Insights into the Practical Use of Fenbendazole against Sparicotyle chrysophrii (Monogenea) Infection in Sparus aurata (Teleostei)

The microcotylid Sparicotyle chrysophrii is one of the most harmful parasites for the aquaculture of the gilthead seabream Sparus aurata, for which effective treatments are needed. The efficacy of dietary praziquantel (PZQ, 30–50 mg kg body weight−1 day−1), emamectin benzoate (EMB, 0.015–0.050 mg kg BW−1 day−1), and fenbendazole (FBZ, 40–75 mg kg BW−1 day−1) against S. chrysophrii on gilthead seabream was tested in four different in vivo challenge trials. Specimens of gilthead seabream naturally infected with S. chrysophrii were maintained in three separate recirculating aquaculture systems of 142 L (1 control vs. 2 treated). Fish were fed (ration 1.2% BW day−1) 5 days a week for 4 weeks, alternating weeks with medicated and control feed. On days 0, 14, and 28, samples of 7–9 fish per group were collected and the gills were examined for S. chrysophrii. The gills of hosts treated with EMB and FBZ were evaluated by histopathology. The trials showed that in‐feed PZQ has low palatability, causing rejection which did not allow its efficacy to be adequately investigated. While dietary EMB was associated with adverse effects, such as gill de‐epithelialisation and necrosis, with no demonstrated efficacy against S. chrysophrii. On the other hand, all the fish treated with FBZ lost all parasites, showing 100% efficacy and also suggesting a preventive/repellent action against the monogenean. In conclusion, the present study provides indications for the use of dietary FBZ as a medical device for the treatment/prophylaxis of sparicotylosis in aquaculture.

The distribution of monogeneans of the genus Ligophorus on gills of the soiuy mullet Planiliza haematocheilus

The distribution on the host gills of three monogenean species of Ligophorus Euzet et Suriano, 1977, parasitising soiuy mullet Planiliza haematocheilus (Temminck & Schlegel, 1845) in the Black and Azov seas was studied. Specimens of L. pilengas and L. llewellyni prefer to localize on the same gill sites, namely, I-III gill arches and their medial sectors. The third species, L. kaohsianghsieni , was distributed on the gills more crowdedly, with about 80% of its specimens being present on II gill arch, occurring on the medial and ventral sectors approximately equally. In general, most monogeneans were found on the largest in area and well-watered gill arches and sectors, as well as the anterior hemibranchies, however within these areas they preferred to attach to proximal half of filaments with less amount of water current. The presence of congeners on gills had no significant effect on the distribution of L. pilengas and L. llewellyni . Increasing infrapopulation number resulted in a more uniform distribution of monogeneans on gills; their proportion upsurges significantly on the faster growing anterior hemibranchs as fish size increased.

L-fucoside localization in the gills of the genus Takifugu and its possible implication in the parasitism of Heterobothrium okamotoi (Monogenea: Diclidophoridae)

BackgroundThe monogenean parasite Heterobothrium okamotoi only parasitizes the gills of Takifugu rubripes. In this study, we hypothesized that the carbohydrates contribute to high host specificity of H. okamotoi. MethodsT. rubripes, T. niphobles, T. snyderi, and T. pardalis were used for UEA I staining of the gills and an in vivo challenge test against H. okamotoi. To examine the effect of l-fucose, an in vitro detachment test was conducted using the host's gills. Additionally, fucosylated proteins were isolated from the membrane proteins of T. niphobles gills. ResultsThe location of l-fucoside and the infection dynamics in four species were correlated to some extent; H. okamotoi detached relatively quickly from T. niphobles possessing l-fucoside both on the surface of the gills and in certain types of cells, including mucus cells, but detached slowly from T. snyderi possessing l-fucoside in only certain types of cells, including mucus cells. Under the conditions examined, H. okamotoi exhibited minimal detachment from T. rubripes and T. pardalis, and l-fucoside was not detected. The significantly higher detachment rate of H. okamotoi from the host's gills incubated in l-fucose-containing medium compared with the controls suggests that l-fucose in the non-host gills induced detachment of H. okamotoi. Four fucosylated proteins, including mucin5AC-like, were identified as potential factors for the detachment of H. okamotoi. ConclusionsFucosylated proteins covering the surface of non-host gills might contribute to H. okamotoi detachment. General significanceThis research shows the possible involvement of oligosaccharides in the host specificity of monogenean parasites.

Reproductive strategies of the parasitic flatworm Thaparocleidus vistulensis (Siwak, 1932) (Platyhelminthes, Monogenea) infecting the European catfish Silurus glanis Linnaeus, 1758

The life cycle of Thaparocleidus vistulensis (Siwak, 1932), a host-specific monogenean parasite of European catfish (Silurus glanis Linnaeus, 1758), was investigated by detailed observation of infection dynamics, egg development, hatching rate and in vitro survival rates of the parasite at different life stages at 23 °C. A total of 30 naive fingerlings were infected in three exposure trials by co-habitation with donor fish carrying adult parasites. Two fish were dissected every two days during the 10-day experimental period to explore the development of larvae and juvenile parasites on the host gills. Freshly laid eggs by adult monogeneans were collected and observed daily under a light microscope until hatching. A total of 445 eggs were collected and distributed into wells of 96-well microtiter plates containing filtered fish tank water to determine their hatching rates. A similar method was used to investigate the survival rates of isolated parasites at different developmental stages (larvae, juveniles, and adults). T. vistulensis populations on the European catfish in fish tanks increased markedly within ten days, dependent on the severity of the initial infection levels of the donor fish. The first eggs hatched three to four days after oviposition, and the hatching rate peaked on the fifth day (89.7%). The survival rate for freely swimming oncomiracidia without host was 7.4% after five days, whereas isolated juvenile and adult parasites showed a higher dependence of host contact (survival rates three days post-isolation of 0.9% and 1.6%, respectively). The data allows prediction of parasite-host dynamics and may improve control of gill-disease in cultured European catfish stocks in fish farms.

KANNAPHALLUS RAPHIDIUM N. SP. (MONOGENOIDEA: MAZOCRAEIDEA: HETERAXINIDAE) PARASITIC ON THE GILL LAMELLAE OF THE GOLDEN TREVALLY GNATHANODON SPECIOSUS (CARANGIFORMES: CARANGIDAE) OCCURRING IN THE COASTAL WATERS OF QUEENSLAND AND WESTERN AUSTRALIA.

An undescribed species of KannaphallusUnnithan, 1957 (Monogenoidea: Heteraxinidae) was collected from the gills of the golden trevally Gnathanodon speciosus (Forsskål) (Carangidae) from Moreton Bay, Queensland, during January 2016 and from Ningaloo Reef, Western Australia, during December 2021 and June 2022. The diagnosis for Kannaphallus was emended and the new species, Kannaphallus raphidium, was described. Kannaphallus virilis of Young, nec Unnithan was placed in synonymy with K. raphidium. The distal components of the male reproductive system and the arrangement of the clamp rows of the haptor occurred as mirror images among specimens of K. raphidium, suggesting that the respective antipodes of K. raphidium may have reproductive implications and function in the site selection of the parasite on the host's gills. A specimen of K. raphidium from Western Australia was sequenced for the cytochrome c oxidase subunit 1 (COI) mtDNA and ITS2 rDNA barcoding markers, and the phylogenetically informative 28S rDNA marker. Maximum likelihood and Bayesian inference analyses based on a partial 28S rDNA alignment, including all comparable heteraxinid sequence data available, resolved the Heteraxininae and Cemocotylinae as reciprocatively paraphyletic and provided evidence that Kannaphallus may be paraphyletic. No taxonomic changes concerning the subfamilies and genera of the Heteraxinidae were proposed. Finally, Kannaphallus univaginalisRamalingam, 1960 and Cemocotylelloides univaginalis (Ramalingam, 1960) Nitta, Kondo, Ohtsuka, Kamarudin, and Ismail, 2022 are considered nomen nuda sensu the International Code of Zoological Nomenclature.

Phagocytosis of exogenous bacteria by gill epithelial cells in the deep-sea symbiotic mussel Bathymodiolus japonicus.

Animals that live in nutrient-poor environments, such as the deep sea, often establish intracellular symbiosis with beneficial bacteria that provide the host with nutrients that are usually inaccessible to them. The deep-sea mussel Bathymodiolus japonicus relies on nutrients from the methane-oxidizing bacteria harboured in epithelial gill cells called bacteriocytes. These symbionts are specific to the host and transmitted horizontally, being acquired from the environment by each generation. Morphological studies in mussels have reported that the host gill cells acquire the symbionts via phagocytosis, a process that facilitates the engulfment and digestion of exogenous microorganisms. However, gill cell phagocytosis has not been well studied, and whether mussels discriminate between the symbionts and other bacteria in the phagocytic process remains unknown. Herein, we aimed to investigate the phagocytic ability of gill cells involved in the acquisition of symbionts by exposing the mussel to several types of bacteria. The gill cells engulfed exogenous bacteria from the environment indiscriminately. These bacteria were preferentially eliminated through intracellular digestion using enzymes; however, most symbionts were retained in the bacteriocytes without digestion. Our findings suggest that regulation of the phagocytic process after engulfment is a key mechanism for the selection of symbionts for establishing intracellular symbiosis.

Prevalence and Spatial Distribution of Ectoparasites in Wallago attu of River Penna, YSR District, Andhra Pradesh, India

An ectoparasitic survey on fish Wallago attu (n = 95) of river Penna, YSR district, Andhra Pradesh (India) was executed from August, 2017 to February, 2018. A total of 3202 parasites belonging three ectoparasitic groups viz., three monogeneans - Thaparocleidus indicus, thaparocleidus wallagonius, Mizelleus indicus, one copepod - Ergasilus malnadensis, and one isopod - Alitropus typus were detected from the gills of the examined hosts. Their spatial distributions on the host gills were reported. Only E. malnadensis, T. wallagonius and T. indicus showed aggregate distribution while the remaining two species, M. indicus and A. typus showed random distribution. Only, A. typus, T. wallagonius and T. indicus showed positive and statistically significant correlation with the condition factor. Location wise ectoparasite analysis revealed the higher infestation rates in site-II Somasila backwaters, Vontimitta compared to site-I Chennur. Spatial distribution studies revealed that there is no significant preference for the sides of the host fish. Both the sides of gill arch were equally infected. However, they showed preference within the gill arches. Monogeneans preferred gill arches II, III and IV, whereas copepods and isopods preferred gill arches I and II. There was meagre effect of host size and host sex on the ectoparasitic infection. These types of spatial distribution studies give an accurate location of the parasites to apply the eradication measures and eradicate them efficiently in fish aquaculture.

Occurrence of Protozoan Parasites of Channa Punctatus in Bangladesh

Three species of myxozoa (Henneguya chaudhuryi, Henneguya bengalensis and Myxobolus sp.) and 3 species of ciliophora (Trichodina pediculus, Epistylis lwoffi and Apisoma piscicolum) and two actinosporean stages of myxoza were identified. Some 51.72% of total host fishes which were found infected with at least one of the above mentioned parasites with average load of 95.93±41.53 per infected host. High percentage (98.05) of C. punctatus possessed myxozoan infection and 1.95 had chiliophoran infection. The highest prevalence of parasitic infection was observed in host sample collected from Faridpur district and lowest (33.33%) in fish sample collected from Mymensingh. The association of parasitic infection of H. bengalensis and Myxobolus sp. with study areas was found statistically significant (p=0.024 and 0.049, respectively). Protozoan parasites were most abundant in gills of hosts. Shannon Diversity Index indicated that host fishes were not infested by more parasites and the parasite community was poorly diverged in all study sites. However, Simpson’s Diversity showed that, parasites community was moderately diverged in host fishes collected from Mymensingh district and in rest of the areas parasite community was poorly diverged.
 Asiat. Soc. Bangladesh, Sci. 46(1): 13-25, June 2020

Co-occurrence and niche overlap among gill parasites of the white mullet (Mugil curema Valenciennes, 1836) (Osteichthyes: Mugilidae) from the western Atlantic, Brazil.

Different groups parasitize the gills of fishes, and the organisms can interact in positive, negative, or neutral ways, depending on parasitic abundance, environmental conditions, and the availability of resources. Here, we studied the distribution of ectoparasites on the gills of the mullet Mugil curema in the Cabedelo port region (Brazil), asking if (1) the gill parasites of M. curema fix on specific host gill arches and/or (2) co-occur in the same gill arches within a host individual; (3) if the abundance of one parasite taxon affects the abundance of another on the same gill arches; and (4) considering distinct major groups, if parasites present patterns of co-occurrence on hosts and gill arches different from the expected at random. We used generalized linear models, generalized linear mixed models, and models with zero inflation to define the microhabitats (arches) with the highest abundances of parasites and null models to analyze the co-occurrences of gill parasite groups. Three taxa of Monogenea (Ligophorus brasiliensis Abdallah, Azevedo & Luque, 2009, Ligophorus sp. 1 and Ligophorus sp. 2) and six species of Copepoda were recorded (Bomolochus nitidus Wilson, 1911; Caligus praetextus Bere, 1936; Ergasilus atafonensis Amado & Rocha, 1997;Ergasilus bahiensis Amado & Rocha, 1997; Ergasilus caraguatatubensis Amado & Rocha, 1997 and Ergasilus lizae Krøyer, 1863). We found that, in general, the gill parasites were more abundant/prevalent on specific arches (I and II) of the hosts, shared such preferences and co-occurred on the gill arches. The presence of one taxon influenced the occurrence of another only in the arches I and II; as a result, the infracommunities were characterized as interactive in the gills of this host species.

Molecular analyses of the gill symbiosis of the bathymodiolin mussel Gigantidas platifrons.

SummaryAlthough the deep-sea bathymodiolin mussels have been intensively studied as a model of animal-bacteria symbiosis, it remains challenging to assess the host-symbiont interactions due to the complexity of the symbiotic tissue—the gill. Using cold-seep mussel Gigantidas platifrons as a model, we isolated the symbiont harboring bacteriocytes and profiled the transcriptomes of the three major parts of the symbiosis—the gill, the bacteriocyte, and the symbiont. This breakdown of the complex symbiotic tissue allowed us to characterize the host-symbiont interactions further. Our data showed that the gill's non-symbiotic parts play crucial roles in maintaining and protecting the symbiosis; the bacteriocytes supply the symbiont with metabolites, control symbiont population, and shelter the symbiont from phage infection; the symbiont dedicates to the methane oxidation and energy production. This study demonstrates that the bathymodiolin symbiosis interacts at the tissue, cellular, and molecular level, maintaining high efficiency and harmonic chemosynthetic micro niche.

Microhabitat distributions and species interactions of ectoparasites on the gills of cichlid fish in Lake Victoria, Tanzania

Heterogeneous exposure to parasites may contribute to host species differentiation. Hosts often harbour multiple parasite species which may interact and thus modify each other’s effects on host fitness. Antagonistic or synergistic interactions between parasites may be detectable as niche segregation within hosts. Consequently, the within-host distribution of different parasite taxa may constitute an important axis of infection variation among host populations and species. We investigated the microhabitat distributions and species interactions of gill parasites (four genera) infecting 14 sympatric cichlid species in Lake Victoria, Tanzania. We found that the two most abundant ectoparasite genera (the monogenean Cichlidogyrus spp. and the copepod Lamproglena monodi) were non-randomly distributed across the host gills and their spatial distribution differed between host species. This may indicate microhabitat selection by the parasites and cryptic differences in the host–parasite interaction among host species. Relationships among ectoparasite genera were synergistic: the abundances of Cichlidogyrus spp. and the copepods L. monodi and Ergasilus lamellifer tended to be positively correlated. In contrast, relationships among morphospecies of Cichlidogyrus were antagonistic: the abundances of morphospecies were negatively correlated. Together with niche overlap, this suggests competition among morphospecies of Cichlidogyrus. We also assessed the reproductive activity of the copepod species (the proportion of individuals carrying egg clutches), as it may be affected by the presence of other parasites and provide another indicator of the species specificity of the host–parasite relationship. Copepod reproductive activity did not differ between host species and was not associated with the presence or abundance of other parasites, suggesting that these are generalist parasites, thriving in all cichlid species examined from Lake Victoria.

Host gill attachment causes blood-feeding by the salmon louse (Lepeophtheirus salmonis) chalimus larvae and alters parasite development and transcriptome

BackgroundBlood-feeding is a common strategy among parasitizing arthropods, including the ectoparasitic salmon louse (Lepeophtheirus salmonis), feeding off its salmon host’s skin and blood. Blood is rich in nutrients, among these iron and heme. These are essential molecules for the louse, yet their oxidative properties render them toxic to cells if not handled appropriately. Blood-feeding might therefore alter parasite gene expression.MethodsWe infected Atlantic salmon with salmon louse copepodids and sampled the lice in two different experiments at day 10 and 18 post-infestation. Parasite development and presence of host blood in their intestines were determined. Lice of similar instar age sampled from body parts with differential access to blood, namely from gills versus lice from skin epidermis, were analysed for gene expression by RNA-sequencing in samples taken at day 10 for both experiments and at day 18 for one of the experiments.ResultsWe found that lice started feeding on blood when becoming mobile preadults if sitting on the fish body; however, they may initiate blood-feeding at the chalimus I stage if attached to gills. Lice attached to gills develop at a slower rate. By differential expression analysis, we found 355 transcripts elevated in lice sampled from gills and 202 transcripts elevated in lice sampled from skin consistent in all samplings. Genes annotated with “peptidase activity” were among the ones elevated in lice sampled from gills, while in the other group genes annotated with “phosphorylation” and “phosphatase” were pervasive. Transcripts elevated in lice sampled from gills were often genes relatively highly expressed in the louse intestine compared with other tissues, while this was not the case for transcripts elevated in lice sampled from skin. In both groups, more than half of the transcripts were from genes more highly expressed after attachment.ConclusionsGill settlement results in an alteration in gene expression and a premature onset of blood-feeding likely causes the parasite to develop at a slower pace.

Dactylogyrus spp. (Monogenea, Dactylogyridae) from the Gills of Enteromius spp. (Cypriniformes, Cyprinidae) from the Limpopo Province, South Africa with Descriptions of Three New Species

Monogenean parasites of the genus Dactylogyrus Diesing, 1850 parasitize mostly gills of cyprinoids hosts. Of 100 species currently known from African continent, approximately 35 have been described from Enteromius spp. Results of recent studies indicate that there are still many undescribed species of the genus Dactylogyrus in South Africa and systematic surveys can bring many new findings. During the period April 2015-May 2016, three species of the genus Enteromius were sampled from eight localities across Limpopo Province. Monogenean parasites were collected from the gills of the hosts using stereomicroscopes. Morphometric analysis of the hard parts of the attachment organ and male copulatory organs were performed to confirm species identity. Presence of three new and three previously described Dactylogyrus species is reported. Newly described species include: Dactylogyrus afrohamiltoni sp. nov. from Enteromius afrohamiltoni; Dactylogyrus limpopoensis sp. nov. and Dactylogyrus letabaensis sp. nov. from Enteromius unitaeniatus. In addition, Dactylogyrus afrolongicornis, Dactylogyrus allolongionchus and Dactylogyrus myersi were identified from Enteromius trimaculatus. Newly identified species possess morphometric characters based on which they can be clearly identified from currently known species. Present results show that small barbs, especially those not previously studied for monogenean parasites, are potentially very interesting target to study to recover new species of the genus Dactylogyrus and to bring new contribution to the knowledge of the diversity of African parasites.

Shedding and survival of an intracellular pathogenic Endozoicomonas-like organism infecting king scallop Pecten maximus.

The Lyme Bay marine protected area (MPA) hosts a valuable population of king scallop Pecten maximus L. Recently, an Endozoicomonas-like organism (ELO), infecting host gill epithelial tissue, was associated with king scallop mass mortality events within the Lyme Bay MPA. Currently, very little is known about its transmission and survival outside the host. In this investigation, animals collected outside of reported mortality events showed high levels of ELO infection. Gill tissue disruption and the release of bacteria into the interlamellar space was seen histologically, suggesting shedding of ELO from host animals. To investigate pathogen survival outside the host, infected scallops were maintained in static water for a 24 h period, and then removed. Over the subsequent 8 d, water samples were collected and the quantity of ELO 16S rRNA transcript was measured by TaqManTM quantitative PCR (qPCR). The 16S rRNA transcript quantity was stable outside the host for 6 d before bacteria survival declined 2 logs (7.9 × 108 16S rRNA to 2.3 × 106 transcripts), suggesting that ELO can survive independently outside the host organism. The ELO-specific qPCR probe can therefore be used in future field studies of ELO prevalence within the environment and fauna of the Lyme Bay MPA.