Monogenean Parasites Research Articles

New records of nine monogenean parasites infesting non-native freshwater fish species in New Zealand

ABSTRACT Twenty-one non-native freshwater fish species have established populations in New Zealand, yet only two have been reported with monogenean infestations; grass carp, Ctenopharyngodon idella (Valenciennes in Cuvier and Valenciennes, 1844) and western mosquitofish, Gambusia affinis (Baird and Girard, 1853), each with two identified monogenean species. Based on the diversity of monogeneans known from New Zealand's non-native freshwater fish species in their native and other invaded ranges, it is likely that many other monogeneans could be extant in the country. Accordingly, we surveyed monogeneans from seven freshwater fish species. Eleven monogenean species were found, including nine previously unreported from New Zealand. One represented a genus previously unrecorded in the country, the ancyrocephalid Ligictaluridus pricei (Mueller, 1936), infesting the gills of Ameiurus nebulosus (Lesueur, 1819). Six dactylogyrid monogenean species were found infesting Carassius auratus (L.): Dactylogyrus anchoratus (Dujardin, 1845), D. dulkeiti Bychowsky, 1936, D. formosus Kulweic, 1927, D. inexpectatus Izyumova, 1955, D. intermedius Wegener, 1909 and D. vastator Nybelin, 1924. Further, a Gyrodactylus species was observed from the gills of Carassius auratus, which could not be confidently identified to the species level. Finally, Dactylogyrus minutus Kulweic, 1927, was recorded from Cyprinus rubrofuscus Lacépède, 1803.

Transcriptomic analysis of immune-related genes in Pacific white snook (Centropomus viridis) gills infected with the monogenean parasite Rhabdosynochus viridisi

The parasite Rhabdosynochus viridisi (Platyhelminthes: Monogenea) infects the Pacific white snook Centropomus viridis gills and can cause adverse effects in the aquaculture industry. The immune responses of Pacific white snook to monogenean infections are poorly understood. Thus, this study aimed to identify differentially expressed genes (DEGs) in the gills of Pacific white snook juveniles experimentally infected with R. viridisi, emphasizing immune-related genes and pathways activated or suppressed during the infection. RNA sequencing was performed on the gills of uninfected (control) and infected fish. The algorithm Seq2Fun was selected without a reference transcriptome to map the reads to transcripts of fishes available from a database for gene orthologs (EcoOmics) and obtain the counting table. The ExpressAnalyst software was used for differential expression and functional analyses. A total of 20,106 transcripts were found, and 1430 (7 %) were differentially expressed genes (DEGs) between infected and control groups. We identified 860 (60 %) downregulated and 570 (40 %) upregulated genes. Thirteen canonical pathways after the Kyoto Encyclopedia of Genes and Genomes (KEGG) database were overrepresented, and most of the DEGs were downregulated, suggesting the inactivation of these pathways. The functions of most of the DEGs with higher fold change found in this study are poorly understood in fish. Even though the well-known pro-inflammatory cytokines remained unchanged in infected gills of C. viridis, and transforming growth factor β (tgfβ) was downregulated, interleukin-17 ligands il17d and il17a/f1, as well as C-X-C motif chemokine receptor 2 (cxcr2) genes were upregulated, indicating that the infection with R. viridisi promotes Th17-like immunity. Overexpression of plasma B cell activity markers such as immunoglobulin light chain-like genes and the v-set pre-B cell surrogate light chain 3 (vpreb3) was also detected in this study. The possible implications of DEGs related to calcium imbalance, hypoxia adaptation, hemostasis, and immunity are discussed. These results will support future studies to improve the prevention and treatment of monogenean infections in finfish aquaculture.

Antimicrobial and anthelmintic effects of copper nanoparticles against Koi carp parasites and their toxicity.

This study investigated the invitro antimicrobial and anthelmintic effect of copper nanoparticles (CuNPs) against the bacterium Aeromonas hydrophila, the monogeneans Dactylogyrus minutus, Dactylogyrus extensus, Gyrodactylus cyprini, and the cestode Schyzocotyle acheilognathi, as well as their toxicity to Cyprinus carpio Koi. In the antimicrobial invitro test, the inhibition zone method and minimum inhibitory concentration (MIC) were performed. In order to determine the time and efficacy of monogenean parasite mortality, the parasites were exposed to CuNP concentrations of 20, 50, 100, 150, 200, and 300 mg L-1, and a control group with tank water and one with copper sulphate pentahydrate (CuSO4.5H2O) at a concentration of 0.3 mg L-1, performed in triplicate. The parasites were observed every 10 min for 300 min, and mortality was recorded. For the cestodes, parasites were immersed in CuNP concentrations of 50, 100, 150, and 300 mg L-1. At the end of the invitro tests, the anthelmintic efficacy of each treatment was calculated. To assess the tolerance and toxicity in fish, they were exposed to CuNP concentrations of 0.6, 1.25, 2.5, 5, 10, 20, and 50 mg L-1 for 12 h. The MIC demonstrated that CuNPs effectively inhibited the growth of A. hydrophila up to a dilution of 12,500 mg L-1 and showed an inhibition zone of 14.0 ± 1.6 mm for CuNPs. The results of anthelmintic activity showed a dose-dependent effect of concentration for both groups of parasites, with the most effective concentration being 300 mg L-1 in 120 min. In the toxicity test, the carps showed tolerance to lower concentrations. The study indicated that CuNPs were effective against the studied pathogens. However, it proved to be toxic to fish at high concentrations. The use of low concentrations is recommended still requires further investigation.

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.

New geographic distribution record of Dactylogyrus labei Musselius and Gusev (1976) (Platyhelminthes, Monogenea) of Labeo rohita (Teleostei: Cyprinidae) from Mizoram, northeast India

Dactylogyrus labei is a dactylogyrid monogenean parasite originally described by Musselius and Gusev (1976) from Labeo rohita (Hamilton, 1822) (Teleostei: Cyprinidae) in two alternative forms: a typical from Lucknow, north India and an atypical from Kalyani, east India. Fresh specimens of D. labei were collected from Mizoram in northeast India, and examined morphologically using high-resolution digital image processing and analysis. The recovered monogeneans most closely resembled the atypical form of D. labei, with only minor differences, indicating conspecificity. The atypical form of D. labei is distinguished from other species of the genus by the following combination of characters: the dorsal bar wing-shaped, with a fine membrane on the anterior margin and a fenestration in the middle; the ventral bar casing nail-shaped with two small antero-lateral processes (3-rayed); the male copulatory tube loosely S-shaped, slender, with an inflated initial part; the accessory piece proximally tubular, distally a complex of multi-layered sheath guiding the copulatory tube, and the vagina tubular, with one small loop and vaginal pore surrounded with a flap-like structure. This study expands the geographical distribution of D. labei while improving its morphological descriptions.

Host lifestyle and parasite interspecific facilitation mediate co‐infection in a species‐poor host–parasite system

Despite their important ecological role, questions remain on mechanisms structuring parasite assemblages. We present an endemic and species‐poor parasite–host system of two species of clupeid fishes Limnothrissa miodon, Stolothrissa tanganicae) and two species of monogenean parasites (Kapentagyrus, Dactylogyridae) from Lake Tanganyika as a model to study parasite distribution patterns and co‐infection dynamics in nature. We modelled spatiotemporal dynamics of parasite–host interaction using infection data along the north–south axis of Lake Tanganyika (660 km) over the course of two seasons and four years (1730 fish, 3710 parasites). We found temporal stability of parasite infection, which contrasts with previously reported seasonally driven fluctuations of fish host abundances. We found a difference in spatial structure between the parasite species which follows the contrasting dispersal pattern of their respective host species. On L. miodon, the host species that is infected by the two parasite species, we discovered a positive correlation with host body size for one parasite species, and a negative correlation for the other species. The apparent host‐size related replacement in the two parasite species infecting L. miodon contrasts with the beneficial influence that each of the parasite species has on the other. Parasites have been reported in previous studies to change habitat depending on host size/age. Differences in abundance and prevalence here reported between parasite species infecting the same host species related to the host body length further illustrate the parasites' dependence on changes in lifestyle of the host during its ontogenetic development. Also, possible mechanisms underlying the reported facilitation of infection are discussed. In conclusion, we show that in this closed, species‐poor system parasite infection dynamics are dependent on a combination of host mobility, host lifestyle changes over ontogenetic development, and interspecific interactions between parasites.

Morphological and genetic identification of the gill monogenean parasite (Diclidophora merlangi) that infects Twobar Seabream Fish (Acanthopagrus bifasciatus) in the Arabian Gulf, Saudi Arabia.

Ectoparasites, particularly monogeneans, negatively affect fish health and growth. This study identified monogenean parasites in the twobar seabream, Acanthopagrus bifasciatus (Sparidae), inhabited the Arabian Gulf (Saudi Arabia). Following that, forty A. bifasciatus fish samples were visually examined for monogeneans. Parasite species were collected from the gills and then analyzed morphometrically, morphologically, and molecularly using the partial regions of the large subunit of ribosomal RNA (28S rRNA) and mitochondrial cytochrome C oxidase subunit I (COI) genes. Fish species were also identified using a DNA barcoding approach based on the COI gene. The monogenean species of Diclidophora merlangi (Diclidophoridae) were found in 45% of the fish species studied. The generic features of the Diclidophora genus distinguish this species. This species discriminated itself from congeners by having a muscular bulb with 17 grooved and recurved hooks, 218±10 (184-267) post-ovarian testes, and four pairs of pedunculated clamps of relative sizes. Partial 28S rRNA sequencing from monogeneans revealed that they grouped with members of the genus Diclidophora, forming a monophyletic group that supported the morphological descriptions. Molecular identification revealed that D. merlangi has a unique barcode made up of a COI sequence. The host identity was established as A. bifasciatus based on the COI gene sequences. Furthermore, a molecular phylogenetic study was performed to determine the phylogenetic affinity of parasite species and fish hosts. This study on Diclidophora species is considered the first record of this genus in the examined area.

Investigating the Parasitic Diversity of Nile Tilapia in the Ghaghara River: A Study on Fish Health and Monogenean Parasites.

This study investigates the presence and diversity of monogenean parasites infecting Nile tilapia (Oreochromis niloticus) in the Ghaghara River, recognizing their significant impact on fish health. Through field surveys, Nile tilapia specimens were collected from various locations along the river and subjected to standard parasitological analyses to identify monogenean parasites. Morphological assessments facilitated species identification and diversity assessments. Preliminary findings reveal a diverse array of monogeneans infecting Nile tilapia in the Ghaghara River, with species richness and prevalence varying across sampling sites, possibly influenced by environmental factors. While some monogenean species exhibit host-specificity, others demonstrate a broader host range. Understanding the distribution and diversity of these parasites would enhance our understanding of fish health and Ghaghara River ecosystem dynamics, informing management strategies for sustaining robust fish populations and promoting eco-friendly aquaculture practices in the region. Moreover, insights gained from this research may contribute to the conservation and management of aquatic ecosystems beyond the Ghaghara River.

An Annotated Checklist of Monogeneans (Platyhelminthes, Monogenea) from Aquatic Vertebrates in Peru: A Review of Diversity, Hosts and Geographical Distribution.

Monogeneans are flatworm parasites that infest fish gills primarily but can also infect various other vertebrates, including amphibians, aquatic reptiles, mammals like hippos, and occasionally invertebrates like copepods, isopods, and cephalopods. Despite their remarkable diversity, our knowledge of monogenean parasites in Peru remains significantly limited, resulting in substantial gaps in our comprehension of their taxonomic identities, host associations, and geographic distribution. To address these knowledge deficits, we present an extensively curated checklist of monogeneans associated with aquatic vertebrates in Peru. This comprehensive compilation is derived from meticulous literature surveys, the examination of specimens deposited in both international and national collections, and the inclusion of additional freshly collected specimens. The checklist offers a thorough repository of data encompassing the diversity, host associations, and geographical distribution of these parasites. Taxonomic discrepancies are addressed through a critical review of the existing literature, supplemented by the direct examination of specimens, including type or voucher specimens, deposited within scientific collections. Additionally, we provide data on the DNA sequences of individual taxa. The compiled list comprises records of 358 monogenean species, including 270 valid species and 88 taxa identified at the family or generic level, all reported across 145 host species in Peru. Predominantly, these parasitic species exhibit associations within fish, with 335 infecting teleosts and 20 affecting chondrichthyans. Three monogenean species have been documented as infecting amphibians, namely Mesopolystoma samiriensis, Polistoma sp. and Wetapolystoma almae. Among the monogeneans reported, 141 were found in marine environments and 214 in freshwater environments. The most diverse families were Dactylogyridae and Diplectanidae, comprising 217 and 24 species, respectively. The hosts that harbored the highest number of monogeneans were Pygocentrus nattereri (with 23 species), followed by Stellifer minor (13 spp.) and Triportheus angulatus (11 spp.). We detected many species that do not have any material deposited in a scientific collection due to the loss or deactivation of the collection. These findings represent only a fraction of the potential diversity, considering the wide variety of aquatic vertebrate hosts inhabiting the tropical and subtropical regions of Peru.

Heritability and predictive ability for the heterobothriosis resistance and growth performance in the tiger pufferfish Takifugu rubripes fed standard or low fishmeal diets

Heterobothriosis resistance and high growth performance are major concerns in the tiger pufferfish (Takifugu rubripes) farming. Our previous small-scale study suggested the feasibility of genomic selection (GS) for these traits but also identified an undesired genetic correlation between them, which could hamper simultaneous genetic improvement. Here, we sought to validate these initial findings through larger samples and crosses and also explore the potential of GS for the individuals fed a normal fishmeal diet and a low fishmeal (LFM) diet. We produced three populations: one was fed a normal diet (PopFM: 1100 individuals) and two were fed an LFM diet (PopLFM1: 993 individuals; PopLFM2: 1017 individuals); all three populations were artificially infected with Heterobothrium okamotoi, a monogenean parasite causing heterobothriosis. We recorded standard lengths of the fish after artificial infection (SLEAI) and the number of parasites on the gill cavity wall (HC) and genotyped genome-wide single nucleotide polymorphisms (SNPs) using genotyping by random amplicon sequencing, direct (GRAS-Di) technology for each sample: PopFM, 12 K SNPs; PopLFM1, 19 K SNPs; PopLFM2, 21 K SNPs. Heritability and prediction ability for each trait were estimated for each population using genomic best linear unbiased prediction (GBLUP), Bayes C, and Bayesian ridge regression methods. SNP effects on each trait were estimated by Bayes C, Bayesian ridge regression, and genome-wide association analyses (GWAS) using the same data sets. We observed moderate to high levels of heritability for HC (0.16–0.57) and SLEAI (0.50–0.77), with predictive ability of 0.25–0.55 for HC and of 0.51–0.73 for SLEAI. These values were slightly larger in LFM diet groups. As reported previously, a weak undesired genetic correlation was observed between the traits, and the correlation was more pronounced in the LFM groups. In conclusion, our results indicate that genetic gain in growth and parasite resistance traits can be expected for the tiger pufferfish through GS, especially for individuals reared on an LFM diet. However, close attention should be paid to the extent of the undesirable genetic correlation between the two traits that may be amplified in the populations fed an LFM diet.

Immune response of the Almaco jack (Seriola rivoliana) against the infestation with Neobenedenia sp. in three cultivated temperatures.

The Almaco jack (Seriola rivoliana) is a marine fish maintained in mariculture systems and frequently infested by monogenean parasites like Neobenedenia sp. Severe infestations can lead to high mortalities and economic losses for farmers. This study evaluated the effects of temperature on the immune response on Almaco jack infested with Neobenedenia sp. We exposed infested fishes at temperatures of 20°C, 24°C, and 30°C for 20days and took samples of different tissues at the beginning of the experiment, and after 3 and 20days. The tissues considered were the skin, thymus, cephalic kidney, and spleen to evaluate the relative gene expression of different genes: Hsp70, IgM, IL-1β, IL-10, and MyD88. Our results showed an increase in IL-1β gene expression in the skin after 20days of infestation but no significant effect of temperature on gene expression, despite increases in infestation rates with temperature. Therefore, relative genetic expression was controlled by the number of parasites and the days post-infestation. These results show that the parasite infestation induced a local response in the skin, but that temperature has an indirect effect on the immune system of Almaco jack.

An Expansion of the Invasive Species Gussevia asota Kritsky, et al., 1989 (Monogenea: Dactylogyridae) In Western Uttar Pradesh, India

Non-native fish species and their parasites are a threat to aquatic ecosystems, posing a risk to inherited communities by diminishing biodiversity and causing severe commercial and public health impacts. Along with their fish hosts, monogenean parasites are often co-introduced into new areas. In the western part of the state of Uttar Pradesh, India, a range expansion for the non-native monogenean parasite was recorded. This study confirmed the co-introduction of the dactylogyrid, Gussevia asota Kritsky et al. (1989), into India with their fish host, the invasive Oscar, Astronotus ocellatus Agassiz, 1831. The present species were also distinguished based on molecular analysis of their 18S rDNA sequence and the haptoral parts and male copulatory organ. Phylogenetic analysis of G. asota showed that it clustered with other dactylogyrid species, supporting the contention that it co-introduced parasites, increasing the number of monogeneans acquired in Indian water.

New record of monogenean parasite Mymarothecium viatorum (Monogenea; Dactylogyridae) in red-bellied pacu (Piaractus brachypomus) in Indonesia

Red-bellied pacu (Piaractus brachypomus) is a popular exotic fish cultured globally for ornamental and human consumption purposes. In Indonesia, this fish is mainly cultured in Java, including to supply seed to other regions for the ornamental fish trade or aquaculture. Although this exotic fish in widely cultured, information on parasitic infections is negligible. Red-bellied pacus were purchased from a fish farmer and examined for monogenean parasite infection. Monogenean parasites were identified based on morphological and molecular characteristics. Histopathological examinations were performed on gills from heavily infected fish. DNA was extracted from an individual monogenean; 18S rRNA PCR product was sequenced and a phylogenetic tree constructed. Morphological and molecular traits identified the monogenean as Mymarothecium viatorum, the first report of the neotropical M. viatorum in this region. The parasite was most likely introduced to Indonesia through the importation of ornamental fish. This parasite had a prevalence of 79% and a mean intensity of 7.1. There was no significant correlation between the parasite abundance and the condition factor of the fish. M. viatorum was more abundant on smaller fish than on larger fish. Gill histopathology showed oedema, severe haemorrhage, and infiltration of inflammatory cells. The occurrence of these parasites could pose a serious threat to the development of red-bellied pacu culture.

Parasites (Monogenea) of tilapias Oreochromis niloticus and Coptodon rendalli (Cichlidae) in a river spring in Brazil.

In the present study, we examined 30 individuals of introduced African cichlids, Oreochromis niloticus and Coptodon rendalli, collected in a river spring of the Pardo River, Paranapanema River basin, southeastern Brazil. Based on morphological and molecular analyses of the partial LSU rDNA gene, we identified four species of monogeneans, Cichlidogyrus tilapiae, C. thurstonae, C. mbirizei, and Scutogyrus longicornis on the gills of O. niloticus, whereas individuals of C. rendalli were infested only with C. papernastrema. This is the first record of C. mbirizei and C. papernastrema in tilapias from Brazil. The ecological consequences of the introduction of exotic species of tilapia such as O. niloticus and C. rendalli along with their monogenean parasites in a wild environment represented by a river spring are discussed. Our new molecular data on Cichlidogyrus and Scutogyrus contribute to the investigation of the phylogenetic interrelationships of these widely distributed genera of monogeneans since their species composition is still unsettled.

Four new species of Cichlidogyrus (Platyhelminthes, Monopisthocotyla, Dactylogyridae) from Lake Victoria haplochromine cichlid fishes, with the redescription of C. bifurcatus and C. longipenis.

African cichlids are model systems for evolutionary studies and host-parasite interactions, because of their adaptive radiations and because they harbour many species of monogenean parasites with high host-specificity. Five locations were sampled in southern Lake Victoria: gill-infecting monogeneans were surveyed from 18 cichlid species belonging to this radiation superflock and two others representing two older and distantly related lineages. We found one species of Gyrodactylidae, Gyrodactylus sturmbaueri Vanhove, Snoeks, Volckaert & Huyse, 2011, and seven species of Dactylogyridae. Four are described herein: Cichlidogyrus pseudodossoui n. sp., Cichlidogyrus nyanza n. sp., Cichlidogyrus furu n. sp., and Cichlidogyrus vetusmolendarius n. sp. Another Cichlidogyrus species is reported but not formally described (low number of specimens, morphological similarity with C. furu n. sp.). Two other species are redescribed: C. bifurcatus Paperna, 1960 and C. longipenis Paperna & Thurston, 1969. Our results confirm that the monogenean fauna of Victorian littoral cichlids displays lower species richness and lower host-specificity than that of Lake Tanganyika littoral cichlids. In C. furu n. sp., hooks V are clearly longer than the others, highlighting the need to re-evaluate the current classification system that considers hook pairs III-VII as rather uniform. Some morphological features of C. bifurcatus, C. longipenis, and C. nyanza n. sp. suggest that these are closely related to congeners that infect other haplochromines. Morphological traits indicate that representatives of Cichlidogyrus colonised Lake Victoria haplochromines or their ancestors at least twice, which is in line with the Lake Victoria superflock being colonised by two cichlid tribes (Haplochromini and Oreochromini).

Uncovering the monogenean species diversity of cyprinoid fish in Iraq using an integrative approach.

The freshwaters of Iraq harbour a high diversity of endemic and phylogenetically unique species. One of the most diversified fish groups in this region is cyprinoids, and although their distribution is relatively well known, their monogenean parasites have only rarely been investigated. Herein, we applied an integrative approach, combining morphology with molecular data, to assess the diversity and phylogeny of cyprinoid-associated monogenean parasites. A total of 33 monogenean species were collected and identified from 13 endemic cyprinoid species. The highest species diversity was recorded for Dactylogyrus (Dactylogyridae, 16 species) and Gyrodactylus (Gyrodactylidae, 12 species). Four species of Dactylogyrus and 12 species of Gyrodactylus were identified as new to science and described. Two other genera, Dogielius (Dactylogyridae) and Paradiplozoon (Diplozoidae), were represented only by 4 and 1 species, respectively. Phylogenetic analyses of the Dactylogyrus and Gyrodactylus species revealed that the local congeners do not form a monophyletic group and are phylogenetically closely related to species from other regions (i.e. Europe, North Africa and Eastern Asia). These findings support the assumption that the Middle East served as an important historical crossroads for the interchange of fauna between these 3 geographic regions.

Prevalence of Parasites in Fish from The Pelagic and Benthic Zones

The present research is a comparative study on the prevalence of parasites in marine finfish among the two major marine zones; namely the pelagic zone and benthic zone. The objectives of the present study were to investigate the parasite prevalence in both zones, as well as to determine the effect of differing marine zones regarding the presence of parasites in fish. A total of 30 individual fish occurring in pelagic and benthic zones were randomly selected from three different fishmongers at a wet market in Bintulu, Sarawak. Both the gill and stomach content of the samples were examined to detect the presence of parasites. Nematodes and trematodes were observed in the intestinal tract of the fish, Cymothoa exigua was found attached to the fish tongue, and monogenean parasites were also detected on the gills. The prevalence of the parasite was roughly equal in Setipinna breviceps, Ilisha megaloptera, and Selaroides leptolepis. The highest prevalence of parasites (87.50%) from fish in the benthic zone based on fish size was for fish measuring between 20.1 - 30.00 cm in total length (P-value=0.3778), whereas for pelagic fish, the highest prevalence of parasites (100%) in fish measurements of 30.1 – 40.0 cm in total length (P-value=0.0044). A major factor for the diversity of marine fish parasites occurring in the different zones is the difference in feeding behavior of the hosts and depth distribution which resulted in low or high rates of parasite infestation.

The puzzling etiologies of transient black discoloration in Nile Tilapia (Oreochromis niloticus) intensively cultured under RAS system

The aim of this study is to identify the hidden etiologies of the black chromo-shifting transient phenomenon affecting Nile tilapia, Oreochromis niloticus, farmed in RAS-controlled ponds together with the assessment of the immunological reaction against the chronic irritating effects of the invasive agent. A total of 100 Nile Tilapia were collected from a private farm at Kafrelsheikh Province, located on the northern side of the Egyptian Nile Delta. The clinical history of the affected fish farm showed an unknown chromo-shifting phenomenon where tilapias were exhibiting severe black skin coloration, which gradually disappeared after removal from the tank’s water. A comprehensive gross examination of the collected fish; including parasitological examination of skin and gill scraps, was performed. Blood biochemical testing was performed on the infested blackish O. niloticus and control non-infested fish. The current study showed that the monogenean parasite, Gyrodactylus cichlidarum, was the abundant parasite detected in the infested fish leading to abnormal black discoloration of skin and disruption of the immune system represented by significant increase of cortisol levels, lysozyme activity and different liver enzymes compared to the control. Treatment trials have been applied with moderate degrees of success, where the monogenean count was sharply decreased, and the normal skin color was remarkably restored, at the end of day 14 post-treatment. A triple treatment plan was initiated through 7 days’ application of 0.7 g/m3 copper sulfates pentahydrate preceded by 1.5 ml/m3 hydrogen peroxide 40% solution for the same period. One day after the end of the initial treatment, a maintenance dosage of 0.095 ml/m3 of glutaraldehyde (15%)/quaternary ammonium compounds (QACs) mixture was administered for 3 days. As a supportive/immune-stimulant regimen, a weekly dosage of vitamin C (0.45 g g/m3) and Saccharomyces cerevisiae (0.45 g/m3) was added into the tank’s water to improve the general fish health.

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.

Anthelmintic efficacy of febantel against a monogenean parasite, Gyrodactylus kobayashii

Monogenean parasites pose a significant challenge to aquaculture, leading to adverse effects on fish health and yields. Current anthelmintic treatments for monogeneans have demonstrated limited efficacy and are further complicated by potential issues, which emphasize the necessity for effective and safe therapeutic strategies to manage monogeneans in aquaculture. In this study, in vivo and in vitro anthelmintic activity of febantel against Gyrodactylus kobayashii on goldfish (Carassius auratus), as well as its toxicity to goldfish were evaluated. In vivo assays indicated that febantel exhibited potent anthelmintic activity against G. kobayashii with an EC50 value of 0.03 mg/L and 100 % anthelmintic efficacy at 0.1 mg/L after 48 h of exposure. Moreover, in vivo trials also revealed a notable post-treatment effect of febantel, where infected goldfish transferred to drug-free water after short 6-h exposure could still result in full eradication of the worms, indicating febantel might induce persistent perturbations in parasite physiology. In vitro assays showed a negative correlation between febantel concentrations and the survival of G. kobayashii. However, increasing the febantel concentration to 2.0 mg/L did not result in the complete death of all worms. Oral administration of febantel demonstrated limited anthelmintic activity, with only 49 % efficacy at a dosage of 200 mg/kg body weight daily over five days. Acute toxicity assays revealed the 48-h LC50 value of febantel was 5.47 mg/L, which was 182.23 times higher than the 48-h EC50 value, indicating that febantel has a favorable safety profile. However, febantel exposure potentially interfered with hepatic metabolism and oxidative status, as indicated by variations in SOD, GST, and P450 gene expression. In conclusion, treatment with 0.1 mg/L febantel for 24 h completely eradicated G. kobayashii infection on goldfish, demonstrating febantel’s potent anthelmintic activity. Coupled with its safety profile and extended post-treatment effectiveness, febantel is a promising candidate for controlling Gyrodactylus infections in aquaculture.