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.

Microcotyle justinei n. sp. (Monogenea: Microcotylidae) from the Gills of the Cardinal Fish Apogon imberbis (Teleostei: Apogonidae) off the Algerian Coast of the Western Mediterranean

PURPOSE

A new monogenean Microcotyle justinei n. sp. (Monogenea: Microcotylidae) is described based on specimens found on the gill filaments of the cardinal fish Apogon imberbis (Apogonidae) off the Algerian coast of the Western Mediterranean.

METHODS

Monogeneans were examined, measured and drawn for a comparative morphological study with other species of Microcotyle and characterised molecularly using a partial fragment of the mitochondrial cytochrome c oxidase subunit 1 (cox1) gene. The identification of fish was confirmed by molecular barcoding using the cox1 gene.

RESULTS

The new species is distinguished from all other species of the genus by a combination of features, such as the number and size of the clamps, the shape and size of the genital atrium and the number of testes. The molecular analysis of the cox1 gene sequences showed that interspecific differences between Microcotyle justinei n. sp. and published sequences of Microcotyle spp. was greater than 8.8%, strongly suggesting that the new species is distinct from other congeners with sequences available on GenBank.

CONCLUSION

The morphological and molecular analyses support the status of M. justinei as a new species. The present finding extends the list of Microcotyle spp. to 72.

The genus Microcotyle in Mediterranean scorpaenoids (Teleostei), including the description of Microcotyle merche n. sp. from Helicolenus dactylopterus (Delaroche, 1809)

More than 65 species of the genus Microcotyle Van Beneden & Hesse, 1863, have been described to date, most of them infecting Perciformes. Among the scorpaenoids (Perciformes, formerly Scorpaeniformes) the species of the genus Microcotyle parasitize sebastids and scorpaenids worldwide. In this study, we provide new morphological and molecular data for Microcotyle spp. in sebastids and scorpaenids from the Western Mediterranean and north-east Atlantic. Specimens of Helicolenus dactylopterus (Delaroche, 1809) (n = 107) and Scorpaena spp. (n = 107) were examined and their microcotylid specimens morphologically and molecularly characterized. Microcotyle merche n. sp. ex H. dactylopterus and specimens of Microcotyle algeriensis Ayadi, Gey, Justine & Tazerouti, 2016 from a new host and locality (Scorpaena scrofa from the north-east Atlantic) are herein described. Both species are phylogenetically close, but their morphology is markedly different mostly because the anterior lobe of the haptor present in other Microcotyle species is almost absent in M. algeriensis. Findings of M. merche n. sp. in the Mediterranean also excludes the presence of Microcotyle sebastis in this sea, encouraging the review of the exceptionally large host range and geographical distribution of this species.

Diclidophora luscae (Monogenea: Diclidophoridae) in pouting, Trisopterus luscus (Linnaeus, 1758) from the northeast Atlantic; epidemiology, morphology, molecular and phylogenetic analysis

Diclidophora (Monogenea) species are gill parasites with a stenoxenic specificity occurring only in Gadiformes. Epidemiological, morphological, molecular and phylogenetic studies were performed on 594 Diclidophora specimens collected from 213 Trisopterus luscus captured in the northeast Atlantic off the Portuguese coast during 2012, 2013 and 2020. Prevalence, parasite abundance and infection intensity were determined. Positive correlation between fish weight and length and infection intensity was observed. The effects of preservation on the parasite morphological features were studied, highlighting that specimen's identification should be reinforced by molecular studies. A sequence of D. luscae capelanii from T. capelanus captured in the Mediterranean Sea included in the 28S rDNA molecular analysis was nested within a robust D. luscae clade. Data analysis suggested that this species is in fact D. luscae, which is compatible with T. luscus and T. capelanus. The identity of fish hosts was confirmed by barcoding. For the first time, data on the infection parameters is shown, highlighting the importance of including this parasite in the monitoring plans for a holistic approach with possible effects for the management of pouting resources aiming of attaining sustainable development and biodiversity conservation measures, according to the 14th objective of the 2030 agenda.

Five new and two known species of Heterobothrium (Monogenea: Diclidophoridae) infecting puffers of the genus Takifugu from Japanese waters

Seven species of puffers of the genus Takifugu caught in Japanese waters were examined for monogeneans on the gills. Five new species of Heterobothrium (H. gotoi n. sp. from T. porphyreus, H. tabetai n. sp. from T. vermicularis, H. aljufailiae n. sp. and H. iwatai n. sp. from T. snyderi, H. matsubarai n. sp. from T. stictonotus) and two known species (H. praeorchis Bychowsky, Mamaev & Nagibina, 1976 from T. pardalis, T. chrysops and T. flavipterus and H. bychowskyi Ogawa, 1991 from T. flavipterus) were found and described. Heterobothrium tetrodonis of Iwata (1991) was synonymized with H. bychowskyi. Currently, a total of 11 species of Heterobothrium, including the seven species in this study, were recorded from nine species of Japanese Takifugu spp. Ten species excluding H. praeorchis were found from a single host species, suggesting that they are highly host-specific and have co-evolved with the host Takifugu spp. Tagia Sproston, 1946 is synonymized with Heterobothrium. Earlier divergence of Heterobothrium of tetraodontid puffers in Diclidophoridae was suggested by the large subunit ribosomal DNA (rDNA) analyses, and interspecific relationships in this genus inferred from the internal transcribed spacer region of rDNA well corresponded to those inferred from their morphology and adhesive mode to the gills. Including the five new species and synonymization of Tagia with Heterobothrium, the genus Heterobothrium now comprises 19 species.

Occurrence and molecular identification of Monogenea from blue-spotted flathead Platycephalus caeruleopunctatus (Scorpaeniformes: Platycephalidae) in Australian waters

This study describes the occurrence and molecular identification of Monogenea from blue-spotted flathead Platycephalus caeruleopunctatus (McCulloch) (Scorpaeniformes: Platycephalidae) from waters off the NSW coast, Australia. Platycephalus spp. are favoured by consumers for delicate, white, mild flavoured flesh and therefore are commercially important species within Australia. Platycephalus spp. are also extensively targeted by Australian recreational fishers. There has been no previous study that has exclusively focused on Pl. caeruleopunctatus in Australia or globally. Although a single study by Dillon (1985), of monogeneans infecting Platycephalus spp. from Australian waters, identified Microcotyle bassensis Murray, 1931 in Pl. caeruleopunctatus. The present study combines both morphological and molecular methods to identify both host and parasites. A total of 116 fish, sourced from the waters off the coast of New South Wales, Australia, were examined. A total of 1498 Monogenea were recovered from the gills. The overall prevalence, mean intensity, and mean abundance were 72%, 18.05, and 12.91, respectively. Monogenea were initially classified morphologically as two different species M. bassensis (family: Microcotylidae) and Platycephalotrema bassense (Hughes, 1928) Kritsky & Nitta, 2019 (family: Ancyrocephalidae). Molecular identification of Monogenea was conducted through sequencing of their mitochondrial cytochrome c oxidase subunit 1 (cox1) and nuclear 28S genes. The specific identification of host Pl. caeruleopunctatus was confirmed through sequencing the cox1 gene. There was no comparable sequence for cox1 and 28S genes available in GenBank for the monogenean species found in the present study. Only a single sequence (obtained from the nuclear ITS2-rDNA) was deposited in GenBank for M. bassensis. However, the phylogenetic analyses of mitochondrial and nuclear sequences revealed that the identified Monogenea clustered according to their familial groups. Platycephalotrema bassense was identified for the first time in Pl. caeruleopunctatus in the present study. This study has provided the first evidence for the exploration of both cox1 and 28S sequences of all Monogenea. The findings of this study serve as a foundation for future monogenean research on other Platycephalus spp. from Australian waters.

Novel molecular data for monogenean parasites of sparid fishes in the Mediterranean and a molecular phylogeny of the Microcotylidae Taschenberg, 1879

During a study of the monogeneans of four sparid fishes (Diplodus vulgaris, Pagellus bogaraveo, Pagrus pagrus and Sparus aurata) from the Western Mediterranean off Algeria, a large collection of parasites was characterised molecularly (28S rRNA and cox1 genes). A total of 46 partial sequences (23 for each gene) were generated from 38 isolates of monogeneans which included four species (Atrispinum acarne, Microcotyle erythrini (sensu stricto), Sparicotyle chrysophrii and Prostatomicrocotylinae gen. sp.) of the family Microcotylidae, two putative species of the family Capsalidae (Encotyllabe spp.), and one species (Choricotyle chrysophryi) of the family Diclidophoridae. Our study provides (i) the first molecular data for the Capsalidae in the Mediterranean; (ii) the first record of a member of the Prostatomicrocotylinae in the Mediterranean and in a sparid fish (D. vulgaris); (iii) the first cox1 sequences for A. acarne; (iv) the second record of M. erythrini (s.s.) from P. pagrus; and (v) the second confirmed by molecular data record of S. chrysophrii in wild populations of S. aurata. The first phylogenetic hypotheses for the family Microcotylidae developed here, revealed the monophyly of the subfamily Prostatomicrocotylinae and the genus Microcotyle but the relationships among the subfamilies were still largely unresolved with the best represented subfamily Microcotylinae being polyphyletic. Our results highlight the importance of molecular methods in the assessment of monogenean diversity and the need for a thorough taxon-sampling approach to increase the accuracy of phylogenetic reconstruction of the relationships of the large and taxonomically complex polyopisthocotylean family Microcotylidae.

Emendation of the genus Neoheterobothrium and a proposal of a new genus Paraheterobothrium (Monogenea: Diclidophoridae) for five species of diclidophorids from Pleuronectiform fishes

Neoheterobothrium chilense González, Oliva & Acuña, 2002 is redescribed based on newly collected specimens from the type host, Hippoglossina macrops and type locality (Coquimbo, Northern Chile). Type specimens of Neoheterobothrium hippoglossini Piasecki, Wierzbicka & Kempter, 2000 and Choricotyle exilis Crane, 1972 are also redescribed. These three diclidophorid monogeneans infecting pleuronectiform flatfishes have pre-ovarian seminal receptacle, ootype inside the semicircle of ovary and elongated pharynx, differentiated from the most similar Orbocotyle Euzet & Suriano, 1975 in that members of the latter genus possess post-ovarian seminal receptacle, post-ovarian ootype and cylindrical or pyriform pharynx. Paraheterobothrium n. g. is proposed for P. chilense n. comb. (type), P. hippoglossini n. comb., P. exilis n. comb., P. papillosum n. comb. and P. syacii n. comb. A redescription of Neoheterobothrium affine (Linton, 1898), the type species of the genus, based on voucher specimens confirmed differences from the new genus in the presence of lamellate plate in the anterior jaw of clamps, absence of seminal receptacle and ovoid pharynx. The genus Neoheterobothrium was emended and N. cynoscioni (MacCallum, 1917) and N. mcdonaldi Payne, 1987 were removed from the genus. Neoheterobothrium now comprises N. affine (type), N. insulare Oliva & Luque, 1995, N. hirame Ogawa, 1999, and N. paralichthyi Suriano & Labriola, 1999, all of them parasites of flatfishes of the genus Paralichthys. Molecular analyses with the internal transcribed spacer 1 distinguished the clade for Paraheterobothrium spp. (P. chilense n. comb. and P. papillosum n. comb.) and Neoheterobothrium spp. (N. hirame, N. affine and N. paralichthyi), supporting this taxonomic emendation.

Triple barcoding for a hyperparasite, its parasitic host, and the host itself: a study of Cyclocotyla bellones (Monogenea) on Ceratothoa parallela (Isopoda) on Boops boops (Teleostei)

Cyclocotyla bellones Otto, 1823 (Diclidophoridae) is a monogenean characterised by an exceptional way of life. It is a hyperparasite that attaches itself to the dorsal face of isopods, themselves parasites in the buccal cavity of fishes. In this study, Cy. bellones was found on Ceratothoa parallela (Otto, 1828), a cymothoid isopod parasite of the sparid fish Boops boops off Algeria in the Mediterranean Sea. We provide, for the first time, molecular barcoding information of a hyperparasitic monogenean, the parasitic crustacean host, and the fish host, with COI sequences.

Redescription and molecular characterization of two species of Pauciconfibula (Monogenea, Microcotylidae) from trachinid fishes in the Mediterranean Sea

Many Pauciconfibula spp. have a long and complicated taxonomic history. The remaining unsolved taxonomic confusion in this genus is impelled by the host range and status of Pauciconfibula spp. from trachinid fishes: Pauciconfibula trachini and Pauciconfibula draconis, from Trachinus radiatus and Trachinus draco (Trachinidae), respectively. Pauciconfibula trachini was reported on Trachinus draco, type host of Pauciconfibula draconis suggesting thus a stenoxenic specificity for the former monogenean and the occurrence of two congeneric polyopisthocotyleans on a single host. Moreover, the validity of Pauciconfibula draconis was repeatedly questioned by several authors, unjustified synonymy between the two species was proposed, and the delimitations between the two species remained unsolved. Original descriptions were also incomplete and poorly illustrated. In this study, we provide a detailed illustrated redescription of both species based on newly collected specimens of Pauciconfibula trachini and Pauciconfibula draconis collected from their type hosts from off three Mediterranean localities: Algeria, Tunisia, and Italy. Integrative taxonomy using COI sequences was applied to resolve the delimitation between Pauciconfibula trachini and P. draconis. This study provides the first DNA barcoding for members of this genus.

A first for Southern Africa: description of a new Heterobothrium (Monogenea: Diclidophoridae) parasitizing the evileye pufferfish Amblyrhynchotes honckenii (Tetraodontiformes: Tetraodontidae)

The monogenean genus Heterobothrium (Monogenea: Diclidophoridae) currently consists of 12 accepted species described globally from various pufferfishes (Tetraodontidae). This includes the economically important Heterobothrium okamotoi Ogawa 1991 that causes severe disease in the cultured tiger puffer Takifugu rubripes in Japan. During parasitological surveys targeting near shore marine fishes of South Africa, a new Heterobothrium was discovered on the gills of five evileye pufferfish Amblyrhynchotes honckenii with a prevalence of 100% and mean intensity of 23 (4-72). Specimens were morphologically studied using both light and scanning electron microscopy and molecularly characterized by sequencing the partial ribosomal gene 28S. Heterobothrium victorwepeneri n. sp. differs from its 12 congeners by a combination of morphological characters, such as fourth clamp pair (anteriormost, 180° inverted) as the smallest with some of the sclerites differing in shape from the other pairs, 8 to 9 genital hooks, number of testes 40-50, and absent isthmus. The 28S tree depicted two main branches, one clustering together species of mazocraeidean families while the other clustered together only species of the Diclidophoridae. Heterobothrium victorwepeneri n. sp. is the first species of its genus to be recorded and described from South Africa and from the tetraodontid A. honckenii. This study also provides for the first time 28S sequence for a species of this highly host-specific genus.

Considerations on the taxonomy and morphology of Microcotyle spp.: redescription of M. erythrini van Beneden & Hesse, 1863 (sensu stricto) (Monogenea: Microcotylidae) and the description of a new species from Dentex dentex (L.) (Teleostei: Sparidae)

Background

Microcotyle erythrini van Beneden & Hesse, 1863 (Platyhelminthes: Monogenea) and other closely related species of the genus are often considered as cryptic. Records in hosts other than the type-host with no species confirmation by molecular analyses have contributed to this situation.

Methods

Gill parasites of five sparid fishes, Boops boops (L.), Pagellus erythrinus (L.), P. acarne (Risso), Dentex dentex (L.) and Pagrus pagrus (L.), from the Western Mediterranean off Spain were collected. Specimens of Microcotyle spp. were characterised both molecularly and morphologically. Partial fragments (domains D1-D3) of the 28S rRNA gene and the cytochrome c oxidase subunit 1 (cox1) gene were amplified and used for molecular identification and phylogenetic reconstruction. Principal components analysis was used to look for patterns of morphological separation.

Results

Molecular analyses confirmed the identity of three species: M. erythrini ex P. erythrinus and Pa. pagrus; M. isyebi Bouguerche, Gey, Justine & Tazerouti, 2019 ex B. boops; and a species new to science described herein, M. whittingtoni n. sp. ex D. dentex. The specific morphological traits and confirmed hosts (P. erythrinus and Pa. pagrus) are delimited here in order to avoid misidentifications of M. erythrini (sensu stricto). Microcotyle erythrini (s.s.) is mostly differentiated by the shape of its haptor, which is also longer than in the other congeners. New morphological and molecular data are provided for M. isyebi from the Spanish Mediterranean enlarging the data on its geographical range. Microcotyle whittingtoni n. sp. is described from D. dentex and distinguished from the remaining currently recognised species of the genus by the number and robustness of the clamps.

Conclusions

New diagnostic morphological traits useful to differentiate Microcotyle spp. are suggested: (i) haptor dimensions including lobes; (ii) the thickness of the clamps; (iii) the size and shape of spines of the genital atrium; (iv) the extension of the posterior extremities of vitelline fields; and (v) the shape of egg filaments. The use of new morphological approaches may allow considering these species of Microcotyle as being pseudocryptic. The use of representative undamaged specimens that have been genetically confirmed as conspecific is considered crucial to avoid abnormally wide morphological ranges that prevent species differentiation.

Towards the resolution of the Microcotyle erythrini species complex: description of Microcotyle isyebi n. sp. (Monogenea, Microcotylidae) from Boops boops (Teleostei, Sparidae) off the Algerian coast

The monogenean Microcotyle erythrini is atypical because it has been recorded from several fish host species in the Mediterranean Sea and Atlantic Ocean, in contrast to many species which are considered strictly specific. This could indicate a true lack of specificity or that several cryptic species are involved. This paper is a partial attempt to solve this problem. Specimens of a monogenean resembling M. erythrini were collected from bogues, Boops boops, caught off Algeria. A comparison with published descriptions and with museum specimens of M. erythrini did not yield any clear morphological difference. However, sequences of cytochrome c oxidase subunit I (COI) differed by 16.3% from that of M. erythrini (from GenBank, material collected from the type-host Pagellus erythrinus), indicating that the species was different. The species from B. boops is therefore described here as Microcotyle isyebi n. sp. and differential diagnoses with Microcotyle species from the Mediterranean and from sparids are provided. These results suggest that a molecular re-evaluation of other M. erythrini-like specimens from various fish hosts could reveal the existence of additional parasite biodiversity.

Three monogeneans parasitic on marine sciaenid fish from Peru including description of Cynoscionicola veranoi n. sp. (Microcotylidae), and redescription of C. americanus Tantaleán, Martínez and Escalante, 1987 and Hargicotyle sciaenae Oliva and Luque, 1989 (Diclidophoridae)

Cynoscionicola veranoi n. sp. (Monogenea: Microcotylidae) is described based on specimens collected from the gills of lorna drum Sciaena deliciosa (Tschudi, 1846) (Sciaenidae) from Peru. The new species can be differentiated from the other congeneric species by the combination of the following characteristics: (1) haptor with two types of clamps, (2) number and shape of the spines in anterolateral pouches of genital atrium (10-11 curved spines and 3-4 short and bifid spines with a knob in each lateral margin), (3) number and shape of the spines in posterolateral pouches of genital atrium (13-18 bifid spines), (4) 4-6 small spherical unarmed pouches in the genital atrium, and (5) 10-15 testes. In addition, a redescription of Cynoscionicola americanus Tantaleán, Martínez and Escalante, 1987 and Hargicotyle sciaenae Oliva and Luque, 1989 (Diclidophoridae) based on examination of type material and newly collected specimens from snakehead kingcroaker Menticirrhus ophicephalus (Jenyns, 1840) and S. deliciosa (type hosts), respectively, are provided herein.

Helminth parasites of South American fishes: current status and characterization as a model for studies of biodiversity

The South American subcontinent supports one of the world's most diverse and commercially very important ichthyofauna. In this context, the study of South American fish parasites is of increased relevance in understanding their key roles in ecosystems, regulating the abundance or density of host populations, stabilizing food webs and structuring host communities. It is hard to estimate the number of fish parasites in South America. The number of fish species studied for parasites is still low (less than 10%), although the total number of host-parasite associations (HPAs) found in the present study was 3971. Monogeneans, with 835 species (1123 HPAs, 28.5%), and trematodes, with 662 species (1127 HPAs, 30.9%), are the more diverse groups. Data gathered from the literature are useful to roughly estimate species richness of helminths from South American fish, even though there are some associated problems: the reliability of information depends on accurate species identification; the lack of knowledge about life cycles; the increasing number of discoveries of cryptic species and the geographically biased number of studies. Therefore, the closest true estimations of species diversity and distribution will rely on further studies combining both molecular and morphological approaches with ecological data such as host specificity, geographical distribution and life-cycle data. Research on biodiversity of fish parasites in South America is influenced by problems such as funding, taxonomic impediments and dispersion of research groups. Increasing collaboration, interchange and research networks in the context of globalization will enable a promising future for fish parasitology in South America.