Descriptions of diplostomid metacercariae (Digenea: Diplostomidae) from freshwater fishes in the Tshwane area

Tegumental topography and molecular characterisation of two trematodes (Platyhelminthes: Digenea) from Clarias gariepinus (Burchell, 1822) in Kenya

The discoveries of new taxonomic features of digenean species through the application of contemporary techniques, such as scanning electron microscopy (SEM) and molecular analysis are still growing. Two species of trematodes Glossidium pedatum and Tylodelphys mashonensis from the intestine and vitreous humour of Clarias gariepinus were recovered from Lake Ol'Bolossat, Kenya. The two endo-helminths were prepared for morphological examination using SEM and molecular characterisation. Additional morphological features were observed for G. pedatum such as domed papillae in the anterior extremity and a protruding cirrus which was unarmed, laterally folded and with a blunt tip as the first such observation for the genus and led to additional characteristics of the diagnosis of the genus. Tylodelphys mashonensis was characterised by a round oral sucker and tribocytic organ rounded with rows of papillae symmetrically arranged. The molecular analyses using ribosomal marker 28S large subunit (LSU) rDNA and mitochondrial (mtDNA) cytochrome c oxidase subunit 1 (cox1) for both G. pedatum and T. mashonensis confirmed the identity of the species and their phylogenetic relationship within the subclass Digenea. This study provides the first mitochondrial (mt)DNA sequence for G. pedatum and also extends the geographical record of two parasites to Kenya.

Review of the metazoan parasites of the economically and ecologically important African sharptooth catfish Clarias gariepinus in Africa: Current status and novel records

One of the most widely distributed African freshwater fish is the African sharptooth catfish Clarias gariepinus (Burchell) that is naturally distributed in 8 of the 10 ichthyofaunal regions of this continent. Clarias gariepinus is a highly valued and cheap staple to local communities and an ideal aquaculture species. Consequently, interest in the parasitic communities of C. gariepinus has increased as parasites may accidentally be ingested by humans when eating uncooked fish or can be introduced into culture systems through fish stocks supplied from local rivers which affect yield, growth, and marketability. This review provides an overview of the ∼107 metazoan parasite species known to parasitise C. gariepinus in Africa and their general life cycles, morphology, paratenic and post-cyclic infections, and the biogeography and validity of records are discussed. A brief overview is included on the application of some of these parasites in environmental studies and their link to human health.

Cryptic speciation among Tylodelphys spp.: the major helminth pathogens of fish and amphibians

Larvae of Tylodelphys Diesing, 1950 are major digenean pathogens of fish and amphibians. Tylodelphys spp. may induce mass mortality of fish and increase their susceptibility to predation. Even though Tylodelphys spp. cause substantial damage to aquaculture systems, surprisingly little is known regarding the taxonomy of this commercially important genus with a limited number of visible autapomorphic identification features. The authors obtained the DNA sequences and analyzed the molecular phylogenetics of Tylodelphys spp. adults isolated from bird hosts of Czech origin and provide comparative measurements of the analyzed species. They identified a previously unknown species complex that is subject to cryptic speciation and was previously morphologically identified as Tylodelphys excavata (Rudolphi, 1803) sensu lato. This species complex consists of three morphologically similar but genetically well-separated species. Tylodelphys excavata sensu stricto remains the dominant Tylodelphys isolated from Ciconia ciconia, which also serves as a satellite host of Tylodelphys circibuteonis Odening, 1962, which is the resurrected species for which birds of prey serve as core hosts. The authors describe Tylodelphys nigriciconis sp. n. Heneberg & Sitko as a new species identified in Ciconia nigra. By providing the first sequences of Tylodelphys podicipina Kozicka and Niewiadomska, 1960, they also show that Tylodelphys immer Dubois, 1961 is a junior synonym of T. podicipina. Further research is needed to match the provided molecular data with the DNA of larval Tylodelphys from outbreaks in commercially exploited fish species.

Resolution of the identity of three species of Diplostomum (Digenea: Diplostomidae) parasitising freshwater fishes in South Africa, combining molecular and morphological evidence

Reliable data on the diversity of the genus Diplostomum (Digenea: Diplostomidae) parasitising freshwater fishes in South Africa, as well as in Africa, is almost non-existent. Most of the morphology-based identifications of species within this genus reported from Africa require critical revision. The aim of the present study was to determine the diversity of Diplostomum metacercariae in South African fishes applying molecular and traditional morphological techniques. To achieve this aim, a total of 216 fishes belonging to 21 species collected in the Rivers Phongolo, Riet, Usuthu and Mooi in three provinces of South Africa were examined. Metacercariae of Diplostomum were recovered from the eye lenses of 38 fishes belonging to five species of the families Anguillidae, Cichilidae and Mochokidae, with an overall low prevalence of infection (18%). Metacercariae were subjected to morphological study and molecular sequencing of the partial mithochondrial cox1 and ribosomal 28S rDNA genes as well as of ribosomal ITS1-5.8S-ITS2 region. Morphological and phylogenetic analyses revealed the presence of three species which matched those previously reported from Nigeria, Iraq and China, therefore those from Tilapia sparrmanii and Synodontis zambezensis were named Diplostomum sp.; those from Anguilla labiata, Oreochromis mossambicus and S. zambezensis were named Diplostomum sp. 14; and those from Pseudocrenilabrus philander were named Diplostomum sp. 16. Geographic distribution of several species of Diplostomum appeared to be wider than expected. Morphological description and novel sequence data generated during this study will contribute to the elucidation of the life cycles of Diplostomum sp., Diplostomum sp. 14 and Diplostomum sp. 16 and advance further research of diplostomids in Africa.

Phylogenetic studies of larval digenean trematodes from freshwater snails and fish species in the proximity of Tshwane metropolitan, South Africa

The classification and description of digenean trematodes are commonly accomplished by using morphological features, especially in adult stages. The aim of this study was to provide an analysis of the genetic composition of larval digenean trematodes using polymerase chain reaction (PCR) and sequence analysis. Deoxyribonucleic acid (DNA) was extracted from clinostomatid metacercaria, 27-spined echinostomatid redia, avian schistosome cercaria and strigeid metacercaria from various dams in the proximity of Tshwane metropolitan, South Africa. Polymerase chain reaction was performed using the extracted DNA with primers targeting various regions within the larval digenean trematodes' genomes. Agarose gel electrophoresis technique was used to visualise the PCR products. The PCR products were sequenced on an Applied Bioinformatics (ABI) genetic analyser platform. Genetic information obtained from this study had a higher degree of discrimination than the morphological characteristics of seemingly similar organisms.

Molecular and morphological characterization of the metacercariae of two species of diplostomid trematodes (Platyhelminthes, Digenea) in freshwater fishes of the Batalha River, Brazil

The Diplostomidae include a large group of flatworms with complex life cycles and are frequently found parasitizing the eyes and central nervous system of freshwater fishes. The morphological identification of the metacercariae at species level is not always possible. Thus, molecular tools have become essential to assist in the parasite species determination. This study was aimed at describing two diplostomid metacercariae found in freshwater fish in São Paulo, Brazil, based on morphological characters and in the genetic characterization of COI sequences. Our results showed that the two recognized taxa (Tylodelphys sp. and Diplostomidae gen. sp.) appear to be different from the species already described in South America. Tylodelphys sp. differs morphologically from Tylodelphys xenopi, T. mashonense, T. jenynsiae, and T. scheuringi. The metacercariae of T. clavata and T. conifera are smaller than Tylodelphys sp., while T. podicipina is larger than the metacercariae described here. The phylogenetic analysis of COI sequences yielded Tylodelphys sp. as the sister species of Tylodelphys sp. 4, a species reported from the brain of the eleotrid Gobiomorus maculatus in Oaxaca, Mexico. The metacercariae identified as Diplostomidae gen. sp. are morphologically different from the known diplostomid metacercariae and did not match with other diplostomid sequences available. Diplostomidae gen. sp. is recovered as the sister species of Diplostomum ardeae. Although the morphological evidence and the COI sequences differentiate the metacercariae found, the absence of adult specimens of both species precludes the specific designation. This is one of the first papers that use an integrative taxonomy approach to describe the species diversity of diplostomid trematodes in Brazil.

Morphological description and molecular analyses of Tylodelphys sp. (Trematoda: Diplostomidae) newly recorded from the freshwater fish Gobiomorphus cotidianus (common bully) in New Zealand

Among eyeflukes, Tylodelphys Diesing, 1850 includes diverse species able to infect the eyes, but also the brain, pericardial sac and body cavity of their second intermediate host. While the genus shows a cosmopolitan distribution with 29 nominal species in Africa, Asia, Europe and America, a likely lower research effort has produced two records only for all of Australasia. This study provides the first description of a species of Tylodelphys and the first record for a member of the Diplostomidae in New Zealand. Tylodephys sp. metacercaria from the eyes of Gobiomorphus cotidianus McDowall, 1975 is distinguished from its congeners as being larger in all, or nearly all, metrics than Tylodelphys clavata (von Nordmann, 1832), T. conifera (Mehlis, 1846) and T. scheuringi (Hughes, 1929); whereas T. podicipina Kozicka & Niewiadomska, 1960 is larger in body size, ventral sucker and holdfast sizes and T. ophthalmi (Pandey, 1970) has comparatively a very small pharynx and body spination. Tylodelphys sp. exhibits consistent genetic variation for the 28S rDNA, internal transcribed spacer (ITS) and Cox1 genes, and phylogenetic analyses confirm that it represents an independent lineage, closely related to North American species. Morphological and molecular results together support the distinct species status of Tylodephys sp. metacercaria, the formal description and naming of which await discovery of the adult. Furthermore, the validity of T. strigicola Odening, 1962 is restored, T. cerebralis Chakrabarti, 1968 is proposed as major synonym of T. ophthalmi, and species described solely on the basis of metacercariae are considered incertae sedis, except those for which molecular data already exist.