Digenean species diversity in teleost fishes from the Gulf of Gabes, Tunisia (Western Mediterranean)

Metazoan ectoparasites of Lithognathus mormyrus (Linnaeus, 1758) from the western coast of Libya

Background

Lithognathus mormyrus fish is one of the fish of high economic importance in the countries of the world in general and the Mediterranean countries in specific, including the Libyan Sea waters, for this it is necessary to know everything related to this type of fish, including its infection with parasites. Parasites are considered one of the factors threatening the life of fish, being one of the food chains and the ecological composition of life.

Aim

The current study aims to isolate and identify the parasites that infect the L. mormyrus.

Methods

A total of 368 specimens of L. mormyrus were collected by fishermen, from the western coast of Libya. The study was focused on metazoan parasites. When fish were fully examined for the presence of ectoparasites under a dissecting microscope with incident light, the software camera connected with a microscope and semichon' acetocarmine technique for identification of parasites.

Results

Two species of Monogenea (Encotyllabe valley, Pagellicotyle mormyri, and Lamellodiscus spp.), Isopoda (Gnathia), Copepoda (Lernaeolophus sultanus), and Annelidae (Trachelobdella lubrica) has been isolated from this species of fish. The highest prevalence of infection was Gnathia parasites (8.47%).

Conclusion

There were differences in the parasite species that infect L. mormyrus from one country to another, and also from city to other cities in the same country, as in the Tunisian waters.

Digenea community structure of the Salema, Sarpa salpa (Linnaeus, 1758) (Teleostei, Sparidae), from the Central coast of Algeria

The main goal of the current work was to describe and analyse the Digenean community structure in Sarpa salpa. A total of 114 specimens of S. salpa were collected from the Central Coast of Algeria at six localities. The fish were immediately transported to the laboratory to be examined for digeneans. From 107 of the 114 S. salpa examined, a total of 8,722 specimens of seven species belonging to three families were recovered. Among them, Robphildollfusium fractum and Mesometra orbicularis were the most prevalent and abundant species. Moreover, Lepocreadium album was found for the first time in S. salpa from the coast of Algeria, and Centroderma spinosissima and Wardula capitellata represent new parasites to the Algerian digenean fauna that infect teleost fish. The component community of these Digeneans is characterised by R. fractum as its dominant species representing 62% of the total number of collected Digeneans, as well by a Shannon diversity index (H') and Dominance Simpson index (D) of 1.03 and 2.23, respectively. According to Spearman's correlation test, Mesometra brachycoelia and W. capitellata were negatively correlated to the host biological factors. On the other hand, R. fractum showed a positive correlation between its mean abundance and the total length of the fish. With these findings, we provided the component structure of the Digenean fauna of S. salpa and highlighted their diversity, contributing to the biodiversity of the parasitic Platyhelminthes in Algeria.

Diversity of digeneans parasitizing Mullus barbatus and Mullus surmuletus (Teleostean, Mullidae) off the coast of Algerian

Mullus barbatus and Mullus surmuletus (Perciformes, Mullidae) are a common marine teleost of great commercial importance in many coastal areas. We studied the communities of Digenea species in two congeneric Mullidae hosts collected on the Algerian coast in the southern Mediterranean. Five hundred and seven M. barbatus and one hundred and twenty-three M. surmuletus were examined. During this work, we collected six species of parasitic Digenea which are related to five different families: Hemiuridae represented by Lecithocladium excisum, Fellodistomidae by Proctoeces maculatus and which is reported only from M. surmuletus, Derogenidae by Derogenes latus, Monorchiidae by Proctotrema bacilliovatum and finally Opecoelidae represented by two species Opecoeloides furcatus and Poracanthium furcatum. A critical systematic study revealed an apparent overlap in morphometric data of the six Digenean species from two host fishes. Therefore, the two mullet species are likely to share the same parasite community, and the stenoxenic specificity of Digenean parasites is briefly argued. Prevalence values showed that in the midst of six hundred and thirty Mullidae, one hundred and ninety-six are parasitized (31.11 %). Statistical tests showed that the most parasitized fish hosts are M. surmuletus with a high prevalence value (47.15 %), and on the other hand, they proved that small fish are more parasitized than others. Also, the lack of homogeneity between the different parasites is reported. We also note that the use of factorial correspondence analysis (FCA) allowed us, for the first time to highlight the distribution of the parasite species identified in the two mullets according to the seasons.

Parasites of Sardinella maderensis (Lowe, 1838) (Actinopterygii: Clupeidae) and Their Potential as Biological Tags for Stock Identification along the Coast of West Africa

This study is the first to provide information on the parasite fauna of Sardinella maderensis along the coasts of Benin and Ghana, and the first to investigate the potential use of parasites as biological tags in fish population studies in the area. It may thus serve as a starting point for upcoming studies. From February to June 2021, a total of 200 S. maderensis were sampled from the fishing port of Cotonou (Benin) and the Elmina landing site (Ghana). The prevalence and abundance of each parasite were recorded. The following are the outcomes of this study: Parasite species, such as Parahemiurus merus, Mazocraeoides sp. and Hysterothylacium fortalezae, were recorded along the coasts of Benin and Ghana, while Anisakis sp(p). and Tentacularia coryphaenae were only recorded along the coast of Benin. Parahemiurus merus was the most prevalent and abundant among all the parasites recorded. Anisakis sp(p). and T. coryphaenae were selected as having potential in the stock identification of S. maderensis. Both parasites were only recorded along the coast of Benin at a low prevalence. As a result, examinations of more S. maderensis from each location for these parasites may justify their use in stock identification studies.

G lugea sp. infecting Sardinella aurita in Algeria

Parasitological examination of the commercially important pelagic fish Sardinella aurita Valenciennes, 1847 (Clupeidae) from the Eastern coast of Algeria revealed xenomas in the peritoneal cavity, suggesting a microsporidian infection. The prevalence of the disease was approximately 30% on average, higher in smaller individuals and showing significant seasonal variation. The xenomas contained numerous ellipsoidal spores, surrounded by a dense layer of connective tissue. Spore sizes were 6.10 ± 0.38 µm length and 3.54 ± 0.43 µm width. Ultrastructural examination by transmission electron microscopy showed various development stages of the parasite, including meronts, sporonts, sporoblasts and mature spores. The internal organization of the mature spores, with a single nucleus, prominent posterior vacuole, a lamellar polaroplast and an isofilar polar tube arranged in a single row, was typical of the genus Glugea. The DNA sequence of the small subunit ribosomal RNA gene confirmed that this parasite belongs to the genus Glugea. Genetic and morphologic comparison with G. sardinellensis, a species previously described in the same host from Tunisia shows many similarities, although some molecular and morphometric inconsistencies precluded the unambiguous assignment of our samples to G. sardinellensis. At the same time, we do not find sufficient grounds to erect a new taxon for our parasite. We discuss the implications of our findings for the current state of the systematics of Glugea.

Drivers of parasite communities in three sympatric benthic sharks in the Gulf of Naples (central Mediterranean Sea)

Sharks play a key role in the functioning of marine ecosystems and maintenance of trophic web balance, including life cycles of parasites co-occurring in their habitats. We investigated the structure of parasite communities of three sympatric shark species (Etmopterus spinax, Galeus melastomus, and Scyliorhinus canicula) and explored both the influence of host features in shaping the communities and their role as biological indicators of environment stability in the Gulf of Naples (central Mediterranean Sea), a geographical area characterized by strong anthropic pressure. Parasites found were all trophic transmitted helminths with a complex life cycle, except Lernaeopoda galei, that is a ecto-parasite copepod. Communities were all similarly impoverished with 4–5 component species and low values of species richness and diversity. Higher abundance of cestode larvae of the genus Grillotia was found in G. melastomus, although their dominance in all host species suggests that the three sharks have a similar role as intermediate/paratenic hosts in local food webs. Similarly, high abundance of Grillotia larvae could also suggest the occurrence of high abundance of largest top predators in the area. Host morphological (fork length in S. canicula and G. melastomus and body condition index in G. melastomus) and physiological (sex and gonadosomatic and hepatosomatic indices in S. canicula) variables were differently correlated to parasite community structures depending by host species. Potential reasons for the present impoverished parasite communities are discussed.

Host biological factors and geographic locality influence predictors of parasite communities in sympatric sparid fishes off the southern Italian coast

Host biological factors and habitat influence the faunal assemblages and biodiversity worldwide, including parasite communities of vertebrate and invertebrate hosts. The ecological relationship between hosts and parasites can be mediated by interaction of host’s biological factors, as their physiological condition, diet and size, with the environmental components, somehow influencing the features of parasite infection in host populations. Here, we used boosted regression tree models to study the parasite communities of two sympatric sparid fishes, the salema Sarpa salpa and the white seabream Diplodus sargus, to investigate the role of specific host’s traits in two contiguous coastal areas along the southern-western Tyrrhenian coast of Italy characterized by different degree of deterioration. Results showed that overall and across all parasite groups (ecto-, endo- and ecto- plus endo-parasites), sampling localities were the most important predictors of abundance, species richness, and diversity for salema. Moreover, seasonality was the main predictor of endo-parasite abundance, while size-related factors explained most of the variation in species richness and diversity. In the white seabream, size-related factors and reproductive cycle-related factors were the most important predictors for the overall parasite abundance and parasite richness, respectively. Our findings suggest that the parasite community of salema and white seabream responded differently to specific biological factors, highlighting how the environmental conditions under which they live may exert a strong influence on the parasite communities of each host fish.

Parasite communities of the white seabream Diplodus sargus sargus in the marine protected area of Medes Islands, north-west Mediterranean Sea

Marine protected areas are considered a useful tool to preserve and recover the biodiversity of ecosystems. It is suggested that fisheries not only affect populations of target and bycatch species but also their parasite communities. Parasites can indicate fishery effects on host species and also on the whole local community, but the effects of fisheries and protection measures on parasite communities are relatively unknown. This study analyses parasite communities of the white seabream Diplodus sargus sargus in order to assess potential effects exerted by protection measures within and by fisheries outside a reserve in the western Mediterranean Sea. This small scale analysis offered the opportunity to study different degrees of fishery effects on parasite infracommunities, without considering climatic effects as an additional factor. Parasite infracommunities of fishes from the no-take zone (NTZ) differed in their composition and structure compared with areas completely or partially open to fisheries. The detected spatial differences in the infracommunities derived from generalist parasites and varied slightly between transmission strategies. Monoxenous parasites were richer and more diverse in both fished areas, but more abundant in the no-take, whereas richness and abundance of heteroxenous parasites were higher for the NTZ. In addition to host body size as one factor explaining these spatial variations, differences within parasite infracommunities between the areas may also be linked to increased host densities and habitat quality since the implementation of the NTZ and its protection measures.

The Diversity of Teleost Fish Trematodes in the Bay of Bizerte, Tunisia (Western Mediterranean)

A total of 39 digeneans species allocated to 28 genera in 12 families were recovered from 534 fishes belonging to 14 species in three families (Carangidae, Mullidae and Sparidae) collected in the Bay of Bizerte off the coast of Tunisia. We provide a host-parasite list of records from this locality, including 63 host-parasite combinations. The Opecoelidae Ozaki, 1925 is the most diverse group with 12 species. The species richness of individual digenean genera in the Bay of Bizerte ranges from 1 - 6 species. The mean number of 2.58 species per host indicates a relatively high digenean diversity in the Bay of Bizerte, which is related to its geographical location, its connection with the neighbouring Bizerte Lagoon and the nature of the bottoms of the littoral marine areas off the northern Tunisian coasts. This diversity is significantly higher than that reported off the southern coast of Tunisia and distinctly lower than that observed for teleost hosts in the Scandola Nature Reserve off Corsica. Generally, the levels of infection in teleosts fishes from the Bay of Bizerte are lower than those from the other two localities.

Helminth parasites of the chub mackerel Scomber colias off the Tunisian coast and their use in stock discrimination

Nine helminth parasites were used as biological tags to discriminate diverse areas of Scomber colias Gmelin, 1789. During three seasons, a total of 369 fish were examined in four zones off the Tunisian coast, including Bizerte in the north, Kelibia and Mahdia in the centre and Zarzis in the south. Discriminant analyses were used to identify distinct areas of S. colias. Fish from Bizerte were grouped as one area and were correlated negatively with the monogenean Grubea cochlear and the digenean Lecithocladium excisum. Specimens from Kelibia and Mahdia were grouped together and were characterized by the ectoparasite Pseudokuhnia minor and by endoparasites Prodistomum orientalis, Monascus filiformis and anisakid larvae. Fish from Zarzis were grouped as one area and were positively correlated with the monogenean G. cochlear and the digenean L. excisum. These results were corroborated by comparing the prevalence and mean abundance of parasites among zones. Results of other discriminant analyses used for the classification of S. colias between localities after pooling specimens from the central areas of Kelibia and Mahdia also allowed the identification of three distinct areas: one in the north, correlated negatively with G. cochlear and L. excisum; one in the centre, characterized by P. minor, P. orientalis, M. filiformis and anisakid larvae; and one in the south, from Zarzis, characterized by G. cochlear and L. excisum. Results of comparisons of infection parameters between seasons and those of seasonal discrminant analyses showed a seasonal stability of communities from the northern and the southern areas. Specimens from the central regions showed variability between seasons, suggesting migratory movements.

The Mediterranean: high discovery rates for a well-studied trematode fauna

Our knowledge of trematode diversity in Mediterranean Sea fishes is based on many contributions since the early 1800s (e.g. by Rudolphi, Stossich, Looss, Bartoli, Bray and Gibson). We have updated data from the Natural History Museum Host-Parasite Database and listed 302 digenean trematode species allocated to 146 genera in 29 families from 192 fish species (27% of the known fish-fauna) belonging to 76 families. The most diverse (with 31-41 species) digenean families (Opecoelidae Ozaki, 1925, Didymozoidae Monticelli, 1888 and Hemiuridae Looss, 1899) represent more than a third of the total richness (36% of species) and have been most frequently recorded (43% of the records). The overall mean number of species per host is close to recent global estimates for digenean richness in teleosts (1.57 vs 2.04, respectively), indicating a high diversity in the Mediterranean. The most diverse host families are also the best studied. However, three speciose host families (Rajidae de Blainville, Gobiidae Cuvier and Myctophidae Gill) appear under-studied and no digenean reports exist for 94 of 169 fish families present in the Mediterranean. Thus, although Mediterranean fishes appear well studied, further efforts are needed. Nevertheless, the descriptions of a large number of new taxa since 2000 indicate that focused efforts have resulted in a high discovery rate (2.4 species per year). Many of these new (often cryptic) taxa are the result of combined morphological and molecular methods, which promise more reliable estimates of digenean diversity in this region. We provide host-parasite lists for 192 species of fish in the Mediterranean comprising 890 host-parasite associations.

Spatial variability of helminth parasites and evidence for stock discrimination in the round sardinella, Sardinella aurita (Valenciennes, 1847), off the coast of Tunisia

Three digeneans - Parahemiurus merus (Linton, 1910), Aphanurus stossichii (Monticelli, 1891) and Lecithochirium sp. - and one tetraphyllidean cestode larva were used as biological tags to discriminate the stock of Sardinella aurita (Valenciennes, 1847). In total, 579 fish were examined in five zones off the Tunisian coast, including Bizerte and Kelibia in the north, Mahdia in the east, Gabes and Zarzis in the south. Discriminant analyses used for the separation of S. aurita allowed for the identification of two discrete stocks. Sardinella aurita from Bizerte, Kelibia and Zarzis clumped together as a single stock. Parahemiurus merus and A. stossichii were the most important species in determining the location of sampled fish from these regions. Specimens from Mahdia and Gabes were grouped as one stock characterized by the presence of Lecithochirium sp. and larvae of the Tetraphyllidea. These results were corroborated by comparing the parameters of prevalence and mean abundance of parasites among zones. The separation of S. aurita between localities after pooling specimens from Bizerte, Kelibia and Zarzis and separately pooling those from Mahdia and Gabes also allowed the identification of two discrete stocks, one in offshore waters from Bizerte, Kelibia and Zarzis characterized by the digeneans P. merus and A. stossichii and one in inshore waters from Mahdia and Gabes characterized by Lechithochirium sp. and tetraphyllidean larvae.