Pathogenic endoparasites of the spotted seatrout, Cynoscion nebulosus: patterns of infection in estuaries of South Carolina, USA.

Six types of pathogenic endoparasites in an economically important fish, spotted seatrout Cynoscion nebulosus, were studied in order to test whether prevalence of infection and assemblage richness varied with season, host sex, host size, or host age. Fish were collected from South Carolina estuaries, USA, over 12 months (n = 216; total lengths 15-663 mm). They were screened histologically for presence of Henneguya cynoscioni (Myxozoa) and Cardicola spp. (Digenea) in the heart, Kudoa inornata (Myxozoa) in the skeletal muscle, Sinuolinea dimorpha (Myxozoa) in the urinary system, Ichthyophonus sp. (Mesomycetozoea) in the kidney, and an unidentified microsporidian in the liver. Prevalence of infection was 29.8, 38.6, 47.2, 41.2, 13.6, and 2.8%, respectively. All factors had significant, but varying effects on the parasites. Parasite infections were more prevalent in winter than other seasons for Cardicola spp. and H. cynoscioni, more prevalent in winter and spring for Ichthyophonus sp., and more prevalent in male fish than female fish for K. inornata, S. dimorpha, and Ichthyophonus. Prevalence of infection by the three myxosporeans and Cardicola spp. increased with fish length, whereas prevalence of Ichthyophonus increased with length among young fish, but decreased with length among older fish. None of the factors affected the liver microsporidian, although statistical power was low due to its rareness. Assemblage richness varied between 0 and 5, was greater during winter and in male fish, and increased with fish length and fish age. Our results demonstrate that spotted seatrout are commonly co-infected by multiple pathogenic endoparasites, suggesting these parasites likely play an import role in controlling fish population numbers.

Invasive swimbladder parasite Anguillicoloides crassus: infection status 15 years after discovery in wild populations of American eel Anguilla rostrata.

A year-round survey of American eels Anguilla rostrata was performed at 5 localities in South Carolina (SC), USA, 15 yr after the first infection by the nematode Anguillicoloides crassus was reported from Winyah Bay, SC. Infections by adult stages of A. crassus in the swimbladder lumen occurred with a prevalence of 45% (n = 479), a mean intensity (± SE) of 2.3 ± 0.2 worms per infected eel (range = 1-22), and a mean abundance of 2.0 ± 0.1 among all eels. Infections by larval stages of A. crassus in the swimbladder wall occurred with a prevalence, intensity, and abundance of 29%, 2.4 ± 0.3 (range = 1-15), and 0.7 ± 0.1, respectively (n = 471). Overall prevalence of the parasite (any stage) was 58%, with a mean intensity ± SE of 3.0 ± 0.2 and a mean abundance of 1.8 ± 0.2. Biomass of the adult parasite stage varied significantly with eel body length, but the direction of the effect depended on salinity. Prevalence and intensity of infection by adult nematodes varied by locality but not by eel total length, salinity, or season. Larval prevalence was significantly greater in the winter and spring and also differed among localities. The lack of seasonal effects on infection by the adult worm stage contrasts with studies from higher latitudes in North America and Europe and may be due to the warmer winter temperatures at southern latitudes. Significant variation in infection among localities reflects possible differences in abundance of intermediate and/or paratenic hosts. Overall, infection levels were higher than previous reports for eels in SC but comparable to more recent reports from other areas in North America.

Sinuolinea infections in the urinary system of Cynoscion species (Sciaenidae) and phylogenetic position of the type species of Sinuolinea Davis, 1917 (Myxozoa: Myxosporea).

Myxosporean infections that we diagnosed frequently in the urinary tract of Cynoscion nebulosus (Cuvier, 1830) and Cynoscion regalis (Bloch and Schneider, 1801) (Sciaenidae) collected in the estuarine systems of SC, USA, are described together with their etiological agent. Based on the morphology of spores and plasmodial stages, we identified the agent, in both fish host species, as Sinuolinea dimorpha (Davis, 1916), which is the type species of the genus. Based on sequences of SSU rDNA generated in this study from type host material, this species of SinuolineaDavis, 1917 has found its place in the current phylogenetic reconstruction of Myxozoa and enlarged the limited number of myxosporean genera represented in phylogenetic analyses by sequences of type species. Sequences of SSU rDNA of S. dimorpha from Cynoscion host species formed two clusters, irrespective of their host species, and also revealed differences within each cluster. These findings contribute to the acknowledgement of myxosporean cryptic species diversity, an important topic that emphasizes the general necessity of species delimitation and of continued effort to improve our knowledge of Myxosporea based on both morphology of spores and molecular data.

Henneguya cynoscioni sp. n. (Myxosporea: Bivalvulida), an agent of severe cardiac lesions in the spotted seatrout, Cynoscion nebulosus (Teleostei: Sciaenidae).

A new myxosporean species, Henneguya cynoscioni sp. n., is described from the spotted seatrout, Cynoscion nebulosus (Cuvier) (Sciaenidae) as a causative agent of cardiac henneguyosis. This new myxosporean species is characterized by the morphology of spores and the sequence of SSU rDNA. Examination of 227 spotted seatrout from four South Carolina estuaries in 2008-2010 revealed a 33.5% total prevalence of H. cynoscioni. Henneguya cynoscioni produces lesions in the bulbus arteriosus, its specific site of infection. The severity of lesions and their impact on the bulbus arteriosus is proportional to the number of plasmodial stages developing in this segment of the heart, being most pronounced in host reaction directed against spores liberated from plasmodia.

Use of molecular tools in identification of philometrid larvae in fishes: technical limitations parallel our poor assessment of their biodiversity.

The usefulness of the polymerase chain reaction with restriction fragment length polymorphism (PCR-RFLP) and partial sequencing of the cytochrome oxidase I (COI) gene was tested regarding the utility of these techniques in unraveling philometrid life cycles and, in particular, to determine putative paratenic host species. Our focus was to study three species of philometrids commonly found in the estuaries of South Carolina: Philometroides paralichthydis and Philometra overstreeti from the southern flounder, Paralichthys lethostigma and Philometra carolinensis from the spotted seatrout, Cynoscion nebulosus. A total of 473 fish in 19 species known to be potential prey of the spotted seatrout and the southern flounder were dissected. Of all nematode larvae found in the mesenteries of 53 fish of 10 species, 21 specimens were determined to be philometrids using PCR. The use of PCR-RFLP allowed the identification of larvae of P. carolinensis and P. overstreeti in the freshwater goby, Ctenogobius shufeldti, and P. overstreeti in mummichog, Fundulus heteroclitus. However, 12 RFLP profiles could not be matched to control species, thus demonstrating the limitation of this technique in areas where diversity of philometrids is not well known and higher than anticipated. Similarly, COI procedures provided unknown sequences that did not match those of nine philometrid species used as controls. We concluded that although both techniques showed some usefulness and promise, at this point, however, they demonstrate the need of increasing our knowledge of marine and estuarine philometrid biodiversity.

Philometrids of the southern flounder Paralichthys lethostigma: a multidimensional approach to determine their diversity.

Two species of philometrid nematode, Philometra overstreeti and Philometroides paralichthydis, infect the southern flounder, Paralichthys lethostigma. Individuals of P. overstreeti are located between the teeth and inside the bony part of the branchial arches of the fish. Individuals of P. paralichthydis are associated with the bones of the buccal cavity and among muscles that control the dorsal and anal fins. Sequencing of part of the cytochrome oxidase I gene revealed 4 distinct genetic clades, each corresponding exactly to the 4 respective locations of the parasites in the host, suggesting the need for taxonomic revision. We hypothesized that each clade represented a separate species and, because the worms are morphologically indistinguishable, compared population level parameters of the clades comprising each currently recognized species. For each currently recognized species, the presence of worms from 1 clade was negatively correlated with the presence of worms from the other. Results also indicated significant differences between the clades in prevalences relative to both biotic and abiotic factors. Results clearly indicated major differences in the ecology of the philometrids constituting each clade. Taken as a whole, molecular and ecological data support the contention that the 4 genetic clades are likely 4 distinct species.

Histopathology of two philometrid parasites of the southern flounder, Paralichthys lethostigma.

The southern flounder Paralichthys lethostigma is host to two species of philometrid nematodes in the estuarine systems of South Carolina, USA. Histologic studies showed that all worms were hematophagous and that the host-parasite interface varied according to the worm's location in the fish. Individuals of Philometra overstreeti associated with the teeth induced a degradation of the enameloid epithelium but elicited minimal host reaction, whereas those located in the branchial arches induced an intense inflammatory response. Individuals of Philometroides paralichthydis elicited no host reaction. Those associated with the bones of the buccal cavity were contained in a thick collagenous capsule, whereas those located between the depressor and erector muscles of each fin element displaced or thinned the fin inclinator muscles to the extent of eventually causing their complete atrophy. Often the bulk of gravid worms imposed upon uninfected adjacent fin element muscle groups. Damage induced by these worms are likely to affect feeding and swimming behavior of the infected flounder and thus, impact the population structure of this important fish species.

Kudoa inornata sp. n. (Myxosporea: Multivalvulida) from the skeletal muscles of Cynoscion nebulosus (Teleostei: Sciaenidae).

A new myxosporean species, Kudoa inornata sp. n. (Myxosporea: Multivalvulida), is described from skeletal muscles of the spotted seatrout Cynoscion nebulosus (Cuvier), collected in estuarine waters along the coast of South Carolina, USA. Light microscopic and ultrastructural characters rank this species to the group of Kudoa species with simple-shaped spores. The uniqueness of the SSU and LSU rDNA sequences justifies its status of a new species with sister relationship to Kudoa paniformis. The 100% prevalence in seatrout from four out of five localities sampled and pathogenicity of K. inornata recognized in this study should motivate further screening for infections in its host, which is considered a commercially important game fish with a wide distribution in the Western North Atlantic.

Synchronization of occurrence of the ovarian philometrid, Philometra carolinensis, with the spawning season of its fish host, the spotted seatrout, Cynoscion nebulosus.

The philometrid Philometra carolinensis inhabits the ovaries of the spotted seatrout, Cynoscion nebulosus. A 2-year study in estuaries of South Carolina showed that each year adult female worms were present only during the spawning season of the host and that only sexually mature fish were infected. Overall prevalence was 13.1%. Young-of-the-year fish were uninfected and mature 1-year-old fish were less frequently infected than older fish. Abundance of the philometrid was significantly different in age-1 and -2 spotted seatrout. Prevalence, mean abundance, and intensity peaked during the first 2 months of the host's 4-month spawning season, which then declined abruptly. Occurrence of the philometrid in the fish host was unaffected by water temperature, salinity, and dissolved oxygen. Histological studies revealed that the worms were hematophagous. Worms induced disruption of the ovarian lamellar walls resulting in the interruption of development and the loss of host eggs into the ovarian lumen prior to their maturation. The data show that development of this parasite is linked to the host's reproductive status and suggest that paratenesis plays an important role in the maintenance of the parasite's life cycle.

Three new species of philometrids (Nematoda: Philometridae) from centrarchid fishes in the USA.

The following 3 new species of the Philometridae (Nematoda: Dracunculoidea) are described from freshwater centrarchid fishes (Centrarchidae: Perciformes) from eastern North America on the basis of museum and newly collected specimens: Philometra orbitalensis n. sp. and Philometroides aphanonaris n. sp. from the oculo-orbits and subcutaneous tissues of the head, respectively, of the largemouth bass Micropterus salmoides, and Philometroides wellborni n. sp. from the oculo-orbits of the bluegill Lepomis macrochirus (type host) and the redbreast sunfish Lepomis auritus. Whereas P. wellborni is described from both males and gravid females, the males of P. aphanonaris and P. orbitalensis remain unknown. The type locality of all 3 species is the West Point Reservoir, Alabama-Georgia; P. aphanonaris and P. wellborni have also been recorded from the Santee River in South Carolina. In contrast to other Philometra spp. parasitizing North American freshwater fishes, the gravid females of P. orbitalensis are characterized by large cephalic papillae of the external circle, yellowish body color, location (oculo-orbits) in the host, and by the host type (Centrarchidae). Philometroides aphanonaris and P. wellborni differ from North American congeners from freshwater fishes in the absence of esophageal teeth or a different embossment of the caudal end in gravid females; P. wellborni differs from P. aphanonaris in the absence of cuticular bosses from the caudal end of gravid females and in some other features (extent of embossment, body color, location, and host type).

Metamicrocotyla macracantha, a polyopisthocotylid gill parasite of the striped mullet, Mugil cephalus: population dynamics in South Carolina estuaries.

In the estuarine system of South Carolina (USA), the striped mullet, Mugil cephalus, was found to be parasitized by the polyopisthocotylid monogenean Metamicrocotyla macracantha among other gill parasites. Mullet of various ages were collected monthly for 1 year from oligohaline, mesohaline, polyhaline, and euryhaline localities. The population dynamics of M. macracantha was analyzed according to time of year, different salinity levels, and host age and sex. Out of the 770 mullet studied, 11.2% were infected (mean, two worms per host). Neither prevalence nor mean intensity was correlated with biotic factors. However, significant seasonal variation in prevalence was observed, and the worm was found more frequently in higher salinities. Mean intensity, however, did not change significantly with time of year or salinity. This is the first published report of M. macracantha in the South Carolina estuarine system and represents the northernmost record for this parasite. Furthermore, the lack of common egg-bearing individuals and juveniles indicated that this area is likely the northern limit of the geographical range of M. macracantha, whose life cycle seems restricted to more constant water temperatures than those found at the South Carolina latitudes.

Diamondback terrapins, Malaclemys terrapin, as a sentinel species for monitoring mercury pollution of estuarine systems in South Carolina and Georgia, USA.

Total mercury concentrations were measured in diamondback terrapin blood and scutes collected from four sites in South Carolina, USA, and at a superfund site in Brunswick, Georgia, USA. There was a strong correlation between mercury concentrations in the two terrapin body compartments (Kendall's tau = 0.79, p < 0.001). Mercury concentrations in terrapin scute and blood and in salt marsh periwinkles, Littoraria irrorata, were significantly higher in Brunswick (scute x = 3810.2 ng/g, blood x = 746.2 ng/g) than from all other sites (scute x = 309.5 ng/g, blood x = 43.2 ng/g, p < 0.001). Seasonal fluctuations of total mercury in the blood and scutes of terrapins collected in the Ashley River, South Carolina, were significantly lower in August than in April, June, or October in blood (p < 0.001); however, scute concentrations did not vary seasonally. Overall, we found higher concentrations of mercury in the scutes of females than males (n = 32, p < 0.05). Larger females may preferentially prey on larger food items, like large periwinkles, which had significantly higher mercury levels in their body tissues than smaller periwinkles (p < 0.001). Methylmercury levels in terrapin scutes were measured, revealing that 90% of the total mercury stored in this compartment was in the organic form. A methylmercury biomagnification factor of 173.5 was calculated from snails to terrapin scutes, and we found that mercury levels in scutes were representative of the mercury levels in other compartments of the ecosystem. These findings show that terrapin scutes are good predictors of mercury pollution and that this species could be used as a bioindicator for assessing mercury contamination of estuarine systems.

Stock identification of the sciaenid fish Micropogonias undulatus in the western North Atlantic Ocean using parasites as biological tags.

Proper fisheries management of the Atlantic croaker Micropogonias undulatus is necessary in the United States due to the commercial and recreational importance of this fish species. Croaker stock structure in the western North Atlantic has been investigated in the past by various authors, with inconclusive results. In this study, macroparasites were used as biological tags to identify putative croaker stocks in the area between New Jersey and Florida, which encompasses the Mid Atlantic Bight and the South Atlantic Bight separated at Cape Hatteras, North Carolina. The macroparasite community of the fish was identified, showing the presence of 30 species in four phyla, of which several were new host records, and one species, a monogenean, was new to science. A canonical correspondence analysis was applied to determine the variables responsible for parasite species composition, to resolve the question of croaker stock structure in the western North Atlantic Ocean. This analysis showed that latitude was the deciding variable delineating the parasite community composition of the Atlantic croaker. Among the 30 parasites, 15 were identified as putative tags according to qualitative criteria, and then 10 out of those 15 were selected as being appropriate tags using quantitative criteria. These parasite tags support the presence of two stocks roughly separated at the known biogeographical barrier at Cape Hatteras.

Two new species of Philometra (Nematoda: Philometridae) parasitic in the perciform fish Cynoscion nebulosus (Sciaenidae) in the estuaries of South Carolina, USA.

Two new nematode species of Philometra Costa, 1845, P. carolinensis sp. n. and P. cynoscionis sp. n., are described from the spotted seatrout, Cynoscion nebulosus (Cuvier) (Sciaenidae, Perciformes) in estuaries on the Atlantic coast of South Carolina, USA. Philometra carolinensis (males and gravid and subgravid females) parasitic in the host's ovary is most similar to P. lateolabracis (Yamaguti, 1935) in female morphology, but distinctly differs from it in possessing conspicuously short spicules (81-87 microm long) with heavily sclerotized distal parts, the gubernaculum bearing a reflected dorsal barb, and in the length ratio of the gubernaculum and spicules (1:1.23-1.42) in the male. Philometra cynoscionis (only gravid females) found subcutaneously in the host's tissue (lateral to the ascending process of the premaxilla and also posteromedial to the length of each maxilla) is characterized mainly by the presence of cephalic papillae arranged in two circles (8 large papillae in outer circle and 6 small papillae in inner circle), the absence of caudal projections, the body size (length of gravid female 20-33 mm) and the location in the host.

Population dynamics of the philometrid nematode Margolisianum bulbosum in the southern flounder Paralichthys lethostigma (Pisces: Paralichthyidae) in South Carolina, USA.

This is the first report of the philometrid nematode Margolisianum bulbosum Blaylock and Overstreet, 1999 from the southern flounder Paralichthys lethostigma on the east coast of the USA. Observation of adult female worms was used as an indication of the parasite's presence in the fish. Adult females were found only in P. lethostigma >50 mm total length. The overall prevalence was 74%, with a mean intensity of 5 female nematodes per parasitized fish. Infected flounders were found throughout the year with a statistically significant decrease in intensity in the winter months. Neither salinity, water temperature, fish gender nor fish age were found to influence either prevalence or intensity of infection in the flounder. While larvigerous (gravid) females were found throughout the year, the significant decrease in their occurrence during the summer through fall, in concert with an observed decrease in intensity of infection during the winter, indicated that the life cycle of this philometrid species is likely to be annual.