Salmincola californiensis infected 25 of 31 (prevalence 0.8; intensity 2-35 [mean 6.6 ± standard deviation 7.7; n = 25]) rainbow trout, Oncorhynchus mykiss, from a private trout farm connected to the Watauga River, North Carolina. Salmincola edwardsii infected all of 9 (1.0; 2-43 [9.3 ± 13.0; 9]) brook trout, Salvelinus fontinalis, from Big Norton Prong, a tributary of the Little Tennessee River, North Carolina. Both lernaeopodids are well-known salmonid pathogens, but neither is native to, nor has been previously taxonomically confirmed from, the southeastern United States. Herein, we (1) use light and scanning electron microscopy to identify and provide supplemental morphological observations of these lernaeopodids, (2) furnish complementary molecular sequence data from the 28S rDNA (28S), and (3) document the pathological effects of gill infections. We identified and differentiated these lernaeopodids by the second antenna (exopod tip with large [S. californiensis] vs. slender [S. edwardsii] spines; endopod terminal segment with subequal ventral processes shorter than [S. californiensis] vs. longer than or equal to [S. edwardsii] dorsal hook), maxilliped palp (length typically ≤1/3 [S. californiensis] vs. 1/3-1/2 [S. edwardsii] subchela length exclusive of claw), and bulla (sub-circular and concave on manubrium's side [S. californiensis] vs. non-stellate [S. edwardsii]). Analysis of the 28S rDNA sequences confirmed our taxonomic assignments as demonstrated by 100% sequence similarity among the sympatric, morphologically-conspecific isolates. Histopathology revealed focal gill epithelial hyperplasia, obstruction of interlamellar water channels, lamellar fusion, and crypting of gill filaments. High intensity infections by either lernaeopodid are surveillance-worthy because they are potentially pathogenic to trout in the southeastern United States.

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We describe a new fish blood fluke (Digenea: Aporocotylidae: Electrovermis zappum n. gen., n. sp.) and its life cycle in the intertidal zone adjacent to Mobile Bay (north-central Gulf of Mexico). This is the first elucidated aporocotylid life cycle that includes a chondrichthyan definitive host or a bivalve intermediate host. The new species undergoes asexual reproduction within the gonad of the variable coquina clam before maturing in the heart of the lesser electric ray. These adults and cercariae had identical 28S, 18S, and ITS2 nucleotide sequences. The new genus is similar to Ogawaia Cutmor et al., 2018 by having an inverse U-shaped intestine, a looping testis, and a uterus having distinct ascending and descending segments. It differs by having a body that is ≥ 30 × longer than wide, a testis with >30 curves, an obvious cirrus sac enveloping an extremely elongate cirrus, an ovary anterior to the seminal vesicle, and a post-gonadal uterus. The new species further differs from the type species of Ogawaia (Ogawaia glaucostegi Cutmore et al., 2018) by having a massive seminal vesicle (>10% of body length), a cirrus sac enveloping an extremely elongate cirrus, and a slightly sinuous uterus. Histology confirmed gametogenesis in an infected coquina clam but no discernible cellular response to infection was observed. We also i) characterize a second morphologically and genetically distinct cercaria (perhaps representing an innominate chondrichthyan aporocotylid) infecting the green jackknife clam in Mississippi Sound (north-central Gulf of Mexico), ii) compare all known aporocotylid cercariae infecting estuarine and marine mollusks and polychaetes and iii) provide a key to identify those cercariae. A phylogenetic analysis including nucleotide sequences from adult and cercarial specimens of the newly collected fish blood flukes further supports the notion that chondrichthyan aporocotylids are monophyletic and use bivalves as the first intermediate host; perhaps unlike any other blood fluke lineage.

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We herein diagnose blood fluke (Digenea: Aporocotylidae) infections in sea cagereared cobia (Rachycentron canadum) from Nha Trang Bay, Vietnam, using morphology, nucleotide sequences, scanning electron microscopy, and histopathology. This is the first report of this blood fluke beyond the Gulf of Mexico and contributes to our understanding of the disease implications of aporocotylid infections among marine aquacultured fishes. Blood flukes were morphologically identified as Psettarium cf. anthicum by having the combination of an extremely elongate body with rows of straight, ventrolateral tegumental spines and a sinistral posterolateral protuberance, an H-shaped intestine with asymmetrical posterior ceca, a lobed ovary, an ootype posterior to the male genital pore, and an extensively convoluted uterus located between the ovary and ootype. A comparison of the large subunit ribosomal DNA (28S), small subunit ribosomal DNA (18S), and internal transcribed spacer 2 (ITS2) derived from blood flukes infecting cobias in Nha Trang Bay and Gulf of Mexico revealed 5 (99.5% similarity in 28S), 3 (99.8%, 18S), and 12 (98.9%, ITS2) nucleotide differences between the geographic isolates. Adult blood flukes pierced the endocardium and penetrated the spongy myocardium or lesioned endocardium of the cobias from Nha Trang Bay. The associated heart lesion comprised fibro-granulomatous endocarditis with accompanying endocardial thrombi, including focal effacement of the endocardium adjacent to thrombi, hyperplasia of endocardial cells yielding a thickened endocardium within which adult flukes resided or fluke remnants were located, clusters of large epitheliod granulomas within thrombi and within the basal endocardium, and minute granulomas in spongy myocardium enclosing probable blood fluke eggs. These pathological alterations suggested that heavily-infected cobia may suffer reduced cardiac output via thrombi blocking normal blood flow and emboli causing infarcts. Acute mortality may be likely for heavily-infected cobias during periods of high cardiac output, e.g., during feeding in a sea cage, if concomitant with, or resulting in, circulation of emboli. The lesioned endocardium may reduce efficiency of respiratory gas exchange to cardiac myocytes as well as impair endocardial cell immune function.

We used microscopy and molecular biology to provide the first documentation of infections of Myxobolus cerebralis (Myxozoa: Myxobolidae), the etiological agent of whirling disease, in trout (Salmonidae) from North Carolina (USA) river basins. A total of 1085 rainbow trout Oncorhynchus mykiss, 696 brown trout Salmo trutta, and 319 brook trout Salvelinus fontinalis from 43 localities across 9 river basins were screened. Myxospores were observed microscopically in pepsin-trypsin digested heads of rainbow and brown trout from the Watauga River Basin. Those infections were confirmed using the prescribed nested polymerase chain reaction (PCR; 18S rDNA), which also detected infections in rainbow, brown, and brook trout from the French Broad River Basin and the Yadkin Pee-Dee River Basin. Myxospores were 9.0-10.0 µm (mean ± SD = 9.6 ± 0.4; N = 119) long, 8.0-10.0 µm (8.8 ± 0.6; 104) wide, and 6.0-7.5 µm (6.9 ± 0.5; 15) thick and had polar capsules 4.0-6.0 µm (5.0 ± 0.5; 104) long, 2.5-3.5 µm (3.1 ± 0.3; 104) wide, and with 5 or 6 polar filament coils. Myxospores from these hosts and rivers were morphologically indistinguishable and molecularly identical, indicating conspecificity, and the resulting 18S rDNA and ITS-1 sequences derived from these myxospores were 99.5-100% and 99.3-99.8% similar, respectively, to published GenBank sequences ascribed to M. cerebralis. This report comprises the first taxonomic circumscription and molecular confirmation of M. cerebralis in the southeastern USA south of Virginia.