Page 182 - 《水产学报》2025年第12期

张金叶，等 水产学报, 2025, 49(12): 129414

analyses were run simultaneously for three million Type host: Asian goldfish Carassius auratus
generations, with sampling every 200 generations Linnaeus, 1 758 (Cyprinidae)
and the first 25% of samples discarded as the burn- Site of infection: Tip of the gill filament
in. At the conclusion of the program, the average Prevalence: 91.67% (10/12)
standard deviation of split frequencies was 0.011 Intensity of infection: 7-15 myxoplasmodia
946. The ML trees were calculated one hundred gen- per hemibranch
erations. The trees were modified and annotated by Type locality: Xiushan County, Chongqing
MEGA 11 and Adobe Photoshop CC 2017. (28º 45' N, 108º 98' E), China.
Deposition of type materials: Syntype speci-
1.4 Scanning electron microscopic (SEM) ana-
mens (No. CQXS-Mx-2021062401) have been
lysis
deposited at the Collection Center of Type-speci-
For scanning electron microscopy, myxospores
mens, Chongqing KLAB, Chongqing Normal Uni-
was fixed in 2.5% glutaraldehyde in 0.1 mol/L versity, China.
phosphate-buffered saline (PBS) at 4 °C for 2 h.
Etymology: The species is named from
After washing 3 times with PBS, the fixed samples Xiushan County, Chongqing, China, where the host
were dehydrated in a graded series of ethanol for 15
fish were caught.
min and then substituted with isoamyl acetate of the Description: Gross pathological examination
same concentration series for 20 min. The dehyd- revealed that obvious erosion predominantly local-
rated samples were dried using vacuum freezing ized to the distal margins of the gills, accompanied
and sputter coated with gold. Finally, the coated by pallor and vascular congestion at the proximal
specimens were placed on a grid and visualized filament junctions (Plate I-1). While no obvious
using a scanning electron microscope (Hitachi S- lesions and other pathogens were detected in other
4800, Japan) at a voltage of 1.0 kV. organs and tissues upon gross and microscopic eval-
1.5 Histopathological examination uation.
The cysts were whitish and spherical, with
Gill tissues were fixed in Bouin’s fluids for 24
diameters ranging from 0.2 to 0.6 mm, positioned
h, subsequently dehydrated through a series of
near the gill filament tips (Plate I-2 and Plate II-4,
gradually increasing strength ethanol solutions, hya-
5). Mature spores featured a tapering anterior and a
linized using xylene, and embedded in paraffin wax.
blunt-rounded posterior, exhibiting a drop-shape in
Tissue sections, measuring 5 μm in thickness, were
frontal view and melon-seed shape in sutural view
stained with hematoxylin and eosin (H.E), then
(Plate I-3, 4, 7). Most myxospores were encased in
sealed by neutral balsam. Microscopic observation
a transparent membrane sheath, featuring a straight
and photo-documentation of the slides were conduc- and distinct sutural line (Plate I-4-7). Morphomet-
ted by the above-mentioned microscope.
rics data indicated the total length and width of
myxospores, including their membrane sheath,
2 RESULTS
measured (20.5 ± 1.4) (18.0-23.2) μm and (11.3 ±
1.1) (9.2-14.2) μm, respectively (n = 50). And the
2.1 Description of species characteristics
pure dimensions of myxospores were (19.2 ± 1.1)
Thelohanellus xiushanensis n. sp. (17.1-21.0) μm in length, 10.0 ± 0.7 (8.7-2.1) μm in
Phylum: Cnidaria Hatschek, 1888 width, and (9.7 ± 0.5) (9.1-10.8) μm in thickness (n =
Class: Myxosporea Bütschli, 1881 25). Polar capsules, oval in shapes, measured (8.0 ±
Order: Bivalvulida Shulman, 1959 0.6) (6.9-9.1) μm in length and (6.6 ± 0.3) (6.1-7.1)
Family: Myxobolidae Thélohan, 1892 μm in width (n = 50). Their opening was anterior to
Genus: Thelohanellus Kudo, 1933 the myxospore (Tab. 1). Polar filaments, with 4-5

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