Page 180 - 《水产学报》2025年第12期

张金叶，等 水产学报, 2025, 49(12): 129414

Key words: Carassius auratus; Thelohanellus xiushanensis n. sp.; morphology; phylogeny; SSU rDNA
Corresponding author: ZHAO Yuanjun. E-mail: zhaoyuanjuncqnu@126.com
Funding projects: National Natural Science Foundation of China (31970409); Projects of Chongqing Science and Technology
Commission (cstc2021jcyj-msxmX0731)

Myxosporean parasites, as one of the pivotal ohanellus wuhanensis Xiao & Chen, 1993 is
stressors in pisciculture, have garnered increasing responsible for epidermal hyperplasia, scale loss,
[1]
attention in recent years . To date, approximately and wasting in juvenile Carassius gibelio Bloch,
half of the over 2 600 species within this taxonomic 1972 with cumulative mortality surpassing 60% in
[2]
[9]
group belong to the Myxobolidae family . Con- the experimental infections ; Thelohanellus hov-
sequently, Myxobolidae is regarded as the most orkai Achmerov, 1960, the causative agent of hem-
biodiversity myxosporean taxon in terms of both orrhagic thelohanellosis in C. carpio, brings preval-
[3]
morphology and geographical distribution . Fol- ence 80% in Japanese intensive aquaculture sys-
[10]
lowing the continuous exploration, more and more tems due to its colonization of connective tissues .
new species and cryptic species will also need to be Given these impacts, there is a pressing need to har-
identified and distinguished. Hence, the number of monize taxonomic refinement with advances in elu-
species will be continually updated and expanded as cidating myxosporean pathogenicity, as both are
our understanding deepens. Moreover, the myxo- critical for developing targeted control strategies for
zoan life cycle encompasses myxospore and actino- the prevention and cure of myxosporidiosis in
spore developmental stages, corresponding to fish aquaculture.
and annelid hosts, respectively. Currently, approx- During a survey of myxosporidiosis in
imately 200 identified actinospore types have been Chongqing, China, a novel Thelohanellus sp. was
reported, which is far from matching with over 2 600 isolated and identified from the gill filaments of C.
[4]
myxosporean species . Furthermore, complete life auratus. The species underwent comprehensive
cycle information is only available for a few myxo- characterization through integrated morphological
[5]
zoan species . Therefore, accurately matching dif- analysis, molecular phylogeny reconstruction, and
ferent life stages has become a crucial aspect of host-habitat profiling. Pathogenicity was further
myxosporean classification. evaluated via histopathological examination of
The genus Thelohanellus, as the sixth most infected gill tissues, which revealed distinct lesion
prevalent myxosporean genus in Myxobolidae, has characteristics associated with parasitic prolifera-
also received growing scientific interest. At present, tion.
over one hundred Thelohanellus species with the
majority forming myxoplasmodia in various tissues 1 MATERIAL AND METHODS
of freshwater fish hosts, have been globally docu-
1.1 Tissues sample collection and species iden-
mented [6-7] . Although most of Thelohanellus species
tification
pose minimal pathogenic threats in aquaculture, cer-
tain species have been implicated in severe out- This study was approved by the Institutional
breaks that drastically reduce host survival rates and Animal Care and Use Committee of the Key Labor-
commercial value. For instance, Thelohanellus atory of Animal Biology of Chongqing Municipal
kitauei Egusa & Nakajima, 1981 induces intestinal Education Commission (Approval ID: zhao-
obstruction in Cyprinus carpio Linnaeus, 1758 via 20210624-01), and all animal experiments were per-
large cystic formations, leading to hemorrhagic formed according to the recommendations in the
[8]
enteritis and mortality rates exceeding 30% ; Thel- Guide for the Care and Use of Animals at the Key
https://www.china-fishery.cn 中国水产学会主办 sponsored by China Society of Fisheries
2