Occurrence and Molecular Identification of Microcotyle sebastis Isolated from Fish Farms of the Korean Rockfish, Sebastes schlegelii

Assessment of Salinomycin's Potential to Treat Microcotyle sebastis in Korean Rockfish (Sebastes schlegelii)

Aquaculture, a crucial sector of the global food industry, faces a myriad of issues due to parasitic invasions. One such parasite, Microcotyle sebastis, which afflicts Korean rockfish in South Korea, has a significant economic impact. The impending danger of resistance to traditional anthelmintics necessitates the exploration of new antiparasitic candidates. Although the efficacy of salinomycin against aquatic parasites such as ciliates and sporozoans is known, its influence on monogeneans has yet to be studied. Therefore, this study investigated the efficacy and safety of salinomycin for the treatment of M. sebastis infections, presenting the first exploration of salinomycin's therapeutic potential against monogeneans. In vitro examinations revealed a minimum effective concentration of salinomycin of 5 mg/kg, which led to necrosis of the haptor upon dislodging from the gill filaments. The one-time oral administration of the drug at concentrations of 5 mg/kg and 10 mg/kg showed a significant dose-dependent reduction in parasite counts, with no apparent behavioral side effects in Korean rockfish. Biochemical analyses monitored the liver, heart, and kidney enzymes, specifically aspartate transaminase (AST), alanine transaminase (ALT), blood urea nitrogen (BUN), and creatine kinase-myocardial band (CK-MB). At both 20 °C and 13 °C, no significant differences were observed in the levels of AST and ALT. However, at 20 °C, alterations in BUN levels were evident on Day 14, a deviation not observed at 13 °C. The CK-MB analysis revealed elevated enzyme levels at both temperatures when compared to the control group, reflecting the similar changes observed in terrestrial animals administered salinomycin. The biochemical data suggest that the oral administration of salinomycin is potentially more favorable at 13 °C than at 20 °C. Although our findings warrant further comprehensive studies, including on the long-term and potential effects on nontarget species and water quality, they also suggest that salinomycin could be considered as an alternative or adjunctive treatment if resistance to the currently used praziquantel against M. sebastis is confirmed.

Correlation of endemicity between monogenean trematode, Microcotyle sebastis, and parasitic copepods in Korean rockfish, Sebastes schlegelii, from a fish farm in Tongyeong-si, Gyeongsangnam-do, Korea

Infestations of parasites, particularly those caused by copepods and monogeneans, are a major hindrance to aquaculture and have a big negative economic impact. Sebastes schlegelii, a farmed Korean rockfish, is particularly prone to copepods and monogeneans. This study comprehended how parasitic copepods and rockfish from a farm in Tongyeong-si, Gyeongsangnam-do, Korea, are related to the monogenean trematode Microcotyle sebastis. Our research revealed that monogeneans predominated, with a rate of 98.4% and an average infection intensity of 7 per infected fish. With an average infection intensity of 4 per sick fish, the infection rate for parasitic copepods was equally considerable, coming in at 91.7%. The high co-infection rate of both parasite families, at 90.8%, is noteworthy. Furthermore, Lepeophtheirus elegans and Peniculus truncatus, 2 parasitic copepod species, were discovered to have M. sebastis eggs attached to their bodies. This demonstrates a connection between parasitic copepod infestations in farmed Korean rockfish and the monogenean trematode M. sebastis. These discoveries highlight the necessity for creating more potent parasite control methods for the aquaculture sector and shed light on the intricate relationships between various parasite species.

The genus Microcotyle in Mediterranean scorpaenoids (Teleostei), including the description of Microcotyle merche n. sp. from Helicolenus dactylopterus (Delaroche, 1809)

More than 65 species of the genus Microcotyle Van Beneden & Hesse, 1863, have been described to date, most of them infecting Perciformes. Among the scorpaenoids (Perciformes, formerly Scorpaeniformes) the species of the genus Microcotyle parasitize sebastids and scorpaenids worldwide. In this study, we provide new morphological and molecular data for Microcotyle spp. in sebastids and scorpaenids from the Western Mediterranean and north-east Atlantic. Specimens of Helicolenus dactylopterus (Delaroche, 1809) (n = 107) and Scorpaena spp. (n = 107) were examined and their microcotylid specimens morphologically and molecularly characterized. Microcotyle merche n. sp. ex H. dactylopterus and specimens of Microcotyle algeriensis Ayadi, Gey, Justine & Tazerouti, 2016 from a new host and locality (Scorpaena scrofa from the north-east Atlantic) are herein described. Both species are phylogenetically close, but their morphology is markedly different mostly because the anterior lobe of the haptor present in other Microcotyle species is almost absent in M. algeriensis. Findings of M. merche n. sp. in the Mediterranean also excludes the presence of Microcotyle sebastis in this sea, encouraging the review of the exceptionally large host range and geographical distribution of this species.

Kannaphallus leptosomus n. sp. (Monogenea: Heteraxinidae: Cemocotylinae) parasitizing Scyris indica (Carangiformes: Carangidae) from Malaysia

A new monogenean species, Kannaphallus leptosomus n. sp., from the gills of the diamond trevally, Scyris indica Rüppell, caught off Terengganu, Peninsular Malaysia is described with molecular data. The new species differs from other species of the genus by the morphology of the largest clamp, the presence of a penis gun-associated needle, the unarmed genital atrium size, and the presence of two independent vaginal tubes. Previous records of Kannaphallus species were compiled, and four nominal species including one species incertae sedis (K. virilis Unnithan, 1957; K. lateriporis Mamaev, 1988; K. leptosomus n. sp.; and K. mochimae Fuentes Zambrano, 1998 incertae sedis) and two undescribed species recorded as invalid names were listed. Cemocotylelloides carangis Ramalingam, 1969 was considered a junior objective synonym of K. univaginalis Ramalingam, 1960; this species was treated as Cemocotylelloides univaginalis n. comb. In addition, Unnithan's materials including type specimens of K. virilis could not be found in specimen repositories in India, and it appears that the specimens were probably not deposited in any institution or have been subsequently lost. Based on the phylogenetic analysis of 28S rDNA sequences, Heteraxinidae was broadly divided into two clades, and Heteraxininae and Cemocotylinae were shown as polyphyletic groups, respectively.