Abstract
BackgroundThe monogenean Benedenia seriolae parasitizes fishes belonging to the genus Seriola, represents a species complex, and causes substantial impact on fish welfare in aquaculture systems worldwide. This study reports, for the first time, the complete mitochondrial genome of B. humboldti n. sp., a new cryptic species from the South-East Pacific (SEP).MethodsThe mitogenome of B. humboldti n. sp. was assembled from short Illumina 150 bp pair-end reads. The phylogenetic position of B. humboldti n. sp. among other closely related congeneric and confamiliar capsalids was examined using mitochondrial protein-coding genes (PCGs). Morphology of B. humboldti n. sp. was examined based on fixed and stained specimens.ResultsThe AT-rich mitochondrial genome of B. humboldti is 13,455 bp in length and comprises 12 PCGs (atp8 was absent as in other monogenean genomes), 2 ribosomal RNA genes, and 22 transfer RNA genes. All protein-coding, ribosomal RNA, and transfer RNA genes are encoded on the H-strand. The gene order observed in the mitochondrial genome of B. humboldti n. sp. was identical to that of B. seriolae from Japan but different from that of B. seriolae from Australia. The genetic distance between B. humboldti n. sp. and B. seriolae from Japan was high. Minor but reliable differences in the shape of the penis were observed between Benedenia humboldti n. sp. and congeneric species.ConclusionsPhylogenetic analyses based on PCGs in association with differences in the shape of the penis permitted us to conclude that the material from the South-East Pacific represents a new species of Benedenia infecting S. lalandi off the coast of Chile. The discovery of this parasite represents the first step to improving our understanding of infestation dynamics and to develop control strategies for this pathogen infecting the farmed yellowtail kingfish, Seriola lalandi, in the South-East Pacific.
Highlights
The monogenean Benedenia seriolae parasitizes fishes belonging to the genus Seriola, represents a species complex, and causes substantial impact on fish welfare in aquaculture systems worldwide
The protein-coding genes (PCGs) atp8 is lacking in the mitochondrial genome of B. humboldti n. sp., in agreement with that reported for the remaining monogeneans whose mitochondrial genomes have been assembled and annotated [15]
The gene order observed in B. humboldti n. sp. is identical to that reported in B. seriolae from Japan and the congeneric Benedenia hoshinai Ogawa, 1984 [35]
Summary
The monogenean Benedenia seriolae parasitizes fishes belonging to the genus Seriola, represents a species complex, and causes substantial impact on fish welfare in aquaculture systems worldwide. Monogeneans exhibit direct development and do not require an intermediate host to complete their life-cycle, in contrast to that reported for other parasitic flatworms (i.e. digeneans [1]). Monogenean infestations in farmed fish can and do become pathogenic and outbreaks often result in substantial health issues to the fish population in aquaculture systems worldwide [2, 3]. The presence of large numbers of Benedenia spp. parasites during outbreaks causes considerable skin irritation to fish and results in the fish ‘rubbing’ themselves along the bottoms and sides of tanks/cages. Benedenia spp. cause skin injuries in fish that often lead to secondary infections by opportunistic pathogens such as bacteria and/or fungi [5]. Genomic resources are limited in monogenean parasites and this poor knowledge is constraining our understanding of infection mechanisms, virulence and pharmacological resistance, among others, in this and other groups of ectoparasites (but there are exceptions [6, 7])
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