Molecular and morphological analyses reveal that the pathogen Benedenia seriolae (Monogenea: Capsalidae) is a complex species: Implications for yellowtail Seriola spp. aquaculture

Abstract

Monogeneans such as Benedenia seriolae are important pathogens of Seriola spp. that are farmed around the world. In northern Chile, cultures of Seriola lalandi are being developed, and B. seriolae has been recorded in farmed fish and in natural populations. In this study, specimens identified as B. seriolae collected from farmed S. quinqueradiata in Japan were compared with specimens of B. seriolae collected from natural populations of S. lalandi from the northern Chilean coast, and morphometrical and molecular analyses were used to evaluate whether these samples corresponded to the same genetic group. Additionally, our sequences were compared with published sequences of Benedenia spp. from Australia. The morphometrical characteristics of the specimens from Chile and Japan were evaluated using principal component analysis (PCA) and discriminant analysis (DA). For molecular analyses, regions within the 28S ribosomal DNA large subunit (28S rDNA) and mitochondrial gene cytochrome c oxidase 1 (COI) were used. Specimens of S. lalandi from Chile did not exhibit evident morphological (except by a slight difference in penis shape) and morphometrical differences compared with S. quinqueradiata from Japan. For 28S rDNA, the genetic distance between B. seriolae from Chile and Japan was 1.5%. For COI, the genetic distance between B. seriolae from Chile and Japan was 14% and 15.2% for B. seriolae from Chile and Australia. Similarly, the genetic distance between B. seriolae from Japan and Australia was 14.4%. Phylogenetic trees showed three clades: one group from Chile, one from Japan and one from Australia. Thus, our results indicate B. seriolae is a complex species, with three morphologically similar species, each one restricted to a distinct geographic area. Given the differences in biological aspects such as fecundity and development times between species, an effective management strategy to prevent these monogenean epizootics must begin with accurate species identification, which should be considered previous to chemical treatments. Consequently, more biological information must be obtained for B. seriolae from the Chilean coast to understand its developmental timeline and infestation dynamics to control and manage this parasite in farmed yellowtail.