Abstract
Blood flukes are digeneans that infect wild and farmed fish that can cause a severe and potentially lethal disease in farmed fish. These parasites are undetectable in the larval stage based on macroscopic observations in the definitive host with the infection becoming evident when eggs accumulate in the branchial vessels. There are nine known species of the genus Paradeontacylix and seven exclusively parasitize Seriola spp. from several geographical areas. Seriola lalandi aquaculture farms are emerging at various localities in northern Chile. Here, we report, for the first time, two blood fluke species parasitizing S. lalandi in the Southeastern Pacific (Chile). In the laboratory, the gills and heart of fish were removed. The retained blood flukes were separated according to the infection site, fixed in 70% or 95% ethanol for taxonomic and molecular analysis, respectively. Morphometrical differences among the fluke species were evaluated with a principal component analysis (PCA) using proportional body measurements. Phylogenetic trees were constructed based on 28S rDNA, cox1 mDNA using Bayesian inference (BI), and maximum likelihood (ML). Based on morphology, morphometry, and molecular analyses, two new species are proposed: P. humboldti n. sp. from the gills and P. olivai n. sp. from the heart of S. lalandi. Both were clearly distinguished from other species of Paradeontacylix by a combination of morphologic features (posterior tegumental spines, testes arrangement, body size). The genetic distance (based on cox1) among species was >10%. P. humboldti n. sp. and P. olivai n. sp. are sister species (with a common ancestor) independent of P. godfreyi from S. lalandi in Australia. The newly identified parasites may pose a risk to farmed S. lalandi as aporocotylids have been the cause of diseases in farmed fish from other geographical areas. In addition, some cages of S. lalandi are currently maintained in an open circulating system, which could favor the transmission of these parasites (if involved hosts are present in the environment).
Highlights
Blood flukes are digeneans that infect the circulatory systems of wild and farmed fish [1,2,3] and can cause a severe disease in farmed Seriola spp. [4,5,6,7]
By analyzing new DNA sequences from P. humboldti n. sp. and P. olivai n. sp., our analysis complemented the previous analyses on the phylogenetic relationships between species of Paradeontacylix reported [15,16]
We found that P. godfreyi from S. lalandi in the Indian Pacific Ocean, south Australia, is located at the basal position within the Paradeontacylix spp. clade with strong nodal support
Summary
Blood flukes are digeneans that infect the circulatory systems of wild and farmed fish [1,2,3] and can cause a severe disease in farmed Seriola spp. [4,5,6,7]. Hatching miracidia may cause multiple lesions and microhemorrhages, which in turn can trigger an inflammatory response and result in anemia [5]. This is especially the case when a massive hatch occurs, as has been reported for Sanguinicola inermis in Cyprinus carpio [9] and Cardicola sp. In Sparus aurata [10] This pathology could be harmful in the aquaculture industry due this infection becoming evident when eggs accumulate in the branchial vessels and the fish become moribund [11]. The disease has been reported to be responsible for important losses regarding Seriola dumerili aquaculture, reaching 50–80% of the mortalities among fish in the 0+ and 1+ classes [5,12,13]
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