Patterns of genetic variation and life history traits of Zeuxapta seriolae infesting Seriola lalandi across the coastal and oceanic areas in the southeastern Pacific Ocean: potential implications for aquaculture

A century of parasitology in fisheries and aquaculture

Fish parasitological research associated with fisheries and aquaculture has expanded remarkably over the past century. The application of parasites as biological tags has been one of the fields in which fish parasitology has generated new insight into fish migration and stock assessments worldwide. It is a well-established discipline whose methodological issues are regularly reviewed and updated. Therefore, no concepts or case-studies will be repeated here; instead, we summarize some of the main recent findings and achievements of this methodology. These include the extension of its use in hosts other than bony fishes; the improvements in the selection of parasite tags; the recognition of the host traits affecting the use of parasite tags; and the increasingly recognized need for integrative, multidisciplinary studies combining parasites with classical methods and modern techniques, such as otolith microchemistry and genetics. Archaeological evidence points to the existence of parasitic problems associated with aquaculture activities more than a thousand years ago. However, the main surge of research within aquaculture parasitology occurred with the impressive development of aquaculture over the past century. Protozoan and metazoan parasites, causing disease in domesticated fish in confined environments, have attracted the interest of parasitologists and, due to their economic importance, funding was made available for basic and applied research. This has resulted in a profusion of basic knowledge about parasite biology, physiology, parasite-host interactions, life cycles and biochemistry. Due to the need for effective control methods, various solutions targeting host-parasite interactions (immune responses and host finding), genetics and pharmacological aspects have been in focus.

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.

Under the radar: co-introduced monogeneans (Polyopisthocotylea: Gastrocotylinea) of the invasive fish Scomberomorus commerson in the Mediterranean Sea

The Levant Basin is in many ways the world's most invaded marine ecosystem owing to the existence of the man-made Suez Canal. The invasion of free-living organisms through this pathway is increasingly documented and monitored in the past two decades, and their ecological impact recognized. Nonetheless, while tremendous scientific effort is invested in documenting introduced fishes, co-introduction events of these fishes and their parasites have drawn relatively little interest. In our research, we examined the presence of gill parasites (Monogenea) on the invasive narrow barred Spanish mackerel Scomberomorus commerson which has been known in the Mediterranean Sea for 80 years. The gills of S. commerson supported numerous, relatively large monogeneans (Monogenea: Gastrocotylinea), reaching prevalence levels of 100% with a mean intensity of ~ 80 worms per host. Using an integrated molecular and morphological approach, four gastrocotylinean species were identified: Gotocotyla acanthura, Cathucotyle cathuaui, Pricea multae, and Pseudothoracocotyla ovalis. Two species, C. cathuaui and P. ovalis, are reported here for the first time from the Mediterranean. Sequences of the 28S rRNA gene of G. acanthura from native hosts, Pomatomus saltatrix and Trachinotus ovatus, differed from individuals collected from S. commerson by 1.8%. We therefore suggest that the taxonomic status and distribution of G. acanthura should be revisited, and we recommend an integrated approach as essential to accurately detect co-introductions.

Redescription of Zeuxapta seriolae (Meserve, 1938) and Zeuxapta australica Lebedev, 1968 (Monogenea: Heteraxinidae)

Redescription is given of heteraxinid monogeneans Zeuxapta seriolae (Meserve, 1938), type species of the genus, and Zeuxapta australica Lebedev, 1968 (formerly Z. seriolae australica). Type specimens of Z. seriolae from Seriola dorsalis from Galápagos Islands were differentiated from Z. australica specimens collected by Lebedev from Seriola glandis (now Seriola lalandi) from Tasman Sea, the type locality, by the shape of the vagina, which consisted of the transversely oval central body and horizontally extended paired tubes in the former, and the transversely oval central body and short, obliquely posteriad paired extensions in the latter. Zeuxapta japonica (Yamaguti, 1940) and Zeuxapta kahala (Yamaguti, 1968) were synonymized with Z. seriolae. Hitherto undescribed Zeuxapta specimens were also examined; those from Seriola aureovittata from Japan and China, and specimens from Seriola dumerili from Japan and Spain were identified as Z. seriolae, while those from Seriola lalandi from Chile and New Zealand were identified as Z. australica. Specimens from S. lalandi (as Seriola glandis) from Heron Island, Australia described by Rohde in 1978 as Z. seriolae consisted of Z. seriolae and Z. australica.

First Report of Blood Fluke Pathogens with Potential Risk for Emerging Yellowtail Kingfish (Seriola lalandi) Aquaculture on the Chilean Coast, with Descriptions of Two New Species of Paradeontacylix (Aporocotylidae)

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).

Towards the resolution of the Microcotyle erythrini species complex: description of Microcotyle isyebi n. sp. (Monogenea, Microcotylidae) from Boops boops (Teleostei, Sparidae) off the Algerian coast

The monogenean Microcotyle erythrini is atypical because it has been recorded from several fish host species in the Mediterranean Sea and Atlantic Ocean, in contrast to many species which are considered strictly specific. This could indicate a true lack of specificity or that several cryptic species are involved. This paper is a partial attempt to solve this problem. Specimens of a monogenean resembling M. erythrini were collected from bogues, Boops boops, caught off Algeria. A comparison with published descriptions and with museum specimens of M. erythrini did not yield any clear morphological difference. However, sequences of cytochrome c oxidase subunit I (COI) differed by 16.3% from that of M. erythrini (from GenBank, material collected from the type-host Pagellus erythrinus), indicating that the species was different. The species from B. boops is therefore described here as Microcotyle isyebi n. sp. and differential diagnoses with Microcotyle species from the Mediterranean and from sparids are provided. These results suggest that a molecular re-evaluation of other M. erythrini-like specimens from various fish hosts could reveal the existence of additional parasite biodiversity.

Morphological and molecular analyses of Pseudomazocraes sulamericana n. sp., Pseudomazocraes selene Hargis, 1957, Cemocotyle carangis (MacCallum, 1913) and Zeuxapta seriolae (Meserve, 1938) (Monogenea: Mazocraeidea) from carangid fishes in the south-western Atlantic Ocean

An integrative taxonomy approach was followed to analyse morphological and molecular characters of the monogenean species Pseudomazocraes selene, Cemocotyle carangis and Zeuxapta seriolae; specimens were collected from the gills of the carangid fishes Selene vomer, Caranx latus and Seriola lalandi caught off the coasts of the states of Rio de Janeiro and Santa Catarina, Brazil. The research revealed the presence of Pseudomazocraes sulamericana n. sp., which can be differentiated from other congeners by the shape of clamps mid-sclerite possessing a ventral piece bifurcated at the end, with large and right-angled edges of almost the same length, and by the shape of larval hooks and rounded terminal lappet. New genetic sequences include partial 28S and 18S rDNA genes for all species, ITS1 and 5.8S rDNA for Zeuxapta seriolae and Cemocotyle carangis, and ITS2 and mtDNA cox1 for C. carangis. The phylogenetic concatenated analysis based on partial 28S rDNA and 18S rDNA sequences confirmed the position of C. carangis and Z. seriolae within the Heteraxinidae. The previous phylogenetic position of Chauhaneidae was discussed based on morphological studies and it is now confirmed by molecular data that Chauhaneidae is the sister group of Allodiscocotylidae and Protomicrocotylidae.

Microcotyle visa n. sp. (Monogenea: Microcotylidae), a gill parasite of Pagrus caeruleostictus (Valenciennes) (Teleostei: Sparidae) off the Algerian coast, Western Mediterranean

Parasite biodiversity of fish of the southern part of the Mediterranean sea is still incompletely explored. We describe here Microcotyle visa n. sp. from the gill filaments of the bluespotted seabream Pagrus caeruleostictus (Valenciennes) (Sparidae) collected off the Algerian coast. The identity of fish hosts was confirmed by barcoding. Microcotyle visa n. sp. is herein described and illustrated. Analysis of the cox1 gene of the monogeneans revealed minor intraspecific variation (1.4%), an order of magnitude lower than the distance between this species and other Microcotyle species (10-15 %). Microcotyle visa n. sp. is distinguished from Microcotyle erythrini van Beneden & Hesse, 1863, a congener infesting sparids, on the basis of morphological (size of clamps, number of testes) and molecular (cox1) differences. This is the fourth member of the genus known to parasitise a sparid host. A species of Paramicrocotyle sp. included in the molecular analysis was nested within a robust Microcotyle + Paramicrocotyle clade; in the absence of demonstrated molecular and morphological differences, we consider that Paramicrocotyle Caballero & Bravo-Hollis, 1972 is a junior synonym of Microcotyle van Beneden & Hesse, 1863 and transfer two species of Paramicrocotyle as Microcotyle danielcarrioni (Martinez & Barrantes, 1977) n. comb. and Microcotyle moyanoi (Villalba & Fernandes, 1986) n. comb.

Spatio-temporal patterns of genetic variations in populations of yellowtail kingfish Seriola lalandi from the south-eastern Pacific Ocean and potential implications for its fishery management

The genetic population structure and genetic diversity of yellowtail kingfish Seriola lalandi from the coastal south-eastern Pacific Ocean (SEP) were evaluated at spatiotemporal scale in order to understand the ecology of this species. Between 2012 and 2015, temporal and spatial population genetic structure and a low genetic diversity were detected in S. lalandi from SEP. These results suggest that S. lalandi specimens arriving annually from offshore to the SEP coast could come from at least two genetically distinct populations, revealing a particular life strategy (i.e. reproductive or habitat segregation) for this fish species. Therefore, the SEP coast might constitute a point of population mixing for this species. Additionally, the low genetic diversity of S. lalandi in the SEP could be a result of a founder effect or overfishing. Regardless of the process explaining the genetic diversity and structure of S. lalandi in this geographical area, this new information should be considered in order to implement successful fishery management of this resource in the South Pacific.