Digenean trematodes infecting the frigate tuna Auxis thazard (Scombriformes, Scombridae) off the Rio de Janeiro coast, Brazil, including molecular data

Abstract

Although some parasitological efforts have focused on the frigate tuna Auxis thazard (Lacepède) (Scombriformes, Scombridae) in Brazil, its digenean fauna remains poorly known. Combining morphological and molecular methods, we investigated the diversity of digenean trematodes of A. thazard collected from the coastal waters off the state of Rio de Janeiro, Brazil in 2021. Six species belonging to four families were recorded: the bucephalid Rhipidocotyle cf. angusticolle Chandler, 1941, the didymozoid Didymocystis sp. 6 sensu Louvard et al. (2022), the fellodistomid Tergestia sp., and three hemiurids, Dinurus euthynni Yamaguti, 1934, Lecithochirium floridense (Manter, 1934), and L. synodi Manter, 1931. The current study brings the total number of digenean trematode species parasitising A. thazard in Brazil up to eight, with hemiuroid trematodes being most diverse. Auxis thazard is a new host record for L. floridense, L. synodi and potentially for R. angusticolle. The geographic distribution of several species found in our study appeared to be wider than previously known. Our study is the first to apply a DNA-based approach to digenean diversity in marine fishes in Brazil and we believe that both morphological descriptions and molecular sequence data provided in our study will aid future research assessing the diversity of digenean trematodes of A. thazard and other marine fishes in Brazil.

Hemiurid Trematodes (Digenea: Hemiuridae) from Marine Fishes off the Coast of Rio de Janeiro, Brazil, with Novel Molecular Data

“…Specimens selected for molecular analyses (i.e., hologenophores) were processed as described in Faltýnková et al [ 18 ], i.e., a small piece of the body of each specimen was excised and used for DNA extraction and the remaining voucher (hologenophore) was used for morphological evaluation. Specimens fixed in formalin (i.e., paragenophores) and the remaining vouchers were stained in Mayer’s hydrochloric carmine solution and mounted as described in Pantoja et al [ 7 ], and thereafter, used for morphological evaluation. Drawings were made by use of a drawing attachment to a light microscope Olympus BX 51.…”

“…Since the first report on helminth parasites in marine fishes in Brazil in 1819, the discovery of these parasites continues to accelerate, with digenean trematodes shown to be one of the most diverse parasite groups [ 4 , 5 ]. However, our knowledge on the actual species diversity of digenean trematodes, their host associations, life cycles, distributions, and phylogenetic relationships remains limited [ 6 , 7 ]. Furthermore, and despite continued interest in this group of parasites, the diversity of digenean trematodes is not reflected in the available genomic data from Brazil.…”

“…Furthermore, and despite continued interest in this group of parasites, the diversity of digenean trematodes is not reflected in the available genomic data from Brazil. To date, there are only five species for which DNA sequence data is available [ 7 ].…”

“…The Hemiuridae is the second most species-rich family among fish digeneans in marine ecosystems in Brazil [ 9 ]. A total of 28 species from 10 genera are known to parasitise fishes from 28 families of 17 orders in Brazil [ 7 , 9 ]. The majority of species were reported from fishes of the family Carangidae (Carangiformes) collected off the Rio de Janeiro coast [ 9 , 15 , 16 ].…”

“…The majority of species were reported from fishes of the family Carangidae (Carangiformes) collected off the Rio de Janeiro coast [ 9 , 15 , 16 ]. Only recently were the first DNA sequences of Brazilian marine digenean trematodes published, with three of them being of hemiurids [ 7 ].…”