Lecithochirium monticellii digenetic trematode parasites of Trichiurus lepturus (Actinopterygii) from the state of Rio de Janeiro, Brazil, with notes on its taxonomy

Trichiurus lepturus (Actinopterygii, Perciformes) is a commercially and economically important fish. A total of 60 specimens of this cutlassfish were collected of the coast the municipalities of Niterói and Cabo Frio, state of Rio de Janeiro, Brazil. The fish were measured, necropsied, filleted and had their organs investigated for digenetic trematodes. Taxonomic identification was based on morphological and morphometric characters. The specimens of T. lepturus were parasitized with adult specimens of Lecithochirium monticellii. Parasite indices of prevalence, intensity, mean intensity, abundance, mean abundance, range of infection, and site of infection of parasitic species were evaluated. Notes on the taxonomy of the parasite were also included. This is the first report of L. monticellii parasitizing T. lepturus in Brazil.


INTRODUCTION
The cutlassfish Trichiurus lepturus, L. 1758 (Actinopterygii, Perciformes), is considered a benthopelagic species and is found on continental shelves and underwater slopes from the surface to 2000 m deep in tropical and temperate waters that are not of low salinity (Nakamura & Parin 1993, Martins & Haimovici 1997. Considered one of the six species with the highest volume of fish landings in the world (Martins & Haimovici 2000, FAO 2005, Martins et al. 2005, Chiou et al. 2006, Bittar et al. 2008, T. lepturus has great commercial importance in the state of Rio de Janeiro (Meyer & Smale 1991, Martins & Haimovici 1997, Figueiredo & Menezes 2000.
Parasites of the genus Lecithochirium Lühe 1901 (Hemiuroidea, Hemiuridae, Lecithochiriinae) are commonly observed in the stomach and intestine of marine teleost fish throughout the world (Yamaguti 1971, Bray 1991, Gibson et al. 2002, Shih et al. 2004, Kohn et al. 2007, Al-Zubaidy 2010, Feki et al. 2016, Claxton et al. 2017. Species of this genus have been described as having complex morphology, with variation in, and different combinations of, internal and external structures that provide specific taxonomic characteristics. As a result, a large number of species have been described for the genus. However, some reviews have considered such differences to be intraspecific variation and thus proposed synonimizing several of the names (Manter 1934, 1954, Linton 1940, Skrjabin & Guschanskaja 1955, Nasir & Diaz 1971, Yamaguti 1971, Bray 1991.
The present study aimed to taxonomically identify specimens of digenetic trematodes in T. lepturus commercialized along the coast of the state of Rio de Janeiro, Brazil, and to present their parasite indices of prevalence, mean intensity, mean abundance, range of infection and infection sites.

MATERIALS AND METHODS
Between June 2017 and February 2018 a total of 60 specimens of Trichiurus lepturus, (74 -142 cm total length, 0.400 -3.0 kg weight) were obtained in small markets selling fish caught from offshore of the municipalities of Niterói (22°53'00" S, 43°06"13" W) and Cabo Frio (22°52'46" S, 42°01"07" W), in the state of Rio de Janeiro, Brazil. The specimens were transported in isothermal boxes with ice to Laboratório de Parasitologia, Instituto Biomédico, Universidade Federal Fluminense, in the municipality of Niterói, state of Rio de Janeiro. The specimens were identified to species according to Figueiredo & Menezes (2000), and then necropsied for analysis of stomach contents and the intestines, which revealed the presence of a species of digenetic trematode. The helminths were fixed with AFA, stained with Semichon carmine or Delafield hematoxylin and whole mounted in Canada balsam (Knoff & Gomes 2012), and then analyzed using a Zeiss Axiophot brightfield microscope. Measurements (in mm) were made with the aid of an Olympus BX-41 brightfield microscope with an ocular micrometer. Measurements are provided as ranges followed by means in parentheses. Taxonomic classification of the parasites followed Gibson et al. (2002). Voucher specimens were deposited in the Helminthological Collection of the Oswaldo Cruz Institute (CHIOC), FIOCRUZ, Rio de Janeiro, RJ, Brazil. Parasitological terminology followed Bush et al. (1997).

RESULTS
Forty-three of the 60 specimens of T. lepturus analyzed were parasitized with a total of 929 adult specimens of a species of digenetic trematode. The majority of specimens were found alive and exhibiting high motility. The parasites included some immatures and exhibited pronounced variability in size, indicating continuous recruitment. The parasites were identified as follows: • , and a long muscular, protrusible, hermaphroditict duct that opens in the genital pore. Genital pore median, at or slightly posterior to pharyngeal level. Ovary rounded, smooth, post-testicular, intercecal, at mid-hindbody or more posteriorly, at some distance from posterior testis, in the same field of testes but in separated zones, margins often obscured by uterine loops. Uterus descending into postvitelline space, reaching ecsoma and filling most of the hindbody, metraterm entering sinus sac ventrally, joining male duct slightly anterior to ejaculatory vesicle. Vitellaria paired, contiguous, overlapping posterior portion of ovary, one tri-and one quadri-lobed with lobes somewhat longer than wide. Eggs small and operculate, numerous. Excretory pore terminal, excretory duct bifurcating posterior to ventral sucker, arms unite dorsally to oral sucker.

DISCUSSION
The morphology and morphometry of the specimens of L. monticelli of the present study are in accordance with the specimens descried by Linton (1940) According to Nasir & Diaz (1971) and Bray (1991) the genus Lecithochirium contains about 100 nominal species, including morphologically and morphometrically closely related species, some of which have been synonimized. It should be noted that when describing L. microstomum from T. lepturus from Galveston Bay, Texas, USA, Chandler (1935) pointed out that the species Distomum monticellli could be a species of Lecithochirium, and that it could even be the same that he had described: "…although some of the forms referred by Linton (1898Linton ( , 1901Linton ( , 1905 to Distomum monticelli may be species of Lecithochirium and may even be identical with the form here described. …". In addition, all six species of Lecithochirium recorded parasitizing marine teleosteal fish in Brazil have morphological structures within the same size range, and L. manteri and L. microstomum have been recorded parasitizing T. lepturus (Kohn et al. 2007). Therefore, we suggest future studies aim to verify the validity of these species.