Flagfin or striped mojarras of the Gerreidae Family are a relevant ecological and biological resource in rivers, estuaries and coastal lagoons in tropical areas (^{Aguirre-León and Yáñez-Arancibia, 1986}; ^{Díaz-Ruiz et al., 2003}). They are also a fishing resource locally used as bait, and barely for human consumption (^{Jiménez-Badillo et al., 2006}); however, it is critical to determine if such consumption poses risks to human health. Eucinostomus melanopterus has no records of helminth parasites, while Eugerres plumieri include Caballerorhynchus lamothei and Gorgorhynchoides bullocki from the southeastern Gulf of México (^{Salgado-Maldonado and Amin, 2009}); Cucullanus sp., Contracaecum sp., Hysterothylacium sp., Pseudoterranova sp., Spirocerca sp., Dollfusentis chandleri, G. bullocki, Neodiplectanum wenningeri, Haliotrema sp., Ascocotyle (A.) leighi, Cryptogonimus sp., Diplostomum sp., and Mesostephanus appendiculatoides from Chetumal Bay, Quintana Roo (^{Aguirre-Macedo et al., 2007}; ^{Sánchez-Ceballos et al., 2010}); Aristocleidus hastatus from the Máquinas River, Los Tuxtlas, Veracruz (^{Mendoza-Franco et al., 2009}); and Pleorchis magniporus from Florida, USA (^{Overstreet et al., 2009}). Other helminth parasites have also been recorded in other species from the Gerreidae Family, such as Diapterus auratus (Mendoza-Franco et al., 2009; 2018; ^{Monks et al., 2009}; ^{Zarza-Meza et al., 2016}), Diapterus rhombeus (Mendoza-Franco etal., 2008; Salgado-Maldonado and Amin, 2009) and Eugerres brasilianus (Mendoza-Franco et al., 2008). Therefore, we have a partial knowledge about worm parasites that is infecting E. plumieri, but no knowledge on the helminths that parasitizing E. melanopterus. On this basis, we are describing in the present study the prevalence and mean intensity of parasites for both hosts.

The helminthological study was performed on 19 specimens of E. plumieri [total length 8.4-13.3 cm (11.4 ± 1.1 cm), weight 20.0-98.0 g (51.3 ± 20 g)] and on 14 specimens of E. melanopterus [total length 5.4-13.5 cm (7.9 ± 1.9 cm), weight 3.0-54.0 g (14.7 ± 12.8 g)], which were captured between March and October 2017, in the Arroyo Moreno, Boca del Rio, Veracruz, México (19°06'01'' N -96°06'43'' W and 19°07'07'' N - 96°07'49'' W), by local fishermen using throw nets. Specimens were examined within 24 hours post-capture. All tissues and organs, excepting bones and blood, were reviewed under a stereomicroscope. The parasites were fixed in hot formalin 4 % and preserved in 70 % alcohol. Then, permanent preparations were made, stained with Mayer's Carmine or Gomori's triple stain, cleared with clove oil, and mounted in Canada balsam (^{Lamothe-Argumedo, 1997}; ^{Vidal-Martínez et al., 2001}).

Voucher parasite specimens were deposited at the Colección Nacional de Helmintos, Instituto de Biología, UNAM, México. Prevalence (percentage of infected fish) and mean intensity (average of helminths found in infected fish for each helminth species) were calculated according to ^{Bush et al. (1997)}.

A total of 461 individual helminths (69 in E. melanopterus and 392 in E. plumieri) were recovered, belonging to 12 taxa (five species, five genus and two families). Nine taxa in E. melanopterus: three monogeneans; three digeneans (one adult and two metacercariae); one larval cestode; and two larval nematodes. Eugerres plumieri hosted nine taxa: three monogeneans; four digeneans (three adults and one metacercaria), one larval cestode, and one larval nematode. Helminths with the highest prevalence were Neodiplectanum mexicanum (29 %) infecting E. melanopterus; Aristocleidus hastatus (37 %) and Neodiplectanum mexicanum (32 %) both infecting E. plumieri. Parasites with the highest mean intensity were Crassicutis marina (57) and A. hastatus (31.4 ± 29.5) infecting E. plumieri; Stephanostomum sp. (17.5 ± 23.3) infecting E. melanopterus (Table 1). Six common species were registered in both hosts: A. hastatus, N. mexicanum, C. marina, Stephanostomum sp., and the larvae of Tetraphyllidae and Cucullanus sp. However, the prevalences of parasite species between both hosts showed no difference (p = 0.428, Fisher's exact test). It is essential to highlight that this study contributes to 16 new host records and three new local records (Table 1).

Table 1 Prevalence, mean intensity, and site of infection of helminth parasites in Eucinostomus melanopterus and Eugerres plumieri, from Arroyo Moreno, Boca del Rio, Veracruz, México. 

¹ *, new host record for Eucinostomus melanopterus; **, new host record for Eugerres plumieri; f, new geographical record; l, larva; m, metacercaria; mi, mean intensity; n, number of hosts examined; nhp, number of hosts parasitized; p, plerocercoide; (p%), prevalence.

² G, Gills; I, Intestine.

Regarding new host records, nine species were found in E. melanopterus and seven species in E. plumieri increasing from 16 to 23 known taxa in the latter host, of which it shares the records of Cucullanus sp., with hosts from Chetumal, Quintana Roo (^{Sánchez-Ceballos et al., 2010}), and A. hastatus with hosts from the Tuxtlas, Veracruz (^{Mendoza-Franco et al., 2009}). The prevalences that we recorded for the monogeneans of both hosts were lower than that of Aristocleidus hastatus (100 %) in E. plumieri from Veracruz (Mendoza-Franco et al., 2009) and Neodiplectanum mexicanum (100 %) in D. rhombeus from Campeche (Mendoza-Franco et al., 2008). While for nematodes, even when they are low, they were slightly higher than those registered for Cucullanus sp. (2 %) and Hysterothylacium sp. (3.5 %) parasites of E. plumieri from Chetumal (Sánchez-Ceballos et al., 2010). On the other hand, the number of species registered in the present study, nine species for both hosts, including those of E. plumieri, are less than the 13 species accumulated in hosts from Chetumal, due probably to the sample size (68 hosts, n = 10, ^{Aguirre-Macedo etal., 2007}; n = 58, Sánchez-Ceballos et al., 2010), plus and the conditions of the collection sites. In this respect, the proximity of the river's mouth to the sea could facilitate the presence of hosts and parasites from both fresh and sea water, increasing or decreasing the number of species found in our study compared to that in Chetumal where the conditions can limit the presence of intermediate and definite hosts, regulating intestinal helminth infections (Aguirre-Macedo et al., 2007). Such is the case of acanthocephalan, which was not recorded in the fish species examined here, but they are registered in gerreids from other sites as the southeastern of the Gulf of México (^{Monks et al., 2009}; ^{Salgado-Maldonado and Amin, 2009}), Chetumal (Sánchez-Ceballos et al., 2010), and Tamiahua (^{Zarza-Meza et al., 2016}). The fact that E. melanopterus and E. plumieri share about 50 % of parasite species could be because they belong to the same family and are distributed in tropical latitudes along the Atlantic west coast (^{Aguirre-León and Yáñez-Arancibia, 1986}). For instance, the monogeneans A. hastatus, N. mexicanum, Neodiplectanum magnodiscatum, and Octouncuhaptor eugerrei infect the same hosts in México, Venezuela, and Panama (Mendoza-Franco et al., 2008; 2009). Finally, no species posing zoonotic risks were registered (e.g. Anisakis sp., or Gnathostoma sp.; Salgado-Maldonado et al., 2005), but viral or bacterial infections in fish could be latent (^{Sánchez-Domínguez et al., 2015}), because two municipal plants pour treated water into the Arroyo Moreno (^{López-Portillo et al., 2009}), with all the health risks that this could imply.