Metazoan parasite communities of three endemic cichlid fish species from the upper Grijalva River, Chiapas, Mexico

In the neotropics, the family Cichlidae (Perciformes: Actinopterygii) constitutes a diverse group of freshwater fishes, with around 50 genera and 500 species (Kullander, 1998; Chakrabarty, 2004). In Mexico, cichlids are represented by 57 species belonging to 11 genera, whose diversity is mostly found in hydrological systems from southeastern Mexico, such as the Grijalva River Basin (GRB), which is considered a regional centre of endemism for cichlids (Miller et al., 2005; Soria-Barreto & Rodiles-Hernández, 2008; Lowe-McConnell, 2009; Gómez-González et al., 2015).

To date, more than 200 parasitic helminth species have been recorded in 237 species of cichlids from Africa and America (Vanhove et al., 2016). In Mexico, this fish family is well studied (Vidal-Martínez et al., 2001) and harbours the highest helminth richness (69 species), followed by Goodeidae (51) and Ictaluridae (40) (Garrido-Olvera et al., 2012; Martínez-Aquino et al., 2014). However, there are few data on the metazoan parasites and their communities in endemic cichlids of Mexico, such as Chiapaheros grammodes (Taylor & Miller, 1980), Vieja breidohri (Werner & Stawikowski, 1987) and V. hartwegi (Taylor & Miller, 1980). These cichlids inhabit the upper GRB and are considered endangered species (DOF, 2010; Salgado-Maldonado, 2011). In order to know the biodiversity of metazoan parasites from aquatic vertebrates in Mexico, the main goal of this study was to determine the metazoan parasite fauna of these three endemic cichlid species in the upper GRB, and to describe their metazoan community structure in terms of taxonomic composition, species richness and diversity. We hypothesize that metazoan communities of the three endemic cichlids have low species richness and diversity with a similar composition of species like that of their congeners in the Southern Mexico. Moreover, it will be characterized by the presence of high number of digenean and specialist parasites.

Fishes were collected from the Angostura Dam (upstream) (16°06’28.4”N; 92°41’26.9”W) and Columbus Lakes (downstream) (15.2°42’31.9”N; 92°39’13”W), both located in the upper GRB (Fig. 1). A total of 84 C. grammodes (total length: 6.13 – 10.66 cm), 180 V. breidohri (9.5 – 14.56 cm) and 153 V. hartwegi (11.33 – 15.95 cm) were captured between November 2008 and July 2009 in both localities, using a 2 m diameter cast net with a 2.5 cm mesh. Living fish were transported in separated containers with artificial aeration to El Colegio de la Frontera Sur (ECOSUR), San Cristobal de las Casas, Chiapas, Mexico. Fishes were euthanized with a 100 mg/L of benzocaine until opercular movements ceased. Parasites were counted, preliminarily identified and fixed depending on the taxonomic group (Vidal-Martínez et al., 2001). Individual parasites were isolated from each organ, cleaned with physiological saline and preserved in vials with 4 % formalin or 70 % alcohol (Moravec et al., 1995).

Fig. 1

Platyhelminthes (trematodes, cestodes), hirudineans and acanthocephalans were stained with Carmine as described by Vidal-Martínez et al. (2001). Nematodes and pentastomids were cleared in graded solutions of glycerine-water (Moravec et al., 1995; Silva et al., 2015). Infection parameters, such as prevalence, mean abundance and mean intensity were those proposed by Bush et al. (1997), whereas parasite species were classified as autogenic (i.e., mature in fishes or other aquatic hosts, are incapable of crossing land barriers between freshwater bodies) and allogenic (i.e., mature in mammal or bird hosts and use fish only as intermediate and paratenic host) (Esch et al., 1988; Salgado-Maldonado et al., 2016). Moreover, parasites were assorted as specialists (i.e., those restricted to one species, genus or host family) and generalists (i.e., those parasitizing several – two or more – host families) (Rohde, 1993).

Infracommunities were described by the mean number of parasite species, individual helminths, and Brillouin diversity index (IDB) (Krebs, 1989). For component communities ecological descriptors were analysed at the diversity, richness and dominance levels (Holmes, 1987). Shannon-Wiener index (H) as a measure of diversity, Shannon evenness index (equitability of the species present) (J) and Berger-Parker index (IBP) as a measure of the numerical dominance, were also calculated (Krebs, 1989). A Kruskal-Wallis test (H) was used to determine the significant differences in the community component parameters among different host species (Sokal & Rohlf, 1995). The Spearman range coefficient (rs) was used to correlate the values of J with the diversity of the communities of the three cichlid species (Krebs, 1999).

The research related to animal use has been complied with all the relevant institutional policies for the care and use of animals in Mexico (DOF, 2001).

A total of 18 metazoan parasite taxa (11 adults and 7 larval stages): 1 Monogenea, 6 Digenea, 1 Cestoda, 4 Nematoda, 2 Acanthocephala, 1 Hirudinea, 1 Pentastomida and 2 Copepoda, were found in 417 fishes. Out of the hosts examined, 390 (90 %) were infected by at least one parasite taxon. Sixteen parasite taxa were present in V. breidohri, 15 in V. hartwegi and 14 in C. grammodes. Seven of the 18 parasite taxa were collected from the digestive tract (intestine and stomach), 5 in gills, 3 in fins, 2 in eyes, muscles and mesenteries and 1 in liver. Digeneans were the richest group in the three cichlid species, with 4 metacercariae and 2 adult forms. The monogenean Sciadicleithrum bravohollisae Kritsky, Vidal-Martínez & Rodríguez-Canul, 1994 and the nematode Cucullanus angeli Cabañas-Carranza & Caspeta-Mandujano, 2007 are considered as specialists, while the remaining 16 were generalists. Twelve taxa were cataloged as autogenic and 6 larval stages as allogenic; while 14 metazoans were endoparasites and 4 ectoparasites (Table 1).

Chiapaheros grammodes and V. hartwegi are new host records for 16 taxa, while all parasites in V. breidohri are new reports. Prevalence ranged 1−78 % in the three cichlids, with Crassicutis cichlasomae Manter, 1936 in V. breidohri and V. hartwegi (78 % and 72 %, respectively) and Contracaecum sp. type 2 and Diplostomum (Austrodiplostomum) cf. compactum (Lutz, 1928) in C. grammodes (69 % and 62 %, respectively) as those with the highest values. On the other hand, Raillietnema kritscheri Moravec, Salgado-Maldonado & Pineda-López, 1993 in V. hartwegi (8 ± 66.06 and 48.16 ± 144.5), Posthodiplostomum cf. minimum (4.02 ± 5.11 and 11 ± 7.60) and C. cichlasomae (9 ± 13.11 and 11.07 ± 14.1) in V. breidohri, and Neoergasilus japonicus (Harada, 1930) in C. grammodes (4 ± 6.35 and 16 ± 17.19) and V. breidohri (1.16 ± 3.98 and 23.33 ± 25.47), were the species with the highest values of mean abundance and intensity, respectively (Table 1).

Parasite infracommunities showed low diversity, number of species and individual metazoans in the three cichlid hosts. The mean species number was variable (1.94 ± 1.44−2.28 ± 1.21) and relatively higher in C. grammodes, while V. hartwegi showed higher number of individuals (17.11 ± 47.06) than the two other cichlid hosts. The IDB index was similar in the three cichlid species, but relatively higher in C. grammodes (0.03) than in V. breidohri and V. hartwegi (Table 2). The overall component community had values similar in all descriptors among cichlids (Table 2). Total species number was identical in V. breidohri (16), V. hartwegi (15) and C. grammodes (14). The average number of parasites per individual host was 19, with V. hartwegi as the host with the highest number of individual parasites (2984). The H index had little variation in the three cichlid species, although it was relatively higher for C. grammodes (2.97). The J index had a range of 0.48-0.50, but was relatively high in C. grammodes.

Evenness (J) was positively correlated with diversity values in the communities of the three cichlid species (rs = 8.43; p < 0.03), meaning that the most diverse communities were those with the higher uniformity in species abundance. The IBP oscillated between 0.21−0.39, but was relatively high in V. hartwegi. The dominant metazoan species for C. grammodes, V. breidohri and V. hartwegi were P. cf. minimum, C. cichlasomae and R. kritscheri, respectively (Table 2). There were significant differences in the mean individual numbers of parasite species among different host species (H = 99.21; p = 0.001).

The parasite fauna of the three species of cichlids from the upper GRB is composed of 18 taxa, all of them have been previously reported in other cichlids from Southeastern Mexico (Campeche, Chiapas, Oaxaca, Quintana Roo, Tabasco, Veracruz and Yucatan) (Salgado-Maldonado et al., 1997, 2005; Vidal-Martínez et al., 2001; Violante-González & Aguirre-Macedo, 2007; Violante-González et al., 2008a; Salgado-Maldonado, 2008, 2011, 2016) and in other fish families (Atherinidae, Clupleidae, Eleotridae, Goodeidae, Mugilidae, Pimelodidae and Profundulidae) (Montoya-Mendoza et al., 2004; Salgado-Maldonado et al., 2005; Martínez-Aquino et al., 2014; Pinacho-Pinacho, 2015). Despite this fact, almost all parasites reported herein represent new host and geographical records probably due to hosts have been poorly parasitologically studied or not studied at all (e.g. V. breidohri) in the Grijalva river basin. The parasites species were shared among the three cichlid species, as a consequence of their phylogenetic relationships, similar feeding habits, and low host specificity of helminths (Salgado-Maldonado et al., 2005; Salgado-Maldonado, 2008).

The number of parasites species recovered from C. grammodes (14), V. breidohri (16) and V. hartwegi (15) was relatively higher than those reported by Vidal-Martínez et al. (2001) and Salgado-Maldonado (2011) in C. grammodes (6) and V. hartwegi (1) from Chiapas and for others cichlids species; e.g., Thorichthys helleri (Steindachner, 1864) (5) from Tabasco, Cichlasoma trimaculatum (Günter, 1868) (12) in Guerrero and C. fenestratum (Günter, 1860) (11) in Veracruz (Jiménez-García, 1993). These differences could be a consequence of the abundance of intermediate hosts in the region, size, diet and geographic range of examined hosts. The feeding habits of V. breidohri and V. hartwegi consist mainly of aquatic plants, detritus and invertebrates (Rodiles-Hernández and González-Díaz, 2006, Ceballos et al., 2016) that could have favored the consumption of snails, such as Pyrgophorus coronatus (Pfeiffer, 1840), Biomphalaria obstructa Morelet, 1849 and B. helophila (d’Orbigny, 1835), which are present in the region and involved in the life cycles of many metazoans (see Aguirre-Macedo et al., 2011, 2016; Martínez-Aquino et al., 2017). On the other hand, C. grammodes feeds mainly on aquatic insects (e.g., Trichoptera, Odonata, Megaloptera) and small fish. Differences in the feeding items might generate variation on the species richness, diversity and infection parameters between host species (see Violante-González et al., 2008a, b; Gómez-González et al., 2015).

Digeneans were the most abundant and dominant group of helminths in the three endemic cichlids. This pattern agrees with that found by Violante-González et al. (2008a), who reported several digenean species in C. trimaculatum. Digeneans are also the numerically dominant group in many parasite communities of freshwater fishes in Mexico (Salgado-Maldonado et al., 2005; García-Prieto et al., 2014). Apparently, its high abundance in cichlids has been linked to the shallow waters and high productivity of aquatic systems that encourage the occurrence of intermediate (mollusks) and definitive hosts (fish-eating birds) (Aguirre-Macedo et al., 2011, 2016).

The higher proportion of adult stages (11) and autogenic species (12) suggests that these cichlids play an important role as definitive hosts for most helminth taxa in the upper GRB and that these metazoans mature within the aquatic environment. Occurrence of Schyzocotyle acheilognathi (Yamaguti, 1934) in the three cichlids represent new host records for this Asiatic parasite that was introduced into Mexico along with carp (Cyprinus carpio Linnaeus, 1758) (Salgado-Maldonado & Pineda-López, 2003; Suárez-Morales et al., 2010). Neoergasilus japonicus (also co-introduced along with C. carpio) has been recently reported from the same hosts/sites from the upper GRB (see Suárez-Morales et al., 2010), while S. acheilognathi has already been recorded in all Mexican states (with exception of Baja California) (Salgado-Maldonado & Rubio-Godoy, 2014).

Infracommunities showed low species richness, number of individuals and diversity, like those in Cichlasoma istlanum (Jordan & Snyder, 1899), C. synspilum Hubbs, 1935 and C. trimaculatum from Guerrero and Campeche (Vidal-Martínez & Kennedy, 2000; Violante-González et al., 2008a). Probably, the main factors structuring the infracommunities were the feeding habits and variation in the availability of infective larval stages. These factors structured the infracommunities through the accumulation of free-living cercariae (e.g., D. (A.) cf. compactum, C. cf. complanatum and P. cf. minimum), or ingestion of infected preys, such as snails (e.g., C. cichlasomae) or small crustaceans (e.g., Contracaecum sp. type 2) (Aguirre-Macedo et al., 2011, 2016). The feeding habits of V. breidohri and V. hartwegi consist mainly of aquatic plants and a wide variety of snails (Gómez-González et al., 2015), that could have favoured the parasite infections of intermediate hosts (e.g., snails P. coronatus, B. obstructa and B. helophila), involved in the life cycles of many metazoans (Aguirre-Macedo et al., 2011, 2016; Martínez-Aquino et al., 2017). On the other hand, C. grammodes feeds mainly on aquatic insects (e.g., Trichoptera, Odonata, Megaloptera) and small fish that might produce little variation on their community descriptors (species richness, diversity) and infection parameters (mean abundance) between host species (Violante-González et al., 2008a,b; Gómez-González et al., 2015).

Overall component communities in the three cichlids were poor in species and number of metazoans, when comparing with other tropical cichlids: Mayaheros urophthalmus (Günther, 1862) group (= Cichlasoma urophthalmum) (38 species), Parachromis managuensis (34 species), Thorichthys helleri (32 species), Vieja fenestrata (= Cichlasoma fenestratum) (37 species) and Petenia splendida (27 species) (Salgado-Maldonado & Kennedy, 1996; Salgado-Maldonado et al., 2005). Generally, helminth communities in freshwater fish are isolationist in structure and stochastic in composition, thus reflecting their low species richness and diversity (see Vidal-Martínez & Kennedy, 2000; Kennedy, 2006; Salgado-Maldonado et al., 2019). This pattern is probably due to several factors, such as geography and geology (contemporary and past) of regions and drainages, different environmental conditions, historical ecology of both hosts and parasites, feeding behavior and specializations of the host, which contribute to the structuration of the communities of parasites (Choudhury & Dick, 2000).

Helminth species reported herein have clearly a Mesoamerican affinity and some with relatively high host specificity (i.e., C. angeli and S. bravohollisae), parasitizing almost exclusively cichlid fishes (Aguilar-Aguilar et al., 2008; Salgado-Maldonado, 2008). Others (i.e, P. cf. minimum, Contracaecum sp. type 2, D. (A.) cf. compactum, Ergasilus sp.), due to their low host specificity, have extended their distribution to some other regions of the Mexican highlands; while some others represent introduced and broadly distributed parasites (i.e., S. acheilognathi and N. japonicus). In conclusion, the parasite community of C. grammodes, V. breidohri and V. hartwegi is similar to that reported for other cichlids in Southeastern México and characterized by the presence of typical parasites of cichlids, with a high number of digenean and generalist parasites.

The authors fully declare that there is no financial or other potential conflict of interest.