Diversity of Parasites in Two Sympatric Species of Brazilian Tetras (Characiformes: Acestrorhamphidae) in the Caatinga Domain, Northeastern Brazil

Abstract

This study investigates the parasitic biodiversity of the fish species Astyanax bimaculatus and Psalidodon fasciatus in a stream located in the Chapada do Araripe Environmental Protection Area (APA), state of Ceará, Brazil, contributing to the understanding of parasitic fauna diversity of freshwater fish in neotropics. In total, 292 fish specimens were collected and analyzed, identifying 13 parasite taxa in A. bimaculatus and 11 in P. fasciatus. Several parasite groups were identified, including myxozoans, monogeneans, digeneans, and nematodes. The host A. bimaculatus exhibited a higher number of parasite taxa and abundance compared to P. fasciatus. The lower sample size for P. fasciatus reflects its naturally lower abundance in the wild, but the analyses accounted for sampling bias, ensuring comparisons of the parasite communities of these two fish species. The parasite communities of both species showed high similarity, indicating potential host-switching or co-evolutionary patterns. Positive correlations were observed between parasite diversity, species richness, abundance, and host weight/length. The study expands the knowledge of parasite–host associations and the geographical distribution of parasite species in Northeastern Brazil, a region where such data remain underreported.

1. Introduction

Parasites are a fundamental part of communities and ecosystems and are often neglected in fauna survey studies [1,2,3,4]. Inventories of these organisms have an important role in biodiversity studies [5] because these studies allow for understanding the biogeography, phylogeny, and distribution of parasite populations and their intermediate and definitive hosts [6]. Due to their long-term close association with a wide variety of invertebrate forms, fish exhibit a greater quantity and diversity of parasites than any other group of vertebrates [7]. These organisms are ubiquitous components in freshwater fish and highly sensitive to environmental or anthropogenic disturbances [8,9].

Characiformes is an order of Actinopterygii fishes that encompasses 210 genera and 1674 species exclusively of freshwater habitats [10,11]. The South American continent has the largest diversity of freshwater fishes in the world, including the Acestrorhamphidae family with a total number of 685 species identified [12], including species allocated to the genus Astyanax Baird and Girard (1854) and Psalidodon Eigenmann, 1911. These genera include fishes that are popularly known in Brazil as “piabas” or “lambaris” [13]. They are very diverse genera in freshwater ichthyological fauna in the Neotropical region, having about 150 species that are very abundant in the Brazilian hydrographic basin, especially in Brazilian Northeast [14].

In addition to the difficulty in characterizing a typical Caatinga ichthyofauna, studies on the parasitofauna are scarce for the region under study. One factor to be considered regarding the importance of conducting studies on the diversity and structure of parasitic biological communities in these areas is the fact that these environments present a high degree of endemism and reduced physical dimension, making these works a priority, given their environmental vulnerability. Despite the high diversity of hosts, only a few studies on fish parasites are available for freshwater systems in Northeastern Brazil. An inventory of the parasitofauna of freshwater fish in Brazil, conducted by Eiras et al. (2010) [15], documented 1034 parasitic associations in 451 species of freshwater fish. In Northeastern Brazil, recent studies have been carried out by Silva et al. (2020 and 2021) [16,17], Carvalho et al. (2021 and 2022) [18,19], Diniz et al. (2022) [20], Alexandre et al. (2022) [21], Antunes et al. (2022) [22], Sousa et al. (2022, 2023, and 2024) [23,24,25], Yamada et al. (2024) [26], and Falkenberg (2024) [27], which registered 267 parasite–host associations.

Phylogenetically related fish species that share the same habitat are more likely to have a similar composition of parasites in their parasitic community structure. This similarity may be shaped by evolutionary processes like co-speciation or host-switching and further enhanced by common or generalist parasites infecting hosts that coexist in sympatry [28]. Among freshwater fishes, especially in intermittent systems, closely related species in the same habitat have greater access to a shared pool of local parasites, leading to high similarity in their parasite communities [29]. Although host phylogeny has been shown to have a limited impact on parasite diversity and community structure, similarities in parasite communities can still emerge among fish species with similar ecological traits, such as size, habitat preferences, trophic level, and depth distribution [30,31,32,33,34,35,36,37,38].

In this sense, the present study aimed to inventory the parasitic biodiversity of the fish species A. bimaculatus and P. fasciatus from streams located in an area of Chapada do Araripe APA in the municipality of Crato, Ceará state, Brazil. For this, we analyzed the parasitic communities in these two sympatric fish species, investigating their diversity, abundance, and similarity among parasitic populations, as well as correlating these aspects with host characteristics. Our hypothesis is that these two sympatric fish species, with similar ecological characteristics and phylogenetically closely related will have similar parasitic fauna.

2. Results

A total of 292 hosts were analyzed, being 242 A. bimaculatus (standard length range: 3.39–12.31 cm) and 50 P. fasciatus (standard length range: 3.34–6.4 cm). A. bimaculatus exhibited higher parasite species richness (13 taxa) compared to P. fasciatus (11 taxa). Additionally, A. bimaculatus showed higher diversity and evenness indices (H = 2.012; E = 0.784) than P. fasciatus (H = 1.176; E = 0.490). Parasite prevalence ranged from 0.80% to 31% in A. bimaculatus and from 2% to 28% in P. fasciatus (

Table 1. Fish parasites of A. bimaculatus from the Batateiras River, municipality of Crato, Ceará state, Brazil. Site of infestation/infection (SI), number of hosts parasitized (HP), prevalence (P), mean intensity (MI), mean abundance (MA), confidence interval (CI), and Poulin’s discrepancy index (D).

Parasite	SI	HP	P% (CI)	MI (CI)	MA (CI)	D
Myxozoa
Henneguya sp.	Gills	2	0.8 (0.01–3.0)	9.5 (4.0–9.5)	0.08 (0–0.34)	0.99
Monogenea
Anachantocotyle anachantocotyle *	Gills	21	8.7 (6.0–13.0)	2.1 (1.5–3.1)	0.18 (0.10–0.32)	0.94
Characithecium costaricense	Gills	75	31.0 (25.0–37.0)	3.01 (2.37–3.97)	0.93 (0.69–1.28)	0.84
Characithecium sp. 1 *	Gills	63	26.0 (21.0–32.0)	4.52 (3.56–5.83)	1.18 (0.82–1.64)	0.86
Characithecium sp. 2 *	Gills	20	8.3 (5.0–12.0)	1.35 (1.1–1.5)	0.11 (0.06–0.16)	0.93
Diaphorocleidus sp. 1	Gills	67	27.7 (22.0–34.0)	4.49 (3.54–6.0)	1.24 (0.88–1.74)	0.85
Diaphorocleidus sp. 2	Gills	21	8.7 (5.0–13.0)	6.81 (4.57–9.57)	0.59 (0.31–1.03)	0.95
Urocleidoides trinidadensis	Gills	68	28.1 (22.0–34.0)	2.29 (1.88–2.83)	0.64 (0.47–0.85)	0.83
Digenea
Ascocotyle sp.	Gills	6	2.5 (0.9–5.3)	2.0 (1.17–2.83)	0.05 (0.02–0.11)	0.98
Diplostomidae gen. sp.	Eyes	2	0.8 (0.1–3.0)	3.0 (2.0–3.0)	0.02 (0–0.08)	0.99
Wallinia caririensis	Intestine	49	20.2 (15.4–25.9)	9.69 (7.01–13.7)	1.96 (1.36–3.05)	0.91
Nematoda
Procamallanus (Spirocamallanus) hilarii	Intestine	29	12.0 (8.2–16.8)	1.69 (1.38–2.14)	0.2 (0.13–0.32)	0.91
Spiroxys sp.	Mesentery	3	1.2 (0.3–3.6)	1.33 (1.0–1.67)	0.02 (0–0.04)	0.99

* New record of parasite–host association.

and

Table 2. Fish parasites of P. fasciatus from the Batateiras River, municipality of Crato, Ceará state, Brazil. Site of infestation/infection (SI), number of hosts parasitized (HP), prevalence (P), mean intensity (MI), mean abundance (MA), confidence interval (CI), and Poulin’s discrepancy index (D).

Parasite	SI	HP	P% (CI)	MI (CI)	MA (CI)	D
Monogenea
Characithecium costaricense	Gills	4	8.0 (2.2–19.2)	1.5 (1.0–1.75)	0.12 (0.02–0.28)	0.91
Dactylogyridae gen. sp.	Gills	1	2.0 (0.1–10.6)	2.0	0.04 (0–0.12)	0.96
Diaphorocleidus sp. 2 *	Gills	1	2.0 (0.1–10.6)	2.0	0.04 (0–0.12)	0.96
Diaphorocleidus kabatai	Gills	14	28.0 (16.2–42.5)	10.4 (6.27–17.3)	2.92 (1.53–5.83)	0.85
Gyrodactylus sp. 1 *	Gills	1	2.0 (0.1–10.6)	2.0	0.04 (0–0.12)	0.96
Gyrodactylus sp. 2 *	Gills	1	2.0 (0.1–10.6)	1.0	0.02 (0–0.06)	0.96
Trinibaculum pinctiarum	Gills	10	20.0 (10.0–33.7)	3.0 (1.9–4.81)	0.6 (0.28–1.28)	0.86
Digenea
Diplostomidae gen. sp. *	Eyes	5	10.0 (3.3–21.8)	1.6 (1.0–2.2)	0.16 (0.04–0.34)	0.91
Wallinia caririensis	Intestine	2	4.0 (4.0–13.7)	2.0	0.08 (0–0.2)	0.94
Nematoda
Procamallanus (Spirocamallanus) hilarii	Intestine	7	14.0 (5.8–26.7)	1.71 (1.0–3.0)	0.24 (0.08–0.58)	0.89
Spiroxys sp.	Mesentery	1	2.0 (0.1–10.6)	1.0	0.02 (0–0.06)	0.96

* New record of parasite–host association.

). It is important to note that the lower sample size for P. fasciatus reflects its naturally lower abundance in the wild. This justifies the observed differences in parasite diversity, evenness, taxa richness, and abundance between the two host species. The data presented are consistent with ecological patterns of host availability and parasite–host interactions. A comprehensive list of all parasite records in hosts of the genera Astyanax and Psalidodon from the Neotropical region is provided in Table S1 of the Supplementary Materials.

The parasite component communities of the two host species showed high similarity in both presence/absence (Jaccard similarity index = −0.06; p = 0.904) and abundance (Bray–Curtis similarity index = −0.09; p = 0.965). Furthermore, A. bimaculatus presented significantly higher diversity (U = 3.1596; p < 0.05), evenness (U = 3.9165; p < 0.05), and abundance (U = 3.5882; p < 0.05) in its parasite community compared to P. fasciatus. Positive correlations were observed between Shannon–Wiener diversity index (H), species richness, parasite abundance, and the host’s weight and length (host characteristics) (

Table 3. Correlation between host characteristics and parasite diversity metrics for A. bimaculatus and P. fasciatus from the Batateiras River, municipality of Crato, Ceará state, Brazil. Spearman correlation coefficients (rs) and associated p-values (p) are shown for each correlation. All the results are significant (p < 0.05).

Host Species	Correlation	rs
A. bimaculatus	Shannon vs. host length	0.42
	Richness vs. host length	0.44
	Abundance vs. host length	0.45
	Shannon vs. host weight	0.40
	Richness vs. host weight	0.43
	Abundance vs. host weight	0.45
P. fasciatus	Shannon vs. host length	0.70
	Richness vs. host length	0.70
	Abundance vs. host length	0.69
	Shannon vs. host weight	0.68
	Richness vs. host weight	0.70
	Abundance vs. host weight	0.69

).

The similarity analyses showed that the parasite infracommunities of the two host species were similar (ANOSIM; r = −0.054, p = 0.93). The SIMPER analyses revealed that the parasite species contributing most to this similarity were the monogeneans D. kabatai (22.9%), Diaphorocleidus sp. 1 (17.7%), C. bifurcuprolatum (14.7%), C. costaricensis (8.0%), T. pinctiarum (6.9%), Diaphorocleidus sp. 2 (6.4%), and U. trinidadensis (5.4%), along with the digenean W. caririensis (13.2%) and the nematode P. (S.) hilarii (4.6%). The NMDS analysis clearly shows that the parasite infracommunities of the two host species are significantly similar (Figure 1), which is supported by the ANOSIM results.

3. Discussion

Parasite communities in sympatric hosts with comparable ecological traits and close phylogenetic relationships often exhibit similar patterns of parasite community structuring, particularly when these hosts have overlapping diets in their habitat [39]. This study corroborated the observed similarity in parasite infracommunity structure among sympatric hosts. The parasite infracommunities of A. bimaculatus and P. fasciatus, which share similar ecological characteristics and are phylogenetically related, were found to be significantly similar, as demonstrated by the ANOSIM and NMDS analyses. These findings reinforce the idea that ecological and phylogenetic factors play a key role in shaping parasite communities in closely associated host species.

The similarity observed in the parasite infracommunities of both host species suggests possibilities of host-switching events or co-evolutionary dynamics [40,41,42]. Phylogenetically related host species may harbor similar parasite communities due to shared evolutionary history [43]. Parasites often have co-evolved with their hosts, so closely related hosts may have similar susceptibility to specific parasites. Host behavior and habitat use can lead to exposure to similar parasites [44]. Parasites also can be shared by two host species through processes like host-switching or spillover [45]. If two host species are closely linked ecologically, parasites may transfer between them, leading to similarities in their parasite communities [46]. Both hosts inhabit the same environment and likely share similar resources, which can facilitate the transmission and establishment of shared parasite species. These findings align with previous studies [47,48], which suggest that sympatric hosts with overlapping diets and ecological niches often exhibit comparable parasite communities.

Through a review of parasitic helminths in South American fishes, Luque et al. (2017) [49] concluded that the Monogenea species represent the group with the highest richness, with 835 species recorded in different countries and 1133 host–parasite associations, followed by the Digenea species with 662 species recorded and 1127 host–parasite associations. The co-evolutionary associations, host-switching, and adaptations of the parasites with fish may be among the mechanisms to explain the high success of Monogenea and Digenea in their respective habitats [50]. The high richness of these two groups is interpreted as a result of site specialization, life cycle adaptation, and dietary specialization. The fact that the Monogenea species are still more diversified than the Digenea species may be associated with the development time and monoxenous life cycle, whereas the life cycle of the Digenea species is more complex due to the multiple hosts they infect, namely, a heteroxenous life cycle [50].

There are other reasons why the Monogenea species exhibit high richness: they are extremely diversified in terms of their morphological structures, primarily by the morphology of the haptor (attachment organ), which plays a crucial role in the specialization and adaptation of parasites to hosts; they have a well-resolved phylogeny (at least at the family level) and tend to exhibit host specificity, with most species infesting only one or very few host species [51]. This specificity can be understood as a result of a co-speciation process between the parasite and host and other adaptive and non-adaptive processes such as speciation through host-switching [52,53,54,55].

Several studies have described the structure of parasitic communities of the genus Astyanax and Psalidodon [22,56,57,58], noting that P. fasciatus was previously classified within the genus Astyanax [13]. According to Lizama et al. (2008) [56], studies of parasitic communities in these genera demonstrate that such species serve as intermediate hosts for various species of endoparasites, with a wide variability in the diversity of stages, a fact that may consider these species as “potential faunal indicators” [59]. The SIMPER analysis identified specific parasite species, such as the monogeneans D. kabatai and Diaphorocleidus spp., and the digenean W. caririensis as major contributors to the similarity between the parasite communities. These species may have broader host specificity or higher ecological plasticity, allowing them to exploit both host species effectively.

The results indicate that there is a significant correlation between the diversity and abundance of parasites (measured through the Shannon index and parasite richness and abundance) and host characteristics (host length and weight), both for A. bimaculatus and P. fasciatus. The positive correlation values between the Shannon index, richness, and abundance of parasites and host length indicate that as the host length increases, the diversity and abundance of parasites also increase. This can be explained by larger hosts generally having greater availability of resources and space, which may favor the colonization and establishment of a higher richness and abundance of parasites [60,61].

Similarly, the results show a positive correlation between the diversity and abundance of parasites and host weight. This suggests that heavier hosts may harbor a greater diversity and quantity of parasites. This can be attributed to the availability of food resources and the fact that heavier hosts can sustain a higher parasite load [62,63]. The relationship between host length and parasite diversity/abundance has important implications in parasitic ecology and community dynamics [64]. Therefore, in this study, the results suggest that host size plays an important role in determining parasite richness and abundance, with larger hosts having a more diverse and numerous communities of parasites.

In conclusion, this study significantly contributes to the understanding of parasitic biodiversity in freshwater fish, especially in species from the Neotropical region, being possible to identify seven new parasite–host associations. The high similarity in parasitic infracommunities between the two sympatric fish species, A. bimaculatus and P. fasciatus, suggests a possible relationship between phylogeny, habitat-sharing, and diet in structuring these communities. Additionally, the identification of new occurrences of parasites in both species expands knowledge about the geographical distribution of these organisms. These results reinforce the importance of parasitological studies in conservation areas, such as Chapada do Araripe APA region, for understanding the dynamics of parasitic communities and their relationship with the health of aquatic ecosystems. More studies regarding this may provide valuable insights for biodiversity conservation and sustainable management of natural resources in the region.

4. Materials and Methods

4.1. Study Area

The hydrographic basin of Northeastern Brazil is partly influenced by the Caatinga domain [65], among them the Salgado sub-basin. The main river of this sub-basin is the Salgado, formed by the confluence of the Batateiras River, which is the main tributary of the right bank of the Jaguaribe River [66]. The Salgado River has a length of 308 km and drains an area of 12,636 km² covering 24 municipalities, totaling 9% of Ceará state territory. The region located between the Salgado sub-basin has four conservation units whose borders extend beyond the sub-basin boundaries, including the Chapada do Araripe Environmental Protection Area (APA) and the Sítio Fundão State Park where the Batateiras River is born in the municipality of Crato, Ceará state, Brazil [67].

The collections were performed in the Batateiras River (Figure 2), which is located between latitude 7°13′54.21″ S and longitude 39°26′11.66″ W and the climate according to the Köppen classification is BSh (semi-arid climate). The rate of evaporation typically exceeds the rate of precipitation causing high temperatures during most of the year, with rainfall concentrated in a short period [68].

4.2. Host Collection and Laboratory Procedures

Four collections were made between August and December 2018 and February and June 2019. The hosts were collected using different fishing gear like cast nets, dip nets, and trawl nets. After sampling, the fish were individualized in plastic bags, frozen, and taken to the laboratory for parasitological analysis. From each captured fish, the following data were collected: sampling date and location, standard length (cm), total weight (g), and sex. The fish specimens were identified by experts from the ichthyological collection of the Universidade Federal da Paraíba (UFPB).

4.3. Parasitological Analyzes

Fish body, fins, nasal cavity, and gills were examined for ectoparasites. The gills were removed and placed in petri dishes and examined for ectoparasite helminths using a stereomicroscope. After external analyses, a longitudinal incision in the ventral surface was made, and all internal organs were removed and separated. The visceral cavity and all organs were examined using a stereomicroscope to find endoparasites. All helminths collected were preserved in 70% ethanol solution. For parasite identification, the methods used to enhance the visualization of structures varied according to the parasite group: Myxozoa specimens were gel-mounted to visualize the spores; Monogenea specimens were mounted on permanent slides using Grey–Wess medium for the study of sclerotized structures (hooks, anchors, haptor bars, vagina, and copulatory complex); Digenea specimens were stained with Carmine and mounted in slides with Canada balsam; Nematoda specimens were clarified with lactic acid and mounted in semipermanent slides [69]. The identification was according to Cohen et al. (2013) [70], Moravec (1998) [71], and Thatcher (2006) [7].

4.4. Statistical Analysis

The parasite communities were analyzed at infracommunity (all the individuals of all parasite species in an individual fish) and component community (all the parasites in a sample of a given fish species) levels [72]. The ecological descriptors of the prevalence, mean intensity, and mean abundance of infestation/infection were calculated for each component of parasitic communities according to Bush et al. (1997) [72]. These indices are presented with the confidence intervals (95% confidence level) and the Poulin’s dispersion index (D), as suggested by Reiczigel et al. (2019) [73]. The discrepancy index was calculated to evaluate the distribution of parasite species within host populations [74]. To measure the similarity of parasitic communities between the two host species, the Jaccard (J) and the Bray–Curtis (B) indices were used. The Jaccard index is based on the presence and absence of sampled local species and ranges from 0 (different) to 1 (similar). The Bray–Curtis index (B) takes into account the differences in abundance of each parasite species shared between the two hosts [75,76]. Mean abundance, species richness, and Shannon index between both hosts were compared using the Mann–Whitney (U) test. A Spearman’s rank correlation coefficient (rs) analysis was conducted to evaluate the relationship between host characteristics and parasite diversity metrics. An analysis of similarity (ANOSIM) was conducted to test for differences in parasite communities between the two fish species. A similarity percentage analysis (SIMPER) was also used to identify which parasite taxa contributed most to the community’s similarity. Additionally, a two-dimensional non-metric multidimensional scaling (NMDS) plot was generated to visualize the parasite community structure in the two fish species, offering a graphical representation of community similarities [77]. For similarity analyses, the data were transformed using a base-10 logarithm. Statistical analyses were made using Statistica software version 7.1 and PAST software. The level of significance used was p < 0.05.