Abundance of Procamallanus (Spirocamallanus) inopinatus (Nematoda: Camallanidae) in Characiformes fish and associated factors in Midwest Brazil

Abstract

The success of Procamallanus (Spirocamallanus) inopinatus infection in fish involves a complexity of variables. This study aims to evaluate the relationship between abundance of P. (S.) inopinatus with biometric and somatic parameters, sex, relative condition factor (Kn) and hosts diet, as well as to evaluate length relationship of the parasites and the hosts. The fishes were collected by the mesh method and data, length, weight, sex, gonad and liver weight, Gonadosomatic index (GSI) and hepatosomatic index (HSI), Kn and stomach content were recorded. Twenty-seven specimens of P. (S.) inopinatus were collected in the intestine from Serrasalmus rhombeus and 52 from Leporinus friderici. In general, the prevalence, mean intensity and mean abundance of infection was higher in L. friderici. The total abundance was explained by the variables GSI, HSI total length, gonad and liver weight. Fish relative condition factor (kn) and sex were not influenced by the infection, being that the parasite infection did not impair the body condition of the hosts. There is no relationship between host length and parasite length in any of the evaluated fish species. On average, S. rhombeus parasites are 0.69 cm larger than L. friderici parasites.

Key words
Fish parasite; food guild; lotic environment; nematoda; parasitological descriptors

INTRODUCTION

Nematoda of the genus Procamallanus Baylis, 1923 (Camallanidae, Procamallaninae) are predominantly parasites of freshwater fish (Moravec 1998). In South America, these parasites occur in Argentina, Paraguay, Peru, Venezuela and Brazil (Moravec et al. 1997, Kohn et al. 2011, Tavares-Dias et al. 2017, Oliveira et al. 2018, Morais et al. 2019, Ramallo et al. 2020, Rivadeneyra et al. 2020). Camallanid nematodes, such as Procamallanus (Spirocamallanus) inopinatus Travassos, Artigas & Pereira, 1928 infects several South American freshwater fish, including the ones living in Brazil (Neves et al. 2020). Infection by P. (S.) inopinatus can induce pathological lesions and reduce host fitness. Brycon cephalus (Characiformes) parasitized by P. (S.) inopinatus showed ulcer and necrosis in the intestine and decreased weight (Rivadeneyra et al. 2020). However, no harm was observed in infected Serrasalmus rhombeus (Linneaus, 1776) (Lima 2010) and Leporinus friderici Bloch, 1794 (Oliveira et al. 2017). In general, nematodes do not cause great damage to wild fish. Nevertheless, the fish health can be compromised by environmental stress increasing their susceptibility to parasitic harm (Cohen et al. 2020).

Host fish size, considered an expression of its age, has continuous growth throughout life that, in a way, influences the size of parasitic infrapopulation, as well as the abundance of parasites, showing that this density can increase with the size and age of the host, which will allow a larger body surface area available for attachment (Poulin & Leung 2011, Tavares-Dias et al. 2014). Besides, several abiotic factors influence the parasites abundance, such as physical and chemical properties of the water, depth of the habitat, seasons (Tavares-Dias et al. 2017, Oliveira et al. 2018, Morais et al. 2019) and geographic factors (Cantatore & Timi 2015) and other factors can be influence the parasite infrapopulation size such as environmental changes, period of exposure of the fish to the parasites and type of food ingested by the host (Moreira et al. 2005, Poulin & Leung 2011, Takemoto et al. 2009, Bellay et al. 2013, Tavares-Dias et al. 2014).

Prevalence, intensity, and abundance of P. (S.) inopinatus are dependent on population densities of intermediate and definitive hosts present in aquatic ecosystems (Blasco-Costa et al. 2015), as well as on predator-prey interaction associated to the parasitic infection (Neves et al. 2020). Thus, acquisition and maintenance of parasites in host fish are explained by heterogeneous behavior patterns, which are considered the main factors that explain the non-uniformity of parasitic abundance (Amarante et al. 2016).

In Brazil, P. (S.) inopinatus was found in five orders as Characiformes, Cichliformes, Osteoglossiformes, Pleuronectiformes and Siluriformes with 71.6% of freshwater teleost species parasitized by this nematode species belong to the order Characiformes (Neves et al. 2020). The wide distribution of P. (S.) inopinatus in freshwater ecosystems in Brazil was associated with its low specificity for host fish (Yamada & Takemoto 2013, 2017, Morais et al. 2019, Neves et al. 2020). Nonetheless, only two records were reported in the Tocantins River basin, at the UHE Lajeado reservoirs and the São Salvador UHE reservoir (Yamada & Takemoto 2013), and the knowledge concerning parasitic fauna and host-parasite interactions of these Characiformes species remain scarce in this basin.

The knowledge of parasitic fauna of freshwater fish has made it possible to draw up lists of the biodiversity of helminths from different basins. Such information can further be used to examine the ecosystem function and evaluate their state of conservation in the neotropical zone (Salgado-Maldonado 2006, Salgado-Maldonado & Rubio-Godoy 2014). Thus, the current study aimed to evaluate the relationship between abundance of P. (S.) inopinatus with biometric and somatic parameters, sex, relative condition factor (Kn) and total diet of the two host fish species S. rhombeus and L. friderici from the upper Tocantins river basin, Midwest Brazil, as well as to evaluate the length relationship of the parasites and the length of the hosts. The association of organs such as liver and gonads, total length, weight, and relative body condition factor (Kn) to parasite abundance is an important method to understand the ecological relation between host and parasite (Pavanelli et al. 2013). Furthermore, the abundance of P. (S.) inopinatus are dependent on population densities of intermediate and definitive hosts present in aquatic ecosystems (Blasco-Costa et al. 2015), as well as on predator-prey interaction associated to the parasitic infection (Neves et al. 2020).

MATERIALS AND METHODS

The study was carried out on the Traíras River (Figure 1a-c), one of the main tributaries of the Maranhão River, both belonging to the Hydrographic Basin of the Tocantins-Araguaia River, located in the municipality of Niquelândia, State of Goiás, Brazil (Segplan 2019). Four sampling sites (S1, S2, S3 and S4) are located in the Private Reserve Legado Verdes do Cerrado (Figure 1c). This study was approved by the Chico Mendes Institute for Biodiversity Conservation - ICMBio (process n. 02010.000260/01-73) and by the Biodiversity Authorization and Information System - SISBIO (process n. 71279-1) and was developed in accordance with the principles adopted by the National Council for the Control of Animal Experimentation (CONCEA) and with approval from the Ethics Committee in the Use of Animals of State University of Goiás (N° 003 - CEUA/ UEG).

Figure 1
Sampling sites along the Traíras River basin, municipality of Niquelândia, State of Goiás, Brazil. (a) map of Brazil with delimitation of the Cerrado Biome; (b) map of the State of Goiás, with emphasis on the municipality of Niquelândia; (c) map of the Traíras River basin and sampling sites (S1 to S4) in the Private Reserve Legado Verde do Cerrado (dashed area), Niquelândia, Goiás, Brazil.

A total of 17 specimens of S. rhombeus and 23 specimens of L. friderici were collected during October 2019 and January 2020 (Tables SI and SII in Suplementary Material) by the mesh method (waiting nets) using meshes with openings between 12, 15, 25, 40, 50 and 80 mm between opposite nodes accordingly to Oliveira & Tejerina-Garro (2010) with modifications. Fish species were identified according to Melo et al. (2005). Afterwards, the fish were anesthetized in clove-oil-derived eugenol (250 mg L^-1) in a 13-L box (45.5 x 30 x 10 cm) and euthanized by hypothermia (Aydin & Barbas 2020). Next, the biometric parameters of fish, such as total length (TL) (cm), standard length (SL) (cm), total weight (TW) (g), were measured. Fish were stored in a polystyrene box with ice and transported to the laboratory and kept in a freezer (-20 °C) until further analysis. All the fishes were defrosted and necropsied for parasites analysis. The eyes, gills, muscle and visceras were carefully dissected and individualized in a Petri dish with physiological solution (0.8% NaCl) (Eiras et al. 2006) and examined under a stereoscopic microscope (STEMI 508; Zeiss, UK).

Relative body condition factor was determined by the following equation: Kn = (observed total weight / expected total weight) (Le Cren 1951). Gonadosomatic index (GSI) and hepatosomatic index (HSI) were determined by the following equations: GSI = (gonad weight / total weight) x 100 and HSI = (liver weight / total weight) x 100 (Muniz et al. 2016), respectively. Furthermore, four gonadal maturation stages (immature, maturing, mature, and spawned) were established for females and males according to color, transparency, superficial vascularity, flaccidity, size and position in the abdominal cavity and, specifically in the case of ovaries, the degree of oocytes visualization (Vazzoler 1996).

Nematodes were collected under a stereomicroscope (STEMI 508; Zeiss), fixed by immersion in Alcohol-Formaldehyde-Acetic Acid - AFA (Ethanol 70º GL; Formalin 40%; Glacial Acetic Acid P.A. 100%) solution for 24 h, then preserved in 70% ethanol, followed by clarification with four drops of Amann’s Lactophenol solution (Eiras et al. 2006). Identification and characterization of nematodes were based on dichotomous keys (Moravec 1998, Thatcher 2006), updated by articles from new records (Oliveira et al. 2017, Tavares-Dias et al. 2017, Morais et al. 2019). Nematodes were identified, and recorded using a STEMI 508 stereomicroscope (Zeiss) associated with the AxioCam 105 color camera and the ZEN Blue 2.6 software. Life stage, morphological structures, and sex were determined on a light microscope (Olympus, US).

For scanning electron microscopy (SEM) analysis, the nematodes were fixed by immersion in 10% paraformaldehyde for 4 h, washed in 0.2 M PBS buffer at pH 7.2, dehydrated in an increasing series of ethanol (70% and 100%), dried with liquid carbon dioxide (CO₂) in a critical point dryer (Autosamdri® 815 A). Then, the dry parasites were coated with gold in a Denton Vacuum Sputter Coater (Denton Vacuum, LLC, Moorestown, NJ, USA) and analyzed by a scanning electron microscope (SEM) (Jeol JSM-6610).

Prevalence, mean intensity and mean abundance of parasites were determined according to Bush et al. (1997). Thus, the prevalence was estimated by dividing the number of fish parasitized by the number of fish analyzed multiplied by 100; the mean intensity was obtained by dividing the number of parasites found by the number of parasitized fish; and the mean abundance was calculated by dividing the number of parasites found by the number of fish analyzed. Additionally, the parasites total length (TL) (mm) was measured using a microscope with an eyepiece micrometer (Olympus, US).

After dissecting the fish, stomachs were fixed by immersion in 10% formalin for 30 days (Magnoni 2009) and subsequently kept in 70% ethanol. Stomach content analysis was based on the method of volumetric or gravimetric frequency (volume of the item in relation to total volume of food in the stomachs) (Kawakami & Vazoller 1980). For diet composition, the degree of gastric repletion (0-3) was recorded (Hyslop 1980). Food items consumed by the fish were classified into six categories: i) plant material - flowers and leaves (new or disintegrating); ii) fish - whole fish or pieces, scales, pieces of fins and skeleton; iii) insect - immature stages and adult insects (aquatic and terrestrial); iv) sediment - various granulometries and with different amounts of algae, organic matter and debris; v) crustacean - crab and shrimp legs, shrimp, crab, copepods; vi) seeds.

Student t-test was used to evaluate whether the two fish species and sex differ in relation to the (Kn) (Siegel 1975). Also, Pearson’s correlation was used to assess the relationship between parasite length and host length. Monte Carlo test with 1000 randomizations was used to determine the accuracy of Student t-test. All analyses were conducted in the WPerm package in R. Furthermore, Fisher’s non-parametric test was used to assess whether the abundance of parasites has any effect on the host sex. This analysis was used based on the fact that normality and homoscedasticity assumptions were not achieved according to the Shapiro-Wilk and Levene tests, respectively. The Fisher’s non-parametric test was conducted in GraphPad Prism 6.

To investigate the influence of biometric parameters and total diet of the hosts on the abundance of parasites, model selections were made using the Akaike’s Information Criterion (AIC) (Burhman & Anderson 2002). This analysis consists of the construction of several linear regression models with the selection of those that best explain the variable of interest. The AIC values were corrected considering the sample size (AICc), thus models with delta value AICc <2 were considered as good models (Burhman & Anderson 2002). Before conducting the models selection, the existence of collinearity between the biometric variables of the hosts was evaluated using the Variance Inflation Factor. Variables with VIF> 10 were considered collinear (Alin 2010). Thus, the variables used to predict abundance of parasites in L. friderici were length, Kn, gonad weight, GSI, liver weight, HSI and total diet. For the models of S. rhombeus, length, Kn, gonad weight, HSI and total diet were used. Variance Inflation Factor was calculated using the vifstep function of the usdm package (Naimi 2017) in RStudio software (R Core Team 2020). Linear regressions and model selection were performed using the Sam program (Rangel et al. 2010). The significance level of p<0.05 was assumed for all analyses. Graphics were made using GraphPad Prism 6 software.

RESULTS

A total of 79 specimens of P. (S.) inopinatus was collected in the hosts intestinal lumen, of which 27 was found in S. rhombeus and 52 in L. friderici from S1, S2, S3 and S4 (Figure 1). The total infection prevalence in S. rhombeus and L. friderici was 53% (9 parasitized/17 analyzed) and 74% (17/23), respectively. The mean intensity and mean abundance were 3.0 ± 1.7 (ranging from 1–5 parasites per infected host) and 1.59 ± 0.9 (1–2 parasites per analyzed host) in S. rhombeus, and 3.06 ± 1.0 (2–4 parasites per infected host) and 2.26 ± 0.6 (1–3 parasites per analyzed host) in L. friderici, respectively. Biometric parameters and somatic indexes of both host fish (S. rhombeus and L. friderici) are recorded (Table SI, SII).

To assess whether infection by P. (S.) inopinatus influenced the biometric parameters and somatic indexes of the hosts, several models were generated by linear regression to explain the abundance of parasites in L. friderici (n = 127 models) and in S. rhombeus (n = 31 models). The best model to explain the parasitic abundance in L. friderici includes the variables TL, gonad weight, GSI, liver weight and HSI (R² = 0.65; delta AIC = 0). The length proved to be the most important variable among the linear regression models for L. friderici (Importance = 0.91). However, when this variable was analyzed independently, it was not considered ideal to explain the abundance of parasites (R² = 0.14; delta AIC = 6.67), as it was not significant (rs = -0.07; p = 0.73). In opposition, the best model for S. rhombeus included only the gonadal weight (R² = 0.08; delta AIC = 0) (Importance = 0.38). Nevertheless, another four models with unique variables were also considered to be relevant for S. rhombeus (delta AIC <2), and include total diet (R² = 0.06; delta AIC = 0.48) (Importance = 0.30), HSI (R² = 0.03; delta AIC = 1.01) (Importance = 0.25), total length (R² = 0.007; delta AIC = 1.46) (Importance = 0.24) and Kn (R² = 0.004; delta AIC = 1.51) (Importance = 0.21).

Parasitic abundance did not influence the IGS of L. friderici (R² = 0.009; delta AIC = 10,055), while the IGS of S. rhombeus was not selected for analysis with the linear regression models because it was excluded by the Variance Inflation Factor (VIF> 10). Regarding L. friderici gonadal maturation stages, 41.18% were in immature stage, 5.88% in maturing stage, 17.65% mature stage and 35.29% in spawned stage.

Results showed high percentage of S. rhombeus (58.8%) and L. friderici (73.9%) infected by P. (S.) inopinatus. Among the infected S. rhombeus, 55.6% were male and 44.4% female, while 41.2% of infected L. friderici were male and 58.8% female. However, total parasite abundance did not differ significantly between sexes of both fish hosts (Fisher’s exact test, p = 0.26).

The relative condition factor (Kn) of L. friderici (1.00 ± 0.15) and S. rhombeus (1.01 ± 0.11) showed no significant difference between infected and non-infected fish (t = 0.028; p = 0.97) (Figure 3).

Figure 3
Relative condition factor (Kn) of Leporinus friderici (1.00 ± 0.15) and Serrasalmus rhombeus (1.01 ± 0.11) not infected and infected by Procamallanus (Spirocamallanus) inopinatus. Fish were collected in the Traíras river, upper Tocantins river basin, Goiás. Results are expressed as mean values ± 95% confidence intervals.

Serrasalmus rhombeus presented a carnivore feeding behavior ingesting mainly small fish and insects, while L. friderici ingested a wide variety of food items, such as plant material, terrestrial insect, crustacean, sediment, fish and seeds (Table II). Food items and their volumes varied between fish species from the same site and among each fish species from different sampling sites. The total diet of S. rhombeus influenced the abundance of parasite (R² = 0.063; delta AIC = 0.485) (Importance = 0.30). However, total diet did not change the parasitic abundance in L. friderici (R² = 0.002; delta AIC = 10.231).

Table I
The total length mean (mm) (mean ± SD) in 26 (XXVI) infrapopulations of Procamallanus (Spirocamallanus) inopinatus of Leporinus friderici (I-XVII) and Serrasalmus rhombeus (I-IX) from the Traíras river, upper Tocantins river basin, Goiás. N: Number of parasitized hosts, nº: number gravid females, n.o.: no observation, (n): number of parasites collected from each hosts.

Hosts Characicformes and infrapopulations (n)		Mean length		Gravid females
	N	Non-gravid Female	Male	n°	Mean length
Leporinus friderici	17
I (2)		-	-	2	12.99±8.5
II (2)		n.o.	-	2	n.o.
III (3)		-	-	3	25.73±4.6
IV (2)		-	-	2	23.85±0.4
V (1)		-	-	1	18.40±0
VI (1)		-	-	1	20.32±0
VII (1)		-	-	1	17.95±0
VIII (1)		-	-	1	20.77±0
IX (1)		-	-	1	19.25±0
X (4)		-	-	4	20.89±1.6
XI (1)		-	-	1	21.32±0
XII (1)		13.67±0	-	0	-
XIII (1)		-	-	1	17.32±0
XIV (21)		n.o.	n.o.	0	-
XV (3)		-	15.87±0	-	-
XVI (2)		-	-	2	19.86±1.4
XVII (5)		11.36±3.9	-	0	-
Serrasalmus rhombeus	9
I (5)		-	-	5	30.95±2.8
II (7)		-	-	7	27.35±5.9
III (2)		n.o.	-	2	n.o.
IV (1)		-	-	1	20.21±0
V (3)		27.91±0.9	-	0	-
VI (2)		-	-	2	25.68±6.0
VII (3)		-	-	3	26.27±6.0
VIII (2)		-	-	2	20.84±0.5
IX (2)		n.o.	-	2	-

Table II
Volume (cm³) of food items obtained from the stomachs of Leporinus friderici and Serrasalmus rhombeus from the Traíras River, upper Tocantins River Basin, Goiás. N: Number of stomachs analyzed, n.o.: no observation. Results are express as mean ± SD.

Hosts Characicformes and food items (cm³)	N	Sites
		S1	S2	S3	S4
Leporinus friderici	23
Plant material		6.1 (0.9 ± 0.7)	n.o.	0.5 (0.5 ± 0)	4.45 (2.2 ± 1.4)
Fish		0.9 (0.5 ± 0.1)	n.o.	n.o.	n.o.
Terrestrial insect		3.7 (0.5 ± 0.5)	n.o.	n.o.	0.3 (0.3 ± 0)
Sediment		0.8 (0.2 ± 0.2)	n.o.	n.o.	0.2 (0.2 ± 0)
Crustacean		1.6 (0.8 ± 1.0)	n.o.	n.o.	n.o.
Seeds		0.2 (0.2 ± 0)	n.o.	n.o.	n.o.
Total		13.3	n.o.	0.5	4.95
Serrasalmus rhombeus	17
Plant material		n.o.	0.2 (0.2 ± 0)	n.o.	n.o.
Fish		8.4 (2.8 ± 2.8)	20.8 (5.2 ± 4.4)	4.1 (4.1 ± 0)	1.7 (1.7 ± 0)
Terrestrial insect		n.o.	n.o.	1.3 (1.3 ± 0)	2.1 (2.1 ± 0)
Total		8.4	21.0	5.4	3.8

There are significant differences in the length of the infrapopulations of P. (S.) inopinatus between the two host species (t = -0.69; p = 0.0012). Serrasalmus rhombeus parasites are 0.69 cm larger than L. friderici parasites. However, there were no relationship between the length of the parasites and the length of the hosts S. rhombeus (r = 0.07; p = 0.84) and L. friderici (r = 0.18; p = 0.51).

Morphological characteristics of P. (S.) inopinatus in S. rhombeus and L. friderici (Figure 2) agreed with the descriptions given by Moravec (1998). Larger sized nematodes with almost smooth cuticle. Oral openning circular, surrounded by eight submedian cephalic papillae arranged in two circlets and small lateral amphids, and an orange-brown and thick-walled buccal capsule approximately as long as wide. The inner oral surface was provided with numerous thin spiral thickenings, which occupied no more than 2/3 of the buccal capsule. Muscular oesophagus expanded at their posterior part was observed. Gravid females showed uterus containing eggs and larvae located in the anteromedial region. Non-gravid females showed uterus not containing eggs and larvae. Adult male (Table I) presented small conical tail, spicules well sclerotized and gubernaculum absent.

Figure 2
Procamallanus (Spirocamallanus) inopinatus in Serrasalmus rhombeus, micrographs at light microscope (a-c) (lateral view of a gravid female) and Leporinus friderici scanning electron microscopy (SEM) (d) (subapical view) and (e) (ventral view). a) Anterior region; b) Uterus with numerous larvae (black arrows); c) Posterior region. d) Cephalic papillae (CP), amphids (AP) of a female. e) tail of the female, in detail the disposition of the anus (A). Abbreviations: OC, Oral Capsule; ME, Muscle Esophagus. Bar scale: a, c = 50 µm; b = 100 µm; d-e = 50 µm.

DISCUSSION

Studies have demonstrated the infection and distribution patterns of P. (S.) inopinatus in freshwater teleost fish in Brazil (Oliveira et al. 2017, Morais et al. 2019, Ailán-Choke et al. 2020, Neves et al. 2020). Our findings contribute to the first record of P. (S.) inopinatus from the upper Tocantins river basin, Midwest Brazil. Prevalence of P. (S.) inopinatus in S. rhombeus (53%) and in L. friderici (74%) observed in this study was similar to that reported in L. friderici (76.6%) from the Amazon River basin (Oliveira et al. 2017), while higher prevalence (90%) was observed in L. friderici from the Paraná River basin (Feltran et al. 2004) and in Astyanax altiparanae (73.3%) from the Paraná River basin (Doro Abdallah et al. 2012). In addition, high prevalence (100%) also was observed in Pygocentrus nattereri Kner, 1858 in delta lakes in Central Amazon (Morais et al. 2019). However, was reported low prevalence of P. (S.) inopinatus in Serrasalmus marginatus Valenciennes, 1837 (5.49%) and Pygocentrus nattereri (22.37%) in the “Rio Negro”, Central Pantanal (Vicentin et al. 2011), as well as in Colossoma brachypomum (Cuvier, 1818) (1.7% to 25.7%) from fish farms in the State of Amapá (Dias et al. 2015) and in Cichlasoma bimaculatum (5.4%) in the Igarapé Fortaleza, State of Amapá (Tavares-Dias et al. 2017). This data show heterogeneity of results regarding the prevalence of P. (S.) inopinatus in the Brazil Characiform fish. Parameters related to trophic levels, life histories, and geographic distributions of fish in Brazilian watersheds are important for understanding infection prevalence levels (Neves et al. 2020).

Our data showed similar mean intensity between S. rhombeus from site S1 and in L. friderici from site S4 with value 4. The mean abundance was higher in L. friderici from site S1. The difference between sampling sites was associated with the variability in the food items consumed by the fish resulting in greater or lower ingestion of intermediate hosts infected by P. (S.) inopinatus. Both parasitological descriptors were higher than those reported for S. rhombeus (Lima 2010) and L. friderici (Oliveira et al. 2017). We can infer that the presence of food itens at as insects (Moreira et al. 2005, Costa Silva et al. 2019), microcrustaceans and molluscs (Camargo et al. 2016, Oliveira et al. 2017) that they are certainly a probable hosts intermediate for P. (S.) inopinatus, and these endoparasite metazoans are usually acquired by ingestion due to their indirect and long life cycle. Thus, larger hosts support a higher degree of infection by these parasites because such parasites are not pathogenic and cause little damage to the host (Hoshino & Tavares-Dias 2014).

To understand the parasite-host-environment relationship, data from host fish such as body length has been considered an important variable. Fish with longer lengths provides a larger surface area for attachment and are considered a more stable habitat for the parasites that, often display a higher longevity compared to the ones living in small fish (Pavanelli et al. 2013). Additionally, small fish offer insufficient habitat spaces for the parasites (Hoshino & Tavares-Dias 2014). On the other hand, there is agreement in the literature on the relationship that the parasites can have a short life cycle and therefore are constantly infected and eliminated by the hosts (Hoshino 2013, Tavares-Dias et al. 2017, Morais et al. 2019). For example, L. friderici from Igarapé Fortaleza, a tributary of the Jari River, showed a positive correlation between total length and abundance of P. (S.) inopinatus (Oliveira et al. 2017). On the other hand, studies conducted with Metynnis lippincottianus (Cope, 1870) from Igarapé Fortaleza, tributary of the Amazon River, Amapá, Brazil, showed that the abundance of P. (S.) inopinatus parasites was higher in small fish (Hoshino 2013), and no effect interaction of fish length and parasitic abundance was observed (Hoshino & Tavares-Dias 2014). This pattern was also observed in fish from the Paraná River (Franceschini et al. 2013, Camargo et al. 2016) and another a tributary of the Amazon River (Tavares-Dias et al. 2017), in which helminth abundance was associated with behavioral factors of the parasite such as a short life cycle or rapid elimination during your passage through the host’s digestive tract. Furthermore, as observed by Franceschini (2013) and Tavares-Dias et al (2017), helminths abundance did not interfere with fish Kn. Even in the case of S. rhombeus in which parasites were 69% larger than parasites from L. friderici, the fish health conditions remained the same regardless of infection.

The host fish sex did not influence the mean abundance and mean intensity of P. (S.) inopinatus in this study. However, the abundance of this parasite in S. rhombeus, from floodplain lakes in Central Amazonia was higher in male fish (Lima 2010). Meanwhile, P. (S.) inopinatus found in marine and freshwater fish hosts, showed higher mean abundance in female hosts (Amarante et al. 2016).

Although P. (S) inopinatus infection did not influence the GSI of S. rhombeus and L. friderici, higher abundance of parasite was observed in fish with immature and maturing gonadal stages compared to other gonadal stages. Alterations on GSI related to parasite abundance has been described in Eustrongylides sp. larvae (Kaur et al. 2013) and Philometra sp. (Selvakumar et al. 2014). The positive correlation could be associated to the fact of the reproductive period is a stressful phase for the fish, as they become more susceptible to infections (Pavanelli et al. 2013). On the other hand, the current study demonstrated that P. (S.) inopinatus infection has no effects on GSI of both host fish.

Food contain observed in S. rhombeus and L. friderici (i.e., plant material, fish, insect, sediment, crustacean, seeds) were similar to those reported for S. rhombeus in “Solimões” floodplain lakes (Lima 2010) and in L. friderici in the Amazon Basin, Brazil (Costa Silva et al. 2019). Also, microcrustaceans and molluscs were identified as food contain for L. friderici from lotic environments (Oliveira et al. 2017), which can reflect a smaller number of these intermediate hosts and, consequently, of endoparasites these environments (Camargo et al. 2016). In Pygocentrus nattereri collected in floodplain lakes in Central Amazonia, Brazil, microcrustacean food item was associated with a higher prevalence of infection by P. (S.) inopinatus (Morais et al. 2019). Therefore, eating habits of host fishes can influence the presence of P. (S). inopinatus (Shamsi 2013). A study on feeding habits and trophic ecology of Lutjanids reported the fish preference for macrocrustaceans living in areas of submerged vegetation, a diet associated to benthic fish (Guevara et al. 2007). This could explain the presence of nematodes in L. friderici, as some parasite groups have an indirect life cycle and their first intermediate host is generally a crustacean among other invertebrates.

Body length is a good predictor of parasite abundance. Larger fishes ingest a higher amount of potentially infected prey. Besides, they are considered a more stable habitat for the parasites that, often display a higher longevity compared to the ones living in smaller fish on the relationship that the parasites can have a short life cycle and therefore are constantly eliminated by the hosts smaller (Pavanelli et al. 2013, Amarante et al. 2016).

Carnivorous fish would be susceptible to obtain larger parasitic abundance because they are at the top of the food chain (Machado et al. 1996). However, in this study, S. rhombeus (carnivore) showed lower abundance of P. (S.) inopinatus in comparison to L. friderici (omnivore). Similar data were reported for S. marginatus from Rio Negro, Pantanal, Mato Grosso do Sul (Vicentin et al. 2011), as well as in Cichlasoma bimaculatum from the Igarapé Fortaleza basin, tributary of the Amazon River, Amapá, Amazon Region (Tavares-Dias et al. 2017). The abundance of P. (S.) inopinatus were similar for detritivorous, omnivorous, carnivorous and piscivorous hosts. These patterns correlated with differences in the transmission strategies of these parasite taxa (Neves et al. 2020). Additionally, carnivorous fish with diets based on invertebrates and fish; and omnivorous fish with diets containing only invertebrates, had higher richness of endohelminth communities than herbivorous and planktivorous fish (Simková et al. 2001, Baia et al. 2018). Thus, omnivorous diet was a predictor that these hosts present diversified consumption of food items, at least when they are still young, which may have caused a higher eating of intermediate hosts, and what the knowledge of the relationship between P. (S.) inopinatus and its intermediate hosts will only be possible when its biological cycle is completely studied in the laboratory (Neves et al. 2020).

We report the first record of nematode P. (S.) inopinatus in two species of Characiformes fish (S. rhombeus and L. friderici) in a river in Central-West Brazil. Procamallanus (Spirocamallanus) inopinatus showed higher mean abundance in L. friderici. Our data showed that the difference between sampling sites was associated with the variability in the food items consumed by the fish resulting in greater or lower ingestion of intermediate hosts infected by P. (S.) inopinatus. The total length was considered the most important variable related to parasitic abundance in L. friderici, although it was not considered ideal to explain the parasitic abundance. The host fish sex did not influence the mean abundance and mean intensity of P. (S.) inopinatus. There are differences in the length of the individuals that make up the infrapopulations of parasites between the two fish species. On average, S. rhombeus parasites are larger than L. friderici parasites.

Thus, we conclude that the success of the infection involves a complexity of variables, with greater importance for the prey-predator relationship. Nonetheless, it will be necessary to perform further studies about the life cycle of P. (S.) inopinatus to clarify which species could act as intermediate and definitive host.

ACKNOWLEDGMENTS

This work was funded by Fundação de Amparo à Pesquisa do Estado de Goiás – FAPEG (proc. n. 201810267001535), and Coordenação de Aperfeiçoamento de Pessoal de Nível Superior – Brazil – CAPES (funding code 001). The authors thank the Reserva Legado Verdes do Cerrado (LVC), Companhia Brasileira de Alumínio (CBA)/Grupo Votorantim and Universidade Estadual de Goiás, Campus Central Sede: Anápolis-CET for supporting the development of the research.

SUPPLEMENTARY MATERIAL

Table SI.

Tabela SII.

REFERENCES

• AILÁN-CHOKE LG, TAVARES LER, LUQUE JL & PEREIRA FB. 2020. An integrative approach assesses the intraspecific variations of Procamallanus (Spirocamallanus) inopinatus, a common parasite in Neotropical freshwater fishes, and the phylogenetic patterns of Camallanidae. Parasitol 147(14): 1752-1764.
• ALIN A. 2010. Multicollinearity. Wiley Interdiscip Rev Comput Stat 2: 370-374.
• AMARANTE CF, TASSINARI WS, LUQUE JL & PEREIRA MJS. 2016. Parasite abundance and its determinants in fishes from Brazil: an eco-epidemiological approach. Rev Bras Parasitol Vet 25(2): 196-201.
• AYDIN B & BARBAS LAL. 2020. Sedative and anesthetic properties of essential oils and their active compounds in fish: A review. Aquaculture 520: 734999.
• BAIA RRJ, FLORENTINO AC, SILVA LMA & TAVARES-DIAS M. 2018. Patterns of the parasite communities in a fish assemblage of a river in the Brazilian Amazon region. Acta Parasitol 63(2): 304-316.
• BELLAY S, OLIVEIRA EF, ALMEIDA-NETO M, LIMA JUNIOR DP, TAKEMOTO RM & LUQUE JL. 2013. Developmental Stage of Parasites Influences the Structure of Fish-Parasite Networks. PLoS ONE 8(10): e75710.
• BLASCO-COSTA I, ROUCO C & POULIN R. 2015. Biogeography of parasitism in freshwater fish: spatial patterns in hot spots of infection. Ecography 38(3): 301-310.
• BURHMAN KP & ANDERSON DR. 2002. Model Selection and multimodel inference: a pratical information-theoretic approach. 2nd. ed. New York: Springer.
• BUSH AO, LAFFERTY KD, LOTZ JM & SHOSTAK AW. 1997. Parasitology meets ecology on its own terms: Margolis et al. Revisited J Parasitol 83(4): 575-583.
• CAMARGO AA, NEGRELLI DC, PEDRO NHO, AZEVEDO RK, SILVA RJ & ABDALLAH VD. 2016. Metazoan parasite of lambari Astyanax altiparanae, collected from the Peixe river, São Paulo, southeast of Brazil. Cienc Rural 46(5): 876-880.
• CANTATORE DMP & TIMI JT. 2015. Marine parasites as biological tags in South American Atlantic waters, current status and perspectives. Parasitol 142(1): 5-24.
• COHEN SC, JUSTO MCN, CÁRDENAS MQ, MENESES YC, BEZERRA CAM & VIANA DC. 2020. Conceitos básicos e estado da arte dos helmintos parasitos de peixes da bacia Tocantins-Araguaia. In: Prandel, JA Conhecimentos teóricos, metodológicos e empíricos para o avanço da sustentabilidade no Brasil. Ponta Grossa: Atena Editora, p. 54-74.
• COSTA SILVA T, PETRÔNICO PB, BATISTA GA, MATHIAS PVC, MENDONÇA CV, CARVALHO JC, MELLO BM & FALEIRO FV. 2019. Guia de Peixes da UHE Estreito. 1ª ed. Goiânia: Biota.
• DIAS MKR, NEVES LR, MARINHO RGB & TAVARES-DIAS M. 2015. Parasitic infections in tambaqui from eight fish farms in Northern Brazil. Arq Bras Med Vet Zootec 67(4): 1070-7076.
• DORO ABDALLAH V, AZEVEDO R, CARVALHO E & DA SILVA R. 2012. New host and distribution records for nematode parasites of Freshwater fishes from Sao Paulo State, Brazil. Neotrop. Helminthol 6(1): 43-57.
• EIRAS JC, TAKEMOTO RM & PAVANELLI GC. 2006. Métodos de estudo e técnicas laboratoriais em parasitologia de peixes. 2ª ed. Maringá: Eduem.
• FELTRAN RB, MARÇAL JÚNIOR O, PINESE JF & TAKEMOTO RM. 2004. Prevalência, abundância, intensidade e amplitude de infecção de nematóides intestinais em Leporinus frideiri (Bloch, 1794) e Leporinus obtusidens (Valenciennes, 1836) (Pisces, Anostomidae), na represa de Nova Ponte (Perdizes-MG). Rev Bras Zoocienc 6(2): 169-179.
• FRANCESCHINI L, ZAGO AC, ZOCOLLER-SENO MC, VERÍSSIMO-SILVEIRA R, NINHAUS-SILVEIRA A & SILVA RJ. 2013. Endohelminths in Cichla piquiti (Perciformes, Cichlidae) from the Paraná River, São Paulo State, Brazil. Rev Bras Parasitol Vet 22(4): 475-484.
• GUEVARA E, ÁLVAREZ E, MASCARÓ M, ROSAS C & SÁNCHEZ A. 2007. Hábitos alimenticios y ecología trófica del pez Lutjanus griseus (Pisces: Lutjanidae) asociado a la vegetación sumergida en la Laguna de Términos, Campeche, México. Ver Biol Trop 55(3-4): 989-1004.
• HOSHINO MDFG. 2013. Parasitofauna em Peixes Characidae e Acestrorhynchidae da Bacia do Igarapé Fortaleza, Estado do Amapá, Amazônia Oriental. Dissertação, Universidade Federal do Amapá.
• HOSHINO MDFG & TAVARES-DIAS M. 2014. Ecology of parasites of Metynnis lippincottianus (Characiformes: Serrasalmidae) from the eastern Amazon region, Macapá, State of Amapá, Brazil. A Scient Biol Sci 36(2): 249-255.
• HYSLOP EJ. 1980. Stomach contents analysis – a review of methods and their application. J Fish Biol 17: 411-429.
• KAUR P, SHRIVASTAV R & QURESHI TA. 2013. Pathological effects of Eustrongylides sp. larvae (Dioctophymatidae) infection in freshwater fish, Glossogobius giuris (Ham.) with special reference to ovaries. J Paras Dis 37(2): 245-250.
• KAWAKAMI E & VAZZOLER G. 1980. Método gráfico e estimativa de índice alimentar aplicado no estudo de alimentação de peixes. Bol Inst Ocean 29(2): 205-207.
• KOHN A, MORAVEC F, COHEN SC, CANZI C, TAKEMOTO RM & FERNANDES BMM. 2011. Helminths of freshwater fishes in the reservoir of the Hydroelectric Power Station of Itaipu, Paraná, Brazil. Check List 7(5): 681-690.
• LE CREN ED. 1951. The length-weight relationship and seasonal cycle in gonad weight and condition in the perch Perca fluviatilis. J Anim Ecol 20: 201-219.
• LIMA MA. 2010. A fauna de parasitas de Serrasalmus rhombeus (Linneaus, 1776) (Characiformes: Characidae) de lagos de várzea da Amazônia Central. Dissertação, Universidade do Amazonas.
• MACHADO MH, PAVANELLI GC & TAKEMOTO RM. 1996. Structure and diversity of endoparasitic infracommunities and the trophic level of Pseudoplatystoma corruscans and Schizodon borelli (Osteichthyes) of the high Paraná River. Mem Inst. Oswaldo Cruz 91(4): 441-448.
• MAGNONI APV. 2009. Ecologia trófica das assembléias de peixes do reservatório de Chavantes (Médio rio Paranapanema. SP/PR). Tese de Doutorado, Universidade Estadual Paulista.
• MELO CE, LIMA JD, MELO TL & SILVA VP. 2005. Peixes do Rio das Mortes. Identificação e ecologia das espécies mais comuns. Cuiabá: Editora Unemat, p. 147.
• MORAIS AM, CÁRDENAS MQ & MALTA JCO. 2019. Nematofauna of red piranha Pygocentrus nattereri (Kner, 1958) (Characiformes: Serrasalmidae) from Amazonia, Brazil. Rev Bras Parasitol Vet 28(3): 458-464.
• MORAVEC F, PROUZA A & ROYERO R. 1997. Some nematodes of freshwater fishes in Venezuela. Fol Parasitol 44: 33-47.
• MORAVEC F. 1998. Nematodes of freshwater fishes of the Neotropical Region. Praha: Academia, 464 p.
• MOREIRA ST, ITO KF, TAKEMOTO RM & PAVANELLI GC. 2005. Ecological aspects of the parasites of Iheringichthys labrosus (Lütken, 1874) (Siluriformes: Pimelodidae) in reservoirs of Paraná basin and upper Paraná floodplain, Brazil. Acta Sci Biol Sci 27: 317-322.
• MUNIZ CC, SANTANA MN & OLIVEIRA-JUNIOR ES. 2016. Índices Morfofisiológicos de Piaractus mesopotamicus (OSTEICHTHYES, CHARACIDAE) na estação ecológica de Taiamã e foz do rio Sepotuba, Brasil. Intercienc 41(10): 674-679.
• NAIMI B. 2017. Uncertainty analysis for SDMs. R Package Version 4.0. (http://CRAN.R-project.org/package=usdm). Accessed 12 March 2020.
  » http://CRAN.R-project.org/package=usdm
• NEVES LR, SILVA LMA, FLORENTINO AC & TAVARES-DIAS M. 2020. Distribution patterns of Procamallanus (Spirocamallanus) inopinatus (Nematoda: Camallanidae) and its interactions with freshwater fish in Brazil. Rev Bras Parasitol Vet 29(4): 1-15.
• OLIVEIRA MSB, LIMA CORRÊA L, PRESTES L, NEVES LR, BRASILIENSE ARP, FERREIRA DO & TAVARES-DIAS M. 2018. Comparison of the endoparasite fauna of Hoplias malabaricus and Hoplerythrinus unitaeniatus (Erythrinidae), sympatric hosts in the eastern Amazon region (Brazil). Helminthol (Pol) 55(2): 157-165.
• OLIVEIRA MSB, GONÇALVES RA, FERREIRA DO, PINHEIRO DA, NEVES LR, DIAS MKR & TAVARES-DIAS M. 2017. Metazoan parasite communities of wild Leporinus friderici (Characiformes: Anostomidae) from Amazon River system in Brazil. Stud Neot Fauna Env 52(2): 146-156.
• OLIVEIRA MP & TEJERINA-GARRO FL. 2010. Distribuição e estrutura das assembléias de peixes em um rio sob influência antropogênica, localizado no alto da bacia do rio paraná - Brasil central. Bol Inst Pesca 36(3): 185-195.
• PAVANELLI GC, TAKEMOTO RM & EIRAS JC. 2013. Parasitologia de peixes de água doce do Brasil. Maringá: Eduem.
• POULIN R & LEUNG TLF. 2011. Body size, trophic level, and the use of fish as transmission routes by parasites. Oecologia 166: 731-738. DOI: 10.1007/s00442-011-1906-3.
• RAMALLO G, CANCINO F, RUIZ AL & AILÁN-CHOKE LG. 2020. Gastrointestinal nematodes of freshwater fish from Pilcomayo River, Argentina, including description of a new species of Procamallanus (Spirocamallanus). Zootaxa 4810(3): 468-480.
• RANGEL TFLVB, DINIZ-FILHO JAF & BINI LM. 2010. SAM: a comprehensive application for Spatial Analysis in Macroecology. Ecography 31(1): 46-50.
• R CORE TEAM. 2020. R: A Language and Environment for Statistical Computing. R Foundation for Statistical Computing. Vienna, Austria. (www.R-project.org/). Accessed 12 March 2020.
  » www.R-project.org/
• RIVADENEYRA NLS, MERTINS O, CUADROS RC, MALTA JCO, DE MATOS LV & MATHEWS PD. 2020. Histopathology associated with infection by Procamallanus (Spirocamallanus) inopinatus (Nematoda) in farmed Brycon cephalus (Characiformes) from Peru: a potential fish health problem. Aquacul Int 28(2): 449-461.
• SALGADO-MALDONADO G. 2006. Checklist of helminth parasites of freshwater fishes from Mexico. Zootaxa 1324: 1-357.
• SALGADO-MALDONADO G & RUBIO-GODOY M. 2014. Helmintos parásitos de peces de agua dulce introducidos. In: Mendoza R & Koleff P (Eds), Especies acuáticas invasoras en México. México: Comisión Nacional para el Conocimiento y Uso de La Biodiversidad, p. 269-285.
• SEGPLAN. 2019. www.imb.go.gov.br/index.php?option=com_content&view=article&id=14&Itemid=218. Accessed 20 March 2019.
  » www.imb.go.gov.br/index.php?option=com_content&view=article&id=14&Itemid=218
• SELVAKUMAR P, SAKTHIVEL A & GOPALAKRISHNAN A. 2014. Prevalence, intensity and gonadosomatic index of a nematode (Philometra sp.) infested in ovaries of Otolithes ruber from Southeast coast of India. Pacif J of Trop Dis 4(S2): S743-S747.
• SHAMSI S, HALAJIANB A, TAVAKOLB S, MORTAZAVID P & BOULTONA J. 2013. Pathogenicity of Clinostomum complanatum (Digenea: Clinostomidae) in piscivorous birds. Res in Vet Scien 95(2): 537-539.
• SIEGEL S. 1975. Estatística não-paramétrica, para as ciências do comportamento. São Paulo: McGraw-Hill do Brasil.
• SIMKOVÁ A, MORAND S, MATEJUSOVÁ I, JURAJDA P & GELNAR M. 2001. Local and regional influences on patterns of parasite species richness of central European fishes. Biodivers Conserv 10(4): 511-525.
• TAKEMOTO RM, PAVANELLI GC, LIZAMA MAP, LACERDA ACF, YAMADA FH, MOREIRA LHA, CESCHINI TL & BELLAY S. 2009. Diversity of parasites of fish from the Upper Paraná River floodplain, Brazil. Braz J Biol 69(2): 691-705.
• TAVARES-DIAS M, OLIVEIRA MSB, GONÇALVES RA, SILVA LMA. 2014. Ecology and seasonal variation of parasites in wild Aequidens tetramerus, a Cichlidae from the Amazon. Acta Parasitol 59(1): 158-164.
• TAVARES-DIAS M, GONÇALVES RA, OLIVEIRA MSB & NEVES LR. 2017. Aspectos ecológicos de los parásitos en Cichlasoma bimaculatum (Cichlidae), pez ornamental de la Amazonia Brasileña. Acta Biol Colomb 22(2): 175-180.
• THATCHER VE. 2006. Amazon fish parasites. 2nd ed. Sofia-Moscow: Pensoft Publishers, 508 p.
• VAZZOLER AEAM. 1996. Biologia Da Reprodução de Peixes Teleósteos: Teoria e Prática. Maringá: Eduem.
• VICENTIN W, VIEIRA KRI, COSTA FES, TAKEMOTO RM, TAVARES LER & PAIVA F. 2011. Metazoan endoparasites of Serrasalmus marginatus (Characiformes: Serrasalminae) in the Negro River, Pantanal, Brazil. Rev Bras Parasitol Vet 20(1): 61-63.
• YAMADA FH & TAKEMOTO RM. 2013. Metazoan parasite fauna of two peacock–bass cichlid fish in Brazil. Check List 9(6): 1371-1377.
• YAMADA FH & TAKEMOTO RM. 2017. How does host ecology influence sampling effort in parasite diversity estimates? A case study using Neotropical freshwater fishes. Acta Parasitol 62(2): 348-353.

Publication Dates

• Publication in this collection
  01 Dec 2023
• Date of issue
  2023

History

• Received
  5 Nov 2022
• Accepted
  12 Mar 2023