Clinostomum complanatum (Digenea, Clinostomidae) density in Rhamdia quelen (Siluriformes, Pimelodidae) from South Brazil

Abstracts

The density of Clinostomum complanatum metacercariae by the body regions and among the size classes of Rhamdia quelen was compared. The host size classes were defined by cluster analysis, using weight and total length as attributes. These values were related with environmental characteristics and host biological data. In all the host size classes H and PeF, CF and PF, and P and AF regions pairs, showed similar density (tested by X² test). The hosts with 30-36 cm showed largest parasite density in all the regions, except in CAV. Fishes smaller than 11 cm did not show significant differences of parasite density in all body regions. In the other classes, H was the most infected region, followed by PeF. The results suggested that the environmental conditions had little importance on the host colonization by metacercariae.

Clinostomum complanatum; Rhamdia quelen; metacercariae density; Jundiá; South Brazil; fish disease; aquaculture

A densidade de metacercárias de Clinostomum complanatum por regiões do corpo entre classes de comprimento de Rhamdia quelen foram comparadas. As classes de comprimento do hospedeiro foram definidas por analises de agrupamentos usando peso e comprimento total como atributos. Estes valores foram relacionados com características do ambiente e dados biológicos disponíveis sobre o hospedeiro. O dendrograma com sete agrupamentos foi o escolhido. O corpo do hospedeiro foi dividido em nove regiões para as necropsias: Cabeça (H); Nadadeiras, Peitoral (PeF); Dorsal (DF); Adiposa (AdF); Caudal (CF); Anal (AF) e Pélvica (PF); Pedúnculo caudal (P); Cavidade Abdominal (CAV). Em todas as classes de comprimento do hospedeiro os pares de regiões H e PeF, CF e PF e P e AF mostraram densidades similares (teste do X²). Hospedeiros com 30-36 cm mostram maior densidade de parasitas em todas as regiões exceto na CAV. Peixes com menos de 11 cm não mostram diferenças significativas na densidade de parasitas nas regiões do corpo. Nas demais classes, H é a região mais infectada, seguida por PeF. Os resultados sugerem que as variáveis ambientais têm pouca importância sobre o processo de colonização por metacercárias.

BIOLOGICAL AND APPLIED SCIENCES

Clinostomum complanatum (Digenea, Clinostomidae) density in Rhamdia quelen (Siluriformes, Pimelodidae) from South Brazil

Rogério Tubino Vianna^I; Joaber Pereira JúniorII, ^*; Deodoro Atlante Brandão^III

^IPrograma de Pós-Graduação em Zoologia; Universidade Federal do Paraná; C. P. 19020; 81531-980; [e-mail]; Curitiba - PR - Brasil

^IIDepartmento de Ciências Morfobiológicas; Fundação Universidade Federal do Rio Grande; C. P. 474; 96650-900; [e-mail]; Rio Grande - RS - Brasil

^IIIDepartamento de Zootecnia; Universidade Federal de Santa Maria; 97105-900; [e-mail]; Santa Maria - RS - Brasil

ABSTRACT

The density of Clinostomum complanatum metacercariae by the body regions and among the size classes of Rhamdia quelen was compared. The host size classes were defined by cluster analysis, using weight and total length as attributes. These values were related with environmental characteristics and host biological data. In all the host size classes H and PeF, CF and PF, and P and AF regions pairs, showed similar density (tested by X² test). The hosts with 30-36 cm showed largest parasite density in all the regions, except in CAV. Fishes smaller than 11 cm did not show significant differences of parasite density in all body regions. In the other classes, H was the most infected region, followed by PeF. The results suggested that the environmental conditions had little importance on the host colonization by metacercariae.

Key words: Clinostomum complanatum, Rhamdia quelen, metacercariae density, Jundiá, South Brazil, fish disease, aquaculture

RESUMO

A densidade de metacercárias de Clinostomum complanatum por regiões do corpo entre classes de comprimento de Rhamdia quelen foram comparadas. As classes de comprimento do hospedeiro foram definidas por analises de agrupamentos usando peso e comprimento total como atributos. Estes valores foram relacionados com características do ambiente e dados biológicos disponíveis sobre o hospedeiro. O dendrograma com sete agrupamentos foi o escolhido. O corpo do hospedeiro foi dividido em nove regiões para as necropsias: Cabeça (H); Nadadeiras, Peitoral (PeF); Dorsal (DF); Adiposa (AdF); Caudal (CF); Anal (AF) e Pélvica (PF); Pedúnculo caudal (P); Cavidade Abdominal (CAV). Em todas as classes de comprimento do hospedeiro os pares de regiões H e PeF, CF e PF e P e AF mostraram densidades similares (teste do X²). Hospedeiros com 30-36 cm mostram maior densidade de parasitas em todas as regiões exceto na CAV. Peixes com menos de 11 cm não mostram diferenças significativas na densidade de parasitas nas regiões do corpo. Nas demais classes, H é a região mais infectada, seguida por PeF. Os resultados sugerem que as variáveis ambientais têm pouca importância sobre o processo de colonização por metacercárias.

INTRODUCTION

The South American Catfish, Rhamdia quelen (Quoy and Gaimard, 1824) (Siluriformes, Pimelodidae) has importance for the pisciculture (Kossowski, 1996) and is found in South and Central America (Silfvergrip, 1996). This fish prefers the muddy bottom covered by leaves and decaying wood that provide protection during the day, and eat on benthic crustacean and zooplankton (Le Bail et al., 2000). R. quelen has a benthic behaviour (Guedes, 1980; Grosser et al., 1994; Bizerril, 1998; Bizerril and Lima, 2000) which facilitate the Digenea recruitment (Eiras et al., 1999, Guzmán-Cornejo and García-Prieto, 1999). Clinostomum complanatum (Rudolphi, 1814) Braum, 1899 (Clinostomidae) metacercariae infect the skin, muscle, fins, head and viscera, causing pathologies and changes in the host behavior, with consequent economic losses in fish farms (Kagei et al., 1984; Eiras, 1994; Mitchell, 1995). The Clinostomum infection increases with the host size, suggesting a cumulative process (Kalantan et al., 1987).

The site of infection is the place in the host body that provides the requirements of the parasite. The occupied site by the parasite in each life cycle stages depends of the type of immediately anterior stage, and the location of the metacercariae will depend on the behavior pattern showed by cercariae (Erasmus, 1972).

In this study the distribution of C. complanatum metacercariae infrapopulations in the body regions of R. quelen of Southern Brazil was defined in distinct host size classes. These results were confronted with the host ontogenetic changes and its environment distribution in order to establish if environmental conditions influenced the host colonization by the metacercariae.

MATERIALS AND METHODS

One hundred and twenty specimens of Rhamdia quelen, caught in the Sarandí stream (32º00'-32º10'S and 32º20'-32º30'W) in Rio Grande, Rio Grande do Sul State, Brazil, between September 1999 and August 2000 were examined in order to determine parasitological index of Clinostomum complanatum metacercariae. For necropsy, each host body was divided in nine regions: Head (H), Pectoral fin (PeF), Dorsal fin (DF), Adipose fin (AdF), Caudal Peduncle (P), Caudal fin (CF), Anal fin (AF), Pelvic fin (PF), Abdominal cavity (CAV) (Fig. 1). The density values (sensu Bush et al., 1997) of C. complanatum by host body regions were compared among and inside each size class using the chi-square test.

The definition of the host size classes limits was assayed in two ways: Initially by using the Sturgers equations (K = 1 + 3.3 x log n) and total width (h = higher length value - smaller length value / K) (Arango, 2001), which resulted eight host size classes. In the second assay, weight (g) and total length (cm) mean values of the eight classes obtained with Sturgers equation were used as attributes in the non-parametric Cluster analysis (Ward Method - Euclidian distance) (Arango, 2001). With this, dendrograms with 5, 6 and 7 size classes were created (Table 3). To determine the best dendrogram, relationships were established with the host biology (R. quelen or similar cogeneric species when necessary) and with space distribution using available dates on the environmental (Table 1 and Fig. 2). The importance and discriminatory capacity of each attribute for cluster definition was obtained by "K - means" algorhytm, that was used to eliminate tendentious definition in its composition (Digbby and Kempton, 1991).

RESULTS

Among 120 examined fishes, 77 were infected with a total of 17777 C. complanatum metacercariae. The 7 size classes dendrogram was adopted because showed the best relationship with host biological and environmental host distribution features (Fig 2). The first sexual maturation length and largest frequencies sizes (Table 1) were determinants for the separation of 3-7 size classes hosts that occurred in the area III (Table 2 and line c from Fig. 2). The general density of C. complanatum showed significant differences both between and within the different R. quelen size classes. The density values of C. complanatum showed no significant differences in all host size classes at the following pairs of body regions: H and PeF; CF and VF; P and AF. The size class 5 shows higher density in all regions, except in CAV (Table 4) and AF. The size class 5 shows higher density in all regions, except in CAV (Table 4). The density into each size class did not show significant difference in class 1 in all host body regions. In the others classes, there were differences and H showed higher densities values, followed by PeF (Table 4).

DISCUSSION

Mardini et al. (1981) observations showed that host class 1 was observed only in area I (Table 2 and Fig. 2) corroborating these results. Although shallow and with little current places, the area I showed low transparency. These features could favor fish larvae survival, as reported by Behr et al. (1999) and also favored the infection by C. complanatum, since its cercariae swimmer actively (Eiras et al., 1999).

However, the smallest infection values (absolute and relative) were observed in the size class 1.

The class 2 hosts were collected in the area II and the differences of environmental features were related with changes in alimentary habit (Guedes, 1980) and alterations of host reproductive behavior (Narahara et al., 1985) (Table 1). The influence of the first sexual maturation length and the largest frequencies sizes on the distribution of R. quelen in the Sarandí stream was similar to observations move by Arratia (1983) who showed Siluriformes environmental distribution changing with their growth. In the present study, C. complanatum density in R. quelen was largest in the head region, especially in the oro-branchial cavity. In Aphanius dispar (Cyprinodontidae) the largest density of these metacercariae was found in the trunk, followed by the head and tail (Kalantan et al., 1987).

This was due to the easiness found by the cercariae invading the sub-opercular tissue, distributing from there to other body regions. Metacercariae of C. marginatum from Loricariichthys platymetopon (Loricariidae), has larger intensity of infection in the buccal cavity and opercle (Eiras et al., 1999). In Amazon, Thatcher (1991) reported the infection by C. marginatum on the gills of Cichla ocellaris (Cichlidae) and in Crenicichla sp (Cichlidae). The data of Thatcher (1991), Eiras et al. (1999) and Kalantan et al. (1987), however, were not obtained with rigorous host body subdivision, as done in this study.

Besides the body regions already mentioned, cysts of C. complanatum were also observed in the barbels, opercle, branchoiostegal membranes, muscles, gills, palate, pharynx and eyes of R. quelen. Eiras et al. (1999) reported cysts in the ocular globule, which did not cause blindness. However, fish vision could be affected by the parasite. This would facilitate the predation by birds (the main final host of Clinostomum).

Most of the Digenea cysts occurred in the trunk, followed by in the fins, usually with larger movement, as caudal and pectoral (Erasmus, 1972), which also contradicted the common belief that these regions were difficult to the cercariae penetration in the host. Eiras et al. (1999) found low infection in the caudal fin and they attributed this to the constant movements of the anal fin. The PeF, AF and CF regions in R. quelen showed the largest densities after H, entering inside of each host size class and the largest densities were in the fins with larger movement (Erasmus, 1972). Holmes (1973) found that parasites with active infection processes selected its site, which was also observed in cercariae of C. complanatum by Krull (1934) and Paperna (1980).

The fact that the density values of C. complanatum observed in the pairs of body regions H and PeF, CF and PF and P and AF were similar in all host size classes suggested that a pattern of site occupation occurred when they had similar environmental conditions. Furthermore, the fact that among the adults, class 5 was the most frequent in the environment (Table 3) and showed the highest metacercariae density in all body regions, except for CAV (Table 4) indicated higher densities than those observed contributing to the host mortality. Hence in these hosts were not detected. It was therefore, possible to suggest that the parasitosis influenced the structure of the host population.

Different sizes of metacercariae of C. complanatum are found in R. quelen, which may point to several subsequent recruitment processes and a cumulative infection. This idea was reinforced by Esch et al. (1975), who found that the parasitic density could be increased by recruitment when a reduction of natural or acquired resistance, elimination of ecological or behavior barriers, and seasonal changes of environmental conditions occurred.

Different sizes of C. complanatum metacercariae found in R. quelen can be evidenced in subsequent recruitment processes and a cumulative infection. The parasitic density in the second intermediate hosts, as R. quelen to C. complanatum, could be increased by recruitment when a reduction of natural or acquired resistance, elimination of ecological or behavior barriers, and seasonal changes of environmental conditions occurred (Esch et al., 1975).The benthonic condition of R. quelen (Bizerril, 1998, Bizerril and Lima, 2000) can also facilitate the cercarial recruitment of C. complanatum (Eiras et al., 1999).

The density differences in the host size classes may be due to the several sizes of corporal surfaces, (Elliott andRussert, 1949, Kalantan et al., 1987). The consistently similar density values of C. complanatum observed in the pairs of body regions H and PeF, CF and PF and P and AF in all the host size classes suggested that the differences in the host location in the environment had little influence on the body regions colonized by the metacercariae. However, as shown in Table 2, it was possible to conclude that as environmental segregation by the different host size classes occurred, the density differences could not be influenced exclusively by body size.

The corporal volume of the parasites could condition the colonization pattern, and this could be a more determining parameter than indexes such as the density (George-Nascimento et al., 2002), but the observations in this study did not agree this. Previous studies have determined the specificity of parasite site of infection and the possibility of discarding parts to minimize fish carcass losses in the industry (Overstreet, 1977; Amato et al., 1990). The high densities and non-specificity of infection site for metacercariae of C. complanatum in R. quelen make it possible to point that the selective discarding of parts of the fish carcass is not feasible.

ACKNOWLEDGEMENTS

The authors are grateful to Dr. José H. da Silva (Departmento de Zootecnia - Universidade Federal de Santa Maria) for his statistical analysis assistance, to Dr. Paulo César Abreu (Departmento de Oceanografia- Fundação Universidade Federal do Rio Grande) for the critical review of the manuscript, to Valdir Ponciano for his assistance with host collection, to João Casimiro and Ieda Quadros (both from Fundação Universidade Federal do Rio Grande) for the slide preparation and Coordenação de Aperfeiçoamento de Pessoal de Nível Superior for supporting (to R. T. V.).

Received: September 29, 2003

Revised: June 28, 2004

Accepted: November 17, 2004

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*

Author for correspondence

Publication Dates

• Publication in this collection
  14 Sept 2005
• Date of issue
  July 2005

History

• Reviewed
  28 June 2004
• Received
  29 Sept 2003
• Accepted
  17 Nov 2004