COMMUNITY ECOLOGY OF METAZOAN PARASITES OF THE ANCHOVY Anchoa tricolor ( OSTEICHTHYES : ENGRAULIDAE ) FROM THE COASTAL ZONE OF THE STATE OF RIO DE JANEIRO , BRAZIL

Between October 2001 and March 2002, 103 specimens of A. tricolor from Angra dos Reis (23°01’S, 44°19’W), in the coastal zone of the State of Rio de Janeiro, Brazil, were analyzed in order to study their metazoan parasite infracommunities. Ten species of metazoan parasites were collected: 4 digeneans, 1 cestode, 1 acantocephalan, 2 nematodes, 1 copepod, and 1 hirudinean; 77.7% of the fishes were parasitized by one or more metazoan, with a mean of 3.5 ± 6.2 parasite/fish. Digenean was the most dominant with 4 species that accounted for 53.2% of the total parasites collected; Ergasilus sp. was the most abundant species. Abundance and prevalence of Parahemiurus merus (Linton, 1910) were positively correlated with the total length of host. Relationships between total body length of fish and both total parasite abundance and mean parasite species richness were observed. Mean parasite diversity of species was correlated to host’s total length, with significant differences found between male and female fishes. Two pairs of larval species showed significant positive association and covariation. The metazoan parasite infracommunities of A. tricolor presented dominance of larval endoparasites; correlation of parasite abundance, diversity, and species richness with host total length; and low number of parasite interspecific relationships. The parasite community of A. tricolor showed some similarities with the parasite community of another South American Atlantic engraulid.


INTRODUCTION
Engraulid fishes are among the principal components of the marine ecosystems in South America.In addition, as primary feeders in the marine food web, engraulids are the main prey item for many species of fishes and are of significant commercial importance in this region (Castello & Castello, 2003;Pessanha & Araújo, 2003).
The anchovy Anchoa tricolor (Agassiz, 1829) is a planktivorous pelagic fish that occurs in coastal zone, in marine and estuarine habitats, and is known to be geographically distributed in the southwestern Atlantic Ocean, from Ceará, Brazil, to Argentina (Figueiredo & Menezes, 1978).Usually occurring in large schools, anchovies feed mainly on crustaceans, larvae, and molluscs.Anchoa tricolor is largely used as bait for commercial fishery, oil, flour, and also canned fish (Silva & Araújo, 2000;Pessanha & Araújo, 2003).
In this report, we analyze at the component and infracommunity levels a metazoan parasite community of A. tricolor from the coastal zone of the State of Rio de Janeiro.
The analysis included only parasite species with prevalence higher than 10% (Bush et al., 1990).The quotient between variance and mean of parasite abundance (index of dispersion) was used to determine distribution patterns; significance was tested using the d statistical test.The dominance frequency and the relative dominance (number of specimens of one species/total number of specimens of all species in the infracommunity) of each parasite species were calculated according to Rohde et al. (1995).The Spearman's rank correlation coefficient r s was calculated to determine possible correlations between the total length of hosts and parasite abundance.Pearson's correlation coefficient r was used to indicate the relationship between the host's total length and parasite prevalence, with previous arcsine transformation of the prevalence data (Zar, 1999).The effect of host sex on abundance and prevalence of parasites was tested using the Z c (normal) approximation to the Mann-Whitney test and the Fisher exact test, respectively.Parasite species diversity was calculated using the Brillouin index (H) (Zar, 1999).The probable variation of diversity in relation to host sex (Mann-Whitney test) and to host total length (Spearman's rank correlation coefficient) was tested.Possible interspecific association between concurrent species was determined using the chi-square test.Possible covariation among the abundance of concurrent species was analyzed using the Spearman's rank correlation coefficient.The ecological terminology used follows Bush et al. (1997).Statistical significance level was evaluated at p ≤ 0.05.Voucher specimens of helminths and hirudineans were deposited in the Coleção Helmintológica do Instituto Oswaldo Cruz (CHIOC), Rio de Janeiro, Brazil; copepods were deposited in the Coleção de Crustacea do Museu Nacional (MNRJ), Quinta da Boa Vista, Rio de Janeiro, RJ, Brazil.

Component community
Ten species of metazoan parasites were found (Table 1).Digeneans was the most prevalent, with 4 species accounting for 53.2% of total parasites collected (Table 2).Ergasilus sp. was the most abundant species, with 122 specimens collected (33.8% of all parasites).Larval endoparasites species represented 39.9% of all parasites collected, adult endoparasites amounted to 25.8%, and ectoparasites made up 34.4%.All parasites of A. tricolor had the typically aggregated distribution pattern observed in many parasite systems (Table 3).Abundance and prevalence of Parahemiurus merus (Linton, 1910) were positively correlated with host's total length (Table 4).The mean abundance and prevalence of all parasite species did not differ significantly between female and male hosts.

Frequency of dominance
Frequency of dominance shared with one or more species

Mean relative dominance
Digenean

DISCUSSION
Some patterns in the structure and composition of the community of metazoan parasites of A. tricolor from Brazil were detected: (1) dominance of endoparasitic larval stage; (2) positive correlation of parasitic abundance and richness with the size of the host; (3) low number of parasitic interspecific relationships.
Dominance of endoparasitic larval stages should be expected because the anchovies feed mainly on zooplanktonic organisms and act as intermediate and/or paratenic hosts for parasites of fishes, birds, and marine mammals.According to Lafferty (1999), some trophically transmitted parasites may infect the same intermediate host and show positive correlations among its intensities that suggest an alternative strategy that increases trophic transmission.Timi et al. (1999a) recorded four species of digeneans parasitic, two of which were in larval stages (metacercaria), in E. anchoita from Argentina and Uruguay.In addition, the dominance of digenean endoparasites has been described for several parasite communities of marine fishes from the coastal zone of southeastern Brazil (Luque et al., 1996;Takemoto et al., 1996;Knoff et al., 1997;Luque et al., 2000;Silva et al., 2000;Luque & Alves, 2001;Tavares & Luque, 2004a, among others).
The copepod Ergasilus sp.showed the highest values of mean abundance and intensity, a pattern possibly related to schooling behavior of A. tricolor (Silva & Araújo, 2000).Parasite transmission between host individuals could have a significant group-living cost (Krause et al., 1999;Ward et al., 2002), and schooling behavior is determinant on a broad scale for parasitic species richness in fishes from the coastal zone of the State of Rio de Janeiro (Luque et al., 2004).Besides, high levels of infestation by copepod ectoparasites has been recorded for some parasite communities of marine fishes from the coastal zone of southeastern Brazil (Cezar & Luque, 1999;Tavares et al., 2001Tavares et al., , 2004b)).
Correlations of parasite abundance, diversity, and species richness with total length of host were also detected in some fishes from the coastal zone of Rio de Janeiro State (Luque & Chaves, 1999;Alves & Luque, 2001;Luque & Alves, 2001;Alves et al., 2002) and are in accordance with the patterns detected by Timi & Poulin (2003) for E. anchoita from Argentina.According to Poulin (1995Poulin ( , 2001a) ) and Bush et al. (2001), larger hosts are also expected to harbor richer parasite fauna because they provide a greater niche variety and can sustain a greater absolute number of parasites.Moreover, Bush et al. (2001) stated that large fish often show ontogenetic shifts in their diet, suggesting that they may be exposed to a greater number of intermediate/ paratenic hosts than small fish, whether detritivorous or phytoplanktivorous.Timi (2003) and Timi & Poulin (2003) have extensively researched the use of parasites of E. anchoita as indicators of population stocks and for modeling predictability for other the parasite communities.Although the sample of A. tricolor was smaller and from one locality only, some similar components such as community richness, mean infracommunity richness, and total prevalence were detected in descriptors of the parasite community.However, the infracommunity composition shows some differences, mainly in the ectoparasites: monogeneans were the only ones recorded for E. anchoita.
On the other hand, in the coastal zone of Rio de Janeiro the digenean Parahemiurus merus prefers a wide spectrum of fish hosts with heterogeneus habitats and feeding behavior (Takemoto et al., 1996;Knoff et al., 1997;Luque & Chaves, 1999;Luque & Alves, 2001;Paraguassú et al., 2002).Timi (2003) also recorded this species parasitizing E. anchoita; however, lower values of prevalence and intensity were recorded.Poulin (2001b) and Poulin & Valtonen (2001) pointed out that many helminth parasites use fish either as a second intermediate or a paratenic host, and if two or more species of larval helminthes simultaneously accumulate in fish over time, a statistical association among these species may be expected.In this study, two pairs of larval endoparasite species were positively associated, although these quantitative relationships should be regarded with caution when explaining a parasite community structure.Lafferty (1999) and Poulin & Valtonen (2001) strongly suggested the possibility that parasites with similar life cycles could enhance their chances of transmission along the food web by associating with intermediate or paratenic host individuals.However, it would be extremely difficult to check this hypothesis.To date, six engraulid species, four of them belonging to Anchoa (Araújo et al., 1997;Silva & Araújo, 2000), have been recorded from the coastal zone of Rio de Janeiro State; studies on the metazoan parasite communities harbored by these species could indicate possible populational patterns and their influence on the structure and predictability of its parasite communities.

TABLE 4 Spearman's rank correlation coefficient (r s ) and Pearson's correlation coefficient (r) values used to evaluate possible relationships among the total length of Anchoa tricolor from the coastal zone of the State of Rio de Janeiro, Brazil, and the abundance and prevalence of its parasite community components.
*Significant values.