Host-parasite interactions between the piranha Pygocentrus nattereri (Characiformes: Characidae) and isopods and branchiurans (Crustacea) in the rio Araguaia basin, Brazil

Abstract

In the tropics, studies on the ecology of host-parasite interactions are incipient and generally related to taxonomic aspects. The main objective of the present work was to analyze ecological aspects and identify the metazoan fauna of ectoparasites that infest the piranha, Pygocentrus nattereri. In May 2002, field samples were collected in the rio Araguaia basin, State of Goiás (Brazil). A total of 252 individuals of P. nattereri were caught with fishhooks and 32.14% were infested with ectoparasite crustaceans. The recorded ectoparasites were branchiurans, Argulus sp. and Dolops carvalhoi and the isopods Braga patagonica, Anphira branchialis and Asotana sp. The prevalence and mean intensity of branchiurans (16.6% and 1.5, respectively) and isopods (15.5% and 1.0, respectively) were similar. Isopods were observed in the gills of the host; branchiurans were more frequent where the skin was thinner, and facilitated attachment and feeding. The ventral area, the base of the pectoral fin and the gular area were the most infested areas. The correlations between the standard length of the host and the variables intensity and prevalence of crustaceans parasitism, were significant only for branchiurans (rs = 0.2397, p = 0.0001; chi2 = 7.97; C = 0.19). These results suggest that both feeding sites and body size probably play an important role in the distribution and abundance of ectoparasites.<br>Nos trópicos, os estudos sobre a ecologia de interações parasito-hospedeiro são incipientes, sendo a maioria de cunho taxonômico. O principal objetivo do presente estudo foi identificar a fauna metazoária de ectoparasitas e analisar aspectos ecológicos da piranha Pygocentrus nattereri. As coletas foram realizadas em maio de 2002, na bacia do rio Araguaia, GO. Com o auxílio de linha e anzol foram capturados 252 exemplares de P. nattereri, dos quais 32,14% estavam infestados por crustáceos ectoparasitos. As espécies de ectoparasitas registradas foram Argulus sp. e Dolops carvalhoi (Branchiura) e Braga patagonica, Anphira branchialis e Asotana sp. (Isopoda). A prevalência e a intensidade média de branquiúros (16,6% e 1,5, respectivamente) e isópodos (15,5% e 1,0, respectivamente) foram similares. Isópodos foram observados nas brânquias do hospedeiro; os branquiúros foram mais freqüentes na região ventral, base da nadadeira peitoral e região gular. Nessas áreas, a pele é mais fina, facilitando a fixação e alimentação do parasita. As correlações entre o comprimento padrão do hospedeiro e as variáveis intensidade e prevalência de parasitismo foram significativas apenas para branquiúros (rs= 0, 2397, p= 0,0001; chi2 = 7,97; C= 0, 19, respectivamente). Os resultados sugerem que os sítios de alimentação e o tamanho corporal dos ectoparasitos provavelmente têm um papel importante na sua distribuição e abundância

Distribution pattern of crustacean ectoparasites of freshwater fish from Brazil

“…Many parasitic crustacean species have preferences for particular sites on hosts in comparison with others (FRYER, 1968;DOUELLOU & ERLWANGER, 1994;CARVALHO et al, 2004;THATCHER, 1998THATCHER, , 2006TAVARES-DIAS et al, 2011SMIT et al, 2014), but this degree of restriction varies among parasite species. Thus, we found that while the lernaeid P. gamitanae infested only the oral cavity and gills of its host characids, L. cyprinacea is a parasite with low specificity that prefers the integument and gills of its hosts.…”

“…These results clearly showed a change of site preference in C. macropomum, for some unknown reason. Both feeding and attachment sites probably play important roles in the distribution of native ectoparasite crustaceans in host fish (FRYER, 1968;DOUELLOU & ERLWANGER, 1994;THATCHER, 1998THATCHER, , 2006CARVALHO et al, 2004;SMIT et al, 2014). Thus, one important reason why parasites prefer specific sites may relate to more effective use of resources such as food, the host species available and the vulnerability of the attachment site.…”

“…Thus, one important reason why parasites prefer specific sites may relate to more effective use of resources such as food, the host species available and the vulnerability of the attachment site. Although one widely accepted view is that the primary function of site restriction is to avoid interspecific competition (CARVALHO et al, 2004;ANEESH et al, 2013), e.g. for space and food, competition seems to have minor importance among parasitic crustaceans.…”

“…Ectoparasitic crustaceans attack the gills, oral cavity, nostrils and/or integument of fish (FRYER, 1968;DOUELLOU & ERLWANGER, 1994;CARVALHO et al, 2004;TAVARES-DIAS et al, 2014), which may give rise to a variety of damage to their hosts. Some species of these parasites may have both direct and indirect effects on fish populations, especially through causing reductions in the hosts' growth and reproduction rates, along with mortality among these fish.…”

“…These factors may lead to significant economic losses for fisheries and aquiculture (FRYER, 1968;POLY, 2008;TAVARES-DIAS et al, 2014). Consequently, parasitism by crustacean species has been recognized as a significant factor that may affect wild natural fish and farmed fish populations (CARVALHO et al, 2004;THATCHER, 2006;TAVARES-DIAS et al, 2011.…”