Recruitment and ecological parameters of three different Anisakid larvae species (Nematoda: Anisakidae) found parasitizing Engraulis anchoita (Pisces: Engraulidae).

GARBIN L.,; DIAZ J.I.,; CARBALLO M.C.,; CREMONTE F.; G.T. NAVONE

Viterbo, Italia.

Congreso; VII International Symposium of Fish Parasites.; 2007

Anisakid nematodes have a worldwide distribution and are associated with fishes, birds, and marine mammals. Transmission of species usually involves aquatic invertebrates and fish as intermediate or paratenic hosts (Anderson, 2000, Cabi Publishing, New York, 650 p.). Species of Contracaecum Raillet and Henry, 1912, (Anisakinae) use piscivorous birds and mammals associated with freshwater, brackish, and marine systems as definitive hosts. Recent studies on Anisakids from Península Valdés, Chubut, Argentina, have demonstrated the presence of Contracaecum pelagicum parasitizing Spheniscus magellanicus (Spheniscidae) (Garbin et al., 2007, Jour. Parasitol. 90: 103-114). Objectives of this work were to demonstrate that Engraulis anchoita (Engraulidae), predilect item prey of the penguin, might be the paratenic host of Contracaecum spp.; and to evaluate the anisakid recruitment and infection caused by a regular anchovy food ingest on Magellanic penguins. A total of 202 anchovies were obtained from fishing ships at the Rawson’s Port, Chubut province, Argentina. Fish were prospected for nematodes and 40 of them were weigthed and measured. Prevalence (P), mean intensity (MI), and mean abundance (MA) were calculated for the three Anisakid genera found. Results were P=52.5%, MI=2.81, and MA=1.47 for Contracaecum spp., P=90%, MI=6.97, and MA=6.27 for Hysterothylacium spp., and P=25%, MI=1.40, and MA=0.35 for Anisakis spp. Mean anchovy weigth was 19.08g (12.89-29.45g). Penguin mean mass of stomach content is 430g with a range between 80 to 1183g (Scolaro et al., 1999, Waterbirds 22: 104-110). Therefore, a penguin might ingest an average of 22.5 anchovies with a minimum of 4.9 and a maximum of 62 individuals daily. In this way, nematode recruitment could be 63.22 (13.77-174.22) individuals in each ingest for Contracaecum spp. third-stage larvae, 156.82 (34.15-432.14) third-stage larvae for Hysterothylacium spp., and 31.50 (6.86-86.80) third-stage larvae for Anisakis spp. This last parasite genus will not be able to stablish at the digestive tract of S. magellanicus taking into account that their definitive hosts are marine mammals. Hysterothylacium spp. will develop to adult since teleost fish are their definitive hosts. Despite the values of prevalence are low for Contracaecum spp. larvae in anchovies (52.5%), we might infer that they could act as paratenic hosts of C. pelagicum due to the low prevalence found in S. magellanicus (40%). Moreover, E. anchoita is the main food resource of penguins which showed a mean intensity of 149 C. pelagicum adult individuals in stomach (Garbin et al., 2007, Jour. Parasitol. 90: 103-114). This mean intensity of Contracaecum sp. on penguins could be explained as a result of several anchovy ingests that penguins do during their development from nestling to adults. On the other hand, adult penguin destiny a big ingest amount of fish to nestlings, for which this habit would contribute to reduce the larval nematode recruitment. In addition, probably not all larvae that come into the bird are able to stablish due to intraspecific competence for space and food resources such as we observed in mature penguins on which third-stage larvae were found in the intestine of these hosts.     Acknowledgements: we wish to thank Lic. Sonia Laurenti for its help to prospect the fish and to Dr. Carlos Ferreiro for his help and gold patience to obtain the anchovy.