Distribution of the exotic parasite, Lernaea cyprinacea (Copepoda, Lernaeidae) in Argentina

Lernaea cyprinacea Linnaeus is an ectoparasitic copepod that infects the gills and skin of various freshwater fishes and amphibians tadpoles. It is capable of infecting fish at high levels, with high pathogenicity and mortality, mainly during the summer season. Besides the effects of penetration, haemorrhages and ulcerations are also caused. The objective of this study was to investigate the presence of L. cyprinacea in natural bodies of water of Argentina in the provinces of Buenos Aires, Mendoza and Río Negro; the finding of the parasite in Choele-Choel, in the province of Río Negro, is the most austral distribution of its presence. In our study, infections with L. cyprinacea showed a low host specific and they were adapted to a large variety of habitats. Introduction Lernaea cyprinacea Linnaeus (Copepoda, Lernaeidae), the anchor worm, is an ectoparasitic copepod that generally infects the gills and skin of various freshwater fishes (Stoskopf, 1993), amphibian tadpoles (Martins and Souza, 1996; Alcalde and Batistoni, 2005) and the larval stage of axolotl (Carnevia et al., 2003). These parasites are distributed naturally in Africa, central Asia, the southern region of Siberia, and have also been reported in Europe, Japan and Israel (Schäperclaus, 1991; Thatcher et al., 1998). The genus L. cyprinacea has been introduced into North and South America by the importation of tropical fishes (Figueira and Ceccarelli, 1991). The species of Lernaea has nine stages in the life cycle, including three free-living naupliar stages, five copepodid stages, and one adult stage (Grabda, 1963; Hoffman, 1999). A er male and female adults mate on the fish host, copulation occurs during the fourth copepodid stage. When the copulation was realized the males presumably dying while the females metamorphose and insert the anterior region of the body into the host tissue and then produce eggs (Hoffman, 1999; Nagasawa et al., 2007). The adult females of the genus Lernaea exhibit an extreme modification of the cephalothorax. The mouth parts of the adult female are severely reduced, the body is elongate and vermiform, and the head is modified into four horn-shaped appendages, which are somewhat long and slender; the two outer or posterior ones are bifurcated and the anterior one is simple (Sco and Sco , 1913). The horns * Corresponding author’s e-mail: [email protected] Bull. Eur. Ass. Fish Pathol., 30(2) 2010, 66 are used for a achment to the host and are buried beneath the epidermis. The abdomen is short and is o en bent dorsally. The genital pore is located at or near the posterior extremity and the egg sacs project well beyond the body (Thatcher and Willians, 1998). Only the adult female lernaeids are parasitic, whereas the males and immature forms of both sexes are free living (Schäperclaus, 1991). L. cyprinacea is capable of massive a ack, with high pathogenicity and mortality, mainly during the summer season. Besides the effects of penetration, haemorrhages and ulcerations are also caused (Carnevia et al., 2003). The most dangerous consequence of an intensive a ack results in blood loss, intense lymphocytopenia, neutrophilia, increase of monocytes (Silva-Souza et al., 2000), and secondary infections (Schäperclaus, 1991). The disease is accompanied by marked emaciation and loss of weight (Stoskopf, 1993; Pavanelli, 1998). The index of mortality is high (Mancini et al., 2008a). The risk of parasite pathogenicity depends on the affected organ, parasitism intensity, environmental conditions and concomitant infections, among other factors (Alvarez Pellitero, 1998). The objective of this study was to investigate the distribution of L. cyprinacea in Argentina, indicating its distribution by province, taking into account that reports of lernaeid parasites infecting freshwater fish in our country are scarce. Material and methods The fish were collected in three Argentinean provinces: Buenos Aires, Mendoza and Rio Negro. A total of 200 Astyanax bimaculatus and 50 Odontesthes bonariensis adult specimens were collected from the Luján river and its flooding lagoons (Buenos Aires) in March-April 2004. Between January and April 2005 a massive mortality of fishes was observed in the dam El Nihuil in the province of Mendoza. The Departamento General de Irrigación (D.G.I) of the government of Mendoza thus sent specimens of Percichthys trucha, Oncorhynchus mykiss and Odontesthes bonariensis to our laboratory. In both cases, the fishes were collected using a nylon gill net and transported alive in plastic bags. The dead fishes were refrigerated until their observation and processing. In January-February 2005, sport fishers captured specimens of Rhamdia quelem in the lagoon Del Burro, origin of the Salado river, Cyprinus carpio in the La Plata river, in the locality Punta Lara (both in the province of Buenos Aires), and Cheirodon interruptus in the Negro river, near the island Choele-Choel (province of Río Negro); the specimens were sent to our laboratory. Specimens of Carassius auratus, Corydoras paleatus, Hypostomus plecostomus and parasitized cichlids were also sent to our laboratory from pet shops of La Plata, province of Buenos Aires. Fishes were examined in the laboratory to determine the presence of parasitic copepods. Parasites were counted and copepods were dissected from the host tissue with needles and preserved in 70% alcohol. Bull. Eur. Ass. Fish Pathol., 30(2) 2010, 67 The parasitological parameter used was the mean intensity. This parameter is the average number of parasites in a positive host. The results were analyzed in a semiquantitative form, considering them as follows: + if the host had 1-3 parasites, ++ if the host had 4-7 parasites, and +++ if the host had 8 or more parasites. Results In the areas studied, L. cyprinacea infected nine species (Table 1), including both wild and pet fish. The infected fish showed severe physical damage in the area of high concentration of adult parasites, where they had caused petechial haemorrhages and ulcers at the site of penetration. The parasites were found on various parts of the host’s body surface and appeared as small worm-like protrusions. L. cyprinacea seems to show a preference for a particular body area for a achment; however, the most heavily infected locations were found behind the gills, skin and the base of the pectoral fins. The lesions found were similar in all fish species. Microscopic observation revealed hyperplasia of the epithelium, abundant infiltration of inflammatory cells (lymphocytes and macrophages) and fibrosis in the site of a achment, not only in the epidermis but also in the dermis and muscular tissue. Discussion Reports of species of lernaeids in South America are scarce, and it should be remembered that there are literally thousands of native freshwater fishes on this continent that have never been examined for parasites (Thatcher, 2000). Table 1. Register of fish parasitized by L. cyprinacea Linnaeus in Buenos Aires, Mendoza and Río Negro provinces. Average intensity: (+)= ≤ 3, (++)= 4 – 7, (+++)= ≥ 8. Locality Provinces Geographical localization Hosts Intensity of parasitism Luján river and its lagoons of flood, Tigre Buenos Aires 34o26’ S 58o32’ W Astyanax bimaculatus Odontesthes bonariensis ++ La Plata river, Punta Lara Buenos Aires 34o49’S 57o59’W Cyprinus carpio + Del Burro Lagoon, basin of the Salado river Buenos Aires 35o41’S 57o55’W Rhamdia quelem + La Plata Buenos Aires 34o55’S 57o57’W Carassius auratus Corydoras paleatus Hypostomus plecostomus + Atuel river, El Nihuil reservoir Mendoza 35o05’S 68o45’W Percichthys trucha Odontesthes bonariensis Oncorhynchus mykiss +++ Negro river, ChoeleChoel island Río Negro 39o22’S 65o43’W Cheirodon interruptus + Bull. Eur. Ass. Fish Pathol., 30(2) 2010, 68 Reports of lernaeid parasites infecting freshwater fish in Argentina are also very scarce. According to Thatcher (2000), Areotrachelus truchae was found in Percichthys trucha (Brian, 1902), Taurocheros salminisii in Salminus brevidens and S. maxillosus (Brian, 1924), Lernaea argentinensis in Pseudoplatystoma coruscan and P. fasciatum (Paggi, 1972) and Taurocheros tarangophilus in Hoplias malabaricus (Paggi, 1976). In relation with L. cyprinacea, Table 2 summarizes the previous findings in Argentina. According to Mancini et al. (2008b), the wild native O. bonariensis and P. trucha, and the introduced species C. carpio and O. mykiss are among the most affected. The pet fish Carassius auratus was the most affected species, but C. paleatus and H. plecostomus were infected as well in the pet shops but not in wild conditions. The finding of infected C. interruptus is the most austral report of infection with Lernaea and the first record of infection in this species. The reproduction of L. cyprinacea is seriously affected by water temperature (Schäperclaus, 1991; Stoskopf, 1993; Pavanelli, 1998). According to Schäperclaus (1991), the life cycle is completed in 100 days at 14°C and in 7-13 days at 28°C, but the optimum temperature lies between 23°C and 30°C. Temperature is considered of great significance; prevalence, abundance and medium intensity of L. cyprinacea had a higher seasonal occurrence during warm months, which coincided with blooms of Cyanobacteria and Dinoflagellates (Mancini, 2006). The prevalence and intensity of infection was significantly reduced in April, which coincides with the decreasing water temperature. Although water temperature plays an important role, it is probably not the only factor affecting the population size of lernaeids. In the province of Mendoza there are three dams: Los Reyunos, Valle Grande and El Nihuil. The last one has a surface temperature of 24.6°C but in January 2005 a massive mortality of fish occurred, since the water temperature increased 2.8°C (Peralta et al., 2006). Choele-Choel is the most austral locality with reports of infection by L. cyprinacea (Figure 1); this could be explained by the high temperatures that the waters of the Negro river can reach in the summer. The record of AIC (Autoridad Interjurisdiccional de Cuencas) indicates that the temperature of the Negro river in January 2005 was 23°C. The existence of the parasite and its pathogenic activity in a very austral locality demonstrates that an increase in temperature generated by contamination or climatic changes could increase significantly the geographical dissemination of L. cyprinacea. The relation between water temperature and infection risk is in agreement with previous findings (Berry et al., 1991; Piasecki et al., 2004). Another parameter that can modify the life cycle of these copepods is water salinity. Some researchers think that the concentration of salts in lakes could determine a reduction in the life time of the Lernidae (Noga, 1996; Mancini et al., 2008a). The lakes of Buenos Aires are shallow, with great variations in the Bull. Eur. Ass. Fish Pathol., 30(2) 2010, 69 Ta bl e 2. P re vi ou s re co rd s of fi sh p ar as iti ze d by L . c yp ri na ce a Li nn ae us in A rg en ti na . Lo ca lit y Pr ov in ce s G eo gr ap hi ca l lo ca liz at io n H os ts R ef er en ce Ba hí a Bl an ca Bu en os A ir es 38 °4 4 ́ S 62 °1 6 ́ W Rh am di a sa po Va no i a nd T an zo la , 2 00 4 N ap os tá G ra nd e st re am , B ah ía Bl an ca Bu en os A ir es 38 °4 8 ́ S 62 °1 4 ́ W O lig os ar cu s j en yn sii G ar ib o i a nd G ua gl ia rd o,