Acanthostomoides apophalliformis (Trematoda: Cryptogonimidae) does not cause detectable mortality in Galaxias maculatus (Teleostomi: Galaxiidae)

HUMAN AND ANIMAL HEALTH

SHORT NOTE

Acanthostomoides apophalliformis (Trematoda: Cryptogonimidae) does not cause detectable mortality in Galaxias maculatus (Teleostomi: Galaxiidae)

Jorge E. RevengaI, ^*; Patricio F. Torres^II; Ines Siegmund^II

^IDepartamento de Acuicultura; CRUB; Universidad Nacional del Comahue; Quintral 1250; [e-mail]; 8400 Bariloche -Argentina

^IIInstituto de Parasitología; Universidad Austral de Chile; casilla 567; Valdivia - Chile

ABSTRACT

The present study was conducted to determine if parasite induced mortality existed in a "puyen" population in Moreno Lake, southern Argentina. Data on both parasite abundance and degree of aggregation of parasite frequency distribution showed the absence of fish mortality induced by A. apophalliformis.

Key words:Galaxias maculatus, Acanthostomoides apophalliformis, parasite-induced host mortality

RESUMO

Acanthostomoides apophalliformis (Trematoda: Cryptogonimidae) não causa mortalidade detectável no peixe Galaxias maculatus (Teleostomi: Galaxiidae) de Argentina do Sul. O "puyen", Galaxias maculatus, é um peixe nativo pequeno que habita a América do Sul e a Oceania. Acanthostomoides apophalliformis é um trematódeo digenético que parasita, freqüentemente, os "puyenes". O estudo atual foi conduzido para determinar se existe mortalidade induzida por parasito no população do "puyen" no lago Moreno, no sul de Argentina. Os dados de abundância do parasito e no grau de aggregação da distribuição de freqüência do parasito, sugerem a ausência de mortalidade induzida por A. apophalliformis em "puyenes".

INTRODUCTION

The "puyen" Galaxias maculatus is a small native fish that inhabits southern South America and Oceania. This is a protected species in Nahuel Huapi National Park and Reserve, southern Argentina. Acanthostomoides apophalliformis is a digenetic trematode whose metacercaria stage frequently parasitizes "puyenes", generally located in the liver (Revenga and Scheinert, 1999a). In a recent study, Revenga et al. (2005) reported mean intensities of 1.8 – 4.4 parasites/infected fish and prevalences of 41.4 -96.7 % in Lake Moreno, southern Argentina. Information on the biology of A. apophalliformis is available in Torres et al., (1988); Ostrowsky et al., (1999); Trochine, (2000). Up to 13 metacercariae have been found in histological liver sections of "puyenes" (representing approximately 15 % of the liver volume), producing atrophy by compression and, in most cases, no inflammatory reaction was found (Revenga, Torres and Siegmund unpublished). Such an extensive alteration is considered a possible cause for inducing host mortality.

Anderson and Gordon (1982) introduced a quantitative approach for detecting signs of parasite-induced host mortality in fish populations. They used simulation experiments (Monte Carlo) and considered a decline of both parasite mean abundance and degree of aggregation of parasite frequency distribution (measured as the variance to mean abundance ratio) in older fishes, to be clear signs (though not conclusive) of such a mortality. The present study applied this quantitative techniques, to determine if damage, observed at histopathological level, induced significant mortality in a "puyen" population in Lake Moreno.

MATERIALS AND METHODS

In January 2001, 477 "puyenes" G. maculatus were obtained in baited traps in Lake Moreno (41º 04´ S, 71º 33´ W), southern Argentina. Traps were submerged at a depth not more than 0.5 m for one day. In the lab, the fishes were measured and dissected under stereomicroscope to collect A. apophalliformis. Parasites were processed according to Ostrowski et al., (1999). In this paper the terms mean abundance, mean intensity and prevalence are used according to the recommendations of Margolis et al. (1982).

RESULTS AND DISCUSSION

Fig. 1 showed that mean abundance of parasites increased steadily with size (as age indicator) of fish (a), whereas variance to mean abundance ratio increased from size class 36-45 to size class 46-55 mm, decreased in size class 56-65 mm and increased again in size class > 65 (b).

This pattern clearly differed from that shown by Anderson and Gordon (1982), for "convex" or "peaked" curves of parasite mean abundance, declining concomitantly with the variance to mean abundance ratio in older fish. It was, therefore, concluded that the lesions occupying up to 15 % of the liver volume and atrophy by compression observed by Revenga, Torres and Siegmund (unpublished) did not induce significant mortality in the "puyen" population studied. Similar results were reported by Revenga and Scheinert (1999b) for Tylodelphys barilochensis, another trematode also infecting "puyenes" as the metacercaria stage.

The fact that both fish and parasites were autochthonous, high parasite abundance (prevalences 41.4-96.7 %), lack of inflammatory reactions in most cases (Revenga, Torres and Siegmund, loc. cit.) and absence of parasite-induced host mortality, suggested that the system had coevolved according to the mutualistic model reviewed by Holmes (1983).

ACKNOWLEDGEMENTS

We thank A. Ruffini for her assistance in the laboratory.

Received: September 14, 2004;

Revised: July 01, 2005;

Accepted: June 05, 2006.

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• Holmes, J. C. (1983), Evolutionary relationships between parasitic helminths and their hosts. In: Futuyama, D. J. and Slatkin, M. (Eds.). Coevolution. Massachusetts: Sinauer Associates. pp. 161-179.
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• Revenga, J. and Scheinert, P. (1999Ş), Infections by helminth parasites in "puyenes", Galaxias maculatus (Galaxiidae, Salmoniformes), from southern Argentina with special reference to Tylodelphys barilochensis (Digenea, Platyhelminthes). Mem. Inst. Oswaldo Cruz, 94, 605-609.
• Revenga, J. and Scheinert, P. (1999b), Absence of Tylodelphys barilochensis (Trematoda: Diplostomidae) Induced Mortality in "puyenes" Galaxias maculatus (Teleostomi: Galaxiidae) from southern Argentina. Mem Inst Oswaldo Cruz, 94, 659-660.
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• Torres, P.; Franjola, R.; Cubillos, V.; Miranda, J. C. and Vera, R. (1988), Parasitismo en ecosistemas de agua dulce en Chile. 1. Presencia de metacercarias del género Stephanostomum (Digenea, Acanthocolpidae) en peces. J. Vet. Med B., 35, 169-177.
• Trochine, C. (2000), Infestación por Acanthostomoides apophalliformis (Trematoda, Acanthostomidae) de la fauna íctica del sistema del lago Moreno. Licenciate thesis, Universidad Nacional del Comahue, Bariloche, Argentina.

*

Author for correspondence

Publication Dates

• Publication in this collection
  23 Feb 2007
• Date of issue
  Sept 2006

History

• Received
  14 Sept 2004
• Reviewed
  01 July 2005
• Accepted
  05 June 2006