Memórias do Instituto Oswaldo Cruz Fundação Oswaldo Cruz, Fiocruz ISSN: 1678-8060 EISSN: 1678-8060 Vol. 97, Num. 1, 2002, pp. 79-80

Mem Inst Oswaldo Cruz, Rio de 
  Janeiro, Vol. 97(1) 2002, pp. 79-80
Myxobolus absonus sp. 
  n. (Myxozoa: Myxosporea) Parasitizing Pimelodus maculatus (Siluriformes: 
  Pimelodidae), a South American Freshwater Fish  
Eduardo F Cellere, Nelson S Cordeiro+, 
  Edson A Adriano  
Departamento de Parasitologia, Instituto de Biologia, 
  Universidade Estadual de Campinas, Caixa Postal 6109, 13083-970 Campinas, SP, 
  Brasil 

  +Corresponding author. Fax: +55-19-3788.6282. E-mail: nsilvac@unicamp.br 
   
Received 23 Frebuary 

  Accepted 16 August 2001 
Code Number: oc02013 
A new myxoporean species is described from 
  a freshwater fish in Brazil. Myxobolus 
  absonus sp. n. was found infecting Pimelodus 
  maculatus captured in the river Piracicaba, 
  State of São Paulo, Brazil. Cysts were found free in the opercular cavity. 
  The spores are large (length-15.7 ± 1.5 µm, width-10.2 ± 
  0.7 µm; mean ± S.D.) and oval in shape, with the anterior end slightly 
  pointed. The spore valves are relatively thin, smooth, and asymmetrical in a 
  frontal view. The polar capsules are pyriform in shape, and unequal in size; 
  the largest are 6.4 ± 0.7 µm long and 3.6 ± 0.5 µm 
  wide, while the smallest are 4.2 ± 0.6 µm long and 2.5 ± 
  0.5 µm wide.  
Key words: Myxozoa - Myxosporea - Myxobolus 
  absonus sp. n. - Pimelodus maculatus - Brazil - South America  

The South American continent, with its numerous 
  rivers, lakes and largest river basin in the world (Amazon basin), has the most 
  diversified fauna of freshwater fish consisting of approximately 8,000 species 
  (24% of all fish species) (Schaefer 1998). There are also numerous species of 
  marine fishes in the continent's coastal waters. In spite of this variety of 
  fish, only 71 (5.7%) of the more than 1,250 Myxoporea species described to date, 
  have been reported in South America, a small number when compared to other regions 
  of the planet. This low number of South American species probably reflects the 
  general lack of studies in this field. In the last 10 years, 17 species of myxosporeans 
  parasitizing South American fish have been described. In this paper, we describe 
  a new Myxosporea species parasitizing Pimelodus maculatus Lecépède, 
  1803, a small feral catfish commonly known as "mandi-amarelo". So 
  far, only two Myxosporea species have been reported to parasitize Pimelodus 
  spp.: Henneguya linearis Gurley, 1893, found in Pimelodus sebae 
  and Myxobolus cunhai Penido, 1927, in Pimelodus clarias (Gioia 
  & Cordeiro 1996). 
 MATERIALS AND METHODS 
   
Adult specimens of P. maculatus were collected 
  between March 1991 and February 1992 in the river Piracicaba, in the municipality 
  of Piracicaba, State of São Paulo, Brazil. The fishes were preserved 
  on ice and immediately transported to the laboratory for autopsy. Spores were 
  obtained from mature cysts and studied fresh in Lugol's iodine solution (2%). 
  The India-ink method was used to detect the mucous envelope of the spores. Dry 
  smears were fixed in absolute methanol and stained with Giemsa before examined 
  with an immersion lens. An average of 30 spores were measured using the dimensions 
  recommended by Lom and Arthur (1989). Measurements were taken from fresh spores 
  obtained from frozen fish and were expressed as the means ± standard 
  deviation (S. D.). Drawing was done with the aid of a camera lucida. Photomicrographs 
  were obtained using a standard Zeiss microscope and Kodak TMAX 100 film. 
RESULTS 
    
Myxobolus absonus sp. n. 
  

  Figs 1-2 
   
Description: spherical whitish plasmodia 
  (cysts) 1-2 mm in size occurred free in the opercular cavity. Spores oval, with 
  the anterior end slightly pointed (Figs 1-2), 
  length-15.7 ± 1.5 µm, width-10.2 ± 0.7 µm; mean ± 
  S.D. The spore valves are thin, smooth and asymmetric in a frontal view (Fig. 
  1); their sutural end is relatively narrow. 
  The two polar capsules are pyriform in shape, and of unequal size (Figs 1-2), 
  the largest being 6.4 ± 0.7 µm long and 3.6 ± 0.5 µm 
  wide and the smallest being 4.2 ± 0.6 µm long and 2.5 ± 
  0.5 µm wide. In lateral view, the polar capsules are in the same plane 
  as the suture line. The polar filament is closely coiled, and aligned perpendicularly 
  to the longitudinal axis of the capsules. In the large capsule, the polar filament 
  has five turns compared to only three in the small capsule. The sporoplasm is 
  large, with two nuclei visible in stained preparations. The iodinophilous vacuole 
  and mucous envelope are absent.  
Type host: Pimelodus maculatus 
  Lacépède, 1803 (Siluriformes: Pimelodidae). 

  Site of infection: opercular cavity (coelozoic parasite). 

  Prevalence: 8.3% (3 parasitized fishes out of 36 examined). 

  Locality: river Piracicaba, near Piracicaba city, State of São 
  Paulo, Brazil. 

  Type material: the slides with stained spores of M. absonus sp. 
  n. (Syntipe) are deposited in the collection of the Museum of Natural History 
  of the Institute of Biology of the State University of Campinas, State of São 
  Paulo, Brazil (accession No.: ZUEC 01; 02; 03). 

  Etymology: the species name is based on the unequal size of the polar 
  capsules. 
DISCUSSION 
  
Comparison of M. absonus sp. n. with Myxobolus 
  spp. found parasitizing South American and other freshwater fishes shows that 
  the distinctive features in M. absonus sp. n. are unequal size of the 
  polar capsules and the asymmetric shape of the valves in frontal view. Of the 
  South American species of Myxobolus, only Myxobolus inaequalis 
  Gurley, 1893 and Myxobolus inaequus Kent and Hoffman, 1948 have polar 
  capsules of unequal size. However, the spores of M. inaequalis are much 
  smaller (5.5 µm x 3.3 µm) than in M. absonus sp. n., while 
  in M. inaequus the spores are larger (19.8 µm x 8.6 µm) than 
  in M. absonus sp. n. and more elongated.  
Of the Myxobolus spp. from other regions 
  of the world which have spores with polar capsules of unequal size, those of 
  M. bilongi Fomena and Bouix, 1994 have dimensions similar to M. absonus 
  sp. n., but the anterior end of the spores is slightly truncated, and the polar 
  filament of the large polar capsule has 9-10 turns while that of the smaller 
  has 6-7 turns, compared to the 5 and 3 turns, respectively, in M. absonus 
  sp. n. 
REFERENCES 

  
Gioia I, Cordeiro NS 1996. Brazilian myxosporidian's 
    check-list (Myxozoa). Acta Protozool 35: 137-149.  
  
Lom J, Arthur JR 1989. A guideline for the 
    preparation of species descriptions in Myxosporea. J Fish Dis 12: 151-156. 
     
  
Schaefer SA 1998. Conflict and resolution: 
    impact of new taxa on phylogenetic studies of the Neotropical cascudinhos 
    (Siluroidea: Loricariidae). In LR Malabarba, RE Reis, RP Vari, ZMS Lucena, 
    CAS Lucena (eds), Phylogeny and Classification of Neotropical Fishes, 
    EDIPUCRS, Porto Alegre, p. 375-400.  

© 2002  
  Instituto Oswaldo Cruz - Fiocruz

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