Scientific Article
ISSN 1678-2305 online version
Santos et al. Bol. Inst. Pesca 2019, 45(2): e449. DOI: 10.20950/1678-2305.2019.45.2.449 1/7
The myxosporidians of the genus Kudoa cause post mortem myoliquefaction in fishery products and may
potentially transmit zoonoses. The present study describes the infection of the skeletal musculature
by Kudoa sp. in two sea catfish species, Cathorops spixii (Agassiz, 1829) and Cathorops agassizii
(Eigenmann & Eigenmann, 1888), captured monthly in an estuary of the municipality of Vigia de
Nazaré, in Pará, northern Brazil between March, 2015, and August, 2016. The morphological features
of the spores are described, and the influence of the seasonal variation on the occurrence of the
parasite is discussed. The specimens were taken to the laboratory for analysis using a hand lens and
light microscopy. When parasites were identified in the musculature, small fragments of the tissue
were removed for histological processing and staining by the Hematoxylin-Eosin, Ziehl-Neelsen, May
Grunwald-Giemsa, and Gomori techniques. The pseudocysts were found in the muscle fibers, and the
spores were star-shaped with elongated extremities and 4 piriform/rounded polar capsules of equal
size. No infections were observed in the fish specimens collected during the rainy season, whereas all
(100%) of the Cathorops specimens examined during the dry season were infected. This indicates that
the ecology and infection patterns of the parasite (identified as a species of the genus Kudoa, on the
basis of its morphological features) is influenced by salinity levels.
Key words: parasite; multivalvulid; histology; myxosporidian; estuary; Cathorops.
Os mixosporídios do gênero Kudoa são causadores de mioliquefação pós-morte em pescado e
apresentam potencial zoonótico. O presente trabalho apresenta infecção por Kudoa sp. em
musculatura esquelética em duas espécies de bagres, Cathorops spixii (Agassiz, 1829) and
Cathorops agassizii (Eigenmann & Eigenmann, 1888) capturados em estuário amazônico,
destacando aspectos morfológicos do esporo e a influência da sazonalidade em sua ocorrência.
No estuário do Município de Vigia de Nazaré, Pará, Brasil, foram capturados 160 espécimes de
Cathorops sp. no período de março de 2015 a agosto de 2016 em coletas mensais. Os exemplares
foram transportados até o laboratório, utilizando lupa e microscópio de luz. Constatada
a presença de parasito na musculatura, pequenos fragmentos do tecido foram retirados
para processamento histológico e coloração por Hematoxilina-Eosina, Ziehl-Neelsen, May
Grunwald-Giemsa e Gomori. Os pseudocistos encontravam-se dentro das fibras musculares e os
esporos apresentavam forma estrelada com extremidades prolongadas, com 4 cápsulas polares
de formato piriforme/arredondadas de tamanhos iguais. Durante os meses que apresentaram
maiores índices pluviométricos, não foi observada infecção parasitária, entretanto, nos meses
com menor índice pluviométrico, a taxa de infecção foi de 100%, dados que sugerem influência
da salinidade nos aspectos ecológicos e infecciosos do parasito, identificado pelos dados
morfológicos como pertencente ao gênero Kudoa.
Palavras-chave: parasito; multivalvulida; histologia; mixosporídeo; estuário; Cathorops.
The diversity of myxosporidian species has been the focus of a range of studies
in many different geographic regions (Lom and Dyková, 2006). In South America,
the Amazon basin, in particular, has enormous potential for the understanding of the
diversity of these parasites, given the region’s considerable fish diversity.
João Lauro Figueiredo dos Santos
Jacqueline Pompeu Abrunhosa
José Ledamir Sindeaux-Neto
Elideth Pacheco Monteiro
Edilson Rodrigues Matos
Universidade Federal Rural da Amazônia – UFRA,
Programa de Pós-graduação em Aquicultura e Recursos
Aquáticos Tropicais, Av. Perimetral, 2501, Terra Firme,
CEP 66077-830, Belém, PA, Brasil.
Universidade Federal Rural da Amazônia – UFRA,
Instituto de Saúde e Produção Animal, Laboratório de
Pesquisa Carlos Azevedo, Av. Perimetral, 2501, Terra
Firme, CEP 66077-830, Belém, PA, Brasil.
Instituto Socioambiental e dos Recursos Hídricos,
Laboratório de Aquicultura Tropical, Av. Perimetral,
2501, Terra Firme, CEP 66077-830, Belém, PA,
Brasil. E-mail:
(corresponding author).
Received: September 25, 2018
Approved: March 01, 2019
Santos et al. Bol. Inst. Pesca 2019, 45(2): e449. DOI: 10.20950/1678-2305.2019.45.2.449 2/7
One myxozoan microparasite that has received considerable
attention in recent years is the genus Kudoa, which causes
post mortem myoliquefaction (degradation of the muscle
fibers, caused by the action of proteolithic enzymes) in fishery
products, rendering the produce unfit for human consumption
(Kawai et al., 2012; Sugita-Konishi et al., 2014). More than
100 Kudoa species have been described (Eiras et al., 2016), but
of these, only Kudoa orbicularis is known to occur in a freshwater
environment (Azevedo et al., 2016). All other species have been
found infecting marine or estuarine fish (Lom and Dyková, 2006;
Eiras et al., 2016).
The species of this genus infect an ample diversity of fish in a
number of different geographic regions, where they may have a
considerable impact on local fisheries and aquaculture operations,
causing economic losses through the myoliquefaction of the
produce (Moran et al., 1999). These authors also recommend the
classification of Kudoa species as zoonotic agents, given their
capacity to cause enterotoxinfections in humans, which provoke
symptoms such as diarrhea, vomiting, and abdominal pain, caused
by the rupture of the gastrointestinal mucosa (Ohnishi et al., 2013;
Sugita-Konishi et al., 2014; Yahata et al., 2015).
To contribute further to the understanding of the distribution
and ecology of Kudoa in South America, the present study
investigated the presence of these parasites in two sea catfish
species (Cathorops spp.) captured in an estuary on the Amazon
coast of Brazil. The morphology of the parasite spore is described,
together with the seasonal pattern in the occurrence of infection.
Fish sampling
The specimens analyzed in the present study were obtained from
the estuary of the Guajará-mirim River, in the municipality of
Vigia de Nazaré (00°51’12” S, 48°08’41” W), in Pará, northern
Brazil. The sample included 82 specimens of Cathorops spixii
and 78 specimens of Cathorops agassizii, which were collected
using cast-nets and hand-lines between March 2015, and August
2016 (SISBIO license number 27,119). The physical-chemical
parameters of the water (temperature, pH, and salinity) were
registered using a multi-parameter apparatus.
The specimens were preserved on ice in styrofoam coolers
for transportation to the Carlos Azevedo Research Laboratory
(LPCA) at UFRA in Belém, Brazil. In the laboratory, the fish
were measured and weighed. For necropsy, the specimens were
anesthetized with 50 mg L
tricain methanesulfonate (MS222
SIGMA), following the recommendations of the UFRA ethics
committee for the use of animals in experimental research
(CEUA: 013/2014). The specimens were then dissected and
the gonads were analyzed to determine their sex. Subsequently,
the specimens were observed under Zeiss stereomicroscopes to
determine the presence of microparasitic cysts. Small fragments
of skeletal muscle were placed on microscope slides in a drop of
water and sealed with a cover slip for the examination of the fresh
material under light microscopy (LM; Zeiss) for the confirmation
of the parasitism.
When the presence of parasites was confirmed, micrographs
of the fresh spores were prepared using a digital camera attached
to the LM, using the AxioVision 5.1 software, to determine the
morphometric features of the species, following Burger and
Adlard (2010). A total of 30 spores per fish were measured to
determine their mean, length, and thickness, and the length and
width of the polar capsules. These findings were compared with
the morphometric data available on the spores of other Kudoa
Preparation of the samples and histological analysis
For the histological analysis, fragments of the muscle tissue,
approximately 0.5 cm thick, were cut from the muscle tissue
of the specimens, and fixed in Davidson solution for 24 hours.
The samples were then dehydrated in a progressive series
of alcohol, and diaphanized in xylol for impregnation and
embedding in paraffin. Sections of 5 µm were then obtained in
a microtome, warmed to 60 °C in a water bath, and then dried
in an oven at 60 °C for 24 hours to guarantee adhesion to the
slide. The sections were then stained with Hematoxilin-Eosin,
Ziehl-Neelsen, May Grunwald-Giemsa, and Gomori (Luna, 1968).
Stained slides were selected for photographic documentation
using a Zeiss microscopic Primo Star AxioCam ERc 5s camera
with AxioVision 5.1 software.
In the Guajará-mirim estuary, the mean water temperature during
the study period was 28.91 ± 0.55 °C (27.67-29.86), with little
variation being found between the first (rainy season) and second
(dry season) halves of the year. However, the pH and salinity varied
considerably between periods, reflecting the influence of rainfall
levels. During the rainy season (January-June), the mean pH was
6.73 ± 0.34 (6.26-7.3), while salinity was 0.01 ± 0.01 (0-0.02),
whereas during the dry season (July-December), the mean pH was
7.71 ± 0.35 (7.3-8.41), and salinity was 6.18 ± 0.87 (5.00-7.55).
The Cathorops specimens collected during the present study
had a mean furcal length of 14.1 cm (10-18 cm) and weight of
48.2 grams (20-102 g). Most (80%) of the individuals were females
(128/160 specimens). The prevalence of parasite infection varied
considerably between seasons, with none of the 80 Cathorops
specimens collected during the rainy season (January-June)
presenting Kudoa sp. (Figure 1) in the musculature. In July, by
contrast, half (10/20) of the Cathorops specimens collected were
infected with Kudoa sp., and all 60 specimens collected between
August and December were infected. The parasites were found in
both the epaxial and hypaxial musculature (Figure 2A).
The pseudocysts were found within the skeletal muscle fibers,
with an elongated shape in the longitudinal view, 1.2(± 0.2) mm
long and 0.3 (± 0.1) mm in width (Figure 2B, C), containing
mature tetra-capsuled spores (Figure 2D). The pseudocysts in the
musculature of the host were identified by the different techniques
(Hematoxilina-Eosina, May-Grunwald-Giemsa, Ziehl-Neelsen,
and Gomori) used to stain the histological sections (Figure 3).