Salt is commonly recommended as an inexpensive treatment against monogenoids in freshwater fish
culture; however, few studies have scientifically evaluated its efficacy. In the present study we tested the
efficacy of salt treatments against Dawestrema cycloancistrium Price & Nowling, 1967 infestation on
farmed “pirarucu” (Arapaima gigas (Schinz, 1822)). Fish-farmers from the city of Iquitos, in Peru started
to notice mortalities on the A. gigas cultivated in their ponds. In order to determine to cause of the
mortalities, 26 samples from 13 fish-farmers were sent to the “Laboratorio de Parasitologia y Sanidad
Acuícola” of the “Instituto de Investigaciones de la Amazonía Peruana”, Iquitos-Peru. Gills analyzed
revealed high infestation levels by D. cycloanistrium. To treat infested fish, salt in three concentrations
-1 -1 -1 -1
were tested: T1 = 15 g·L ; T2 = 25 g·L ; and T3 = 30 g·L . Treatment 3 (30 g·L ) was most effective
against the infestation of D. cycloancistrium. The number of parasites detached and counted 24 h after the
application of treatments was higher than 30 min after, showing that parasites continue detaching from the
gill of their hosts, even 24 h after the application of salt. Other concentrations of salt and different exposure
times need to be tested, in order to find the most effective and safest treatment for A. gigas infested by D.
cycloancistrium.
ISSN Versión impresa 2218-6425 ISSN Versión Electrónica 1995-1043
ORIGINAL ARTICLE / ARTÍCULO ORIGINAL
MORTALITY OF ARAPAIMA GIGAS (SCHINZ, 1822) (ARAPAIMIDAE) CAUSED BY DAWESTREMA
CYCLOANCISTRIUM PRICE & NOWLING, 1967 (MONOGENOIDEA) FROM FISH-PONDS IN THE
PERUVIAN AMAZON AND THE USE OF SALT FOR ITS TREATMENT
MORTALIDAD DE ARAPAIMA GIGAS (SCHINZ, 1822) (ARAPAIMIDAE) CAUSADA POR
DAWESTREMA CYCLOANCISTRIUM PRICE & NOWLING, 1967 (MONOGENOIDEA)
PROCEDENTES DE ESTANQUES DE PECES EN LA AMAZONÍA PERUANA Y EL USO DE SAL
PARA SU TRATAMIENTO
1 Instituto de Investigaciones de la Amazonía Peruana, Laboratorio de Parasitología y Sanidad Acuícola, Av. José A.
Quiñones, Km 2.5 – San Juan Bautista, Iquitos, Loreto, Peru. 0784.
2 Universidad Nacional de la Amazonía Peruana (UNAP), Sargento Lores, 385, Iquitos, Perú
3 Instituto Nacional de Pesquisas da Amazonia (INPA), Av. André Araújo, 2.936 - Petrópolis - CEP 69.067-375 - Manaus –
Amazonas, Brasil.
* Corresponding author: germantiss1106@gmail.com
ABSTRACT
Keywords: fish-farm – Iquitos – Monogenoid – Parasite – sodium chloride
Neotropical Helminthology
235
Neotropical Helminthology, 2019, 13(2), jul-dic:235-243.
1 1 1
Germán Augusto Murrieta Morey ; Clint Sting Chirinos Ramírez ; José Carlos Zumaeta Cachique ; Luciano
1 2 3
Rodríguez Chu ; Paola Vanesa Mendoza Rodríguez &Jeffson Nobre Pereira
ÓrganooficialdelaAsociaciónPeruanadeHelmintologíaeInvertebradosAfines(APHIA)
Lima-Perú
VersiónImpresa:ISSN2218-6425VersiónElectrónica:ISSN1995-1043
Volume13,Number2(jul-dec2019)
Not all species marketed in the Peruvian Amazon
come from fishing in natural environments; some
of them come from aquaculture production that
tries to compensate the decrease of natural
resources, exploited in an unsustainable manner.
This activity in the Peruvian Amazon has been
experiencing a constant growth of more than 15%
per year for a decade. Within the main cultivated
species stands out the arapaima Arapaima gigas
(Schinz, 1822) (Arapaimidae), known in Peru as
“paiche” (García-Dávila et al., 2018).
The arapaima has a high economic potential in fish
farming, both for the production of meat with a
view to national and international markets, and for
the production of fingerlings for exportation to
different countries of the world (García-Dávila et
al., 2018).
With the intensification of breeding systems, there
is a need for greater knowledge about the
appropriate management to provide improvement
in fish health conditions, especially in the early
stages of production, larviculture and fish farming.
At these stages, when fish are continually exposed
to adverse conditions and their immune system still
236
RESUMEN
Palabras claves: Cloruro de Sodio – Iquitos – Monogenoideo – Parásito – Estanque de peces
La sal se recomienda comúnmente como un tratamiento económico contra los monogenoideos en peces
de agua dulce; sin embargo, pocos estudios han evaluado científicamente su eficacia. En el presente
estudio probamos la efectividad del tratamiento con sal contra la infestación de Dawestrema
cycloancistrium Price & Nowling, 1967 en paiches (Arapaima gigas (Schinz, 1822)) provenientes de
cultivo. Piscicultores de la ciudad de Iquitos, Perú, comenzaron a notar la mortalidad en especímenes de A.
gigas cultivados en sus estanques. Para determinar la causa de la mortalidad, se enviaron 26 muestras de
13 piscicultores al Laboratorio de Parasitología y Sanidad Acuícola del Instituto de Investigaciones de la
Amazonía Peruana, Iquitos-Perú. Las branquias analizadas mostraron altos niveles de infestación por D.
cycloanistrium. Para el tratamiento de peces infestados, se probó la sal en tres concentraciones: T1 = 15
-1 -1 -1 -1
gL ; T2 = 25 gL ; y T3 = 30 gL . El tratamiento 3 (30 gL ) demostró ser el más efectivo contra la
infestación por D. cycloancistrium. El número de parásitos liberados y contados 24 horas después de la
aplicación de los tratamientos fue superior a los 30 minutos posteriores a la aplicación del tratamiento, lo
que demuestra que los parásitos continúan separándose de los arcos branquiales de los huéspedes hasta 24
horas después de la aplicación de la sal. Es necesario evaluar otras concentraciones de sal y diferentes
tiempos de exposición para encontrar el tratamiento más efectivo y seguro para A. gigas infestadas por D.
cycloancistrium.
INTRODUCTION does not respond properly, they become more
susceptible to parasites and diseases (Tavares-Dias
& Martins, 2017).
The lack of information, mainly on the production
and management of arapaima, has markedly
impeded the development of fish farming
(Imbiriba, 1991). Within the obstacles found for the
production of arapaima, parasitic diseases play an
important role in the quantity and quality of fish
production (Gaines et al., 2012). Monogenoideans
are ectoparasites with present a direct life cycle and
can rapidly multiply and disperse in fish ponds,
reaching high intensities. These parasites are
responsibles of major losses in fish culture (Flores-
Crespo & Flores, 2003). In the Peruvian Amazon
there are reports concerning to high infestation by
species of Monogenoidea, with cases of mortalities
and economic losses in fish-farmers.
In fish-farming, the salt (sodium chloride) is used
as a mediator of stress when fish are manipulated
(Lim & Webter, 2001) and for treating parasitic
diseases. It is less harmful to fish hosts compared to
other anti-parasitic treatments, such as formalin or
malachite green and its low cost and availability
make it the recommended treatment against a
variety of fish diseases. Nevertheless, despite its
practical use there have been few studies to test the
Neotropical Helminthology, 2019, 13(2), jul-dic Murrieta Morey et al.
effective concentration against monogenoideans.
Taking into consideration the importance of A.
gigas for aquaculture, the risk of infestations by
monogenoideans and the possibility of using salt
for its treatment, the present study evaluated the
parasitism of Dawestrema cycloancistrium Price &
Nowling, 1967 on this fish species, by assessing the
impact imposed by the parasite on its host by
calculating parasitological indices and by testing
the use of salt in different concentrations against
this parasite.
Study area and Fish
Twenty-six A. gigas (21.5 ± 6.5 cm average length;
70.7 ± 15.8 g average weight) were collected from
thirteen fish ponds located along the Iquitos-Nauta
highway in March 2019 (Fig. 1). All specimens of
A. gigas collected belong to one producer, who
distributed all fishes to fish-farmers in February
2019. One week after receiving the fishes, all fish-
farmers started to notice mortalities on some
specimens of A. gigas. Mortalities didn't stop, so,
fish-farmers decided to send samples for
parasitological analyses to the laboratory of
“Parasitología y Sanidad Acuícola” of the
“Instituto de Investigaciones de la Amazonía
Peruana” (IIAP) in Iquitos, Peru. Two specimens of
A. gigas were analyzed from each fish pond.
Collection, identification of parasites and
parasitological indices
In order to determine the species of parasites in A.
gigas and to evaluate the parasitic load, the skin,
gills and internal organs were analyzed. Samples of
the skin were taken by using a spatula and observed
under microscope. Gill archers were removed and
observed under microscope. To analyze internal
organs, a longitudinal cut from the anus to the
operculum opening was made. Organs were placed
individually in Petri dishes and analyzed under
stereoscope.
Gill archers were removed and placed in vials
containing heated water (68 °C). Each vial was
shaken vigorously and 96% ethanol was added
(final concentration approximately 75-80%). The
content of each vial was examined using a
dissecting microscope. Helminths were removed
from the gills or sediment using dissection needles.
Some specimens were stained with Gomori's
trichrome (Humason, 1979) and mounted in
Dammar's gum, to determine internal morphology,
while others were mounted in Hoyer's mounting
medium (Humason, 1979), for the study of
sclerotized structures. Illustrations were prepared
with the aid of a microprojector. Sclerotized
structures of all parasites were photographed with a
digital camera (Axio Cam ERc 5S) connected to a
microscope (ZEISS Primo Star). The identification
of the species was based on the taxonomic keys of
Kritsky et al. (1985). The ecological terms in
parasitology followed those provided by Bush et
al. (1997). In order to compare the results of each
treatment, an ANOVA – Tukey Test was conducted
by using the software BioEstat 5.3.
In vivo tests with A. gigas exposed to of salt
The experimental design was a completely
randomized block with three treatments and three
replicates with one fish each. In vivo tests consisted
of therapeutic baths of 30 minutes with three
-1 -1
concentrations of salt: T1 = 15 g·L ; T2 = 25 g·L ;
-1
T3 = 30 g·L . Therapeutic baths were performed in
50 L glass aquarium, with a static water system and
constant aeration. After 30 min of treatment, fishes
were placed in other glass aquariums with clean
water.
To evaluate the effectiveness of salt in each
treatment, parasites released into the water were
counted. For this, the water from each aquarium
was filtered in qualitative Whatman filter papers n°
1, in order to visualize possible monogenoids
specimens that might have been detached from the
gills. The filtered water and the filter itself were
examined separately in Petri dishes under a
stereoscopic microscope. In order to continue
testing the effectiveness of salt twenty-four h after
the application of each treatment, the water of each
experimental unit was filtered again and analyzed.
This process was repeated during two days.
Physical and chemical parameters
Samples of water from fish-ponds were taken to the
lab in order to measure the values of Nitrite and
Ammonium (ppm). Those parameters were
measured by using a LAMOTE testing kit.
Additionally, information concerning to
O
temperature (T C), dissolved oxygen (ppm) and
MATERIAL AND METHODS
Neotropical Helminthology, 2019, 13(2), jul-dic Mortality of Arapaima gigas caused by Dawestrema
237
pH were measured daily by fish-farmers. That
information was provided to evaluate the influence
of water quality on the infestation of monogenoids.
Ethic aspects
Statement on ethical approval from an ethics
committee and license for working with fish
species were followed according to the following
resolutions: Resolution No132-2014-GRL-
DIREPRO; Resolution No21-2016 GRL-
DIREPRO; and PTH-068-16-PEC-SANIPES.
Identification of the parasite species and
parasitological indices
The monogenoidean Dawestrema cycloancistrium
Price & Nowling, 1967 was identified parasitizing
the gill filaments of specimens of A. gigas, with a
prevalence of 100%, 6320 parasites recorded with
an intensity of 79-880, and mean abundance of
243.1 ± 164.1 (Table 1). The mean number of
parasites recorded was 486 ± 287.
The main characteristics of the species are:
copulatory complex includes a tubular cirrus with
expanded base that coils 6 times, accessory piece
terminally enclosing cirrus shaft. Vagina tubular,
ventrolateral, sclerotized, proximally coiled, with
distal petal-shaped sclerotization protruding from
aperture. Egg elongate ovate, with proximal
filament; exceptionally long. Ventral anchor
robust, with elongate straight point, heavy base,
ornate deep root, superficial root with conspicuous
saddle-like fold; dorsal anchor with curved point
and shaft, fold of superficial root weakly
developed. Ventral bar plate-like, with anterior
medial projection arising near posterior margin;
Dorsal bar with globose ends, heavy ridge along
posterior margin (Figure 2).
RESULTS
Table 1. Parasitological indices of Dawestrema cycloancistrium Price & Nowling, 1967 in infested Arapaima gigas
(Schinz, 1822). AF = analyzed fish; PF = parasitic fish; P% = prevalence; I = intensity; mI = mean intensity; mA =
mean abundance
Fish Farms (FF) AF PF P% I mI mA
FF 1
2
2
100
299 (140-159)
149.50 149.50
FF2
2
2
100
231 (79-159)
115.50 115.50
FF3
2
2 100 251 (96-155)
125.50 125.50
FF4
2
2 100 626 (294-332)
313.00 313.00
FF5
2
2 100 473(231-242)
236.50 236.50
FF6
2
2 100 583(269-314)
291.50 291.50
FF7
2
2 100 1188(308-880)
594.00 594.00
FF8
2
2 100 229(98-131)
114.50 114.50
FF9
2
2
100
682(321-361)
341.00 341.00
FF10
2
2
100
699(333-366)
349.50 349.50
FF11
2
2
100
242(84-158)
121.00 121.00
FF12 2 2 100 199(97-102) 99.50 99.50
FF13 2 2 100 618 (260-358) 309.00 309.00
Neotropical Helminthology, 2019, 13(2), jul-dic Murrieta Morey et al.
238
Efficacy of salt against the infestation of D.
cycloancistrium -1
Treatment 3 (T3 = 30 g·L ) showed the best results
after counting the detached parasites 30 min and 24
h after the application of each treatment. The
number of parasites counted 24 h after was higher
than 30 min after. Additionally, in day 2, the
number of parasites counted was considerably
reduced (table 2). The mean number of parasites
detached recorded after two days of treatment was:
T1 = 16; T2 = 52 and T3 = 167. Tukey test results
showed: T1 and T2 = p > 0.05; T1 and T3 = p < 0.01
and T2 and T3 = p < 0.05.
Physical and chemical parameters
Fish-farmers registered a mean temperature of 28 ±
O -1
2 C, dissolved oxygen of 3.5 ± 1.5 mg·L , pH of
6.5 ± 0.6. Water samples revealed high values of
Nitrite (> 0.05 ppm) and ammonium (> 0.1 ppm).
Table 2. Number of parasites counted 30 minutes and 24 hours after the application of each treatment. T = treatment;
-1 -1 -1
R = replica; T1 = 15 g·L ; T2 = 25 g·L ; T3 = 30 g·L
Day 1 Day 2
Treatments
Number of parasites
counted
30 min after
Number of
parasites counted
24 h after
Number of
parasites counted
30 min after
Number of
parasites counted
24 h after
Sum of
Parasites
T1 R1 2 4 1 1 8
T1 R2 4 15 1 1 21
T1 R3 3 7 6 3 19
T2 R1 18 83 6 2 109
T2 R2 9 24 2 0 35
T2 R3 1 7 3 1 12
T3 R1 65 152 0 0 217
T3 R2 28 105 2 0 135
T3 R3 6 138 7 0 151
Figure 1. Lateral view of specimen of Arapaima gigas (Schinz, 1822). Scale bar = 10 cm.
Neotropical Helminthology, 2019, 13(2), jul-dic Mortality of Arapaima gigas caused by Dawestrema
239
Figure 2. Sclerotised structures of Dawestrema cycloancistrium Price & Nowling, 196. 1. Male copulatory organ
(MCO); 2. Accessory piece; 3. Egg; 4. Ventral bar; 5. Dorsal bar; 6. Ventral anchor; 7. Dorsal anchor. Scale bar: 1 – 2 =
100µm; 3 = 100µm; 4 – 7 = 30µm.
Neotropical Helminthology, 2019, 13(2), jul-dic Murrieta Morey et al.
240
In Peru, there are reports of high levels of
infestation by D. cycloancistrium affecting
specimens of A. gigas from fish-farming
(Iannacone & Luque, 1991; Mathews et al., 2013;
Mathews et al., 2014; Serrano-Martínez et al.,
2015). In the present study, this monogenoid was
identified parasitizing the gills of A. gigas from
different fish-farms located in Iquitos, Peru.
Fish cultivated in fish-farms are exposed to poor
water quality, crowding, inadequate manipulation
and many other stressors which may negatively
affect their immune system and consequently their
resistance to parasitological diseases (Sado et al.,
2010, Jha et al., 2007). In the present study, high
values of Nitrite and Ammonium were registered in
the samples collected from the ponds. We assume
that poor water quality influenced negatively in the
health of the A. gigas, becoming the fish more
susceptible to infestation by monogenoids.
Lentic environments favor the transmission of
monogenoids (Flores-Crespo & Flores, 2003). In
regions with tropical weather, the life cycle of
monogenoids can be completed in h. In this way,
parasites proliferate rapidly, increasing the
transmission from one individual to another.
According to the owners of the sampled fish-farms,
temperatures registered daily oscillate between 27
O
to 29 C, favoring the speed of life cycle of D.
cycloancistrium, justifying the high parasitological
indices recorded.
Pavanelli & Takemoto (2008) recommended the
use of salt in concentrations between 1 to 3%
during 60 min for treating ectoparasites
infestations. According to Vargas et al. (2003), the
treatment using 3% of salt for 10 min is efficient
against the parasitism by species of Gyrodactylus
von Nordmann 1832 but is less efficient against
species of Dactylogyrus Diesing, 1850. Kubitza
(2000) suggested a higher concentration of salt (3.5
to 5% for five to 10 minutes) and Cone (1995)
recommended using 4.5 to 5% of salt for 2.5
minutes. The results of those authors showed that
the use of one product can be effective for some
species but ineffective for others. In this way, it is
important to test the effectiveness of one product
for a defined species because not all species can
react in the same way against any treatment.
Exposing freshwater organisms to saline
conditions disrupts their osmoregulation, resulting
in water loss and dehydration. Ectoparasites or
free-living parasitic stages are more severely
affected by such disruption in osmoregulation
compared to their fish host (Shephard, 1994). Salt
baths using high concentrations during a short
exposition time act aggressively against parasites
and are more effective than long-term baths (Bakke
et al., 2007). In the present study the treatment
using the highest concentration of salt showed the
best results. The absence of motility and the
detachment of the parasites during the application
of the treatment and 24 h later confirm the
efficiency of salt in high concentrations against the
infestation of D. cycloancistrium.
Salt is a safer treatment option in aquaculture
compared to other broad anti-parasitic treatments
such as formalin or malachite green, despite reports
of increased mortalities amongst fish (Buchmann,
1997). In the current study, no mortalities occurred
during the application of treatments but we
consider necessary to test other concentrations of
salt and different exposition times, in order to find
the most effective and safer treatment for A. gigas
infested by D. cycloancistrium.
We thank Project PIP PAICHE and the fish-farmers
associated to the project for providing the fish used
in the present study.
DISCUSSION
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