Field observations revealed, for the first time, cases of predation on Gordius austrinus by Salmo trutta in Risopatrón Lake, Aysén Region, Chile. Reinvestigation by SEM of the characteristics of the posterior end and of the cuticle of the specimens of horsehair worms collected inside the stomach of brown trout allow us to assign the specimens to the species Gordius austrinus. Also we could show that in some specimens the cuticle of mid body and terminal end presented structural alterations, due to the action of the digestive juices of the fish. This finding implies the extension of the distribution range of G. austrinus.Facultad de Ciencias Naturales y Muse

Habit, Evelyn

Ortiz-Sandoval, Juan J.

Villalobos, Leonor Cristina de

English

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Gayana72(l): 31-35,2008 ISSN0717-652X
FINDING OF GORDIUS AUSTRINUS DE VILLALOBOS, ZANCA & 
IBARRA - VIDAL, 2005 (GORDIIDA, NEMATOMORPHA) IN THE STOMACH 
OF SALMO TRUTTA (SALMONIFORMES) IN PATAGONIA
HALLAZGODE GORDIUS AUSTRINUS DE VILLALOBOS, ZANCA & 
IBARRA - VIDAL, 2005 (GORDIIDA NEMATOMORPHA) ENLA DIETA DE 
SALMO TRUTTA (SAEMONIFORMES) ENPATAGONIA
Cristina de Villalobos12, Juan J. Ortiz-Sandoval3 & Evelyn Habit3
'Facultad de Ciencias Naturales y Museo. Paseo del Bosque S/N 1900 La Plata, Argentina. 
2Comisiónde Investigaciones Científicas Provincia de Buenos Aires. La Plata, Argentina. 
E-mail for correspondence: viHalo@fcnym.unlp.edu.ar 
'Unidad de Sistemas Acuáticos, Centro de Ciencias Ambientales EULA-Chile, Universidad de Concepción, 
Concepción, Chile.
ABSTRACT
Field observations revealed, for the first time, cases of predation on Gordius austrinus by Salmo trutta in Risopatron 
Lake, Aysen Region, Chile. Reinvestigation by SEM of the characteristics of the posterior end and of the cuticle of the 
specimens of horsehair worms collected inside the stomach of brown trout allow us to assign the specimens to the species 
Gordius austrinus. Also we could show that in some specimens the cuticle of mid body and terminal end presented 
structural alterations, due to the action of the digestive juices of the fish. This finding implies the extension of the 
distribution range of G. austrinus.
Keywords: Nematomorpha, Gordius austrinus, predation, Salmo trutta, Patagonian Lakes.
RESUMEN
En trabajos de campo se pudo observar, por primera vez, casos de depredación de Salmo trutta sobre Gordius austrinus 
en el Lago Risopatrón, Región de Aysén, Chile. El análisis ultraestructural (MEB) realizado sobre los especímenes de 
gordiidos, colectados dentro del estómago de la trucha café, sobre las características del extremo posterior y la cutícula, 
permitieron asignarlos a la especie Gordius austrinus. Asimismo, mostró que en algunos especímenes la cutícula de la 
región media del cuerpo y el extremo posterior presentaban alteraciones en su estructura, probablemente debidas a la 
acción de los jugos digestivos del pez. Este hallazgo implica la ampliación del rango de distribución de G. austrinus.
Palabras claves: Nematomorpha, Gordius austrinus, depredación, Salmo trutta, Lagos Patagónicos.
INTRODUCTION
Gordiida or horsehair worms, as they are commonly 
called, are worm-like organisms free-living in streams 
and other freshwater environments as adults, where 
they copulate and lay their eggs. The preparasitic larvae 
hatch from eggs in water (Zanca et al. 2007). Part of the 
life cycle is parasitic, in which larvae infect host that are 
usually arthropods (De Villalobos et al. 2003, De 
Villalobos & Ronderos 2003).
Previous studies reported several cases of predation 
on gordiids by freshwater fish (Cochran et al. 1999, 
Poinar2001, Kinziger etal. 2002, Ruiz & Figueroa 2005). 
In this paper we report, for the first time, cases of 
predation on adult of Gordius austrinus (De Villalobos 
et al. 2006) in Chile and show by SEM the damage 
caused by the digestive juices of the fish on the cuticle 
of this species of horsehair worms. All the specimens 
studied corresponded with the descriptions of specimens 
from Gordius austrinus that were described by De
31
Gay ana 72(1), 2008
Villalobos et. al. (2006). Also, this paper implies the 
extension of the distribution range of the species.
MATERIAL AND METHODS
During summer 2006, 81 specimens of Salmo trutta 
(Linnaeus, 1758) were collected using gillnets of 
different mesh size (15,20,30,50,60,70 and 120 mm 
bar mesh size) placed at different depth in six lakes of 
South Chile. Aysen Region. From north to south: 
RisopatronLake (44° 15'39”S - 72° 31'12”W, Palena 
Riverbasin),LasTonesLake(44o45'04"S-72°12'22"W, 
Cisnes River basin), Thompson Lake (45°38'18"S - 
71°47'15"W, Aysen River basin). La Paloma Lake 
(45°52 '40" S - 72°04 T4 " W, Ay sen River basin), Riesco 
Lake (45°29'56"S - 72°40'40"W, Aysen River basin) 
and Tranquilo Lake (46°37'49"S - 72°47T3 "W, Baker 
River basin). Stomach contents were preserved in 
formalin 10% and then analyzed under 
stereomicroscope. Samples of nematomorphs were 
preserved for scanning electron microscopy.
To examine specimens by scanning electron microscopy 
(SEM), fragments of worms (mid-body and posterior 
end) were washed with distilled water, dehydrated in 
an increasing ethanol series prior to their study. They 
were critical point dried, mounted on bronze blocks 
and gold-sputter coated. Observations were performed 
using a JEOL JSM 6360 LV scanning electron 
microscope. Body measurements were made with 
outstretched worms using a ruler. Diameters were 
measured under dissecting microscope using a 
calliper ruler.
Material investigated by SEM was mid body and 
posteriorend: 4 males (MZUC 33137, MZUC 33138, 
MZUC 33139, MZUC 33140) (inside stomach of S'. 
trutta) from RisopatronLake in Aysen, Chile.
RESULTS
Only fishes collected in the Risopatron Lake had 
nematomorphs in their stomachs. In three of the seven 
brown trout specimens (2 females, 37.6 and 38.6 cm 
total length; 1 male, 48.6 cm total length) collected in 
this lake, 4 whole specimens of nematomorphs 
belonging to Gordius austrinus, were found in the 
stomach contents (Figs. 1-3).
Figure 1. Gordius austrinus. Ventral view of the posterior end. (A) Lobes and semicircular postcloacal crescent; scale: 
200 pm. (B) Detail of one lobe showing the cuticle partially modified; scale: 50 pm.
Figura 1. Gordius austrinus. Vista ventral del extremo posterior. (A) Lóbulos y cresta postcloacal; escala: 200 pm. (B) 
Detalle de un lóbulo mostrando la cutícula parcialmente modificada; escala: 50 pm.
32
Finding of Gordius austrinus in Salmo trutta-. De Villalobos, C.etal.
Figure 2. Gordius austrinus. (A) Cuticle of the medial region of the body showing the epicuticle partially destroyed; 
scale: 20 pm. (B) Mid body cuticle with some mucus secretion; scale: 20 pm.
Figura 2. Gordius austrinus. (A) Cutícula de la región media del cuerpo mostrando la epicuticula parcialmente destruida; 
escala: 20 pm. (B) Cutícula de la región media del cuerpo con una secreción de tipo mucosa; escala: 20 pm.
Figure 3. Gordius austrinus. (A) Ventral view of the posterior end showing at the apex of the lobes a spoon shaped cavity 
and the semicircular postcloacal crescent; scale: 200 pm. (B) Mid body cuticle without damage; scale: 100 pm.
Figura 3. Gordius austrinus. (A) Vista ventral del extremo posterior mostrando una cavidad en forma de cuchara en el 
ápice de los lóbulos y la cresta postcloacal semicircular; escala: 200 pm. (B) Cutícula de la región media del cuerpo sin 
daños; escala: 100 pm.
Description of the material investigated'. The newly 
reported specimens, in spite of their cuticular alter­
ations, corresponds with the descriptions of speci­
mens from Gordius austrinus that were described 
by de Villalobos et al. (2006), being type locality 
Agüita de la Perdiz, Pozo de Vertiente, Concepción. 
The body color is dark brown. In the anterior end a 
white cap is absent. The Posterior end is bilobed. 
Lobes vary between515.7 pinto 557.8 pm long and 
210.5 pinto 252.6 pm wide. They are moderately
33
Gay ana 72(1), 2008
long and not diverging (Figs. 1 A, 3 A). The apex of 
the lobes forms a spoon shaped cavity. Posterior 
of the cloacal opening is a semicircular postcloacal 
crescent. Anterior to the postcloacal crescent there 
is a depression with a central cuticular protuber­
ance where the cloacal opening lies (Figs. 1 A, 3 A). 
The cuticle in this depression is smooth. In the 
precloacal region there is a parabolic intergumentary 
ledge which bounds the cloacal depression. The 
cuticle of the terminal end and the body cuticle in 
three of the four specimens collected, showed modi­
fications due to the action of the digestive juices 
of the predator (1 A, IB). The epicuticle is partially 
destroyed although the alternating layers of the 
fibres of the endocuticle canbe observed (Fig. 2A) 
(De Villalobos & Restelli 2001). Likewise, some 
mucus secretion can be seen on the cuticle which 
possibly corresponds to the digestive of S', trutta 
(Fig. 2B). In the fourth specimen (223mm length/ 
1.3mm wide) the cuticle of the body and posterior 
end (Figs. 3 A, 3B) maintain the normal characteris­
tics for this species (De Villalobos et al. 2006) and 
show the posterior end bilobed. Posterior of the 
cloacal opening is a semicircular postcloacal cres­
cent. Anterior to the postcloacal crescent there is a 
depression with a central cuticular protuberance 
where the cloacal opening lies. The cuticle in this 
depression is smooth. In the precloacal region there 
is a parabolic intergumentary ledge which bounds 
the cloacal depression. The body cuticle with trans­
verse oriented slender folds with scattered short 
bristles. This specimen had possibly been swal­
lowed close to the moment of the fish capture and 
therefore the action of the digestive juices had not 
yet affected it.
Dimensions: 41mm. 125mm. 223mm. 260mminlength 
and 0.4mm, 0.51 mm, 1.3 lmn and 1.51 lmn in diameter 
respectively.
Remarks: Although possibly by the action of the 
digestive juices, the distribution patterns of the 
bristles at the posterior end are not so evident, the 
analysis of the characteristics of the posterior end 
and of the cuticle allow us to assign the specimens 
collected in the stomach of S. trutta to the species 
Gordius austrinus.
Finding of G. austrinus inRisopatronLake. Chilean 
Patagonia, implies the extension of its distribution 
range. Previous record indicated a distribution range 
between 20° 21'to 41° 67 'S and 70° 16 'to 72° 30' W. 
Now. we extended its latitudinal distribution until 
44°27'S in Chile.
DISCUSSION
The amount of fish collected in different freshwater 
environments in Chile is high in comparison with 
the scarce incidence of gordiids as part of their diet 
(Ruiz & Figueroa 2005). This could be explained 
because gordiids are generally found rolled in the 
lower part of the aquatic vegetation or with vegetal 
debris (leaves, sticks, etc.) at the bottom of streams, 
places where they can easily camouflage and be 
protected from predators (Hanelt et al. 2005). 
However, there are times when horsehair worms are 
highly vulnerable to a predator like a fish: 1) when 
the gordiids adults emerge, in aquatic enviromnents. 
from their insect host which they previously induced 
to suicide (Thomas et al. 2002, Ponton et al. 2006), 
2) when they form the “Gordian knots” in order to 
reproduce (McLennan & MacMillan 1984, Cochran 
et al. 1999) or 3) when in calm waters gordiids swim 
with slow movements being easily detected by a 
predator (Hanelt etal. 2005).
There are previous reports on the predation of horse­
hair worms by Salmo trutta. in different countries, 
for the United States of America (Clemens 1928, 
Cochran et o/. 1999, Kinzigcr <?/«/. 2002), for Canada 
(Scott & Crossman 1964) and for New Zealand 
(McLennan & MacMillan 1984). For South America. 
Ruiz & Figueroa (2005) point out the presence of a 
specimen of nematomorph, not determined, inside 
the stomach of a brown trout in Chile, and also in 
native fishes like Basilichthvs australis Eigenmann, 
1928 andPercichthvs trucha (Valenciennes. 1833). 
Common result for all these reports is that predation 
on horsehair occurs in oligotrophic aquatic systems. 
Salmonids we found with Gordius austrinus in theirs 
stomachs correspond to adults samples that have 
been described as highly piscivorous (Jonsson et 
al. 1999, Macclii et al. 1999). It is probable that 
Gordius is not an optimal prey since its biomass is 
low comparable to fishes or other prey items like 
decapods. The finding of G austrinus only in 3 of 81 
S. trutta analyzed, and only in one of 5 lakes stud­
ied. indicates trout are probably not selecting gordiids 
as prey, or maybe they are not abundant in the other 
analysed lakes (Risopatron Lake. Las Torres Lake. 
Thompson Lake. Riesco Lake. Tranquilo Lake).
The results of our studies show that G. austrinus is 
part of the diet of the brown trout from Chile. Also 
we showed by SEM, that within the stomach of the 
fishes due to the digestive juices the cuticle of the 
horsehair worms was damaged or altered. The 
34
Finding of Gordius austrinus in Salmo trutta-. De Villalobos, C.etal.
presence of G. austrinus in Risopatrón Lake allows 
extending its distribution for Chile (De Villalobos et 
al. 2006).
ACKNOWLEDGMENTS
We thank Waldo San Martin for help with field work. 
Funding was provided under project DIUC- 
Patagonia 205.310.042-ISP of Universidad de 
Concepción. We also acknowledge an NSF-PIRE 
award (OISE 0530267) for support of collaborative 
research on Patagonian Biodiversity.
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Recibido: 15.10.07
Aceptado: 17.05.08
35


Finding of Gordius austrinus De Villalobos, Zanca & Ibarra - Vidal, 2005 (Gordiida, Nematomorpha) in the stomach of Salmo trutta (Salmoniformes) in Patagonia

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Finding of Gordius austrinus De Villalobos, Zanca & Ibarra - Vidal, 2005 (Gordiida, Nematomorpha) in the stomach of Salmo trutta (Salmoniformes) in Patagonia

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