A NEW HEDRURID SPECIES (NEMATODA) FROM GALAXIID FISHES IN PATAGONIA

(ARGENTINA) AND INFECTION OF AMPHIPODS AS INTERMEDIATE HOST

Norma L. Brugni and Gustavo P. ViozziLaboratorio de Parasitologıa, INIBIOMA (Universidad Nacional del Comahue-CONICET). Quintral 1250, (8400) Bariloche, Argentina.e-mail: nbrugni@crub.uncoma.edu.ar

ABSTRACT: During a parasite survey of galaxiid fishes (Galaxiidae) from Patagonian Andean lakes, a new species of nematode,Hedruris suttonae n. sp. was collected from the stomach of the native Galaxias maculatus (Jenyns) and G. platei (Steindachner).Specimens were examined by light and scanning electron microscopy, especially head morphology, female caudal prehensile structure,and distribution of spines. The new species is distinguished by body and tail size, morphology and size of spicules, the arrangement ofcaudal papillae in the male, the female caudal hook, and size of eggs. Hyalella patagonica (Ortmann), a Neotropical species ofAmphipoda, is reported as its natural intermediate host. Data regarding prevalence and mean intensity in the intermediate anddefinitive hosts are included. The diet and habitat of the hosts, the percentage of gravid females, the high values of prevalence, andmean intensity in galaxiid fishes, as well as the wide distribution of H. suttonae, collectively indicate that, in these oligotrophic Andeanlakes, G. maculatus and G. platei are true definitive hosts of this nematode.

Species of Hedruris Nitzsch, 1821 belong to the monotypic

Hedruridae and have a worldwide distribution. The genus

includes 22 nominal species (Bursey and Goldberg, 2000, 2007),

which are characterized by the female prehensile structure and a

caudal hook. They have heteroxenous life cycles, with fishes,

amphibians, and reptiles as their definitive hosts. One hedrurid

species, H. spinigera Baylis, 1931, has been cited as infecting

Galaxias maculatus (Hine et al., 2000) in New Zealand. In

Argentinean Patagonia, Hedruris sp. has been reported to infect

native galaxiid fishes (Galaxiidae), i.e., G. maculatus (Jenyns)

(Ortubay et al., 1994; Revenga et al., 2005; Viozzi et al., 2009) and

G. platei Steindachner (Ortubay et al., 1994). It has also been

reported from the stomach of piscivorous native fish such as

Percichthys trucha (Cuvier et Valenciennes) as well as introduced

salmonids (Ortubay et al., 1994).

Galaxias maculatus is a small fish and has been reported from a

variety of habitats in Australia, Tasmania, Lord Howe Island,

New Zealand, Chatham Island, southern Chile, southern Argen-

tina, and Malvinas Islands (Berra et al., 1996; McDowall, 2000),

whereas G. platei is distributed in southern South America (Chile

and Argentina) and the Malvinas Islands, inhabiting the deep

zones of the lakes (Milano et al., 2002). In the northwestern

Argentinean Patagonian lakes, both species have landlocked

populations (Cussac et al., 2004).

Hedruris androphora Nitzsch, 1821 and H. ijimai Morishita,

1926 develop as larvae in freshwater isopods and reach sexual

maturity in amphibians (Petter, 1971; Hasegawa and Otsuru,

1979). Moniez (1889) suggested that amphipods could be the

intermediate host of the Neotropical species H. oriestae, which

develops in fishes. In Argentinean Patagonian lakes, the

amphipod Hyalella patagonica Ortmann (Hyalellidae) is one of

the major food items in the diet of galaxiids but has only been

reported as a host for acanthocephalans (Semenas et al., 2002;

Rauque and Semenas, 2007).

The aim of the present study is to describe a new species of

Hedruris from the stomach of G. maculatus and G. platei and to

identify the intermediate host.

MATERIALS AND METHODS

Specimens of both galaxiids were captured during summers between1995 and 2003 in Andean Patagonian lakes (Table I). Galaxias maculatuswere collected using baited traps from the coast, transported alive to thelaboratory, and necropsied within 48 hr of capture. Specimens of G. plateiwere captured with gillnets, transported freshly killed to the laboratory,and immediately examined using a dissecting microscope. Specimens ofthe amphipod H. patagonica were captured from November 1998 toJanuary 1999, by nets, in Lake Moreno (41u039S–71u319 W) and weredissected using a stereoscopic microscope in the laboratory.

Nematodes were removed from fish and amphipods, fixed in 5%formalin, and cleared in Aman’s lactophenol for light microscopeinvestigation. Selected specimens from fishes were dehydrated in a gradedethanol series, critical point dried, coated with gold, and examined using aJSM T100 scanning electron microscope (JEOL, Tokyo, Japan).Illustrations were prepared with aid of a camera lucida. Somemeasurements were obtained using a calibrated curvimeter for cameralucida drawings. The morphometric data are based on 20 mature malesand 30 females with larvigerous eggs. Eggs were obtained from the vulvarregion of dissected worms. All measurements are expressed in micrometersunless otherwise stated, with the mean followed in parentheses by therange. In addition, voucher specimens of Hedruris sp. (MACN-Pa 466)deposited by Viozzi et al. (2009) were examined to compare with our ownmaterial. Specimens of G. maculatus (462) and G. platei (60) were collectedfrom a total of 22 Andean Patagonian lakes between 39u099S–71u179Wand 45u159S–71u129W, and specimens of H. patagonica (1,452) werecollected from Lake Moreno (Table I).

Specimens were deposited in the Coleccion Nacional de Parasitologıa,Museo Argentino de Ciencias Naturales Bernardino Rivadavia, BuenosAires, Argentina (MACN-Pa); Coleccion Parasitologica de la UniversidadNacional del Comahue, Bariloche, Argentina (UNCo-Pa); ColeccionHelmintologica del Museo de La Plata, La Plata, Argentina (CHLMP);and the U.S. National Parasite Collection, Beltsville, Maryland (USNPC).

RESULTS

Adult nematodes of a new species of Hedruris were found

parasitizing the stomach of the fishes. The specimens of Hedruris

sp. from G. maculatus deposited by Viozzi et al. (2009) were

morphometrically similar to the specimens of the new species.

Larval stages and immature adults (fifth stage) of Hedruris sp.

were found in the hemocoel (dorsally to the gut) of the amphipods

(Fig. 4). The prevalence of infection was 17%, the mean intensity

1.3, and the maximum intensity registered was 6 larvae in a single

specimen. The larvae exhibited extreme precocity, and the

morphological characteristics of these immature adults are exactly

identical with those of adults from fishes, except by their smaller

sizes and absence of eggs.

Received 14 July 2009; revised 15 August 2009; accepted 1 September2009.DOI: 10.1645/GE-2251.1

J. Parasitol., 96(1), 2010, pp. 109–115

F American Society of Parasitologists 2010

109

DESCRIPTION

Hedruris suttonae n. sp.(Figs. 1–3)

Diagnosis: Habronematoidea, Hedruridae. Body cuticle thick, transver-sally striated. Cephalic end with 2 large lateral pseudolabia, each bearingpair of small apical digitiform papillae, 1 amphid, and pair of lateral sessilepapillae. Base of each pseudolabium supported by posteriorly directedcuticular ridge. Dorsal and ventral labiae (interlabia) between pseudola-bia, each with anteriorly directed lobe, curved over surface of apicalregion, and 2 bifurcated lateral cuticular structures, with cuticular ridgeposteriorly directed between bifurcations. Base of each interlabiumsupported by large, posteriorly directed ridge. Buccal cavity thin walled,flattened laterally, with sclerotized annulus at junction with esophagus.Esophagus not clearly divided into muscular and glandular portions.Deirids simple, anterior to nerve ring. Female with posterior sclerotizedhook for attachment to host; male generally found encircling female.

Male (based on 20 specimens): Body length 8.9 (8.0–10.5) mm,maximum body width 234 (202–269). Pseudolabia 83 (60–96) long.Esophagus 1.3 (1.1–1.5) mm long. Deirids 217 (156–288), nerve ring 264(197–317), and excretory pore 458 (341–576) from anterior extremity.Posterior end of body spirally coiled in 3 rings, with caudal alae. Ninepairs of postcloacal papillae, 8 subventral, and last pair lateral. Arearugosa with up to 8 ventral longitudinal ridges with scale-like bosses,extending 2.9 (2.2–3.9) mm from cloaca. Spicules 232 (214–286) long,markedly slender, fused in distal two thirds, with membranous expansions.Gubernaculum lacking. Tail 368 (286–464) long, with a pair of very smallventro-lateral phasmids, just posterior to last pairs of postanal papillae.

Female (based on 30 gravid specimens): Body length 9.5 (8.3–12) mm,maximum body width 435 (346–509). Pseudolabia 100 (89–115) long.Esophagus 1.6 (1.4–1.9) mm long. Deirids 240 (204–281), nerve ring 295(257–346), and excretory pore 481 (403–576) from anterior extremity.Vulva 246 (192–336) from anus. Prodelphic, vulva leading to singleovijector joining the uterus. Egg-filled uterus occupying the entire bodycavity when gravid. Tail curved dorsally 485 (393–643) long, with eversibleprehensile structure (holdfast) armed with sclerotized hook, having centralpiece 197 (173–218) long, and 2 lateral projections 124 (109–155) long.Accessory elongate sclerotized support formed by two arms 334 (214–400)long, extending subventrally from hook base to near anus. Cuticularspines only on posterior part of body. Spines distributed in 2 areas, 1 withsharply pointed spines near region of anus, and other, with scale-like

spines on the dorso-lateral surface of holdfast. Nonmammilated eggs 43(41–55) long and 17 (14–20) wide, operculated at both poles, containingfully developed larva.

Taxonomy summary

Type host: Galaxias maculatus (Jenyns).Maximum intensity: Sixty-two, Lake Fonck.Other definitive host: Galaxias platei Steindachner.Maximum intensity: 548, Lake Coyte.Type locality: Lake Moreno (41u039S–71u319W), Patagonia, Argentina.Percentage of gravid female (Lake Moreno): In G. maculatus 91%, in G.

platei 81%.Other localities: See Table I.Prevalence and mean intensity in other localities: See Table I.Site of infection: Stomach. Females attached to mucosa by the caudal

hook, males free or coiled around females (sometimes more than 1 foreach female).

Specimens deposited: Holotype male and allotype female (MACN-Pa)406-1 and paratypes (MACN-Pa) 406-2 (5 males and 8 females), paratypes(UNCo-Pa) 129 (6 males and 10 females), paratypes (CHLMP) 4927 (5males and 8 females), and paratypes (USNPC) 102470 (3 male and 3female) deposited in the USNPC. Voucher specimens of parasitizedHyalella patagonica (MACN-In) 37715 and larvae from Hyalellapatagonica (MACN-Pa) 485/1.

Etymology: The new species is named in honor of Dr. Carola AnaSutton, for her contribution to the taxonomy of parasitic Nematoda.

Remarks

Species of Hedruris are distinguished each other on the basis of thearrangement of caudal papillae in the male and appearance of eggs(Bursey and Goldberg, 2007). Of the 22 nominal species, Hedruris suttonaen. sp. is most similar to H. androphora Nitzsch, 1821, H. orestiae Moniez,1889, H. ijimai Morishita, 1926, H. basilichtensis Mateo, 1971, and H.moniezi Ibanez and Cordova, 1976, in that males of the new species exhibit9 pairs of caudal papillae and that these are arranged posterior to thecloaca (Mateo, 1971; Petter, 1971; Ibanez and Cordova, 1976; Bursey andGoldberg, 2000). However, H. andorophora and H. ijimai have mammil-lated eggs (non-mammilated in H. suttonae). The remaining species areNeotropical and all from Lake Titicaca (Peru). Hedruris suttonae differs

TABLE I. Localities, sampling size, prevalence, and mean intensity of Hedruris suttonae n. sp. in Galaxias maculatus and Galaxias platei.

Fish Lake Coordinates Sample size Prevalence (%) Mean intensity

G. maculatus .Norquinco 39u099S–71u179W 26 42 2.4

.Quillen 39u259S–71u259W 10 40 1.8

.Tromen 39u329S–71u279W 24 46 4.5

.Machonico 40u219S–71u269W 24 71 9.7

.Pudu Pudu 40u239S–71u289W 19 63 5.3

.Hermoso 40u239S–71u299W 14 14 1.0

.Villarino 40u289S–71u359W 20 45 2.1

.Falkner 40u299S–71u299W 20 15 2.7

.Filo Hua Hum 40u309S–71u179W 20 15 4.0

.Traful 40u379S–71u259W 24 8 1.0

.Espejo 40u419S–71u409W 24 13 3.7

.Espejo Chico 40u419S–71u429W 24 38 16.1

.Correntoso 40u449S–71u399W 28 11 1.3

.Nahuel Huapi 40u489S–71u399W 25 8 4.0

.Patagua 40u519S–71u509W 28 21 4.7

.Moreno 41u039S–71u319W 44 54 20.7

.Mascardi 41u179S–71u389W 32 28 2.2

.Fonck 41u199S–71u459W 12 92 10.5

.Hess 41u239S–71u439W 17 29 4.6

.Steffen 41u319S–71u339W 27 33 2.0

G. platei .Moreno 41u039S–71u319W 29 52 4.7

.Cisne 42u369S–71u569W 11 27 2.0

.Coyte 45u159S–71u129W 20 95 145.9

110 THE JOURNAL OF PARASITOLOGY, VOL. 96, NO. 1, FEBRUARY 2010

FIGURE 1. Hedruris suttonae n. sp. Male: (A) Anterior end (lateral view). (B) Head end (frontal view). (C) Posterior end (lateral view). (D) Spicules(ventral view). Female: (E) Posterior end (lateral view). (F) Detail of vulvar region (lateral view). (G) Hook with accessory sclerotized support (ventralview). (H) Larvigerous egg.

BRUGNI AND VIOZZI—HEDRURIS SUTTONAE N. SP. 111

FIGURE 2. Scanning electron micrograph of Hedruris suttonae n. sp. Male: (A) Anterior end (fronto-dorsal view). (B) Anterior end (fronto-lateralview). (C) Anterior end (frontal view). (D) Detail of pseudolabium with amphid (arrow). (E) Posterior end (dorso-lateral view). (F) Detail of area rugosa(ventral view).

112 THE JOURNAL OF PARASITOLOGY, VOL. 96, NO. 1, FEBRUARY 2010

FIGURE 3. Scanning electron micrograph of Hedruris suttonae n. sp. Female: (A) Posterior end (lateral view). (B) Posterior end (ventral view). (C)Detail of vulva and anus (ventral view). (D) Hook retracted (caudal view). (E) Hook everted (caudal view). (F–G) Detail of anal region spines. (H) Scale-like spines surrounding retracted hook.

BRUGNI AND VIOZZI—HEDRURIS SUTTONAE N. SP. 113

from H. basilichtensis by the larger total length of female (4.6–9.4 in H.basilichtensis). It differs from H. basilichtensis and H. orestiae by the largerspicules in males (175–193 in H. basilichtensis and 178–194 in H. orestiae).The new species also differs from H. orestiae by the larger eggs (31–42 inH. orestiae). Hedruris suttonae resembles H. moniezi in the length ofspicules but differs from it by the smaller hook of females (251–292 in H.moniezi) and the smaller accessory elongate sclerotized supports of thehook (575–582 in H. moniezi). The new species also has larger eggs (42–44in H. moniezi). Hedruris spinigera has been also reported to infect the samefish host species (G. maculatus) (Hine et al., 2000) and other freshwaterfishes in New Zealand (Stokell, 1936). Hedruris suttonae differs from H.spinigera by the number of male caudal papillae (10 in H. spinigera) andthe larger eggs (35–42 in H. spinigera).

DISCUSSION

The life cycles of the species of Hedruris are known only for H.

androphora and H. ijimai, whose intermediate hosts are species of

Asellus Geoffroy (Isopoda); their definitive hosts are amphibians

(Petter, 1971; Hasegawa and Otsuru, 1979). As was suggested by

Moniez (1889) for H. oriestae, the larvae of H. suttonae were

found in amphipods. In H. patagonica, the larvae show extreme

precocity as was observed previously for H. androphora and H.

ijimai (Petter, 1971; Hasegawa and Otsuru, 1979).

Stokell (1936) found specimens of H. spinigera in the native and

introduced species of fishes from a lake in New Zealand. This

author suggested that a crustacean of the genus Tenagomysis

Thomson (Mysida) would be the intermediate host for H.

spinigera, because it was an important food item in the diet of

the parasitized native fishes. The author stated that the

introduced trout of the same lake seem to become infected post-

cyclically, via ingestion of infected smelt. Moravec (1998, 2007)

asserted that amphibians are the true host for Hedruris species, so

fishes should not be considered true definitive hosts but only

accidental facultative post-cyclic hosts. However, amphibians

have never been recorded in the diet of these fishes (Cervellini et

al., 1993; Milano et al., 2002). Moreover, the high prevalence and

mean intensity in galaxiid fishes, the high percentage of gravid

females, and the wide distribution of H. suttonae collectively

indicate that, in these oligotrophic Andean lakes, G. maculatus

and G. platei are true definitive hosts of this nematode.

Furthermore, it uses amphipods as intermediate hosts, which

are important food items in the diet of both G. maculatus

(Macchi, 2004) and G. platei (Milano et al., 2002).

Galaxiid fishes become parasitized when eating infected H.

patagonica. However, piscivorous fishes, such as P. trucha and

salmonids, probably acquire the infection mostly through post-

cyclic transmission, by consumption of infected G. maculatus, as

has been reported for another generalist parasite, Acanthocephalus

tumescens (Rauque et al., 2002). This kind of transmissions occurs

when a parasite is ingested as adult within its definitive host, then

surviving and parasitizing the predator (Nickol, 1985).

Based on the present survey and unpublished observations, we

conclude that the only species of Hedruris present in Patagonian

Andean lakes is H. suttonae. As a consequence, Hedruris sp.

reported from G. maculatus and G. platei by Ortubay et al. (1994),

Revenga et al. (2005), and Viozzi et al. (2009) should be

considered to represent the new species described herein.

ACKNOWLEDGMENTS

This work is dedicated to the memory of Dr. Carola Ana Sutton, whoworked for many years in the La Plata Museum, and died during thepreparation of this manuscript. We thank Celina Digiani, PatriciaSarmiento, and Rafael Urrejola for assistance with scanning electronmicroscopy. The present study was supported by Grant from UniversidadNacional del Comahue, Argentina (B 137) and CONICET-PIP 02752,Argentina.

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