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RESEARCH NOTE
The Occurrence of Stenurus australis Tantalean and Sarmiento, 1991 (Nematoda: Metastrongyloidea) in the Porpoise Phocoena spinipinnis (Burmeister, 1865) on the Southern Coast of Chile
Patricio Torres, Patricio Cortes, Jorge A Oporto, Lila Brieva, Ricardo Silva
Code Number: OC94031
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Text: 9K
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Instituto de Parasitologia, Universidad Austral de Chile, Casilla 567, Valdivia, Chile
Key words: Stenurus australis - Phocoena spinipinnis - Chile
In Chilean territorial waters, including the Antarctic territory, there are about 46 marine mammal species (W Sielfeld 1983 Mamiferos Marinos de Chile, Ediciones de la Universidad de Chile, Santiago, 199 pp.). Among these is the coastal cetacean Phocoena spinipinnis (Burmeister, 1865), which lives in the South Pacific, from Paita (Peru) up to Cabo de Hornos and in the South Atlantic and from the southern part of Brazil to Tierra del Fuego (Sielfeld loc. cit., M Pinedo et al. 1992 Cetaceos e Pinnipedes do Brasil, Manaus UNEP/FUA 213 pp.).
Research on parasites of Chilean marine mammals is scarce (J Fernandez 1987 Parasitol al Dia 11: 120-125), and regarding P. spinipinnis only one paper is recorded on gastrointestinal helminths, in which the nematodes Anisakis simplex (Rudolphi, 1809, det. Krabbe, 1878) and Pseudoterranova sp., the acanthocephalan Polymorphus (Polymorphus) cetaceum (Johnston and Best, 1942) and the trematode Sinthesium tursionis (Marchi, 1873), were found (P Torres et al. 1992 J Wild Dis 28: 313-315).
The present study reports the prevalence and mean intensity of infection by the nematode Stenurus australis Tantalean and Sarmiento, 1991, in 33 specimens of P. spinipinnis, accidentally entangled in gillnets near Queule (39^o 22'S, 73^o 13'W), on the coast of southern Chile. The cetaceans were collected between 1990 and 1991 and examined either immediately or after being kept up to three months at 20 oC; the necropsy was carried out according to K Norris (1966 J Mammal 42: 471-476). The nematodes were isolated from the auditive ducts and nasal and pterygoid sinuses, fixed in 70% ethanol and cleared in lactophenol for morphological study. Some specimens were dehydrated in an ascending series of ethanol, treated with acetone-ether, air dried and coated with gold palladium to be examined with a Scanner Nanolab 2000 (Bausch and Lomb Instruments). The prevalence and mean intensity terms were used according to L Margolis et al. (1982 J Parasitol 68: 131-133).
The length (cm)/weight (kg) of the cetaceans (mean +/- standard deviation) was of 170 +/- 8.5/78 +/- 17.3 for the mature females and of 147.2 +/- 5.2/51.4 +/- 7.3 for the immature specimens. In the mature males the length/weight was of 174 +/- 7.6/80.4 +/- 10.4 and in the immature ones were 143 +/- 6.9/46.8 +/- 2.5.
In this study the presence of S. australis in P. spinipinnis is recorded for the first time on the Chilean coast. Previously, this species had only been registered from this same host on the Peruvian coast (T Tantalean, L Sarmiento 1991 Publ Mus Hist Nat UNMSM 36: 1-4). Observations of S. australis with a scanning electron microscope (SEM) are reported for the first time (Figs 1-4). The morphological characteristics of S. australis specimens were similar as described, with optical microscopy, by Tantalean and Sarmiento (loc. cit.). These authors did not describe the presence of two lateral papillae in the external circle of papillae that surrounds the mouth of nematodes, but our observations with SEM in Chilean and Peruvian material of S. australis confirm their existence, as described in other Stenurus spp.
Morphological characteristics and measurements (in micrometers, unless otherwise indicated) of 20 nematodes of each sex were the following:
General - Anterior extremity of body stout with posterior half tapering. Buccal cavity with thick walls. Mouth surrounded by inner circle with six papillae and external circle consisting of two lateral and four submedian papillae. Longitudinal cuticular ridges arise posterior to the cephalic region.
Males - Body 13.6-19.1 (15.8) mm long, 228-319 (287) maximum wide. Buccal capsule 7-11 (10) long, 14-18 (15) wide. Esophagus 288-378 (324) long, 50-72 (60) maximum wide. Nerve ring 90-130 (110), cervical papillae 166-234 (202), and excretory pore 191- 241 (221) from anterior end, respectively. Bursa copulatrix with two lateral lobes more developed than dorsal lobe. The five rays of the bursa are distributed in two small and thin ventral rays 11-22 (15) long, two broad and trifid lateral rays 32-43 (39) long, with three distal papillae, and medial ventral papillae; and one dorsal ray 43-54 (48) long, with two lateral papillae, in distal region. Medial papilla on anterior lip of cloacal aperture. Spicules equal in size, similar in shape, 101-122 (112) long. Gubernaculum 43-61 (47) long.
Females - Body 20.0-28.4 (24.6) mm long, 455-592 (523) maximum wide. Buccal capsule 11-18 (14) long, 18-29 (24) wide. Esophagus 374-414 (394) long, 68-82 (77) maximum wide. Nerve ring 108-144 (131), cervical papillae 234-331 (237), and excretory pore 205-280 (268) from anterior end, respectively. Vulva 22-40 (34) from anus. Anus 22-32 (25) from posterior end. Vaginal sphincter 47-72 (58) long, 54-68 (62) wide. Vulva without appendages. Eggs (n=50) 78-112 (93) long, 43-76 (60) wide. Larvae (n=50) of first stage obtained from eggs 162-277 (215) long, 11-14 (13) wide.
TABLE
Prevalence and intensity of infection by Stenurus australis in Phocoena spinipinnis along the coast of southern Chile
======================================================= Cetaceans Infected/ Prevalence Mean intensity examined (range) ------------------------------------------------------- Females mature 7/7 100 1254 (214-2549) immature 4/5 80 1460 (311-3120) total 11/12 91.6 1329 (214-3120) Males mature 15/15 100 2221 (112-5178) immature 4/6 66.6 198 ( 1- 535) total 19/21 90.4 1795 ( 1-5178) ------------------------------------------------------- Total 30/33 90.9 1624 ( 1-5178) =======================================================
All animals parasited by S. australis showed specimens in the auditive ducts and pterygoid sinuses. Worms at the level of the nasal sinuses were only observed in three hosts.
The prevalence and intensity of infection by S. australis are shown in Table. The prevalence of infection by S. australis with regards to the total number of animals of each sex turned out to be similar. The prevalence of infection was greater in mature specimens of both sexes. The mean intensity was greater in the males spe-cimens.
The life cycles of Stenurus spp., are unknown. The diet of P. spinipinnis consists mainly of fish. Frequencies of 99.2% fish and 0.8% cephalopods were found in the stomach contents of 18 specimen of P. spinipinnis from Queule area (Torres et al. loc. cit.). This suggests that these prey, fishes particularly, could participate in the transmission of the infection by S. australis to cetaceans.
The infection by Stenurus spp. and other helminths of the auditive ducts have been considered as a potential factor of the stranding of cetaceans (S Ridgway & M Dailey 1972 J Wild Dis 8: 33-43, M Dailey & R Stroud 1978 J Wild Dis 14: 503-512, Heckmann et al. 1987 Great Bas Nat 47: 355-372, Morimitsu et al. 1992 J Wild Dis 28: 656-658). The presence of Stenurus spp. has been associated with obstruction of the auditive passages and osseous lesions in P. phocoena (Linnaeus, 1758), which would hinder their normal reaction to the sounds in the water (L Arvy 1982 Inv Cet 14: 233-335). Strandings of P. spinipinnis on the coast of Chile have not been reported and the possible pathogenicity of S. australis at present is unknown.
Voucher specimens were deposited in the collection of the Institute of Parasitology, Universidad Austral de Chile, Valdivia, Chile (IPUAT No. 0230-0232).
Acknowledgements - To lic. Julio Reyes from Peruvian Center of Cetological Studies (Lima, Peru) for sending us specimens of S. australis of P. spinipinnis from the coast of Peru.
Copyright 1994 Fundacao Oswaldo Cruz - FIOCRUZ The following images related to this document are available:Halftone images[oc94031a.gif]Photo images[oc94031a.jpg] |
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