Hysterothylacium aduncum aduncum (Rudolphi, 1802)

Moravec, F. & Nagasawa, Kazuya, 2000, Some anisakid nematodes from marine ® shes of Japan and the North Paci ® c Ocean, Journal of Natural History 34 (8), pp. 1555-1574 : 1560-1563

Hysterothylacium aduncum aduncum (Rudolphi, 1802)

( Figure 3 ) Ascaris adunca Rudolphi, 1802; Contracaecum benimasu Fujita, 1932 ; C. hyppoglossi Fujita,

1932; C. hypomesi Fujita, 1932 ; C. ochotense Fujita, 1932 ; C. crassicaudatum Fujita, 1939 ;

C. elongatum Fujita, 1939 ; C. longispiculum Fujita, 1940 ; C. mesopi Fujita, 1940 ; C. okadai

Fujita, 1940; C. oshoroensis Fujita, 1940 ; C. salvelini Fujita, 1940 .

Description

Rather large nematodes, females somewhat longer than males. Lips of approximately equal size, provided with wide membranous ¯anges, these being broadest just posterior to middle of lips. Dorsal lip with two lateral double papillae; subventral lips with amphid, adjacent medio-lateral double papilla and single lateral papilla. Interlabia rather large, triangular, broad, provided with distinct cuticular margin. Cervical lateral alae starting a short distance below level of base of subventral lips, gradually becoming wider and extending posteriorly to about oesophagus end level. Oesophagus long, slightly broader posteriorly than anteriorly. Nerve ring encircling oesophagus approximately at border of ®rst and second ®fths of its length. Ventriculus almost spherical, approximately as wide as oesophagus; ventricular appendix narrow, somewhat shorter or longer than intestinal caecum. Excretory pore slightly posterior to level of nerve ring. Caecum narrow, c. one quarter to one half length of oesophagus. Rectum a hyaline tube surrounded by three large, unicellular rectal glands. Tail of both sexes conical, relatively short; its tip covered by numerous minute spines.

Male (®ve specimens). Length of body 31,044 ±57,186, maximum width 515± 1030. Maximum width of lateral alae 36±44. Length of lips 152±252. Interlabia 68±100 long. Length of oesophagus 3410±4959, width 174±305. Nerve ring and excretory pore 783±1157 and 827±1175, respectively, from anterior extremity. Ventriculus 244±261 Ö 183±296; ventricular appendix 948±1566 long and 87±157 wide. Intestinal caecum 1366±1984, forming 28±52% of oesophagus length. Length ratio of caecum and ventricular appendix 1: 0.9±2.1. Spicules slender, alate, equal, 1305±3132 long, representing 3.6±5.5% of body length. Caudal papillae: 15±27 pairs of small subventral preanal papillae, one pair of minute adanal papillae and six to seven minute postanal papillae. Tail conical, relatively short and broad, measuring 160±539 in length; tail tip 20±28 long.

Female (three specimens): Length of body 59,328±79,907, maximum width 1236±1442. Length of lips 256±372. Interlabia 104±160 long. Length of oesophagus 6247±7091, width 339±348. Nerve ring and excretory pore 1349±1479 and 1322± 1627, respectively, from anterior extremity. Ventriculus 348±392 Ö 331±461; ventricular appendix 1392±2192 long and 174±209 wide. Intestinal caecum 2784±3106, forming 43±47% of oesophagus length. Length ratio of caecum and ventricular appendix 1:1.4 ±2.0. Vulva pre-equatorial, 24,226±27,707 from anterior end of body, at 34±38% of body length. Vagina muscular, directed posteriorly from vulva. Uterus opposed. Anterior ovary extending somewhat anterior to vulva. Eggs almost spherical, thinwalled, non-embryonated; mature eggs (n 5 10) measuring 44±54 in diameter. Tail short and broad, measuring 513±566 in length; tail tip 44±48 long.

Host. Steelhead trout, Oncorhynchus mykiss (Walbaum) ( Salmonidae , Salmoniformes ).

Site of infection. Intestine.

Locality. OOEshore waters of the North Paci®c Ocean (50 ss 42 ¾ N, 179 ss 32 ¾ W; 49 ss 31 ¾ N, 177 ss 33 ¾ W; 49 ss 31 ¾ N, 177 ss 33 ¾ W) (8± 17 July 1981).

Prevalence and intensity. 100% (12 ®shes infected / 12 ®shes examined); 9±16 (mean 12) nematodes per ®sh.

Comments

Although H. aduncum has been dealt with by many authors, until now there have been doubts as to the correctness of some identi®cations of this parasite, with worldwide distribution and reported from a large variety of hosts ( Bruce et al., 1994). The most complete descriptions of this species were provided by Hartwich (1975) and Soleim and Berland (1981). Petter et al. (1995), using the method of biometrical multivariate analysis, compared nematode samples from many ®sh hosts from the north-eastern Atlantic and the seas of northern Europe; they concluded that H. gadi (MuÈller, 1776) , considered a valid species by Hartwich (1975), was only a subspecies of H. aduncum .

The present study of specimens collected from steelhead trout, O. mykiss , from the North Paci®c Ocean shows that they belong to H. aduncum aduncum (based on the shape and width of lateral alae and the length of spicules in relation to length of the body). The general morphology of these specimens has shown that they are very similar (both in morphology and measurements) to the nematodes described by Moravec et al. (1985) as H. aduncum from salmonid and some other ®shes from fresh waters in Hokkaido, Japan, which evidently also belonged to the subspecies H. aduncum aduncum . Although H. aduncum is typically a marine parasite, Moravec et al. (1985) and Moravec and Nagasawa (1986) suggested that its life cycle could be completed in fresh waters; this was demonstrated experimentally by Yoshinaga et al. (1987).

Although H. aduncum has been reported from many ®sh species belonging to diOEerent orders, according to Hartwich (1975) in the North and Baltic Seas it parasitizes only clupeids (Clupeiformes), whereas its records from other ®shes are uncertain. On the other hand, Petter et al. (1995) have recorded H. aduncum aduncum from Clupeiformes, but also from Beloniformes, Pleuronectiformes , Lophiiformes and Gadiformes . In marine and fresh waters in Japan, adult H. aduncum aduncum (reported as H. aduncum ) were found, for example, in ®shes of the families Salmonidae ( Oncorhynchus , Salmo , Salvelinus ), Pleuronectidae ( Cleisthenes , Platichthys ), Gobiidae ( Enophrys , Tridentiger ), Embiotocidae (Neoditrema) and Scorpaenidae (Sebastes) (e.g., Moravec et al., 1985, Moravec and Nagasawa, 1985, Ishikura et al., 1995).

Hysterothylaciu m auctum (Rudolphi, 1802) ( Figures 7A ±F) Ascaris aucta Rudolphi, 1802.

Description

Male (one specimen). Body length 9723, maximum width 87. Lips approximately equal in size, 50 long, with membranous ¯anges, these being broadest at middle of lips. Interlabia triangular, 24 long. Cervical lateral alae well developed, 28 wide and 905 long, starting at level of base of lips, becoming gradually wider and extending posteriorly to about oesophagus end level. Oesophagus narrow, 1166 long and 87 in maximum width. Ventriculus 56 Ö 64; ventricular appendix 931 long and 78 wide. Anterior intestinal caecum 792 long and 61 wide, extending nearly to level of nerve ring. Length ratio of caecum and ventricular appendix 1:1.2. Nerve ring and excretory pore 339 and 322, respectively, from anterior extremity. Spicules slender, alate, moderately sclerotized, 648 long. Caudal papillae: 26 pairs of small preanals, one pair of adanals and four pairs of postanals. Tail shortly conical, 52 long, with tip (8 long) covered by numerous minute spines.

Host. Argyrosomus argentatus (Houttuyn) ( Sciaenidae , Perciformes ).

Site of infection. Pyloric caeca.

Locality. East China Sea, oOE Shimabara, Nagasaki Prefecture, Kyushu Island (8.August.198 8).

Comments

The morphology of the only available male is very similar to that of H. auctum , to which it is assigned. In contrast to the description of this species given by Hartwich (1975), the male of the present material is distinctly smaller with markedly shorter spicules and less numerous postanal papillae; but its weakly sclerotized spicules indicate that this is a very young specimen. It diOEers from similar males of H. aduncum mainly in having distinctly shorter spicules and in that its intestinal caecum is markedly longer than a half of the oesophagus (but shorter than the ventriculus and the ventricular appendix together). H. auctum is an insu ciently known species parasitizing mainly marine perciform ®shes in Europe ( Hartwich, 1975). The present occurrence represents new host and geographical records.

Figures

FIG. 3. Hysterothylacium aduncum aduncum (Rudolphi, 1802) from O. mykiss: (A,B) anterior ends of males with diOEerent length of caecum; (C) cephalic end of male, dorsal view; (D) tail of male; (E) distal end of spicule; (F) posterior end of male; (G) tail of female; (H) tail tip of young female; (I) tail tip of male. Scale bars in mm.

FIG. 7. (A±F) Hysterothylacium auctum (Rudolphi, 1802) from A. argentatus, male: (A) anterior end; (B,C) cephalic end, dorsal and ventral views; (D) posterior end; (E) tail; (F) tail tip. (G±I) Hysterothylacium sp. fourth-stage larva from Argyrosomum: (G) tail; (H) cephalic end, lateral view; (I) anterior end. (J±L) Hysterothylacium sp. fourthstage larva from Parapteroides: (J) anterior end; (K) cephalic end, lateral view; (L) tail. Scale bars in mm.