Comparative Parasitology 67(2) 2000 - Peru State College

River, Kobe, Hyogo Prefecture, Japan, and were examined
for larvae of Spiroxys: from the Hatsuka River:
47 Zacco temmincki (Temminck et Schlegel, 1846)
(Cyprinidae) (body length 37-137 mm); 2 Morokojouyi
(Jordan et Snyder, 1901) (Cyprinidae) (54-58 mm);
2 Pungutungia herzi Herzenstein, 1892 (Cyprinidae)
(90-95 mm); 4 Misgurnus anguillicaudatus (Cantor,
1842) (Cobitidae) (46-80 mm); 13 Cobitis biwae Jordan
et Snyder, 1901 (Cobitidae) (38-95 mm); 4 Rhinogobius
flumineus (Mizuno, 1960) (Gobiidae) (33-45
mm); and 1 Odontobutis obscura (Temminck et Schlegel,
1845-1846) (Gobiidae) (96 mm); from the Okuyama
River: 10 Z. temmincki (41-75 mm). Their viscera
were pressed between 2 thick glass plates and
observed under a stereomicroscope with transillumination
to detect Spiroxys larvae. The remaining portions
of the fish were minced and digested with artificial
gastric fluid for 3 hr at 37°C. The residues were
transferred to a Petri dish and examined for nematode
larvae under a stereomicroscope. Larvae detected were
processed as described above for morphological observation.
Scientific names of the fishes follow those
adopted by Masuda et al. (1984).
The third-stage larvae of Spiroxys japonica Morishita,
1926, from the Asian pond loach, M. anguillicaudatus,
and frogs, Rana nigromaculata Hallowell,
1860, and Rana rugosa Schlegel, 1838, captured in
Niigata and Akita Prefectures, northeastern Japan,
where A. japonicus does not occur, were examined for
comparison.
Voucher nematode specimens were deposited in the
United States National Parasite Collection (USNPC),
Beltsville, Maryland, U.S.A., Nos. 89629-89638.
Results
Embryonic development
When the culture started, the nematode eggs
contained 1- to 4-cell-stage embryos. After 2
days of culture, they developed to 16-cell to
morula stage. On days 7 and 8 of culture, tadpole-stage
embryos were seen. On day 10, firststage
larvae showed movement within the eggshell,
and some larvae began to molt to become
second stage. On day 11, molted larvae were
observed. On day 18, eggs began to hatch (Fig.
1), and hatched second-stage larvae were still
enclosed in a sheath, adhered by the tips of their
tails to the bottom of the culture dish. They seldom
swam in the water.
MORPHOLOGY OF HATCHED SECOND-STAGE LAR-
VAE (n = 4): Stumpy worm with tapered posterior
portion (Fig. 1). Enclosed within doublelayered
sheath: outer layer lacking striations,
and inner layer with reticular markings (Figs. 2,
3). Length 330-435, maximum width 25-32.
Anterior end with dorsal sclerotized hooklet
with elongated base (Fig. 2). Esophagus 118-
173 long, widened posteriorly and narrowed at
HASEGAWA ET AL.—LIFE HISTORY OF SPIROXYS HANZAKI 225
level of nerve ring. Nerve ring 65-85 from anterior
extremity. Intestinal wall with brown granules.
Excretory pore, genital primordium, and
anus indiscernible.
Development in intermediate host
Several species of copepods were used for experimental
infection. Preliminary trials revealed
that Mesocyclops dissimilis Defaye et Kawabata,
1993, Macrocyclops albidus (Jurine, 1820), and
3 species of unidentified cyclopoids readily ingested
the hatched larvae, but infection was established
only in the former 2 species. The other
species could not tolerate the infection and soon
died. Hence, the following results were based on
the experiments using M. dissimilis and M. albidus
as intermediate hosts.
After being ingested by the copepods, the larvae
soon migrated to the hemocoel of the host
(Fig. 4). The sheath was not observed in the larvae
that had migrated to the hemocoel. Among
31 M. dissimilis challenged, 15 were found to
ingest the larvae, whereas worm uptake was not
confirmed in the remaining individuals. The larvae
disappeared from the hemocoel of 3 M. dissimilis
by day 7 after infection. The copepods
harboring S. hanzaki larvae became emaciated,
5 of them died by day 10, and 6 more died by
day 20. The larvae recovered by dissecting these
dead copepods showed little development, still
possessing the cephalic hooklet (Fig. 5). In 1 M.
dissimilis, disseminated fatal infection with unidentified
flagellates was caused after migration
of S. hanzaki larvae. Ultimately, only 1 M. dissimilis
survived for more than 25 days. When
dissected on the 35th day of infection, this copepod
harbored 1 living third-stage larva and 1
dead second-stage larva.
Among 10 M. albidus challenged, only 2 were
found to harbor the larvae in the hemocoel on
day 2 after infection, but 1 of them died by day
10. The remaining individual died on day 24,
but 1 third-stage larva was recovered from it by
dissection. The control copepods, 36 M. dissimilis
and 10 M. albidus, were not observed to
be infected with any nematode throughout the
experiment.
MORPHOLOGY OF THE SECOND-STAGE LARVAE
COLLECTED FROM THE INFECTED COPE-
PODS: Identical with that of the hatched larvae
but lacking sheaths; size gradually increased as
the duration of infection lengthened. On day 8
after infection, length 313-333, maximum width
Copyright © 2011, The Helminthological Society of Washington