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Infestation of the Testes of the Japanese Sea Star Asterias

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Infestation of the Testes of the Japanese Sea Star Asterias DISEASES OF AQUATIC ORGANISMS l Published March 27 Dis Aquat Org NOTE Infestation of the testes of the Japanese sea star Asterias amurensis by the ciliate Orchitophyra stellarum: a caution against the use of this ciliate for biological control M. Byrnelv*, A. Cerra', T. ~ishigaki~,M. ~oshi~ 'Department of Anatomy and Histology, F-13, University of Sydney, N.S.W. 2006, Australia 'Department ol Life Science, Tokyo Institute of Technology. 4259 Nagatsuta. Yokohama 226, Japan ABSTRACT: Male inferthty is a new phenomenon affecting noted to exhibit this condition has increased and now populations of the Japanese sea star Asterias amurensis. The male infertility is common in inany populations. agent causing partial or total castration of the testes was iden- The changes seen in the testes of Asterias amurensis tified to be Orchitophyra stellarum, a parasitic ciliate endemic to the north Atlantic. A. amurensis is a new host for 0. stel- are similar to those described for Asterias species from larum, apparently due to the recent introduction of the ciliate the north Atlantic infested with the parasitic ciliate to the Pacific Ocean. This ciliate dlsrupts the germinal layer Orchitophyra stellarum (Cepede 1907, 1910, Burrows and phagocytoses sperm. Male infert~lityof A. amurensis is 1936, Vevers 1951, Jangoux 1987). 0. stellarum is largely effected by the phagocytic response of host's cells specific to the Asteriidae and, within this family, is with each cell engulfing numerous sperm. 0. stellarum 1s highly contagious in A. arnurensls with 100% of the males in known to parasitize 4 genera and 6 species (Jangoux some populations infested. The absence of male sea stars in 1987, Leighton et al. 1991, B. J. Leighton pers. comm.). some populations is also linked to ciliate disease. This report It usually infests male sea stars, where it causes regres- of 0.stellarum from the western Pacific Ocean completes the sion of the germinal epithelium, resulting in partial or circumboreal distribut~onof this parasite. The contagious spread of 0.stellarum in Japan and its abillty to parasitize complete castration of the testis (Bouland & Jangoux several asteroid genera cautions against its use for biological 1988). 0,stellarum was originally described at the turn control of A. amurensis in Japan and of recently established of the century from the gonads of A. rubens from the pest populations of this asteroid in Australia. northeast Atlantic Ocean (Cepede 1907) and was later found in asteroids from the northwest Atlantic and from KEY WORDS: Ciliate disease . Orchitophyra stellarum . Aste- rias amurensis . Biological control the Mediterranean Sea (Burrows 1936, Smith 1936, Febvre et al. 1981).This long-standing Atlantic distnb- ution of 0.stellarum changed with the recent discovery of this parasite in the gonads of Pisastel. ochraceus, a Asterias an~urensisis a locally abundant sea star in common asteroid in the northeast Pacific Ocean Japan and has long been an important research organ- (Leighton et al. 1991).In addition to causing regression ism for biologists investigating fertilization and de- of the testes, the ciliate caused morbidity and mortality velopment (Kume & Dan 1968, Longo et al. 1995). In of P. ochraceus, symptoms not normally associated with recent times, however, it has become difficult to obtain the disease. The greater virulence of the disease in P. sperm from A. amurensis even during the peak spawn- ochraceus was taken to suggest that this asteroid is a ing period of populations previously known to be a new host for 0. stellarum (Leighton et al. 1991). The reliable source of gametes. This change in the repro- range of 0. stellarum has increased in P. ochraceus duction of A. amurensis was first noted in 1990 when populations and a second northeast Pacific species, Ev- infertile males with discoloured and hardened testes asterias troscheli, has recently succumbed to the para- were encountered. These testes were observed at a site (B. J. Leighton pers. comm.). time in the reproductive cycle when copious amounts of The aim of this investigation was to identify the sperm should have been present (Ino et al. 1955, &m agent affecting the testes of Asterias amurensis. Ultra- 1968). Since 1990, the incidence of male A. arnurensis structural examination of the gonads revealed the presence of Orchitophyra stellarum. The effect of this ciliate on A. amurensis is described and the host's O Inter-Research 1997 Resale of full article not permitted 236 Dis Aquat Org response is compared to that documented for other 2a, b). Equally spaced longitudinal rows of cilia, called Asterias species (Vevers 1951, Bouland & Jangoux kinet~es,extend from the surface (Fig. le). 1988). This report from Japan, together with the pres- During the 1996 breeding season, ciliate infestation ence of 0.stellarurn in Canada (Leighton et al. 1991), was widespread in 2 of the Asterias arnurensis popula- shows that this species now has a circumboreal dis- tions examined. At Tokyo Bay 100% of the males (n = tribution. Our observations coincide with the dramatic 100) had parasitized gonads and at Otuchi Bay 38 % of increase of A, amurensis in Australia, where biological the males (n = 80) were infested. Male A. arnurensis control of this recently introduced pest is being con- were not present in the Ise Bay sample (n = 50). Field sidered (Byrne 1996, Byrne et al. 1996, Viney 1996).In surveys at Tokyo Bay revealed that ciliate disease is as- light of this new phenomenon, we present a cautionary sociated with a marked decrease in the proportion of assessment of 0. stellarum as an agent for biological male sea stars with sex-ratios of 1:l observed at the be- control. ginning of breeding and ratios 10:l or 20:l in favour of Materials and methods. During the 1996 breeding females observed at the end of breeding. A similar season, Asterias amurensis was collected by SCUBA decline in the male population is reported for other from populations in northern and central Japan. Speci- Asterias species infested by Orchitophyra stellarum mens were collected from Tokyo Bay (35" 15'N, (Claereboudt & Bouland 1994) and also for Pisaster 139" 45' E) and Ise Bay (34"301S, 136" 50' E) in January ochraceus (Leighton et al. 1991). The decrease in the and from Otuchi Bay (39" 20'S, 142" 00' E) in February. number of male A. amurensis in Tokyo Bay and the ab- At each site, samples of 50 to 200 A. amurensis were sence of males from Ise Bay indicate that ciliate disease collected at a depth of 2 to 3 m. The northern-most site, may cause host mortality, as suggested for A. vulgaris Otuchi Bay, is in northern Japan and the southern-most and P. ochraceus (Leighton et al. 1991, Claereboudt & site, Ise Bay, is in central Japan. These sites are ap- Bouland 1994).Although mortality of A. amurensis was proximately 740 km apart and are separated by over not observed in the field, diseased specimens were 1000 km of shoreline. The specimens were dissected more prone to autotomise their arms and die in aquaria, and examined for the presence of diseased gonads. Dis- compared with uninfected specimens. A. arnurensis eased gonads were examined by light (LM) and trans- migrates into shallow water for breeding and so the mission electron rnicroscopy (TEM).For histological ex- preponderance of females in the sampled populations amination, the gonads were fixed in 10 % formalin or in may be due to mortality of males in deep water. Bouin's fluid, dehydrated in a graded series of ethanols, Orchitophyra stellarum was only evident in mature embedded in paraffin and sectioned (7 pm thick). The testes. The disease developed progressively. In the sections were stained with haematoxylin and eosin. For early stages of the disease, the ciliates were inter- LM and TEM, pieces of gonad were fixed in 2.5% spersed with sperm (Fig. la, c) and, in later stages, glutaraldehyde in 0.45 pm filtered seawater for 1 h, completely occluded the gonadal lumen (Fig. lb). transferred to 70% alcohol and dehydrated in a graded Early in the breeding season infected testes had an series of ethanols. The tissues were then rinsed in active spermatogenic layer and contained viable sper- acetone and embedded in Spurr's resin. Thick sec- matozoa which could be used for fertilization. The tions (0.7 pm) were stained with 1 % toluidine blue in lumen of diseased testes contained spermatozoa, cili- 0.5 % ethanolamine. For TEM, ultrathin sections were ates and phagocytes (Figs. la-e, 2a-d). Disruption of stained with uranyl acetate and lead citrate and viewed the germinal layer was indicated by the presence of in a Phillips 400 transmission electron microscope. immature sperm in the lumen which had detached Results and discussion. D~seasedgonads of Asterias from a spermatocyte column (Fig. 2c). The ciliates amurensis were readily detected due to their atypical appeared to disrupt the germinal layer by their brown colour, shrivelled appearance and hard texture. locomotory activity. They occasionally inserted their In all cases the diseased specmens were male. Histo- anterior end between adjacent spermatocyte columns logical examination of the testes revealed the presence thereby causing the columns to separate (Fig. lc). As of small groups or extensive aggregations of ciliates in the parasite population increased, the amount of sperm the lumen (Fig. la-c). Ultrastructurally, these ciliates decreased until there were no germ cells evident. In were indistinguishable from the Orchitophyra stel- the advanced stage of the disease, A, amurensis have larum described in the testes of A, rubens and A, vul- hardened testes filled with ciliates and phagocytes. garis (Bouland et al. 1987, Bouland & Jangoux 1988, The symptoms exhibited by A. amurensis in response Claereboudt & Bouland 1994). 0,stellarum is fusiform to 0.
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