Light and electron microscopic observations of sporogenesis in the myxosporida, Ceratomyxa shasta (Noble, 1950)

Abstract. The stages of development leading to sporogenesis of Ceratomyxa shasta (Noble) were investigated by light and electron microscopy. Salmonid fishes were infected by exposing them to water containing the infectious stage and intestinal material was fixed at weekly intervals. Signs of intestinal infection were barely detectable by 7 days following exposure where trophozoites and later developmental forms were present, but by 14 days a large number of pansporoblasts could be detected in varying stages of development. By 21 days the majority of caeca were completely occluded and infection had spread throughout the connective tissues attached to the caeca.
The early developing trophozoites contained two or more nucleated cells within a mother cell. There was some evidence of multiplication of nuclei by fission. The sporoblasts usually contained twelve nucleated cells that gave rise to two groups of six cells (sporonts) and resulted in the formation of two spores in each mother cell. Each spore was formed by two sets of bilaterally arranged cells consisting of the main germinative cell or sporoplasm, the anteriorly placed capsule cells and the outer envelope or spore valve cell that surrounded the others and formed the spore covering.
As the spore matured the two germinative cells interacted with each other by pseudopodial extensions and appeared to fuse to form a diploid cell. The position of the cells laterally and slightly posteriorly to the central suture line formed a bilaterally curved spore. Mature spores when examined with the electron microscope were condensed, dark staining and relatively featureless, with a lateral measurement of 15 μm and an anterior-posterior measurement of 7μm.     

Reservoir hosts and new clupeoid host records for the myoliquefactive myxosporean parasite Kudoa thyrsites (Gilchrist)

Abstract. The myxosporean parasite Kudoa thyrsites (Gilchrist) is well recognised as a cause of flesh liquefaction post-mortem in several fishes from both hemispheres. The observation of this condition in cultured mahi mahi, Coryphaena hippurus L., in Western Australia led us to search for possible reservoirs of infection amongst the abundant clupeoid fishes of the area. Prevalent and severe infections were found in Sardinops sagax neopilchardus (Steindachner), which we consider to be a major reservoir host for K. thyrsites in south-west Australian coastal waters. The parasite occurred less frequently in Spratelloides robustus Ogilby, Sardinetla lemuru Bleeker and Engraulis austratis (Shaw) from the same waters. Infection was not detected in Hyperlophus vittatus (Castelnau), Etrumeus teres (De Kay) or Nematalosa vlaminghi (Munro), which may reflect differences in range or dietary composition. Engraulis japonicus (Temminck & Sehlegel) imported from Japan were also infected, but a single sample of E. mordax Girard from California contained only an equipolar Kudoa species. These records expand the known host range of K. thyrsites to 20 species in 10 families, and several of these host species appear to be major reservoirs of infection in certain locations. Flesh spoilage due to the liquefactive effects of the parasite could occur in any of these hosts, and was seen here in S. sagax neopilchardus, S. robustus and E. japonicus in association with mature spores. Detection of infection with ultra-violet light was found to be ineffective because a cellular host response was not mounted by the clupeoids.     

Morphology of Ichthyophonus hoferi assessed by light and scanning electron microscopy

Abstract. The morphology of Ichthyophonus hoferi in vitro at pH 3.5 and 7.0 is described using light and scanning electron microscopy. Only vegetative growth was observed. At pH 3.5, hyphal growth was seen. The hyphae of I. hoferi are characterized by evacuated hyphal walls with the cytoplasm migrating to the apex and no septation. In contrast, the growth at pH 7.0 is mainly seen as spherical bodies which vary in size and are uni- to multinucleate. Amoeboid bodies showing slow movements were observed within 3–6 h of transfer to pH 7.0. We propose a life-cycle involving the germination of thick-walled multinucleate spores in the fish stomach as a response to the low pH. The hyphae then penetrate the digestive tract and rupture when they reach a blood vessel (neutral pH), whereby uni- and binucleate bodies and/or amoeboid bodies are released. The small cells are transported in the blood vessels and spread in the organs richly supplied with blood (heart, kidney, spleen, liver and muscle tissue) where they grow to form multinucleate spores.     

Host response to the chondracanthid copepod Chondracanthus goldsmidi,a gill parasite of the striped trumpeter,Latris lineata (Forster), in Tasmania

The chondracanthid copepod, Chondracanthus goldsmidi is an ectoparasite of gills, inner opercula and nasal cavities of cultured striped trumpeter, Latris lineata (Forster). Whilst often present in high numbers (up to 60 parasites per host), little is known about its effect on striped trumpeter. In this study C. goldsmidi was associated with extensive epithelial hyperplasia and necrosis. Pathological changes were most pronounced near the parasite’s attachment site, with papilloma‐like growths surrounding the entire parasite resulting in deformation of the filament. The number of mucous cells increased near the parasite attachment sites on both the opercula and gills. Mast cells were absent in healthy gills; in contrast numerous mast cells were identified in the papilloma‐like growths. Immunostaining identified piscidin‐positive mast cells in the papilloma‐like growths, presenting the first evidence of piscidin in the family Latridae.     

长江口纹缟虾虎鱼精子、卵子及受精过程扫描电镜观察

采用电镜对长江口纹缟虾虎鱼成熟精子、卵子及受精早期精子入卵过程进行了观察。结果显示:纹缟虾虎鱼成熟精子由头部和尾部两部分组成。头部呈圆形或近圆形,无顶体,细胞核长径为1.15±0.28μm,短径为0.97±0.22μm,尾部鞭毛长为8.17±1.12μm。核膜外具有双层质膜,质膜表面不平整,在核膜和双层质膜中间有较大空隙存在。中心粒复合体位于植入窝内。袖套两侧分布有2～3个较大的线粒体。鞭毛为典型的"9+2"结构,有侧鳍。成熟卵呈圆形,卵膜表面多沟和嵴,具单一受精孔,孔洞区外径约5μm,孔内壁呈螺旋嵴。在卵的植物极有一盘状突起,突起的中间为圆形,周边有呈网状结构的粘丝与卵壳膜连接。纹缟虾虎鱼精子入卵速度较快,受精过程较短,受精后10～18 s完成精子入卵过程。     

Light and electron microscope observations on extrasporogonic and sporogonic stages of a myxosporean parasite of the genus Sphaerospora Thelohan, 1892 from Atlantic salmon, Salmo solar L., in Scotland

Abstract. Juvenile Atlantic salmon from a number of freshwater hatcheries in Scotland were found to be infected by a myxosporean parasite of the genus Sphaerospora. Fish first became infected in June by extrasporogonic stages which could be found in the blood and kidney interstitium. These consisted of a primary cell containing one to over one hundred secondary cells. Some secondary cells contained one or two tertiary cells. Sporogony was disporous and occurred later in the kidney tubules. The development of both extrasporogonic and sporogonic stages was studied by light and transmission electron microscopy.     

Field emission scanning electron microscopy and transmission electron microscopy studies of the chorion, plasma membrane and syncytial layers of the gastrula-stage embryo of the zebrafish Brachydanio rerio: a consideration of the structural and functional relationships with respect to cryoprotectant penetration

The structure of the chorion and plasma membranes of gastrula‐stage zebrafish Brachydanio rerio embryos were studied using field emission scanning electron microscopy (FE‐SEM) and transmission electron microscopy (TEM). These studies confirm the outer chorion membrane complex to be 1.5–2.5 μm in thickness and to consist of three layers, electron‐dense outer and innermost layers (0.2–0.3 and 1.0–1.6 μm in thickness respectively) separated by an electron‐lucent middle layer (0.3–0.6 μm in thickness). The middle and inner layers are pierced by pore canals. A granular to farinaceous nature of the thin outer surface of the outer layer of the chorion has been revealed for the first time. The study provides original TEM images of the plasma membrane structures of gastrula‐stage embryos, and FE‐SEM and TEM images showing the plasma membrane to have three morpohologically distinct regions, being prominently ridged and folded at the surface of the blastoderm, smooth over the syncytial layer at the vegetal pole and with an intermediate region between the animal and vegetal pole where folding develops in advance of the expanding blastodermal disc of cells. FE‐SEM and TEM studies reveal details of the syncytial layer (1–4 μm thick) beneath the smooth plasma membrane at the vegetal pole, containing cytoplasmic organelles and small yolk globules. The significance of the structural detail shown in these studies is considered in the light of the difficulties experienced in cryopreservation of the embryo resulting from the inability of achieving cryoprotectant penetration of the yolk mass.     

Alterations in the epidermis of the carp,Labeo rohita (Cyprinidae: Cypriniformes), infected by the bacteria,Aeromonas hydrophila: A scanning electron microscopic,histopathological and immunohistochemical investigation

This study was carried out to comprehend the pathogenicity of the bacteria in the epidermis of Labeo rohita inoculated with Aeromonas hydrophila. Alterations in the histopathology of the epidermis were examined using scanning electron microscopy, light microscopy and the localization of iNOS and caspase 3 + ve cells by means of immunohistochemical methods. Skin samples obtained from infected fish at different intervals 2, 4, 6, 8 and 10 days showed significant changes in the cellular components of the epidermis. Epithelial cells often appeared hypertrophied with fragmented and loosely arranged microridges, and in the process of exfoliation. Mucous goblet cells increased significantly in density. Club cells showed degenerative changes, often with simultaneous confluence of adjacent cells and release of their contents. Increase in density of iNOS and caspase 3 + ve cells indicates inflammatory response and apoptosis. This study could provide valuable information on the pathogenesis of the disease, and disease outbreaks in farmed fish. Further, it could provide useful guidelines for fish farmers to take preventive measures for the control of the disease.     

Molecular characterization,virulence profiling,antibiotic susceptibility,and scanning electron microscopy of Flavobacterium columnare isolates retrieved from Nile tilapia (Oreochromis niloticus)

Aquaculture International - Columnaris is a common flavobacterial disease affecting tilapia aquaculture. Flavobacterium columnare has been identified as being responsible for the heavy mortalities...     

Infection of the epaulette shark, Hemiscyllium ocellatum (Bonnaterre), by the nematode parasite Proleptus australis Bayliss (Spirurida: Physalopteridae)

Seventy-two epaulette sharks, Hemiscyllium ocellatum (Bonnaterre), were infected with the nematode parasite Proleptus australis Bayliss, 1933. The parasite population was overdispersed. Infection intensity ranged from 3 to 1002 worms per fish stomach, and there was a positive correlation between shark length and number of parasites present. The majority of worms were attached to the stomach wall, and scanning electron microscopy and histological examination showed that worms penetrated the stomach lining. Worms were observed within the lamina propria of the stomach and occasionally penetrated the muscularis mucosa. Little to no inflammatory or cellular immune reaction to the presence of the parasites was observed, except in one case where a worm was being degraded by a host tissue response. There was a large amount of connective tissue proliferation as a result of nematode attachment, but no obvious effects on the overall health of the sharks were seen. Three sharks were also found to be infected by the cestode Callitetrarhynchus sp.     

Integumental damage caused by Dolops ranarum (Stuhlmann, 1891) (Crustacea: Branchiura) to Clarias gariepinus (Burchell), with reference to normal histology and wound-inflicting structures

Abstract. The African catfish, C. gariepinus (Burchell), a candidate species for aquaculture in southern Africa, is frequently infested by the branchiuran ectoparasite Dolops ranarum. Normal integument, as well as damage caused by this parasite, is described by means of scanning electron microscopy and histology. Wound healing and the attachment and feeding mechanism of the parasite is described.     

Observations on the host-parasite relations of the Pacific whiting, Merluccius productus (Ayres), and two myxosporean parasites, Kudoa thyrsitis (Gilchrist, 1924) and K. paniformis Kabata & Whitaker, 1981

Abstract. Muscle samples from 178 Merluccius productus were examined for two myxosporean parasites, Kudoa thyrsitis and K, paniformis. Kudoa paniformis was found in 51% of the samples, while K. thyrsitis and mixed infections were observed in 7% and 17% of the samples respectively. An inflammatory response that resulted in an encapsulation around a completely replaced muscle fibre was observed in infections with either parasite. Presporogenic and sporogenic stages were common while stages that may represent early forms of the parasites were only rarely observed.     

Henneguya shaharini sp. nov. (Protozoa: Myxozoa), a parasite of marble goby, Oxyeleotns marmoratus (Bleeker)

Abstract. Henneguya shaharini sp. nov. is described from marble goby, Oxyeleotns marmoratus , collected in the State of Selangor, Malaysia. Cysts occurred in the gill filaments. The histopathological examination revealed intralamellar and inter-lamellar forms of infection. A host tissue response against the parasite was seen in some fish.     

Induced resistance in rainbow trout, Oncorhynchus mykiss (Walbaum), to gill disease associated with the microsporidian gill parasite Loma salmonae

Branchial xenomas were detected by week 5 and disappeared by week 10 after naive juvenile rainbow trout, held at 14.5 °C, were fed or intubated with Loma salmonae ‐infected gill tissue preparations. Upon re‐challenge with L. salmonae , these fish were protected from disease and branchial xenomas did not develop. Branchial xenomas were never detected in naive fish held at 10 °C and exposed to L. salmonae . When these fish were re‐challenged with L. salmonae at 14.5 °C, they were also protected from the disease. Branchial xenomas also developed after naive fish, held at 14.5 °C, were injected intraperitoneally with a semipurified preparation of fresh spores, but generally did not develop after intraperitoneal injection with a preparation of spores subjected to freezing and thawing before use. Fish that had received fresh spores intraperitoneally were completely resistant to disease when re‐challenged via oral delivery of spores, whereas those that had received frozen spores were incompletely, but significantly, protected from disease compared with naive fish. We conclude that infection with L. salmonae induces strong protection towards the disease upon re‐exposure to spores, and that the protection does not depend on the completion of the parasite's life cycle, thus establishing the basis for further research on vaccine development for this disease.