Deaths in Australian freshwater fishes associated with Chilodonella hexasticha infection

The cause of the deaths of bony bream and other native fish in the Finke River near Alice Springs in winter 1984 was infection with the protozoan ciliate Chilodonella hexasticha. The parasites induced severe generalised epithelial hyperplasia in the gills, which would have compromised respiratory exchange and killed the fish through hypoxaemia. It is suggested that similar winter epizootics of ectoparasites have contributed to previous deaths of fish observed in the Finke River, in association with dry season conditions of low water temperatures and flow rates.     

Microsporidiosis due to a pleistophorid in marron, Cherax tenuimanus (Smith), (Decapoda: Parastacidae)

Abstract. Microsporidiosis in the freshwater crayfish Cherax tenuimanus (Smith), or marron, was found to be due to a pleistophorid characterized by a single sporulation sequence producing eight, 16, 32 or 64 monomorphometric spores in a sporophorous vesicle with a fine two-layered wall. Infection occurred predominantly in locomotor, cardiac and gastrointestinal striated muscle. The disease ranged from subclinical infections where haemocytic encapsulation and infiltration of the spore masses controlled its progress, to fulminant disease with multifocal infection in the absence of effective haemocytic responses. The lethal lesions in the latter cases appeared to be those in the proventriculus. Prevalence of infection and incidence of mortality were low. The same microsporidian was found in subclinically infected C. quinquecarinatus (Gray) and C. quadricarinatus (von Mortens).     

Description of Vavraia parastacida sp. nov. (Microspora: Pleistophoridae) from marron, Cherax tenuimanus (Smith), (Decapoda: Parastacidae)

Abstract. A plcistophorid microsporidian is described from marron, Cherax tenuimanus (Smith). The parasite is polysporous, forming eight, 16, 32 or 64 ovoid spores in persistent, two-layered mcrontogcnctic sporophorous vesicles. Nuclei remain isolated throughout merogony and sporogony. The sporophorous vesicle forms from the amorphous coat surrounding meronts, which thickens and condenses into two layers during sporogony. The parasite is placed in Vavraia Weiser, 1977, and named Vavraia parastacida sp. nov.     

Spinal curvatures and an encephalotropic myxosporean, Triangula percae sp. nov. (Myxozoa: Ortholineidae), enzootic in redfin perch, Perca fluviatilis L., in Australia

Abstract. A new myxosporean, Triangula percae sp. nov., (Myxozoa: Ortholineidae) from the brain of redfin perch, Perca fluviatilis L., is described. Spinal curvatures are prevalent in many perch populations in Victoria, Australia, Triangula percae infection was detected in all perch displaying spinal curvatures and in 67% of normal perch from Lake Nillahcootie in north east Victoria. Perch populations exhibiting spinal curvatures in several other waterways were also infected with Triangula percae but the infection was absent in one population which was apparently normal. Triangula percae infection is, thus, considered to be the cause of a proportion of the spinal curvatures. Certain fish surviving outbreaks of epizootic haematopoietic necrosis virus (EHNV) also developed spinal curvatures, which may have been due to viral infection of the central nervous system.     

Evaluation of lipid spray beads for the delivery of water-soluble materials to a marine suspension-feeder, the Manila clam Tapes philippinarum (Deshayes 1853)

We describe the development and evaluation of a new microparticle for delivering low-molecular weight, water-soluble materials to suspension feeders. Spray beads successfully incorporated materials dissolved in an aqueous phase or as dry particulate, within a triacylglyceride bead composed of tripalmitin, 600 mg g⁻¹ tripalmitin/400 mg g⁻¹ triolein, or 600 mg g⁻¹ tripalmitin/400 mg g⁻¹ fish oil.
Riboflavin was successfully incorporated (up to 44 mg g⁻¹ lipid) and retained (up to 98% over 24 h in seawater) as dry particles in all three mixtures of lipid. Aqueous oxytetracycline hydrochloride or polymeric dye were incorporated (45.6 mg g⁻¹ lipid and 18.1 mg g⁻¹ lipid, respectively) and retained best (99% and 94%, respectively) in spray beads composed of tripalmitin. The addition of triolein or fish oil to the lipid bead reduced incorporation and retention efficiencies for aqueous core materials by up to 75%.
Manila clam seed readily ingested and digested lipid microparticles, spray beads and lipid-walled microcapsules. Microparticles composed of tripalmitin were excreted with their payloads intact. Intact microparticles composed of 600 mg g⁻¹ tripalmitin/400 mg g⁻¹ fish oil were largely absent in faecal strands suggesting successful release and delivery of microparticle contents to clams.
Spray beads composed of tripalmitin softened with 400 mg g⁻¹ fish oil represent an effective microparticle type for delivering low-molecular weight, water-soluble materials to aquatic suspension feeders.     

Myoliquefaction post-mortem ('milky flesh') due to Kudoa thyrsites (Gilchrist) (Myxosporea: Multivalvulida) in mahi mahi, Coryphaena hippurus L.

Abstract. Myoliquefaction occurred post-mortem in wild and cultured mahi mahi, Coryphaena hippurus L., stored on ice, and the flesh disintegrated upon cooking. The condition was associated with multifocal infection of muscle with Kudoa thyrsites (Gilchrist). Histiolysis is presumably due to enzymes excreted by the parasite, including collagenases, as the collagen fibres of the intermyotomal connective tissues were ruptured and hypochromatic. Myofibre changes were limited to hyaline degeneration and loss of myofibrillar detail. Kudoa thyrsites occurs commonly in Australian populations of the type host species, Thyrsites atun (Euphrasen), which represent a partly sympatric reservoir of infection for C. hippurus. The successful culture of C. hippurus may require selection of disease-free sites or use of filtered water supplies.     

Epizootic haematopoietic necrosis, a new viral disease in redfin perch, Perca fluviatilis L., in Australia

Abstract. An epizootic disease in redfin perch, Perca fluviatilis L., in north-east Victoria, Australia, was found to be caused by a recently described iridovirus. The acute disease is characterized by necrosis of the renal haematopoietic tissue, liver and spleen, with variable involvement of the pancreas. Transmission studies confirmed that the iridovirus is the causative agent of the disease. High mortalities occurred in 0+ juveniles in early summer and appear to be a recurrent seasonal event, whereas more sporadic outbreaks occurred in older age classes. Carrier fish were detected at low prevalence. The disease is described as epizootic haematopoietic necrosis (EHN) and is the only viral disease of fish known to occur in Australia.     

Experimental transmission and pathogenicity of epizootic haematopoietic necrosis virus (EHNV) in redfin perch, Perca fluviatilis L., and 11 other teleosts

Abstract. The epizootiology of epizootic haematopoietic necrosis virus (EHNV) was examined by experimental transmission and pathogenicity trials in the first known host species, Perca fluviatilis L., and 11 other introduced and native teleosts of Australia. Perca fluviatilis and four other species were highly susceptible to disease following bath exposure to EHNV. Three species developed disease only when inoculated by intraperitoneal injection, and four species wore resistant to infection under the experimental conditions employed. Renal haematopoietic necrosis was the most consistent lesion produced, with hepatic, splenic and pancreatic necrosis also occurring in certain species. The resistance of the virus to desiccation, disinfectants, high and low pH and temperature, and to prolonged storage at selected temperatures was assessed, demonstrating that the virus can survive for long periods in the aquatic environment and on fomites. Carrier individuals of P. fluviatilis, Salmo gairdneri Richardson, Maccullochella peeli (Mitchell), and possibly other teleosts, represent a further reservoir of infection. However, the virus could not be isolated from common insect and crustacean prey species, and no parasitic vectors were identified. It is proposed that EHNV has contributed to serious population declines of native species in recent decades, particularly of Macquaria australasica (Cuvier), Galaxias olidus Günther and Bidyanus bidyanus (Mitchell). Salmonids are also known to be naturally and experimentally susceptible to the virus.     

Bizarre organism from the skin of mahi mahi, Coryphaena hippurus L. (Teleostei: Coryphaenidae)

Abstract. Superficial stellate cells of an unknown origin were detected on the epidermis of juvenile mahi mahi, Coryphaena hippurus L., up to 60 days of age. The cells occurred in large numbers, and were detected in both wild and cultured fish. International authorities were unable to identify the organism and there was no pathology associated with the presence of the cells on the skin. Because of the fine cytoplasmic interdigitations between the organism and the host cell, and the close ecological association with both wild and cultured juveniles examined, it was thought that the cells could possibly be highly modified skin cells. We report here that the spinous cells possess DNA sequences encoding 16S subunit ribosomal RNA genes distinct from those of mahi mahi, and also that restriction enzyme digests of genomic DNA from the spinous cells and from mahi mahi produced distinct patterns after electrophoretic separation. This suggests that the spinous cells are a bizarre commensal organism displaying a close physical and ecological association with the fish host.