Frances Stephens

Haliotrema Abaddon N. SP. (Monogenoidea: Dactylogyridae) from the Gills of Wild and Maricultured West Australian Dhufish Glaucosoma Hebraicum (Teleostei: Glaucosomatidae), in Australia

Haliotrema abaddon n. sp. (Dactylogyridae) is described from the gills of West Australian dhufish Glaucosoma hebraicum (Teleostei: Glaucosomatidae), from the Indian Ocean near Fremantle, Western Australia. The parasite is recorded from cultured dhufish and from a major portion of the known geographic distribution of its host. In cultured dhufish, H. abaddon causes branchitis and hyperplasia and metaplasia of the lamellar epithelial cells and may be a limiting factor in the development of an economically feasible mariculture industry. Comparable prevalences and densities of the parasite on wild and cultured dhufish were observed. In heavily infested captive fish, clusters of eggs (egg strands) appear to restrict blood flow to localized regions of the gills as a result of entanglement of egg filaments with secondary gill lamellae. Hatching of oncomiracidia occurs in 7–10 days at 20–25 C.

Treatments to control Haliotrema abaddon in the West Australian dhufish, Glaucosoma hebraicum

Haliotrema abaddon is a significant monogenean parasite of the gills of maricultured Western Australian dhufish, Glaucosoma hebraicum, and can cause severe gill pathology. A series of trials was undertaken using infested fish in 120-l glass aquaria to assess the safety and efficacy of some potential “in water” treatments, including trichlorphon, praziquantel, formalin, toltrazuril and a freshwater bath. Treatment efficacy was established by assessment of the number of parasites found in tank sediment immediately following treatment and by examination of gills for parasites using a gill biopsy technique. Praziquantel bathes, 2 mg l−1 of 30-h duration, were the most safe and effective treatment. Freshwater bathes of below 2‰ salinity for 90 min were effective but highly stressful for the fish. Trichlorphon 0.5 mg l−1 for 30 h was safe and relatively effective. Formalin, 25 ppm, and toltrazuril, 12.5 mg l−1, were safe but resulted in the removal of insufficient parasites to recommend it as a treatment for dhufish infested with H. abaddon.

Detection and characterization of viruses of the genus Megalocytivirus in ornamental fish imported into an Australian border quarantine premises: an emerging risk to national biosecurity

This report documents an emerging trend of identification of Megalocytivirus-like inclusions in a range of ornamental fish species intercepted during quarantine detention at the Australian border. From September 2012 to February 2013, 5 species of fish that had suffered mortality levels in excess of 25% whilst in the post-entry quarantine and had Megalocytivirus-like inclusion bodies in histological sections were examined by PCR. The fish had been imported from Singapore, Malaysia and Sri Lanka. Ninety-seven of 111 individual fish from affected tanks of fish tested were positive for the presence of Megalocytivirus by PCR. Sequence analysis of representative PCR products revealed an identical sequence of 621 bp in all cases which was identical to a previously characterized Megalocytivirus (Sabah/RAA1/2012 strain BMGIV48). Phylogenetic analysis of available Megalocytivirus major capsid protein (MCP) sequences confirmed the existence of 3 major clades of Megalocytivirus. The virus detected in this study was identified as a member of Genotype II. The broad host range and pathogenicity of megalocytiviruses, coupled to the documented spread of ornamental fish into the environment, render this a significant and emerging biosecurity threat to Australia.

Histopathology of oedema in pearl oysters Pinctada maxima

In October 2006, severe mortalities (80 to 100%) were reported in pearl oyster Pinctada maxima production farms from Exmouth Gulf, Western Australia. Only P. maxima were affected; other bivalves including black pearl oysters P. margaratifera remained healthy. Initial investigations indicated that the mortality was due to an infectious process, although no disease agent has yet been identified. Gross appearance of affected oysters showed mild oedema, retraction of the mantle, weakness and death. Histology revealed no inflammatory response, but we did observe a subtle lesion involving tissue oedema and oedematous separation of epithelial tissues from underlying stroma. Oedema or a watery appearance is commonly reported in published descriptions of diseased molluscs, yet in many cases the terminology has been poorly characterised. The potential causes of oedema are reviewed; however, the question remains as to what might be the cause of oedema in molluscs that are normally iso-osmotic with seawater and have no power of anisosmotic extracellular osmotic regulation.

The effect of CO2-rich ground water on the West Australian dhufish (Glaucosoma hebraicum)

Abstract The effect of high CO 2 saline ground water on the blood oxygenation properties of the West Australian dhufish was evaluated following ill thrift of wild caught dhufish held in the water. The Bohr factor was calculated for whole blood from captively bred dhufish to assess the potential effect of increased p CO 2 on oxygenation of dhufish haemoglobin. Blood pH, p CO 2 , electrolytes and haematological parameters were determined for two groups of captively bred dhufish held long term in seawater and high p CO 2 ground water, respectively. Chemical analysis of the two water sources was performed. Ground water in dhufish tanks had a pH of 7.7 (seawater pH 8.1) and p CO 2 6.45 mm Hg (seawater 1.50 mm Hg). Dhufish whole blood had a large Bohr factor. Dhufish acclimated to ground water had increased plasma p CO 2 , HCO 3 − , haemoglobin content, haematocrit and erythrocyte counts. The increase in haemoglobin content was the result of an increase in erythrocytes.

New pathological condition in cultured mulloway Argyrosomus japonicus: histopathological, ultrastructural and molecular studies

Mulloway Argyrosomus japonicus is a native fish species in Western Australia, for which aquaculture production has recently been developed. A single cohort was stocked in a cage offshore at Geraldton, Western Australia, at a water depth of 6 m. Fish appeared healthy before stocking. Routine histological analysis was carried out from 10 mo post stocking and until completion of harvest (about 2.5 yr post stocking). No gross pathology was evident. Microscopically, however, granulomatous lesions were present in the kidneys of almost 100% of the fish examined. Enclosed in the granuloma was an aggregate of organisms, 4.2 to 5.4 µm in diameter. Kidney granulomas appeared as multi-focal aggregates. Granulomas at different stages of formation and finally fibrosing granulomas were observed. Granulomas also appeared infrequently in other organs: a few granulomas were found in the liver and spleen and a single granuloma in the heart of one fish. Transmission electron microscopy (TEM) revealed that the organism was composed of 2 cells, an outer cell enclosing an inner cell. The inner cell was surrounded by a double membrane and the outer cell by a single membrane. Cellular material, presumably of parasitic nature, surrounded the outer cell. The organism contained primitive mitochondria and abundant free ribosomes. Small subunit ribosomal DNA (SSU rDNA) sequence obtained by PCR revealed an 84% sequence identity with the myxosporean Latyspora scomberomori. Based on TEM and preliminary molecular results, we suggest that the organism is the extrasporogonic developmental stage of a myxozoan parasite, which failed to form spores in the mulloway host.