This is the first report of betanodavirus infection in 2 species of finfish, Kuhlia rupestris (jungle perch) and Ambassis marianus (estuary perchlet). This report also describes isolation of betanodavirus from infected pond water using the SSN-1 cell line. Histopathology of K. rupestris larvae revealed vacuolation in the eye and brain, which was confirmed using betanodavirus-specific immunohistochemistry. The eye and brain from A. marianus and betanodavirus isolated from pond water were confirmed using real-time PCR and Sanger sequencing. High throughput sequencing was used to obtain betanodavirus sequences from paraffin blocks containing infected K. rupestris. The phylogenetic analysis of betanodavirus RNA1 and RNA2 sequences from all 3 sources were associated with the red-spotted grouper nervous necrosis virus (RGNNV) genotype. The RNA1 nucleotide sequence from jungle perch showed 100% identity with the betanodavirus water isolate and 99.37% identity with A. marianus. Furthermore, we have demonstrated the usefulness of combining recovery of viable virus from environmental samples through fish cell line culture with PCR testing as a means of validating the efficacy of chlorination to eradicate betanodavirus from the pond environment.

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Betanodavirus infections have a significant impact through direct losses and trade restrictions for aquaculture sectors in Australia. The giant grouper, Epinephelus lanceolatus, is a high-value, fast-growing species with significant aquaculture potential. With subacute to chronic mortalities reported from a commercial aquaculture facility in northern Queensland, the viral nervous necrosis in the affected fish was confirmed using a RT-qPCR followed by virus isolation using the SSN-1 cell line. The RNA1 and RNA2 segments were sequenced and nucleotide sequences were compared with betanodavirus sequences from GenBank. Phylogenetic analysis revealed that both these sequences clustered with sequences representing red spotted grouper nervous necrosis virus genotype and showed high sequence identity to virus sequences affecting other grouper species. This is the first report confirming infection by betanodavirus in E. lanceolatus from Australia with successful isolation of the virus in a cell culture system, and analysis of nearly full length RNA1 and RNA2 sequences.

Francisellosis is a bacterial disease with increasing economic impacts in the culture of tilapia and Atlantic cod since emerging in 1992. Two main strains – Francisella noatunensis subsp. orientalis (Fno) and F. noatunensis subsp. noatunensis (Fnn), have been identified, causing both acute and chronic granulomatous systemic disease. The piscine host range is increasing and Francisella culture should be included in routine diagnosis. Differentiation from the major zoonotic F. tularensis and opportunistic zoonotic F. philomiragia when dealing with environmental soil and water samples from fish farms is important. Diagnosis can be challenging but presentation of granulomatous pathology in fish should require use of cysteine supplemented selective media, culture at 15–28°C or culture in fish cell lines and specific PCR to exclude piscine Fno or Fnn. Control of infections in fish rely on appropriate antibiotic selection although in the long term an effective commercial vaccine that includes the pathogenic species of Francisella is required.

Fish collected after a mass mortality at an artificial lake in south-east Queensland, Australia, were examined for the presence of nodularin as the lake had earlier been affected by a Nodularia bloom. Methanol extracts of muscle, liver, peritoneal and stomach contents were analysed by HPLC and tandem mass spectrometry; histological examination was conducted on livers from captured mullet. Livers of sea mullet (Mugil cephalus) involved in the fish kill contained high concentrations of nodularin (median 43.6 mg/kg, range 40.8–47.8 mg/kg dry weight; n = 3) and the toxin was also present in muscle tissue (median 44.0 μg/kg, range 32.3–56.8 μg/kg dry weight). Livers of fish occupying higher trophic levels accumulated much lower concentrations. Mullet captured from the lake 10 months later were also found to have high hepatic nodularin levels. DNA sequencing of mullet specimens revealed two species inhabiting the study lake: M. cephalus and an unidentified mugilid. The two mullet species appear to differ in their exposure and/or uptake of nodularin, with M. cephalus demonstrating higher tissue concentrations. The feeding ecology of mullet would appear to explain the unusual capacity of these fish to concentrate nodularin in their livers; these findings may have public health implications for mullet fisheries and aquaculture production where toxic cyanobacteria blooms affect source waters. This report incorporates a systematic review of the literature on nodularin measured in edible fish, shellfish and crustaceans.