Sea lice Lepeophtheirus spinifer, Tuxophorus sp. and Caligus sp. infections on wild-caught queenfish Scomberoides commersonnianus from northern Australia.

Studies of ectoparasites of wild-caught queenfish Scomberoides commersonnianus from several areas in northern Australia were reviewed to investigate relationships between parasite burdens, environmental conditions and external lesions. A sample of 27 queenfish captured near a dredge spoil disposal site in Gladstone Harbour, Queensland, Australia, in January 2012 was anomalous, with a high percentage of fish (66.6%) exhibiting grossly visible skin lesions including foci of erythema and petechial haemorrhages, particularly on the pectoral girdle and ventrolateral surfaces. Microscopically, lesions comprised acute epidermal erosion, ulceration and/or perivascular dermatitis with dermal oedema and depigmentation. Skin lesions were associated with high prevalence (100%) and intensity (mean = 21.2 copepods fish-1, range 4-46) of infection by sea lice Lepeophtheirus spinifer. Only queenfish infected with >10 L. spinifer presented with skin lesions. This is the first record of L. spinifer from Australia. In contrast, grossly visible skin lesions were not reported from queenfish (n = 152) sampled from other sites in the Northern Territory and Queensland, where the sampled fish had a much lower prevalence (51.3%) and intensity (mean = 3.54, range 0-26) of copepod (L. spinifer, Caligus spp. and Tuxophorus sp.) infections. Copepods from queenfish in studies undertaken outside Gladstone Harbour exhibited an over-dispersed pattern of infection, with the vast majority (n = 137, or 90.1%) of fish infected with <5 copepods. These data demonstrate that heavy L. spinifer infections, combined with poor water quality and/or direct exposure to contaminated dredge spoil and blooms of the cyanobacterium Lyngbya majuscula, can be associated with cutaneous disease in wild-caught queenfish.

Pathology of finfish and mud crabs Scylla serrata during a mortality event associated with a harbour development project in Port Curtis, Australia.

The objective of this study was to assess the extent and describe the nature of a multi-species marine finfish and crustacean disease event that occurred in Gladstone Harbour, Australia, 2011-2012. Finfish were examined for this study in January to April 2012 from sites where diseased animals were previously observed by the public. Gross abnormalities, including excessive skin and gill mucus, erythema, heavy ecto-parasitism, cutaneous ulceration, corneal opacity, and exophthalmos, were higher (25.5%) in finfish from Gladstone Harbour (n = 435) than in those from an undeveloped reference site, 250 km to the north (5.5%, n = 146, p < 0.0001). Microscopic abnormalities, especially non-infectious erosive to ulcerative dermatitis and internal parasitism, were more prevalent in fish from Gladstone Harbour (n = 34 of 36, prevalence = 94.4%) than in fish from the reference site (3 of 23, prevalence = 13.0% p < 0.0001). The prevalence of shell lesions was higher in mud crabs Scylla serrata sampled from Gladstone Harbour (270 of 718, prevalence = 37.5%) than from the reference site (21 of 153, prevalence = 13.7%; p < 0.0001). The significantly higher prevalence of ulcerative skin disease and parasitism in a range of species suggests affected animals were subjected to influences in Gladstone Harbour that were not present in the control sites. The disease epidemic coincided temporally and spatially with water quality changes caused by a harbour development project. The unique hydrology, geology, and industrial history of the harbour, the scope of the development of the project, and the failure of a bund wall built to retain dredge spoil sediment were important factors contributing to this epidemic.

Case-control study of epidemic mortality and Cardicola forsteri-associated disease in farmed southern bluefin tuna (Thunnus maccoyii) of South Australia.

Cardicola forsteri is a blood fluke that is highly prevalent among cultured southern bluefin tuna (SBT), Thunnus maccoyii, in South Australia. The role of C forsteri in annual SBT mortality outbreaks, which peak 6 to 12 weeks poststocking, is unknown. The objective of this study was to identify lesions unique to cultured SBT that died during a mortality event in 2009 and to determine the significance of C forsteri-associated lesions. Cultured SBT were sampled from 4 pontoons of a single site in Spencer Gulf that experienced a mortality epidemic that spanned 5 to 14 weeks poststocking. Study SBT comprised 7 that died during peak mortality, 27 that did not die, and 10 wild-caught (noncultured) SBT. All cultured SBT had branchitis and myocarditis due to C forsteri, whereas no life stages of C forsteri were histologically identified in any wild-caught SBT. Mortality was associated with the presence of severe branchitis (P<.005), and the odds of severe branchitis were 90 times greater for SBT that died than for SBT that were live caught during peak mortality (95% confidence interval, 5 to 1,684). In SBT that had died, no lesions other than those associated with C forsteri were of sufficient severity or physiologic significance to account for death. Other lesions common among cultured SBT included systemic granulocytic perivascular infiltrate, granulocytic gastric infiltrate, hepatic lipidosis, visceral granulomas, and branchial parasitic infestation. This study shows for the first time that a substantial proportion of poststocking mortality in cultured SBT is strongly associated with severe branchitis caused by C forsteri.

Histopathological survey of lesions and infections affecting sick ornamental fish in pet shops in New South Wales, Australia.

The objective of this study was to describe the frequency of histopathological lesions and categorize histopathologically evident infections in sick ornamental fish from pet shops in New South Wales, Australia. We examined 108 fish that had evidence of morbidity or mortality, including 67 cyprinids, 25 osphronemids, 11 poeciliids, 4 characids and 1 cichlid, sourced from 24 retail outlets. Conditions frequently observed in the study population included branchitis (62/86, 72.1%), visceral granulomas (41/108, 38.0%), dermatitis (17/55, 30.9%), wasting (31/108, 28.7%), and intestinal coccidiosis (18/104, 17.4 %). Branchitis and dermatitis were usually due to monogenean flukes, or flagellate or ciliate protozoa. Intralesional Microsporidia (16/41, 39.0%), mycobacteria (7/41, 17.%), or Myxosporidia (5/41, 12.2%) were identified in the majority of fish with visceral granulomas; however, special stains were critical in their identification. The proportion of histologically evident infections was remarkably high (77/108, 71.3%), and parasitic infections predominated. Many pathogens identified in the study have low host specificity and/or direct life cycles which would facilitate transmission to exposed naive fish populations, potentially posing a threat to native and commercial fish populations. Those caring for sick ornamental fish should take appropriate steps to investigate infectious disease and should take precautions that prevent the spread of pathogens.

Random and systematic sampling error when hooking fish to monitor skin fluke (Benedenia seriolae) and gill fluke (Zeuxapta seriolae) burden in Australian farmed yellowtail kingfish (Seriola lalandi).

The Australian farmed yellowtail kingfish (Seriola lalandi, YTK) industry monitor skin fluke (Benedenia seriolae) and gill fluke (Zeuxapta seriolae) burden by pooling the fluke count of 10 hooked YTK. The random and systematic error of this sampling strategy was evaluated to assess potential impact on treatment decisions. Fluke abundance (fluke count per fish) in a study cage (estimated 30,502 fish) was assessed five times using the current sampling protocol and its repeatability was estimated the repeatability coefficient (CR) and the coefficient of variation (CV). Individual body weight, fork length, fluke abundance, prevalence, intensity (fluke count per infested fish) and density (fluke count per Kg of fish) were compared between 100 hooked and 100 seined YTK (assumed representative of the entire population) to estimate potential selection bias. Depending on the fluke species and age category, CR (expected difference in parasite count between 2 sampling iterations) ranged from 0.78 to 114 flukes per fish. Capturing YTK by hooking increased the selection of fish of a weight and length in the lowest 5th percentile of the cage (RR = 5.75, 95% CI: 2.06-16.03, P-value = 0.0001). These lower end YTK had on average an extra 31 juveniles and 6 adults Z. seriolae per Kg of fish and an extra 3 juvenile and 0.4 adult B. seriolae per Kg of fish, compared to the rest of the cage population (P-value < 0.05). Hooking YTK on the edge of the study cage biases sampling towards the smallest and most heavily infested fish in the population, resulting in poor repeatability (more variability amongst sampled fish) and an overestimation of parasite burden in the population. In this particular commercial situation these finding supported that health management program, where the finding of an underestimation of parasite burden could provide a production impact on the study population. In instances where fish populations and parasite burdens are more homogenous, sampling error may be less severe. Sampling error when capturing fish from sea cage is difficult to predict. The amplitude and direction of this error should be investigated for a given cultured fish species across a range of parasite burden and fish profile scenarios.