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Barbara F. Nowak - One of the best experts on this subject based on the ideXlab platform.

  • Changes in the Splenic Melanomacrophage Centre Surface Area in Southern Bluefin Tuna (Thunnus maccoyii) Are Associated with Blood Fluke Infections
    Pathogens, 2021
    Co-Authors: Barbara F. Nowak, Mai Dang, Claire Webber, Lukas Neumann, Andrew Bridle, Roberto Bermudez, Daryl Evans
    Abstract:

    Melanomacrophage centres (MMCs) are aggregates of macrophages accumulating various pigments. They have been proposed as an indicator of fish immune response. Blood flukes are common parasites in farmed fish. Two cohorts of wild Southern Bluefin Tuna (Thunnus maccoyi) were examined at transfer, before treatment against blood flukes (pre-treatment) and at harvest. MMCs were assessed in histological sections using image analysis, while Cardicola forsteri and Cardicola orientalis infection severity was determined using qPCR, count of adult flukes in heart flushes and count of eggs in gill filaments. Fish from both cohorts showed the same pattern in the changes in the surface area of MMCs. The surface area of splenic MMCs increased over the ranching duration and was positively correlated to the PCR determined copy numbers of Cardicola forsteri ITS2 rDNA in the gills of those fish. However, the infection with blood fluke was more variable, both between cohorts and individuals within the same cohort. Eggs of blood fluke were detected in renal MMCs using histology. Cardicola forsteri had a higher prevalence than Cardicola orientalis. This study contributes to our understanding of blood fluke infections in Southern Bluefin Tuna and their interactions with MMCs.

  • Branchial Pathomorphology of Southern Bluefin Tuna Thunnus maccoyii (Castelnau, 1872) Infected by Helminth and Copepodan Parasites
    Frontiers in physiology, 2017
    Co-Authors: Mark B. Adams, Craig J. Hayward, Barbara F. Nowak
    Abstract:

    Three metazoan parasites, a monogenean Hexostoma thynni and two species of copepods Pseudocycnus appendiculatus and Euryphorus brachypterus are known to parasitize the gills of ranched Southern Bluefin Tuna (SBT) and other Tuna species. However, there is no detailed information describing the pathological response to infection by these parasites in this species. Wild Southern Bluefin Tuna Thunnus maccoyii (approximately 3 years of age), captured and towed to a grow-out site in the waters immediately south of Port Lincoln, South Australia were subsequently sampled (n = 10) monthly from March until August 2004 during commercial harvest operations. Longitudinal sections of gill hemibranchs with attached parasites were excised and fixed for routine histology and immunohistochemistry. Reference samples were also collected from fish displaying no signs of parasitism or other grossly observable anomalies. Two morphologically distinct granulocytes were observed and putatively identified as eosinophils and mast cells. Pathology was localized to filaments upon and immediately adjacent to parasite attachment sites. Branchial cellular responses, adjunct to the attachment of H. thynni by its opisthaptoral clamps, included hyperplasia and inflammation resulting in structural remodeling of branchial tissues. Inflammatory infiltrates were often dominated by putative eosinophils and lymphocytes when parasitized by H. thynni and P. appendiculatus. Gill associated lymphoid tissue infiltrated the lamellar regions particularly in response to helminth infection. A variable response ranging from hemorrhage with minor hyperplasia or fibroplasia and eosinophilic inflammation to a barely discernible change was seen for gill sections harboring P. appendiculatus and E. brachypterus. The magnitude of the host response to attachment by the latter was congruent with attachment proximity and parasite load. On the basis of the host responses reported here and the low intensity of infection observed in other associated studies these gill ectoparasites are currently considered a low risk for wild and ranched adult SBT.

  • Correlation of humoral immune response in Southern Bluefin Tuna, T. maccoyii, with infection stage of the blood fluke, Cardicola forsteri.
    PloS one, 2012
    Co-Authors: Nicole T. Kirchhoff, Mj Leef, Victoria Valdenegro, Craig J. Hayward, Barbara F. Nowak
    Abstract:

    The blood fluke, Cardicola forsteri, is a prevalent infection in ranched Southern Bluefin Tuna. This project aimed to define the timing and intensity of the various developmental stages of C. forsteri within Southern Bluefin Tuna as well as to relate infection to host pathology and immune response. Archival samples from several cohorts of T. maccoyii sampled from 2008 to 2010 were used in this study. The prevalence and intensity of C. forsteri infection was described using heart flushes and histological examination. Humoral immune response, i.e. C. forsteri specific antibody, lysozyme activity, and alternative complement activity, was also described. Based on the validated and detailed C. forsteri infection timeline, relationships between infection events, physiological response, and diagnosis were proposed. Immune response developed concurrently with C. forsteri infection, with the majority of physiological response coinciding with commencing egg production. Further research is needed to confirm the origin of C. forsteri antigen which is responsible for immune response development and how T. maccoyii immune response works against infection. To aide this research, further diagnostic methods for confirmation of infection need to be developed.

  • Assessment of nutritional status and digestive physiology in Southern Bluefin Tuna Thunnus maccoyii fed a modified baitfish diet
    Aquaculture, 2012
    Co-Authors: Mj Leef, Chris G. Carter, Barbara F. Nowak
    Abstract:

    Abstract Southern Bluefin Tuna (Thunnus maccoyii) ranching in South Australia is one of the most valuable finfish aquaculture industries in Australia. This industry is currently highly reliant upon the use of baitfish; however commercial pelleted diets for this species are now available. Despite the economic importance of these animals there is a general lack of knowledge regarding the digestive physiology of Southern Bluefin Tuna. Measurement of the digestive enzymes trypsin (T), chymotrypsin (C) and calculation of T:C ratios are particularly useful in the assessment of nutritional status in fish. In this study T and C activities were measured in ranched Tuna fed a vitamin (Vit) and vitamin + immunostimulant (Vit + Imm) supplemented baitfish diet for 8 weeks. Differences relating to the addition of the supplements were not observed for T, C or T:C ratios suggesting that the supplementation rates did not affect the nutritional status of the Tuna or the quality of the baitfish. Trypsin activity plays a key role in the secretion of chymotrypsin and in this study a significant correlation between these enzymes was found. T, C and T:C were not associated with caecum somatic index, caecum pH, caecum temperature, stomach pH or stomach temperature. Although T and C activities are highly sensitive to feeding, activities of these enzymes did not appear to be affected by the presence of baitfish in the stomach. The presence of baitfish did not appear to affect caecum pH, caecum temperature or stomach temperature. Therefore all data were pooled and a significant correlation between caecum and stomach temperature, explained by the endothermic physiology of Tuna, was observed. Significantly higher stomach pH values were associated with the presence of baitfish and an inverse relationship between stomach pH and stomach temperature was found in fish with empty stomachs but not those that had eaten. These results are indicative of a digestive strategy which employs maintenance of low stomach pH for rapid digestion of a meal. This study represents the first report of digestive enzyme activities and nutritional status for captive Southern Bluefin Tuna fed a standard and modified baitfish diet. In addition to a better understanding of digestive physiology, these results, in combination with the physiological measures of feeding and digestion, will significantly contribute to the further development of an in vitro digestive model for this species. This model will significantly improve the abilities of the Australian Southern Bluefin Tuna industry to assess the predicted digestibility of commercially produced pelleted diets as well as screen novel dietary ingredients prior to full scale and often commercially expensive in vivo trials.

  • Distribution of Cardicola forsteri eggs in the gills of Southern Bluefin Tuna (Thunnus maccoyii) (Castelnau, 1872
    Aquaculture, 2012
    Co-Authors: Catarina Norte Dos Santos, Mj Leef, Nathan J Bott, Brian Jones, Danièle Giblot-ducray, Barbara F. Nowak
    Abstract:

    The distribution of Cardicola forsteri eggs in the gills of Southern Bluefin Tuna (Thunnus maccoyii) was analysed. Eggs were confirmed to be C. forsteri using laser-capture microdissection and quantitative polymerase chain reaction (qPCR) analyses. Prevalence of infection was significantly higher in the second gill arch (χ2 = 6.49, P 0.05). Similarly, there was no significant difference in the intensity of C. forsteri eggs between the gill arches (F = 3.43, d.f. = 2, P > 0.05), or at different depth of sectioning (F = 0.08, d.f. = 1.12, P > 0.05). Results suggest that the presence of C. forsteri eggs in the gills of Tuna is more likely to be detected by sampling the second gill arch. Furthermore, targeting the middle region and increasing the sectioning depth may reduce the proportion of false negatives.

B F Nowak - One of the best experts on this subject based on the ideXlab platform.

  • the Southern Bluefin Tuna mucosal microbiome is influenced by husbandry method net pen location and anti parasite treatment
    bioRxiv, 2020
    Co-Authors: Jj Minich, B F Nowak, Claire Webber, Cecilia Power, Michaela Melanson, Rob Knight, Kirsten Rough, Nathan J Bott, Eric E Allen
    Abstract:

    Aquaculture is the fastest growing primary industry worldwide. Marine finfish culture in open ocean net pens, or pontoons, is one of the largest growth areas and is currently the only way to rear high value fish such as Bluefin Tuna. Ranching involves catching wild juveniles, stocking in floating net pens and fattening for four to eight months. Tuna experience several parasite-induced disease challenges in culture that can be mitigated by application of praziquantel (PZQ) as a therapeutic. In this study, we characterized the microbiome of ranched Southern Bluefin Tuna, Thunnus maccoyii, across four anatomic sites (gill, skin, digesta, and anterior kidney) and evaluated environmental and pathological factors that influence microbiome composition, including the impact of PZQ treatment on microbiome stability. Southern Bluefin Tuna gill, skin, and digesta microbiome communities are unique and potentially influenced by husbandry practices, location of pontoon growout pens, and treatment with the antiparasitic PZQ. There was no significant relationship between the fish mucosal microbiome and incidence or abundance of adult blood fluke in the heart or fluke egg density in the gill. An enhanced understanding of microbiome diversity and function in high-value farmed fish species such as Bluefin Tuna is needed to optimize fish health and improve aquaculture yield. Comparison of the Bluefin Tuna microbiome to other fish species, including Seriola lalandi (yellowtail kingfish), a common farmed species from Australia, and Scomber japonicus (Pacific mackerel), a wild caught Scombrid relative of Tuna, showed the two Scombrids had more similar microbial communities compared to other families. The finding that mucosal microbial communities are more similar in phylogenetically related fish species exposes an opportunity to develop mackerel as a model for Tuna microbiome and parasite research.

  • Relationship between Southern Bluefin Tuna, Thunnus maccoyii, melanomacrophage centres and Cardicola spp. (Trematoda: Aporocotylidae) infection
    'Elsevier BV', 2020
    Co-Authors: Widdicombe M, B F Nowak, Power C, Van Gelderen R, Nj Bott
    Abstract:

    Southern Bluefin Tuna (SBT), Thunnus maccoyii, is ranched off Port Lincoln, South Australia and is Australia's second largest economic finfish aquaculture industry. The biggest threats to SBT health identified by the industry are the blood flukes Cardicola forsteri and C. orientalis (Trematoda: Aporocotylidae). Melanomacrophage centres (MMCs) are aggregations of pigmented macrophage like cells present in spleen, kidney and liver of teleost fish. The aim of this study was to quantify MMCs in SBT anterior kidney, liver and spleen to investigate changes in relation to Cardicola spp. Infection. Samples were collected at the end of ranching from pontoons where SBT were treated with PZQ and pontoons with untreated SBT. SBT MMC percentage of surface area cover was highest in SBT spleen and lowest in the liver. Significant positive correlations were identified between SBT MMC area and SBT size in all three organs (p Cardicola spp. gill egg counts, and in the kidney for C. forsteri DNA from SBT hearts and gills (p Cardicola spp. Infection and MMCs have the potential to be used as an indicator to assess health effects that Cardicola spp. have on SBT

  • culturable microbiota of ranched Southern Bluefin Tuna thunnus maccoyii castelnau
    Journal of Applied Microbiology, 2013
    Co-Authors: Victoria A Valdenegrovega, S Naeem, J Carson, J P Bowman, J Tejedor L Del Real, B F Nowak
    Abstract:

    Aims: The Australian Tuna industry is based on the ranching of wild Southern Bluefin Tuna (SBT, Thunnus maccoyii). Within this industry, only opportunistic pathogens have been reported infecting external wounds of fish. This study aimed to identify different culturable bacteria present in three cohorts of SBT and to determine normal bacteria and potential pathogens in isolates from harvest fish and moribund/dead fish. Post-mortem changes in the microbiota were also studied. Methods and Results: Moribund/dead showed a greater proportion of members from the family Vibrionaceae than harvested fish; the latter presented mainly non-Vibrio species. In harvested fish spleens, Vibrio splendidus I complex was the most commonly identified group among Vibrio isolates, while most groups from the family Vibrionaceae were isolated from gills. For moribund/dead, Vibrio chagasii and Photobacterium damselae subsp. damselae were common in gill, spleen and kidney samples. Non-Vibrio isolates from gills were characterized using 16S rRNA sequencing as Flavobacteriaceae and classes Gammaproteobacteria and Alphaproteobacteria, mainly from the genera Winogradskyella and Tenacibaculum. Post-mortem changes showed dynamic shifts in bacterial dominance in gills, with Vibrionaceae and non-Vibrio spp. found in similar proportions initially and types related to Pseudoalteromonas ruthenica prevailing after 27 h. Spleen samples showed little bacterial growth until 5 h post-mortem, while various Vibrio-associated species were isolated 27 h post-mortem. Conclusions: Bacterial isolates found include a range of potentially pathogenic bacteria that should be monitored though most of them have yet to be associated with disease in Tuna. Significance and Impact of the Study: This study forms a foundation for future research into the bacterial population dynamics under different culture conditions of SBT. An understanding of the bacterial compositions in SBT is necessary to evaluate the effects of some bacterial species on their health.

  • gross and histopathological characteristics of two lipomas and a neurofibrosarcoma detected in aquacultured Southern Bluefin Tuna thunnus maccoyii castelnau in south australia
    Journal of Fish Diseases, 2008
    Co-Authors: Colin Johnston, T J Bayly, Marty R. Deveney, B F Nowak
    Abstract:

    Three visible lesions were examined from two specimens of Southern Bluefin Tuna. The lesions were examined grossly and two were identified as lipomas, the third bore similarities to a schwannoma. Histopathology confirmed that two consisted of mature adipocytes consistent with a diagnosis of lipoma. The third lesion consisted of spindle cells in Antoni A and B patterns and was tentatively diagnosed as a malignant schwannoma. Immunohistochemistry identified both S100 and glial fibrillary acid protein expression within the lesion, which, together with the histopathological appearance, is consistent with a diagnosis of neurofibrosarcoma.

  • an epizootic of caligus chiastos on farmed Southern Bluefin Tuna thunnus maccoyii off south australia
    Diseases of Aquatic Organisms, 2008
    Co-Authors: Craig J. Hayward, Hamish M. Aiken, B F Nowak
    Abstract:

    ABSTRACT: In some years, large numbers of Caligus chiastos have been observed on the external surfaces of Southern Bluefin Tuna, particularly on the head and eyes, in some sea cages in Spencer Gulf, Australia. As no epidemiological data were available, we monitored sea lice on Tuna (N = 130) in 4 research cages sampled at 6 wk intervals during the 2005 farming season. No lice were observed on a sample of 10 wild-caught Tuna when the cohort was transferred to cages in early April. By late May more than half the sampled Tuna (22 of 40) were infected, with up to 42 parasites; we also recorded one unidentified Caligus sp. at this time. In early July the number of Tuna infected with lice declined to 10%; in the final sample in late August none were detected. Prevalence in May was significantly higher than on other dates (p ≤ 0.001), whereas mean abundances did not differ significantly (p > 0.05). The decline in prevalence corresponded with a seasonal fall in temperature, from ca. 17°C in May to 14°C in August. Counts of lice at the peak of infection were associated with the severity of eye damage (Spearman’s rank correlation coefficient, rS, 38df = 0.654, p < 0.001); this may be because lice graze on the cornea or because Tuna injure their eyes when flashing (rubbing against objects). Counts at this time were also strongly and inversely correlated with the condition index (rS, 38df = –0.707, p < 0.001). It appears that Tuna become infested with adult sea lice via wild teleosts and elasmobranchs attracted to sea cages. KEY WORDS: Sea lice · Caligids · Copepoda · Parasite · Southern Bluefin Tuna · Thunnus maccoyii · Epidemiolog

Christopher M. Burke - One of the best experts on this subject based on the ideXlab platform.

  • Production, characterisation and diagnostic use of antisera to Southern Bluefin Tuna (Thunnus maccoyii Castelnau) immunoglobulin
    Aquaculture, 2001
    Co-Authors: M. Watts, Barry L. Munday, Christopher M. Burke
    Abstract:

    Sheep polyclonal antisera and one monoclonal antiserum (mAb) were prepared against purified Southern Bluefin Tuna (Thunnus maccoyii Castelnau) immunoglobulin, and also rabbit polyclonal antisera were prepared against isolated immunoglobulin H chains. Activity and specificity were determined in immunoblots following SDS-PAGE in reducing and non-reducing conditions. In reducing conditions, the mAb and rabbit antisera reacted specifically with H chains of purified SBT Ig, and only with bands consistent with H chains in sera from other Thunnus spp. No cross-reactivity with reduced serum from any other teleost was found for the mAb, and only minimally for the rabbit antisera, but sheep antisera were less specific and reacted with bands other than those attributable to immunoglobulin. The antisera were used in serological assay development and detected the presence of infection with the blood fluke, Cardicola forsteri, a recently described pathogen of farmed Southern Bluefin Tuna.

  • Isolation and partial characterisation of immunoglobulin from Southern Bluefin Tuna Thunnus maccoyii Castelnau
    Fish & shellfish immunology, 2001
    Co-Authors: M. Watts, Barry L. Munday, Christopher M. Burke
    Abstract:

    Specific and total serum immunoglobulins were extracted by immunoaffinity, mannan-binding protein and Protein A affinity chromatography from Southern Bluefin Tuna (Thunnus maccoyii Castelnau) immunised with rabbit IgG, and from non-immunised Southern Bluefin Tuna. SDS-PAGE in 10% reducing gels revealed two heavy chains with molecular weights of approximately 74.6 +/- 1.3 kDa and 71.2 +/- 0.9 kDa, and two light chains with molecular weights of approximately 29 +/- 1.2 kDa and 28 +/- 1.0 kDa. Under non-reducing, but denaturing, conditions in 4% and 5% SDS-PAGE gels, a high molecular weight and a low molecular weight fraction were demonstrated. By gel filtration using Sephacryl HR 300 a molecular weight of 845 kDa, consistent with a tetramer, was obtained for the high molecular weight fraction, and a molecular weight of 168 kDa, consistent with a monomer, was obtained for the low molecular weight fraction. The extinction coefficient at A280 for the purified immunoglobulin (Ig) was determined to be 1.24. Tuna a-rabbit IgG Ig was reactive with all non-reduced mammalian IgG antigens tested, suggesting that common conformational antigenic determinants were recognised.

M. Watts - One of the best experts on this subject based on the ideXlab platform.

  • Production, characterisation and diagnostic use of antisera to Southern Bluefin Tuna (Thunnus maccoyii Castelnau) immunoglobulin
    Aquaculture, 2001
    Co-Authors: M. Watts, Barry L. Munday, Christopher M. Burke
    Abstract:

    Sheep polyclonal antisera and one monoclonal antiserum (mAb) were prepared against purified Southern Bluefin Tuna (Thunnus maccoyii Castelnau) immunoglobulin, and also rabbit polyclonal antisera were prepared against isolated immunoglobulin H chains. Activity and specificity were determined in immunoblots following SDS-PAGE in reducing and non-reducing conditions. In reducing conditions, the mAb and rabbit antisera reacted specifically with H chains of purified SBT Ig, and only with bands consistent with H chains in sera from other Thunnus spp. No cross-reactivity with reduced serum from any other teleost was found for the mAb, and only minimally for the rabbit antisera, but sheep antisera were less specific and reacted with bands other than those attributable to immunoglobulin. The antisera were used in serological assay development and detected the presence of infection with the blood fluke, Cardicola forsteri, a recently described pathogen of farmed Southern Bluefin Tuna.

  • Isolation and partial characterisation of immunoglobulin from Southern Bluefin Tuna Thunnus maccoyii Castelnau
    Fish & shellfish immunology, 2001
    Co-Authors: M. Watts, Barry L. Munday, Christopher M. Burke
    Abstract:

    Specific and total serum immunoglobulins were extracted by immunoaffinity, mannan-binding protein and Protein A affinity chromatography from Southern Bluefin Tuna (Thunnus maccoyii Castelnau) immunised with rabbit IgG, and from non-immunised Southern Bluefin Tuna. SDS-PAGE in 10% reducing gels revealed two heavy chains with molecular weights of approximately 74.6 +/- 1.3 kDa and 71.2 +/- 0.9 kDa, and two light chains with molecular weights of approximately 29 +/- 1.2 kDa and 28 +/- 1.0 kDa. Under non-reducing, but denaturing, conditions in 4% and 5% SDS-PAGE gels, a high molecular weight and a low molecular weight fraction were demonstrated. By gel filtration using Sephacryl HR 300 a molecular weight of 845 kDa, consistent with a tetramer, was obtained for the high molecular weight fraction, and a molecular weight of 168 kDa, consistent with a monomer, was obtained for the low molecular weight fraction. The extinction coefficient at A280 for the purified immunoglobulin (Ig) was determined to be 1.24. Tuna a-rabbit IgG Ig was reactive with all non-reduced mammalian IgG antigens tested, suggesting that common conformational antigenic determinants were recognised.

  • fatal encephalitis due to the scuticociliate uronema nigricans in sea caged Southern Bluefin Tuna thunnus maccoyii
    Diseases of Aquatic Organisms, 1997
    Co-Authors: Barry L. Munday, P J Odonoghue, K M Rough, M. Watts, T M Hawkesford
    Abstract:

    A syndrome characterized by atypical swimming behaviour followed by rapid death was first reported in captive Southern Bluefin Tuna Thunnus maccoyii (Castelnau) in the winter of 1993. The cause of this behaviour was found to be a parasitic encephalitis due to the scuticociliate Uronema nigricans (Mueller). Based on parasitological and histological findings, it is proposed that the parasites initially colonise the olfactory rosettes and then ascend the olfactory nerves to eventually invade the brain. Possible epidemiological factors involved in the pathogenesis of the disease include water temperature (>18 degrees C) and the immune status of the fish.

Craig J. Hayward - One of the best experts on this subject based on the ideXlab platform.

  • Branchial Pathomorphology of Southern Bluefin Tuna Thunnus maccoyii (Castelnau, 1872) Infected by Helminth and Copepodan Parasites
    Frontiers in physiology, 2017
    Co-Authors: Mark B. Adams, Craig J. Hayward, Barbara F. Nowak
    Abstract:

    Three metazoan parasites, a monogenean Hexostoma thynni and two species of copepods Pseudocycnus appendiculatus and Euryphorus brachypterus are known to parasitize the gills of ranched Southern Bluefin Tuna (SBT) and other Tuna species. However, there is no detailed information describing the pathological response to infection by these parasites in this species. Wild Southern Bluefin Tuna Thunnus maccoyii (approximately 3 years of age), captured and towed to a grow-out site in the waters immediately south of Port Lincoln, South Australia were subsequently sampled (n = 10) monthly from March until August 2004 during commercial harvest operations. Longitudinal sections of gill hemibranchs with attached parasites were excised and fixed for routine histology and immunohistochemistry. Reference samples were also collected from fish displaying no signs of parasitism or other grossly observable anomalies. Two morphologically distinct granulocytes were observed and putatively identified as eosinophils and mast cells. Pathology was localized to filaments upon and immediately adjacent to parasite attachment sites. Branchial cellular responses, adjunct to the attachment of H. thynni by its opisthaptoral clamps, included hyperplasia and inflammation resulting in structural remodeling of branchial tissues. Inflammatory infiltrates were often dominated by putative eosinophils and lymphocytes when parasitized by H. thynni and P. appendiculatus. Gill associated lymphoid tissue infiltrated the lamellar regions particularly in response to helminth infection. A variable response ranging from hemorrhage with minor hyperplasia or fibroplasia and eosinophilic inflammation to a barely discernible change was seen for gill sections harboring P. appendiculatus and E. brachypterus. The magnitude of the host response to attachment by the latter was congruent with attachment proximity and parasite load. On the basis of the host responses reported here and the low intensity of infection observed in other associated studies these gill ectoparasites are currently considered a low risk for wild and ranched adult SBT.

  • Correlation of humoral immune response in Southern Bluefin Tuna, T. maccoyii, with infection stage of the blood fluke, Cardicola forsteri.
    PloS one, 2012
    Co-Authors: Nicole T. Kirchhoff, Mj Leef, Victoria Valdenegro, Craig J. Hayward, Barbara F. Nowak
    Abstract:

    The blood fluke, Cardicola forsteri, is a prevalent infection in ranched Southern Bluefin Tuna. This project aimed to define the timing and intensity of the various developmental stages of C. forsteri within Southern Bluefin Tuna as well as to relate infection to host pathology and immune response. Archival samples from several cohorts of T. maccoyii sampled from 2008 to 2010 were used in this study. The prevalence and intensity of C. forsteri infection was described using heart flushes and histological examination. Humoral immune response, i.e. C. forsteri specific antibody, lysozyme activity, and alternative complement activity, was also described. Based on the validated and detailed C. forsteri infection timeline, relationships between infection events, physiological response, and diagnosis were proposed. Immune response developed concurrently with C. forsteri infection, with the majority of physiological response coinciding with commencing egg production. Further research is needed to confirm the origin of C. forsteri antigen which is responsible for immune response development and how T. maccoyii immune response works against infection. To aide this research, further diagnostic methods for confirmation of infection need to be developed.

  • an epizootic of caligus chiastos on farmed Southern Bluefin Tuna thunnus maccoyii off south australia
    Diseases of Aquatic Organisms, 2008
    Co-Authors: Craig J. Hayward, Hamish M. Aiken, B F Nowak
    Abstract:

    ABSTRACT: In some years, large numbers of Caligus chiastos have been observed on the external surfaces of Southern Bluefin Tuna, particularly on the head and eyes, in some sea cages in Spencer Gulf, Australia. As no epidemiological data were available, we monitored sea lice on Tuna (N = 130) in 4 research cages sampled at 6 wk intervals during the 2005 farming season. No lice were observed on a sample of 10 wild-caught Tuna when the cohort was transferred to cages in early April. By late May more than half the sampled Tuna (22 of 40) were infected, with up to 42 parasites; we also recorded one unidentified Caligus sp. at this time. In early July the number of Tuna infected with lice declined to 10%; in the final sample in late August none were detected. Prevalence in May was significantly higher than on other dates (p ≤ 0.001), whereas mean abundances did not differ significantly (p > 0.05). The decline in prevalence corresponded with a seasonal fall in temperature, from ca. 17°C in May to 14°C in August. Counts of lice at the peak of infection were associated with the severity of eye damage (Spearman’s rank correlation coefficient, rS, 38df = 0.654, p < 0.001); this may be because lice graze on the cornea or because Tuna injure their eyes when flashing (rubbing against objects). Counts at this time were also strongly and inversely correlated with the condition index (rS, 38df = –0.707, p < 0.001). It appears that Tuna become infested with adult sea lice via wild teleosts and elasmobranchs attracted to sea cages. KEY WORDS: Sea lice · Caligids · Copepoda · Parasite · Southern Bluefin Tuna · Thunnus maccoyii · Epidemiolog

  • Serological evidence of an antibody response in farmed Southern Bluefin Tuna naturally infected with the blood fluke Cardicola forsteri.
    Fish & shellfish immunology, 2008
    Co-Authors: Hamish M. Aiken, Craig J. Hayward, Philip Crosbie, Marianne Watts, Barbara F. Nowak
    Abstract:

    In this study, adaptive immune response was investigated in farmed Southern Bluefin Tuna, Thunnus maccoyii, infected with a sanguinicolid Cardicola forsteri. A cohort (Cohort(2005)) of Southern Bluefin Tuna was sampled between March 2005 and August 2006. Samples were taken at the transfer of wild caught Tuna to sea cages and then at regular intervals. Parasite intensity, abundance and prevalence data were recorded. An ELISA was developed to detect and quantify an antibody response against the blood fluke in Southern Bluefin Tuna serum. Intensity and prevalence of the blood fluke were shown to peak in May 2005 at 10.9 flukes per infected fish (SE=1.72) and 97.5% prevalence and then decreased to low prevalence (10%) and intensity (1.0). There were no significant changes in prevalence or intensity in 2006. Antibody titres and seroprevalence increased from 1.37 U microl(-1) and 10% at transfer in March 2005 to reach a peak in December 2005 of 25.86 U microl(-1) (SE=6.26 U microl(-1)) and 66.66%. No significant changes were observed in antibody titres for the same cohort of fish during 2006. Parasitological and serological values from Cohort(2005) were compared to a 2006 cohort (Cohort(2006)) in March 2006 and August 2006 to determine if prior infection in Cohort(2005) elicited any protection against infection in 2006. Although significant differences were not observed in intensities between cohorts it was shown that Cohort(2005) had significantly lower abundances and prevalences of blood fluke infection than Cohort(2006). Although there was no significant difference in mean antibody titres between cohorts in March 2006, the mean antibody titre of Cohort(2006) was significantly greater than that of Cohort(2005) in August 2006. No significant differences were observed in seroprevalence. This is one of the few studies to demonstrate the development of acquired resistance in fish against a parasite in an aquaculture environment under natural infection conditions.