Doctoral Theses
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The Doctoral Theses collection contains digital copies of AUT doctoral theses deposited with the Library since 2004 and made available open access. All theses for doctorates awarded from 2007 onwards are required to be deposited in Tuwhera Open Theses unless subject to an embargo.
For theses submitted prior to 2007, open access was not mandatory, so only those theses for which the author has given consent are available in Tuwhera Open Theses. Where consent for open access has not been provided, the thesis is usually recorded in the AUT Library catalogue where the full text, if available, may be accessed with an AUT password. Other people should request an Interlibrary Loan through their library.
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Browsing Doctoral Theses by Supervisor "Alfaro, Andrea C"
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- ItemApplication of Encapsulation Technology to Improve the Growth Rate of New Zealand Black-footed Abalone (Haliotis iris)(Auckland University of Technology, 2020) Masoomi Dezfooli, SeyedehsaraAbalone is a marine gastropod mollusc belonging to the family Haliotidae. Black-footed abalone, (Haliotis iris) bred and harvested uniquely in New Zealand, has a high market demand due to its high quality and chemical-free farming process. However, the slow growth rate of abalone has limited its sustainable production. Many studies have shown that probiotics can improve the growth rate and health of abalone. However, effective delivery of probiotics to farmed abalone has remained a challenge. Conventional probiotic delivery methods through culture water or as feed supplements may lead to environmental contamination, loss of activity and insufficient dosages. This thesis aims to develop a new probiotic delivery system to enhance health and growth rate of black-footed abalone. A literature review was conducted to analyse the application of encapsulation technology in developing novel delivery methods for various bioactives including probiotics, nutrients and immunostimulants to farmed aquatic species (Chapter 2). A pre-formulation study was performed to confirm the beneficial characteristics of probiotics previously isolated from healthy abalone. The three bacterial species namely Exiguobacterium sp., Enterococcus sp. and Vibrio sp. were characterised and their abilities to help in feed digestion were confirmed (Chapter 3). The probiotic bacteria were then encapsulated in chitosan and alginate-based microparticles. The efficiency of microparticles in encapsulating the probiotics and creating a pH-dependent release in the simulated gastric and intestinal fluids of abalone were demonstrated. The developed microparticles displayed floating behaviour in seawater, hence, they were immobilised in alginate beads to improve their accessibility to abalone. Fluorescence microscopy suggested minimum leach of the encapsulated bacteria into seawater followed by the successful delivery of microparticles into abalone’s gastrointestinal tract (GIT). The high load of probiotic bacteria in the GIT of probiotic-fed animals illustrated the potential of the developed microparticles as new carriers for oral administration of probiotics to abalone (Chapter 4). To simplify the production process of encapsulated probiotics, an extrusion method was utilised to develop chitosan-coated alginate beads instead of microparticles. Encapsulated probiotic beads with desired properties including spherical shape, fast sinking, high palatability, high stability and minimum release in seawater were obtained. The tracking experiment using fluorescent-labelled probiotics confirmed the successful delivery of the encapsulated probiotics into the GIT of probiotic-fed abalone (Chapter 5). The efficiency of the developed beads to improve the health and growth of abalone were assessed by performing a two-month feeding trial. Four different dietary treatments including 1) conventional feed, 2) feed sprayed with probiotic culture, 3) combination of encapsulated probiotics and conventional feed, and 4) encapsulated probiotics containing nutrients were used to feed juvenile black-footed abalone. Diet 4 successfully improved growth performance, feed utilisation, feed conversion rate and reduced feed wastage. Flow cytometric analysis revealed a lower level of oxidative stress associated with diet 4 compared to the other diets. Metabolomics analysis on abalone foot muscle further revealed that abalone fed with diet 4 differentially regulated 31 metabolites mostly composed of free amino acids which may indicate a better delivery of feed. Therefore, chitosan-coated alginate beads can be considered as an effective probiotics and nutrients delivery method to black-footed abalone capable of increasing abalone health and growth performance while minimising feed wastage, environmental impact and hence feed cost (Chapter 6). In conclusion, an encapsulated system was developed to deliver viable probiotics as well as nutrients to farmed black-footed abalone. The developed system was capable of protecting its contents in seawater, delivering them to the GIT of abalone, enhancing health and growth and achieving high consumption rates as well as minimising wastage. The encapsulated delivery system developed in this thesis can be scaled up for commercial production, and adaptation of such technologies could help to further develop abalone aquaculture industry in New Zealand and abroad in a sustainable manner.
- ItemAquaculture of the New Zealand Geoduck Clam (Panopea zelandica)(Auckland University of Technology, 2023) Sharma, ShaneelThe geoduck Panopea zelandica has had significant interest from aquaculture New Zealand. To pave the way for the establishment of geoduck aquaculture, information on all areas of geoduck production needs to be determined. The aim of this thesis was to identify conditions and evaluate potential bottlenecks within hatcheries, during transport, and growout. Within hatcheries, much needed information on the successful broodstock conditioning and subsequent larval development was obtained. Investigations into diet ratios of Tisochrysis lutea (ISO) and Chaetoceros muelleri (CM) during the conditioning period revealed important carry over effects. Broodstock that were conditioned on similar proportions of ISO:CM produced embryos that had the highest survival, highest transition into D – veligers, and had the lowest incidence of abnormalities. Fertilization success and embryonic development under different thermal conditions was also explored. Highest rates of fertilization were achieved at the highest temperature (23.7°C) tested. However, there appears to be a thermal maximum for the optimal development of P. zelandica, and embryos were greatly hindered at temperatures >18.5°C due to an increase in cellular blebbing of the developing embryosarising from uneven cell division. Once P. zelandica embryos have transitioned into D – veligers, they remain within the water column for up to 19 days prior to settlement. Therefore, it is no surprise that food availability on its own is a common stressor for the developing larvae. P. zelandica larvae of different ages were subjected to different diet ratios and subjected to acute thermal stress. This study showed that susceptibility of larvae to thermal stress was reduces with increasing larval age, suggesting that older larvae are better able to acquire and store exogenic resources. To establish the crucial link between hatcheries and growout sites, the behavioural and physiological responses during transport and recovery of juveniles was investigated for the first time. The duration of emersion had a clear effect on overall response and recovery. Following 3h of transport, smaller changes within haemolymph osmolality, haemocyte parameters and metabolism were experienced compared to 8h of transport. Also, animal behaviour returned to normal faster within the 3h transport group. Even after 5 days of recovery in standard conditions, the effects of emersion were still evident within the 8h transport group with the use of succinate to fuel the respiratory chain. However, it does appear that given the right conditions and enough food resources, the animals are able to successfully restore internal energy reserves. The final study investigated the potential threat of marine heatwaves to juvenile geoducks within growout sites. This novel study focused on characterising animal behaviour, haemocyte subpopulations, and heat shock protein (hsp79 and hsp90). Geoducks appear to be highly sensitive to the effects of temperature, with animals actively borrowing out of the sediment when temperatures reached 25°C. This was also evident in the haemocyte populations, as there was an increase in the abundance of granulocytes and haemocyte aggregations indicating poor health conditions. However, an increase in the expression of hsp70 does suggest that the animals were actively trying to counter the effect of cellular damage incurred due the thermal strain. In summary, this thesis provides important information on selected factors crucial for the development of aquaculture of P. zelandica in New Zealand.
- ItemInvestigation and Characterization of Pathogens and Parasites on New Zealand Aquaculture Shellfish(Auckland University of Technology, 2022) Muznebin, FarhanaShellfish, including New Zealand Greenshell™ mussels (Perna canaliculus), New Zealand black-footed abalone (Haliotis iris) and flat oysters (Ostrea chilensis) are susceptible to a number of pathogens and diseases which threaten the aquaculture industry. In recent years, the high mortality of these species in both wild and farm settings has increased in frequency and magnitude. These mortality events often take place in summer (summer mortality), with shellfish succumbing to heat stress and pathogen loadings. However, there is a lack of information on the combined effects of acute heat stress and immune stimulation, as well as the specific mechanisms of the effects, susceptibility and resilience. Therefore, a better understanding is needed of the health status and capacity of shellfish to survive and overcome these events. Key to this understanding is the investigation of host-pathogen-environment interactions during mortality events and transmission pathways of infections. Histology, one of the most useful and imperative diagnostic techniques, was applied for the detection and identification of protozoa (Perkinsus olseni, apicomplexan X [APX], Bonamia exitiosa and B. ostreae, gut protozoan), ciliates (Scyphidia-like, Sphenophrya-like and unidentified disintegrated), fungi (Microsporidium rapuae), cestodes (Bucephalus longicornutus and Gymnophallid-like metacercaria), microbes (intracellular microcolonies of bacteria, Vibrio-like bacteria) and copepods from different tissues of H. iris, O. chilensis and P. canaliculus collected from Moana Blue Abalone Ltd., Kaiaua mussel farms and oyster farms in the Marlborough Sounds, New Zealand. Subsequent in situ-hybridization confirmed the identity of P. olseni in H. iris and P. canaliculus. This is the first detailed description of P. olseni in H. iris. There is a close relationship between the health status of abalone and the presence or absence of parasites, which may assist with identifying and characterising abalone health risks. Consequently, the findings of this thesis increase our in-depth understanding of pathogen infections in abalone, including host immune responses which may be used as early warning signs of health issues in wild and cultivated abalone in New Zealand. Furthermore, this is the first report on seasonal variations of P. olseni and APX in P. canaliculus. There was a significant association between seasons and the presence of P. olseni and APX in mussels. The abundance of B. ostreae, P. olseni and APX for whole animals and different tissues was evaluated semi-quantitatively using modified grading scales. Inflammatory tissue responses and abnormal tissue structures were also assessed semi-quantitatively. The modified grading schemes were employed to assess the health state of oysters, as well as improve the understanding of the progression of B. ostreae disease in oyster tissues. In this investigation, B. ostreae microcells were detected inside haemocytes of O. chilensis. The haemocytes presence in a variety of tissues within oysters indicated B. ostreae was present at these sites. Moreover, diapedesis was noticed in tissues containing B. ostreae in haemocytes and suggesting a route of disease transmission. A new classification scheme for P. canaliculus haemocytes was developed using Giemsa-stained smears, which is improved and more representative for the characterization of haemocytes (eight distinct types). The successful observation of phagocytic performance indicates that granulocytes only exhibit phagocytosis, and the phagocytic activity changed with season and temperature. Multidisciplinary methods including enzyme staining reactions, flow cytometry, and metabolomic profiling were used to investigate the combined effects of acute thermal stress and immune stimulation on mussels exposed to different temperatures (26°C vs 15°C) and endotoxin injection (with vs without). Positive enzyme reactions of the marker enzymes (acid phosphatase [ACP] and phenoloxidase [PO]) only detected in granulocytes, and for the first time, ACP and PO were evaluated in P. canaliculus. At the higher water temperature, free fatty acid constituents increased in mussel haemolymph and free amino acids decreased which supports higher energy demand and metabolic rate due to thermal stress. Survival data confirmed a severe physiological impact of the high-temperature treatment through incidences of mortality. However, thermal stress combined with endotoxin exposure did not lead to a synergistic effect on mortality. These findings provide new insights into the relationship between thermal stress and immunity to better understand the immune defence system in mussels. In summary, the information of this thesis helps to draw inferences about specific infection patterns relating to disease development and transmission mechanisms, assess host-pathogen interactions, to better understand the immune function and the overall health of shellfish for disease mitigation of these important aquaculture species. This information is crucial to develop disease management strategies and early warning systems for aquaculture species to ensure the sustainability of wild and farmed shellfish populations.