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dc.contributor.advisorLokman, Pieter Mark
dc.contributor.advisorSymonds, Jane, E.
dc.contributor.advisorBruce, Michael
dc.contributor.authorKohn, Yair Yaacov
dc.identifier.citationKohn, Y. Y. (2013). Reproductive Biology Of Hapuku (Polyprion Oxygeneios): A New Aquaculture Species (Thesis, Doctor of Philosophy). University of Otago. Retrieved from
dc.description.abstractThe present study aimed to improve the reproduction success of captive hapuku by establishing methods for sex identification of broodstock (Chapter 2), by identifying predictors of egg quality at the time of spawning (Chapter 3), by investigating fertilized egg protein contents and its relationship to egg quality (Chapter 4) and by measuring the effects of the androgen 11- ketotestosterone on lipid contents, gonadal development and levels of gonadotropin receptors (Chapter 5). Three methods namely, ultrasound imaging, the measurement of plasma vitellogenin levels and the measurement of plasma steroid levels were used for sex identification of sexually developing hapuku around the time of the broodstock spawning season. All three methods were successful in sex identification and exhibited different levels of efficacy in identifying the sex of underdeveloped females. Overall, steroid ratio was the most reliable method but the other two methods exhibited some useful advantages and the combination of the results from all methods prevented errors in identification. Various parameters that describe egg quality in fish have been used in the present study to examine their value in predicting hatching success and early larval survival. Of these parameters, blastomere morphology score that was assigned to each egg by examining the symmetry, uniformity of cell size, cell adhesion and margins, correlated well with hatching percentage of individually monitored eggs and had the highest predictive value for batch hatching percentage and early larval survival. The proteome of hapuku fertilized eggs was researched using proteomic iTRAQ analysis. This novel approach was employed to shed light on the mechanisms that drive normal development in the early stages of embryo development. The analysis yielded a description of the major protein groups that are expressed in the fertilized eggs. However, a comparison of egg batches of differing quality based on blastomere morphology did not produce significant differences in the relative expression levels of the identified proteins. A regression analysis identified seven potential proteins that exhibited trends that correlated with egg quality. Despite displaying no statistical significance, these trends are comparable with findings in other studies and thus offer potential targets for future research. Of particular interest was the enzyme iduronate-2-sulfatase that was previously linked to developmental deformities in fish and was found to show a positive trend with increasing egg quality in the present study. The effects of 11-ketotestosterone (an androgen) were tested on immature females that were treated with slow-release implants to evaluate the efficacy of androgens in promoting sexual maturity in juvenile (previtellogenic) hapuku following previous successful reports of positive effects in eels and salmon. When compared with a placebo treated group, no differences in gonadal development or lipid contents were found. However, levels of gonadotropin receptors and cyclic adenosine monophosphate were unexpectedly significantly lower in the treated females. The results suggest that in contrast to other previously studied taxa, androgens may not play an important role in the sexual development of previtellogenic hapuku and perhaps of other previtellogenic perciforms.
dc.publisherUniversity of Otago
dc.rightsAll items in OUR Archive are provided for private study and research purposes and are protected by copyright with all rights reserved unless otherwise indicated.
dc.subjectPolyprion oxygeneios
dc.subjectEgg quality
dc.titleReproductive Biology Of Hapuku (Polyprion Oxygeneios): A New Aquaculture Species
dc.language.rfc3066en of Philosophy of Otago
otago.openaccessAbstract Only
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