Seasonal growth dynamics of two temperate New Zealand finfish, Australasian snapper (Chrysophrys auratus) and yellow-eyed mullet (Aldrichetta forsteri) – two strategies for the common success.
| dc.contributor.author | Flikač, Tomislav | |
| dc.date.accessioned | 2018-10-12T01:25:31Z | |
| dc.date.available | 2018-10-12T01:25:31Z | |
| dc.date.issued | 2018 | en |
| dc.description.abstract | Proteins sourced from the sea make up a crucial part of global food production and considerably supports sustainability of human demographic growth. However, many fish stocks worldwide are overexploited or depleted and production enhancement is required. Here in New Zealand, certain finfish species are targeted to boost production to address the increase in market demand. One of them is Australasian snapper, Chrysophrys auratus, an iconic New Zealand species with a reputable history of exploitation and research whose growth potential is still not fully understood. When compared with kin species (e.g. Sparus aurata – North-East Atlantic /Mediterranean Sea and Pagrus major from North Pacific) it becomes obvious that a further increase in snapper production and exploitation in New Zealand waters should be possible. The main objective of this thesis was to explore the maximum potential growth capacity and the underlying physiology of snapper, as well as yellow-eyed mullet (YEM), Aldrichetta forsteri, as a comparative model species. The objective was investigated at three levels: First, by measuring growth morphometrics, which includes measuring growth parameters, mass and length, and determining supplementary organosomatic indices from fish kept on an unrestricted diet that enabled maximum growth rates. Second, energy generation, utilisation and partitioning requirements in association with such growth performance could be addressed by investigating metabolic (i.e. resting and maximum metabolic rates and associated aerobic metabolic scope) and digestive (specific dynamic action, SDA – increase in metabolic rates due to feeding) capacities. The third addressed the question – what happens on the biochemical level in organs/tissues actively involved in maximum growth performance? This stage was investigated by determining concentrations of key tissue metabolites and activity of enzymes involved in pathways associated with energy production necessary for growth as well as those related to digestion. Finally, this thesis intended to describe characteristics of food limitation in the natural environment of the test species and what would be possible if anthropogenic feeding of wild stocks, as a relatively novel approach for stock enhancement and production expansion, would be introduced. To address the question about maximum growth potential, tank array food unlimited experiments were set to investigate what would be the fastest growth rate that test species can achieve in the wild, based on the assumption that food is limited in the natural habitat. Therefore, the experimental set-up was designed to mimic environmental conditions so that the obtained data could be compared with growth from wild populations. Fish were fed ad libitum for the period of one calendar year and monthly growth variables were measured, and on that basis, annual growth trajectories were constructed. During monthly measurements, fish were sacrificed for tissue and organ sampling required for biochemical profiling. This protocol also provided the opportunity to gather data to compute organosomatic and related indices as contributing information supplementing growth data in explaining growth profiles of the model species. Overall, snapper demonstrated an explicit seasonal growth trajectory where an intense growing season was associated with spring/summer and growth reduction/cessation with winter. YEM, on the other hand, exhibited constant annual growth where challenging winter conditions (e.g. low temperatures) had only minor effects on slowing growth down. In addition, this work demonstrated that one of the most important eco-physiological traits of teleost fish when food is abundant could be to ensure that energy stores are optimised. This appeared to be particularly important for YEM. In snapper, though, with increasing seasonal temperatures after winter, growth compensation was emphasised, but just before winter, growth in mass/length was marginalised and energy reserve deposition prioritised. These findings also closely agreed with the biochemical profile. Metabolic parameters (resting and maximum metabolic rates, and SDA) were investigated at a set of temperatures (i.e. 13, 17 and 21°C), which represent the temperature range that test species experience in natural environments on a yearly basis. Therefore, these data could also be linked with the food unlimited trials. In addition, SDA was determined for a range of different rations to investigate the effects of meal size on SDA response. Temperature was a strong modulator of snapper SDA profile where most parameters measured responded with a clear pattern, whereas YEM had only SDA duration shortened when temperature increased from 17 to 21°C. Similarly, in terms of meal size, all aspects of snapper SDA were affected; still, differences between 0.5 and 1% BM (body mass) rations (only rations that YEM were successfully fed) were not detected for both species. Interspecific comparison revealed that temperature differently affected SDA of 2 species while meal size had more similar effects. Overall, characterisation of metabolic parameters demonstrated that snapper possesses an aerobic capacity that is generally inferior to that of YEM. This was also supported by the findings from the biochemical investigation. Besides, it was evident that temperature affects how snapper assimilate nutrients and partition energy between stores and somatic growth more than YEM. Generally, snapper and YEM demonstrated that they possess two different growth strategies, where YEM on an annual basis prefer to grow unceasingly, which may allude that YEM could have superior growth to snapper. Nevertheless, the capacity of snapper to catch up what was lost during the cold season, once conditions for growth improved in spring/summer, showed that this may not be true. When snapper growth, in terms of muscle/fillet mass, was compared with YEM there was virtually no difference between the two. This demonstrated that neither growth strategy can be regarded as advantageous but rather different. Besides, experimental data were found to be greater than what was found in the wild, suggesting that food may be a limiting factor for the test species to accomplish their maximum growth potential, either because of its seasonal patchiness and/or reduction in quality. | en |
| dc.identifier.uri | http://hdl.handle.net/10092/16110 | |
| dc.identifier.uri | http://dx.doi.org/10.26021/6452 | |
| dc.language | English | |
| dc.language.iso | en | |
| dc.publisher | University of Canterbury | en |
| dc.rights | All Rights Reserved | en |
| dc.rights.uri | https://canterbury.libguides.com/rights/theses | en |
| dc.title | Seasonal growth dynamics of two temperate New Zealand finfish, Australasian snapper (Chrysophrys auratus) and yellow-eyed mullet (Aldrichetta forsteri) – two strategies for the common success. | en |
| dc.type | Theses / Dissertations | en |
| thesis.degree.discipline | Biological Sciences | en |
| thesis.degree.grantor | University of Canterbury | en |
| thesis.degree.level | Doctoral | en |
| thesis.degree.name | Doctor of Philosophy | en |
| uc.bibnumber | 2686122 | en |
| uc.college | Faculty of Science | en |