Includes bibliographical references. / Sustainable diversification and the biological viability of selected aquaculture species are now viewed as being crucial factors that must be assessed in order to introduce the candidate species into commercial production. The biological feasibility of white stumpnose, Rhabdosargus globiceps,as a potential aquaculture candidate, was assessed by examining the ability of the broodstock to be manipulated to spawn in captivity and the viability of the larvae from 0 days post hatch (DPH) to 30 DPH under varied conditions. These factors are recognised as the most significant bottlenecks of development for a potential aquaculture candidate. A compressed photothermal cycle successfully brought about the reproductive maturation of both male and female broodstock. The natural, seasonal reproduction cycle, of the population of Rhabdosargus globiceps in Langebaan Lagoon, and manipulated cycles were comparable with regard to oocyte maturation. Under the compressed cycle an increase in the plasma estradiol 17ß concentration correlated with the increase in oocyte diameter and the presence of late vitellogenic and hydrated oocytes. Reproductively mature broodstock were injected twice with LH-RHa on a 24 hour interval, which successfully induced spawning over four consecutive 24 hour periods. This method of manipulation and induction of spawning was successful twice and the resultant eggs and larvae were used to examine the ontogeny and the optimal rearing temperature of Rhabdosargus globiceps. In the first larval rearing experiment the stages of development from egg to 30 DPH larvae were recorded at 20°C and showed similar developmental stages as other sea bream aquaculture species. The developmental stages were noted as being highly influenced by the available food sources with elevated mortalities recorded during the transitional phase between endogenous food reserves and exogenous feeding. The growth pattern showed the same reduced growth present for other successfully cultured sea bream larvae, suggesting that first feeding and swimbladder inflation was relatively successful. At 30 DPH the larvae reached a mean total length of 11.14 ± 0.44 mm. To determine the optimal rearing temperature and the effect of temperature on embryonic development eggs were placed at three different incubation temperatures (25°C, 20°C and 15°C) and the timing to the developmental stages was recorded from 0 DPH to 30 DPH. Measurements indicated that the larvae reached and exceeded their thermal tolerance at 25°C, with larvae only surviving to 6 DPH at this temperature, while at 20°C the larvae had better growth, and significantly earlier indications and higher percentages of feeding, swimbladder inflation and notochord flexion than at 15°C. The results suggest that the highest quality larvae are achieved at a rearing temperature of 20°C. This thesis describes the induction of spawning and larval rearing of Rhabdosargus globiceps. The ontogeny of the larvae as well as the critical stages of first feeding, swimbladder inflation and notochord flexion are discussed and described in detail. Overall, the life cycle from adult to juvenile was successfully closed and the experiments showed very positive results regarding Rhabdosargus globiceps’ biological capacity and feasibility to become a potential aquaculture candidate in South Africa.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:uct/oai:localhost:11427/9803 |
| Date | January 2013 |
| Creators | Russell, Andrew Peter |
| Contributors | Attwood, Colin, Christison, Kevin |
| Publisher | University of Cape Town, Faculty of Science, Department of Biological Sciences |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Master Thesis, Masters, MPhil |
| Format | application/pdf |
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