https://commons.ru.ac.za/vital/access/manager/Index en-us 5 https://commons.ru.ac.za/vital/access/manager/Repository/vital:74600 Wed 31 Jul 2024 11:31:25 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:68475 Wed 24 Apr 2024 16:14:32 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:2451 Wed 12 May 2021 23:40:14 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:3913 Wed 12 May 2021 23:37:14 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:4433 Wed 12 May 2021 23:33:07 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:3824 Wed 12 May 2021 22:53:35 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:937 Wed 12 May 2021 22:46:38 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:21087 Wed 12 May 2021 22:42:15 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:7046 Wed 12 May 2021 21:03:06 SAST ]]> 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17:34:45 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:3050 Wed 12 May 2021 17:30:46 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:1701 Wed 12 May 2021 17:29:01 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:5093 Wed 12 May 2021 17:15:52 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:1698 Wed 12 May 2021 17:10:17 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:1308 Wed 12 May 2021 16:41:09 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:6170 Wed 12 May 2021 16:31:19 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:6750 Wed 12 May 2021 16:30:27 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:1624 Wed 12 May 2021 16:26:40 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:4556 Wed 12 May 2021 16:21:23 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:4424 Wed 12 May 2021 16:06:45 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:2422 Wed 12 May 2021 15:44:28 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:40265 Wed 12 May 2021 14:26:28 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:42958 Wed 12 May 2021 14:23:41 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:74586 Tue 30 Jul 2024 14:44:42 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:74565 Tue 30 Jul 2024 10:01:35 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:72794 Tue 28 May 2024 14:20:43 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:44208 Tue 14 May 2024 12:09:37 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:38684 Tue 14 May 2024 08:34:37 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:54488 Tue 14 May 2024 07:28:13 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:35516 Tue 13 Aug 2024 10:05:05 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:6999 Tue 10 Aug 2021 12:38:34 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:74014 Tue 09 Jul 2024 12:53:01 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:35509 Tue 09 Aug 2022 15:05:37 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:37970 Tue 07 May 2024 09:43:45 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:72966 Tue 04 Jun 2024 13:23:08 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:72949 Tue 04 Jun 2024 11:39:48 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:72947 Tue 04 Jun 2024 11:33:33 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:57065 Thu 29 Sep 2022 16:58:24 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:7111 Thu 16 May 2024 06:28:25 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:7006 Thu 15 Aug 2024 09:30:31 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:2931 Thu 13 May 2021 13:58:54 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:3289 Thu 13 May 2021 13:37:56 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:5282 50%) comes from Lake Malawi. Bathyclarias nyasensis and other clariid catfish contribute up to > 20% of the total catches. Catches of Bathyclarias nyasensis in the inshore area of the south-east arm of Lake Malawi are declining and a management plan for the fishery is essentially lacking. There is paucity of biological data that precludes the use of any option to manage the species. The principal aim of the thesis was to define the ecological role B. nyasensis, the most abundant and common of the Bathyclarias species. By examining life history characteristics within a food web context, it was hypothesized that the study would provide an insight into the interrelationships between species, and, hence form the basis for the development of a rational exploitation strategy for the species. The study was undertaken in the south-east arm of Lake Malawi (9° 30'S, 14° 30'S). The principal objectives of the study were to investigate the feeding ecology of B. nyasensis by examining morphological characters and structures associated with feeding, diet of B. nyasensis, food assimilated in the species using carbon (∂¹³C) isotope analysis, daily food consumption rate for B. nyasensis; and to relate the feeding ecology to life history traits such as age, growth, and some aspects of the reproductive biology of B. nyasensis. The suitability of sectioned pectoral spines and sagittal otoliths to age B. nyasensis was assessed. Due to reabsorption of growth zones with increasing spine lumen diameter with fish size, and the relatively low number of spines that could be aged reliably, only otoliths were used. The maximum age for B. nyasensis was estimated at 14 vears. Growth was best was described by the four parameter Schnute mc: lt ={42+(81¹·⁸ - 42¹·⁸)x1-e⁻°·°⁵⁽t⁻¹⁾}¹/¹·⁸ over 1-e⁻⁽⁻°·°⁵⁾⁽¹¹⁾ for female, lt={41+(98¹·² - 41¹·²)x 1-e⁻°·°²⁽t⁻¹⁾}¹/¹·² over 1-e⁻⁽⁻°·°²⁾⁽¹³⁾ and for male fish. Age-at-50% maturity for females and males were estimated at 7 years and 4 years, respectively. Typically, fish grew rapidly in the first year, but slower during subsequent years. Smaller fish were found inshore while larger fish were found in offshore regions. It was hypothesised that the rapid growth in the first year and slower growth later is a consequence of change in diet from high quality and abundant food source to a more dilute food and that this may be associated with a shift in habitat. Morphological characters associated with feeding were used to predict the food and feeding behaviour of B. nyasensis. The size of premaxillary, vomerine, pharyngeal dental and palatine teeth and premaxillary and vomerine tooth plates suggested the capability of B. nyasensis to handle both large and small prey, with a propensity towards smaller prey in composition to C. gariepinus. The molariform teeth on the vomerine tooth plate suggested that molluscs form part of the diet. The relative gut length (1.27±0.24) suggested omnivory, with an ability to switch between planktivory and piscivory. Buccal cavity volume and filtering area changed with fish size at 500-600 mm TL upon which it was hypothesised that the fish diet changed to planktivory at this size. Detailed diet analysis provided information upon which the above hypotheses could be accepted. Percent Index of Relative Importance (%IRI) and a multi-way contingency table analysis based on log-linear models were used to analyse diet data. Results showed that B. nyasensis is omnivorous, but with a distinct ontogenetic dietary shift from piscivory to zooplanktivory at 500 - 600 mm TL. The increased buccal cavity volume at the same fish size therefore, suggests that B. nyasensis is well adapted to filter the dilute zooplankton resource. Increased foraging costs of feeding on zooplankton explained the slower growth of larger fish. The dietary shift was finally corroborated by results of the ∂¹³C isotope analysis. A polynomial equation described the change in carbon ratios with fish size: ∂¹³C = - 33.188 + 0.4997L - 0.0045 (total length)² (r² = 0.598, n = 12, p=0.022). The ontogenetic shift in diet was synchronised with a habitat shift postulated in life history studies. In the inshore region, B. nyasensis were predominantly piscivorous (apex predators), and were zooplanktivorous in the offshore region, thereby forming part of the pelagic food web in the latter region. After examining "bottom-up" and trophic cascade theories, it was postulated that perturbations of the B. nyasensis stock would be discernible both at the top and lower trophic levels. As a piscivore and therefore apex predator, effects of overfishing B. nyasensis in the inshore region could cascade to unpredictable ecological changes in inshore areas and, due to the ontogenetic habitat shift, in the offshore regions. Examples of trophic cascade phenomena are provided. On the basis of the feeding study, it was possible to reconstruct the pelagic food web of Lake Malawi. Apart from the lakefly Chaoborus edulis, B. nyasensis is the other predator that preys heavily on zooplankton in the pelagic zone. Perturbations of the B. nyasensis stock could affect size composition of zooplankton which in tum, could affect production of C. edulis, a resource for the top predators in the food web. The findings of the present study contributed to the ongoing debate of introducing a zooplanktivore into the pelagic zone of Lake Malawi. Proponents for the introductions have argued that zooplankton predation by fish is inferior to that of C. edulis. Introduction of a clupeid zooplankton was proposed as a strategy to boost fish production in the lake. The zooplanktivore would either out-compete or prey on C. edulis to extinction. Opponents to this view argued that zooplankton biomass in the pelagic region was too low to support introductions and that the fish biomass in the pelagic region may have been underestimated. Results from the present study suggest that planktivorous fish (including B. nyasensis) might not be inferior to C. edulis in utilising the zooplankton resource; B. nyasensis is well adapted to utilise the dilute zooplankton resource, and by omitting B. nyasensis from previous studies, overall zooplankton predation by fish may have been underestimated by between 7 - 33%. On the basis of the theoretical migratory life history cycle of B. nyasensis, it is recommended that the current interest in increasing fishing effort in offshore areas should proceed with caution. Ecological changes that may have occurred in the inshore areas due to overfishing have probably not been noticed: as the offshore zone has never been fished. The latter zone may have acted as a stock refuge area. Higher fishing intensity in the offshore areas could lead to serious ecological imbalances and instability. The study has shown that life history characteristics studied in the context of the food web, and in the absence of other fisheries information and/or data, strongly advocates the precautionary principle to managing changes in exploitation patterns.]]> Thu 13 May 2021 12:45:47 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:38672 Thu 13 May 2021 09:35:06 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:2937 Thu 13 May 2021 08:13:55 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:705 Thu 13 May 2021 08:11:23 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:6165 Thu 13 May 2021 07:40:36 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:704 Thu 13 May 2021 07:29:03 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:3312 Thu 13 May 2021 07:26:48 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:5667 Thu 13 May 2021 06:25:09 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:710 Thu 13 May 2021 05:55:02 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:3046 Thu 13 May 2021 05:54:55 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:1579 Thu 13 May 2021 05:30:49 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:535 Thu 13 May 2021 04:57:27 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:3798 Thu 13 May 2021 04:31:03 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:1511 Thu 13 May 2021 04:29:19 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:1305 Thu 13 May 2021 04:18:09 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:3333 Thu 13 May 2021 04:16:51 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:3783 Thu 13 May 2021 04:16:00 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:4012 Thu 13 May 2021 03:57:39 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:1557 Thu 13 May 2021 03:49:30 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:2563 Thu 13 May 2021 03:16:42 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:5377 Thu 13 May 2021 03:08:39 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:6164 Thu 13 May 2021 02:07:33 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:4306 (6) > (1). The rate of dimerization has also been compared for complexes (1), [ReO(morph-L)₂(OMe)] (8) and [ReO(spiro-L)₂(OMe)] (13) and the rate of dimerization was found to be fastest for (13). The crystal structures of (1), [ReO(LN0₂)₂(OMe)] (4), (6) and (15) have been determined. The Re(V)-oxo complexes (1), (4) and (6) have a slightly distorted octahedral geometry with the two acylthiourea ligands binding in a cis arrangement in the equatorial plane of the octahedron. The alkoxy and oxo ligands occupy the axial positions and are situated trans to each other. The crystal and molecular structure of complex (15), consist of two slightly distorted octahedral [ReO(L)₂] moieties bridged by an oxygen atom with a Re-O-Re bond angle of 175.2(2)°. The preliminary studies done in the present study have indicated that the complexation chemistry of technetium(V) with the N,N-diethyl-benzoylthiourea is different to that of rhenium (V). The reaction between [n-BuN₄][TcOCl₄] and N,N-diethyl-N'-benzoylthiourea yielded the square pyramidal cationic complex [TcO(L)₂]Cl. By contrast the octahedral methoxy complex [ReO(L )₂( OMe)] was obtained when the analogous Re(V)-oxo precursor, [n-Bu₄N] [ReOCI₄], was reacted with N,N-diethyl-N'-benzoylthiourea under the same reaction conditions.]]> Thu 13 May 2021 02:05:39 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:1302 Thu 13 May 2021 01:48:11 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:5274 Thu 13 May 2021 01:47:33 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:5347 Thu 13 May 2021 01:31:33 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:1739 Thu 13 May 2021 01:14:10 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:3786 Thu 13 May 2021 01:03:59 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:4031 Thu 13 May 2021 01:00:06 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:699 Thu 13 May 2021 00:40:10 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:5625 Thu 13 May 2021 00:20:05 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:1922 Thu 13 May 2021 00:16:56 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:4624 Thu 07 Jul 2022 20:23:25 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:57717 Sat 20 Apr 2024 08:00:43 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:35817 Mon 13 May 2024 14:56:15 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:6749 Mon 13 May 2024 14:30:59 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:6746 Mon 13 May 2024 14:29:48 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:38383 Mon 13 May 2024 12:28:46 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:38882 Mon 13 May 2024 12:01:44 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:6078 Mon 13 May 2024 11:58:46 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:30237 Mon 13 May 2024 11:31:51 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:6912 Fri 26 Apr 2024 12:36:48 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:56886 K+>Al3+>Na+>Ca2+. The trend for melatonin–metal complexes was K+>Li+>Na+>Al3+>Ca2+. The binding and stable complex formation between both ligands, serotonin and melatonin with lithium, potassium and sodium is of biological importance. The binding of serotonin to lithium could provide an explanation for the therapeutic effects of lithium in depression treatment, whereas the binding of aluminium by melatonin could provide insight into the role of this element in the aetiology of Alzheimer's disease.]]> Fri 23 Sep 2022 14:43:22 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:56885 Fri 23 Sep 2022 14:40:38 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:56884 Fri 23 Sep 2022 14:37:23 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:56883 Fri 23 Sep 2022 14:35:53 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:72433 Fri 17 May 2024 04:51:12 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:6661 Fri 10 May 2024 15:59:03 SAST ]]> https://commons.ru.ac.za/vital/access/manager/Repository/vital:43756 Fri 10 May 2024 15:58:41 SAST ]]>