Towards the development of a larval feeding strategy for the white-margined sole (Dagetichthys marginatus)
- Authors: Thompson, Ernst Frederick
- Date: 2014
- Subjects: Flatfishes -- South Africa , Soleidae -- South Africa , Soleidae -- Larvae , Soleidae -- Larvae -- Feeding and feeds , Soleidae -- Larvae -- Physiology , Artemia
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5364 , http://hdl.handle.net/10962/d1012982
- Description: The major bottleneck during the domestication of the white-margined sole Dagetichthys marginatus in South Africa has been low larval survival. The cause of this is not clear but considering current literature on flatfish culture and more specifically soleid culture, nutritional deficiencies are hypothesized to be the main possible cause. Following the importance of nutrition, the first aim of the research was to use an ontogenetic developmental approach to develop a species specific larval feeding strategy. Ontogenetic development of D. marginatus showed that weaning will take place at much later ages than other soleids currently being farmed. This makes the partial replacement of Artemia with a suitable inert diet in co-feeding strategies very important to cut the cost associated of live food production. This leads on to the second aim, in which an 'in vitro' approach was used to model the digestibility of Artemia, which could ultimately contribute towards designing inert feeds with similar digestibility characteristics to Artemia in the future. Obtaining nutrients from food is closely linked to the functional status of the digestive tract, the support organs and the external morphological characteristics required for the ingestion of live or inert feeds. Considering both morphological and physiological ontogenetic development, it is clear that D. marginatus follow a similar pattern to other soleids. Larvae can successfully feed on Artemia as early as 3 days after hatching but exhibit a slow metamorphosis into the juvenile stage when compared to other soleids. The absence of any detectable acidic protease activity during the first 45 days of development and the importance of exogenous enzymes from Artemia all points to limited capacity to digest artificial diets. Prior to modelling the 'in vitro' digestion of Artemia, digestive enzyme activity at different pH's were modelled using functional forms from the normal distributive category of functions. , As there is no substantiated information for the general effects of pH on enzyme activity in the literature for finfish larvae, three species occurring in the same bio-geographical region of Dagetichthys marginatus, namely Sarpa salpa, Diplodus sargus capensis and Argyrosomus japonicus were used to investigate this effect. The fitted parameters, namely the optimal pH and sigma (the slope around the optimal pH) showed two interesting results. When using a negative log likelihood ratio test to test for differences between species for a particular enzyme, the optimal pH for alkaline proteases (7.67), lipase (8.03), amylase (7.69) and phosphatase (9.84) activity was the same for all three species. Furthermore, the study illustrated the potential to detect dietary shifts during ontogenetic development based on changes in enzyme activity around the optimal pH using the sigma parameter. Sarpa salpa showed increased amylase activity and a decrease in protease activity around the optimal pH with increased size, corresponding to a change in diet from zooplankton to algae. The 'in vitro' modelling approach taken in this study was based on known enzyme interactions and dynamics which makes the results very interpretable. from Artemia is achieved based on gut evacuation time and enzyme levels. This 'in vitro' study furthermore clearly indicates the importance of exogenous enzymes from Artemia, contributing as much as 54 percent to protein digestion and 64 – 72 percent to carbohydrate digestion. This was however, only an initial investigation, and further expansion of the model is required to achieve a complete understanding of Artemia digestion and ultimately partial replacement with artificial diets. A feeding strategy for D. marginatus should therefore follow those of other farmed soleids, although there will be a general delay in implementation due to slower development. Problems can thus be solved and improvements made by transferring technology from other soleids to D. marginatus.
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- Date Issued: 2014
Phytochemical analyses and Brine shrimp (Artemia Salina) lethality studies on Syzygium cordatum
- Authors: Chiguvare, Herbert
- Date: 2013
- Subjects: Artemia , Crustacea , Chromatographic analysis , Medicinal plants , Essences and essential oils , Traditional medicine
- Language: English
- Type: Thesis , Masters , MSc (Chemistry)
- Identifier: vital:11336 , http://hdl.handle.net/10353/d1004352 , Artemia , Crustacea , Chromatographic analysis , Medicinal plants , Essences and essential oils , Traditional medicine
- Description: Syzygium cordatum Hoscht ex. C Krauss, also known as water berry, is normally used by the people of South Africa for respiratory ailments including tuberculosis, stomach complaints, treatment of wounds and as emetics. An extract of the leaves can be used as a purgative for diarrhoea treatment. The leaves of Syzygium cordatum Myrtaceae were obtained from the Eastern Cape Province of South Africa, air dried and sequential solvent extraction was done to obtain various non volatile crude extracts. The volatile extract, that is the essential oil was extracted from the leaves using hydrodistillation and analysis of compounds was done by GC/MS for composition. 32 compounds were obtained from the fresh leaves and 18 compounds were obtained from the dry leaves. The fresh oil contains caryophyllene (11.8 percent) and caryophyllene oxide (11.1 percent) as the main sesquiterpene component. α-Pinene(5.0 percent) was the only monoterpene compound identified in the fresh oil in substantial amount. The dry leaves oil had copanene (17.0 percent), β-Caryophellene (26.0 percent), cubenol (6.5 percent) and caryophellene oxide (14.2 percent) as the dominant constituent of the oil. Summary of the classes of compounds in the oil revealed that the chemical profile of both oils were dominated by sesquiterpenoid compounds. This is the first time that terpenoids compounds are being identified in both the fresh and dry leaf oil of S. cordatum. Hexane leaf extract was selected due to the interest in the terpenoid compounds. Column chromatography of the hexane crude gave five (5) of which two are fully reported. The isolates were fully elucidated using spectroscopic methods to be β-Sitosterol (HC3) and Friedela-3-one (HC1A/HC1D). Cytotoxicity analysis was carried out on the crude using the Brine shrimps assay. Isolates 1C and1D showed significant lethality using the brine shrimps assay with lethality values (LC50) of 4.105mg/ml for HC1C and 4.11mg/ml for 1D/1A respectively.
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- Date Issued: 2013
Cranial ontogeny of the sole, dagetichthys marginatus (soleidae), with considerations on the feeding ability of larvae and early juveniles
- Authors: Ende, Stephan Siegfried Werner
- Date: 2008
- Subjects: Soleidae , Fishes -- Larvae -- Food , Flatfishes -- Nutrition , Artemia
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:5250 , http://hdl.handle.net/10962/d1005093 , Soleidae , Fishes -- Larvae -- Food , Flatfishes -- Nutrition , Artemia
- Description: The overall aim of this study was to gain a better understanding of the feeding mechanisms of the larvae and early juveniles of the sole, Dagetichthys marginatus (Soleidae), with which to assess the suitability of current feeding protocols and to facilitate the development of an appropriate pelleted feed. This was achieved by examining the ontogeny of the cranium of laboratory reared sole, with particular emphasis on those elements associated with feeding and by comparing the cranium of juvenile fish with that of adult fish. At 4 dah (days after hatch) Dagetichthys marginatus larvae develop the first rudimentary branchial arches that facilitates the capture and ingestion of food items. Subsequent development of cranial structures, such as the oral jaws, suspensorium, neurocranium, hyoid and branchial arches and the opercular apparatus enables the larvae, at 16 dah, to switch from ram feeding to suction feeding on live prey. The use of live Artemia nauplii from 4 to 16 dah is therefore appropriate. The first morphological asymmetries developed at 16 dah in the dentaries and at 22 dah the maxillae and the premaxillae began to show asymmetries. Teeth were present only on the blind side of the oral jaw elements and during this period (16 to 22 dah) the existing elements began to ossify. From 16 to 35 dah the standard feeding protocol consists of a combination of pelagic (Artemia metanauplii) and benthic prey (dead, frozen Artemia nauplii) and from 25 dah onwards a sinking pellet is provided. The time (dah) at which frozen Artemia and sinking pellets were provided, appropriately corresponded to the initiation of benthic feeding behaviour. However at this stage the use of pelagic Artemia metanauplii is inappropriate and unnecessary. At 31 dah the cranial morphology resembled that of adult fish. Adult D. marginatus display extreme asymmetries among the elements of the oral jaws, the suspensorium and certain elements of the neurocranium. Elements on the blind side are larger and more robust than those on the ocular side and are adapted for feeding, while those on the ocular side appear to have a respiratory function. From 31 dah the cranial elements are identical to those of adult fish, suggesting that no further feeding behavioural changes occurred and that a sinking pellet, of which the nutrient composition meets the requirements of the fish, would be appropriate for ongrowing.
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- Date Issued: 2008
A taxonomic study of Senecio speciosus, Senecio macrocephalus and possible hybrid populations using morphological data, toxicty tests and chromatography
- Authors: Lewis, Gillian Elizabeth
- Date: 1995
- Subjects: Senecio , Senecio -- Analysis , Shrimps , Artemia
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4209 , http://hdl.handle.net/10962/d1003778
- Description: The variation between populations of Senecio speciosus Willd., Senecio macrocephalus DC. and intermediate plants was investigated in a comparative study of morphological characters, toxicity of plant extracts to brine shrimps (Artemia salina) and chromatography of plant extracts. Specimens were collected at 18 localities in the Eastern Cape Province. All these specimens were examined morphologically and chemical extracts were tested for toxicity and by comparative chromatography. The collection of Senecio speciosus and Senecio macrocephalus specimens in the Selmar Schonland Herbarium (GRA) was also examined morphologically. Six geographical areas were represented in the combined collections. Analysis of morphological data separated typical Senecio speciosus and Senecio macrocephalus at either end of hybrid index histograms and principal components analysis diagrams. The intermediate populations displayed morphological characters of both Senecio speciosus and Senecio macrocephalus. Some specimens were intermediate between these two species, falling within the range of variation of these species while others fell outside this range. The Brine Shrimp Assay was used to test for toxicity and to investigate the possibility of using toxicity data as a genetic marker in taxonomic studies. As Senecio speciosus extracts were less than 1% toxic and Senecio macrocephalus extracts were at least 95% toxic to the brine shrimps it is suggested that in this case toxicity can be used as a genetic marker. Toxicity can even be described as a good taxonomic character as discontinuity is very sudden and complete. The intermediate plants in the Grahamstown area were at least 92% toxic to the brine shrimps linking them to Senecio macrocephalus. Thin layer and paper chromatography were used as comparative techniques to study the chemical profiles of the specimens. Alkaloids, terpenoids and flavonoids were studied. Thin layer chromatography to separate the alkaloid components of the plant extracts showed Senecio speciosus and Senecio macrocephalus to have distinct chemical profiles suggesting that they are separate species. The intermediate plants- were found to contain chemical compounds matching either or both Senecio speciosus and Senecio macrocephalus suggesting that they may have arisen by hybridisation. In a preliminary investigation Senecio speciosus extracts showed a complete lack of terpenoid compounds whereas extracts from Senecio macrocephalus and the intermediate specimens tested gave a terpenoid colour reaction in the basal spot only. This links the intermediate populations with Senecio macrocephalus. Paper chromatography to separate the flavonoid constituents of the plant extracts also showed typical Senecio speciosus and Senecio macrocephalus to be distinct. The intermediate populations contained flavonoid compounds from one or both of these species. The populations in the Grahamstown area show morphological features close to and in some cases indistinguishable from Senecio speciosus. Chemically these specimens show some similarities with Senecio macrocephalus. In the East London area specimens show a similar mixture of characters but appear morphologically to be closer to Senecio macrocephalus. However, in the Amatole Mountains, despite both species being present in the same locality it appears that no hybridisation has occurred. It is therefore suggested that at some of the localities where the geographical ranges of Senecio speciosus and Senecio macrocephalus overlap in the Eastern Cape Province hybridisation between these two species occurs.
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- Date Issued: 1995