Browsing by Author "Cyrus, Mark Digby"

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    Chemosensory properties of different Ulva extracts and their effects on Tripneustes gratilla
    (2014) Du Plessis, Darren Scott; Cyrus, Mark Digby; Bolton, John J; Macey, Brett M
    Identifying the chemical compounds that attract urchins to seaweeds will increase sea urchin aquaculture efficiency as these compounds can be utilized in the production of artificial feeds enhancing their attractiveness and palatability. This study investigated the chemosensory preferences of the tropical sea urchin Tripneustes gratilla for four crude extracts of Ulva as well as Fresh Ulva and an artificial feed. The four crude extracts of Ulva (Methanolic, Ethanolic, Chloroform and Chloroform-Methanol extracts) were tested by pair-wise chemosensory trials in a Y shaped maze. Urchins were significantly deterred by both the Chloroform and Chloroform- Methanol extracts as well as the solvent controls and artificial feed, however T. gratilla was significantly attracted to both the Methanolic and Ethanolic extracts. These two extracts were tested individually against Ulva and the urchins could not distinguish between Ulva and the extracts. When these two extracts were tested against one another it was found that the urchins were significantly attracted to the Methanolic extract. The Methanolic extract was then added to the artificial feed and significantly improved the feeds attractability. This indicates that these extracts, or the compounds which are responsible for this effect, can be incorporated into artificial feeds thereby making them more attractive to the sea urchin. The percentage yield of Ulva that each solvent extracted was different, although only the Ethanolic extract was found to be significantly different from the Chloroform and Chloroform-Methanol extracts. Future studies are needed to examine the chemical composition of these specific chemosensory compounds. By incorporating these attractive extracts into artificial feeds, South Africa can potentially improve the cultivation success of T. gratilla therefore expanding the economy of the local aquaculture industry through the export of this highly valued seafood product.
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    Feeding preferences of Tripneustes gratilla Linnaeus Echinodermata Echinodea and the prospect for sea urchin aquaculture in South Africa
    (2008) Scholtz, Rheinhardt; Bolton, John J; Cyrus, Mark Digby
    Sea urchin aquaculture for human food is a major industry, and there are prospects for the industry in South Africa. Feeding preferences of the sea urchin Tripneustes gratilla were tested by two different methods; a touch-preference test and a 48-hour consumption test. A touchpreference is established when the sea urchins' lantern teeth touched an algal species. The 48-hour consumption test was performed with paired combinations using four species of fresh algae. It was hypothesized that the preferred species would be similar in the touch-preference test and the consumption test. Five algal species were used in the touch-preference test; namely, Ecklonia maxima (kelp), Gigartina polycarpa, Grateloupia capensi, Porphyra capensis, and U/va rigida. Four of these species were used in the paired consumption test; namely, E. maxima, G. polycarpa, P. capensis and U. rigida. We found that E. maxima was most preferred in the touch-test followed by P. capensis and U. rigida. This result did not correlate with our consumption test. Here, U. rigida was significantly most preferred followed by E. maxima. Overall, the result is significant in relation to the prospect of echinoculture in South Africa as Ulva may provide a valuable alternate feed or supplement to this new industry. Due to the increase in time provided for the paired consumption test, we found that the paired consumption test was more conclusive in providing a preference for Tripneustes gratilla. Our results agree with literature which suggests that Tripneustes gratilla is a genera list feeder; however, Tripneustes gratilla shows definite preferences. Ulva spp. has been grown on a number of abalone farms in South Africa. Integrated aquaculture using T. gratilla and U. rigida as a biofilter and alternate feed is a very promising idea for echinoculture in South Africa.
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    Use of stable isotope signatures in the macroalga Ecklonia maxima and the filter feeder Mytilus galloprovincialis to determine the extent of sewage dispersal from the Green Point outfall, South Africa
    (2007) Cyrus, Mark Digby; Bolton, John J; Anderson, Robert J; February, Edmund C
    Over the last decade natural abundances of stable isotopes ¹³C and ¹⁵N have been used to investigate the transport pathways of nutrients within aquatic ecosystems, and have contributed new understanding and knowledge to many aspects of ecology, which include tracking the spatial extents of nutrient discharges. In order to assess the uptake of nutrients from the Green Point sewage outfall in Cape Town South Africa, we selected a primary producer, the kelp Ecklonia maxima (for dissolved nutrients) and a filter-feeding organism, the blue mussel Mytilus galloprovincialis (for organic particulates). It was hypothesized that biota within close proximity of the outfall would have isotopic values (signatures) which were closer to the values recorded for sewage and that this signature would become weaker (more positive) with increasing distance from the outfall as the sewage would be diluted and dispersed. Results from our study indicated that the stable isotope abundances of biota near the outfall were significantly affected by sewage. Ecklonia maxima situated on the outfall itself had δ¹⁵N of 1.2±2.3‰, which was extremely depleted relative to our control (8.3±1.1‰), collected at Mauritzbaai. The δ¹⁵N recorded for raw sewage (0.4±0.4‰) was very similar to that of Ecklonia maxima situated on the outfall. Mytilus galloprovincialis were also affected by sewage organic matter however although the effects on the stable isotope abundances were less pronounced as they were relying on more than one source of food. The isotopic values recorded in this study demonstrated that sites which were in close proximity to the outfall and even those just within the study area were contaminated by sewage effluent. From this study we conclude that the δ¹⁵N signatures of Ecklonia maxima and Mytilus galloprovincialis in marine environments can provide a useful means of tracing sewage dispersal in well-mixed ocean conditions, where conventional methods may have failed to reveal the extent of dispersal.
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    The use of ULVA as a feed supplement in the development of an artificial diet and feeding regimes to produce export quality roe from the sea urchin Tripneustes gratilla (Linnaeus)
    (2013) Cyrus, Mark Digby; Bolton, John J; Macey, Brett M
    Tripneustes gratilla is a fast growing, shallow water echinoid, which occurs across the Indo-Pacific, with its south-western limit in warm, temperate waters of South Africa. The success of T. gratilla cultivation depends, in part, on the development of a high quality, costeffective, gonad-conditioning diet that can produce large, marketable quality gonads. The aim of this research was to determine whether Ulva supplementation would improve palatability, consumption and digestibility of an artificial feed administered to T. gratilla and optimise gonad production and quality. At an inclusion level of 20% (20U), Ulva was shown to significantly (p < 0.05) improve the attractiveness and palatability of a formulated feed, compared to a nutritionally equivalent feed that had not been supplemented with dried Ulva (0U). Food consumption rates (FCR) and apparent digestibility coefficients (ADC %) for protein and energy, using insoluble ash as an indigestible marker, were measured for all experimental diets. FCR was significantly higher (p < 0.05) for urchins fed artificial feeds supplemented with Ulva, when compared to urchins fed non-supplemented feeds, suggesting that the inclusion of Ulva into the artificial diets acts as a feeding stimulant.Increased palatability and consumption subsequently led to significantly increased protein retention in urchins fed the 20U diet. The addition of Ulva to artificial feeds also significantly improved gonad colouration duringgonad enhancement trials. Gonad lightness (L*), redness (a*) and yellowness (b*) were quantified using a hand-held reflected-light, fibre-optic spectrophotometer and showed that, at an inclusion level of 20%, Ulva produced gonads that did not differ in colouration from those fed a natural diet of fresh Ulva (FU), and significantly improved gonad colour, particularly gonad yellowness (b*), compared to the same artificial diet without Ulva supplementation. This response was likely related to Ulva's high β-carotene content. The Ulva content of artificial feed significantly improved gonad colouration, while the formulated portion of the feed produced significantly larger gonads than those produced using a natural diet of fresh Ulva. The 20% Ulva inclusion diet, in particular, increased the gonad somatic index (GSI) by 205%, in just nine weeks (7.6 to 23.3%), compared to a 57% increase in the control group (fresh Ulva). Full life-cycle growth trials were also conducted using two of theformulated feeds (20U & 0U), as well as fresh Ulva, to establish appropriate feeding regimes thatcould produce a harvestable product in the shortest time. During grow out, juvenile somatic growth needs to be maximised until an individual reaches marketable size and sexual maturity, which is followed by gonad enhancement, through nutritive cell development,aimed to maximise gonad yield and quality before harvest. The effects of 5 different feeding regimes on somatic and gonadal growth of juvenile T. gratilla were investigated, over a 32 week period. The feeding regimes used were: fresh Ulva (FU) only; fresh Ulva for 20 weeks and the 20U diet for 12 weeks (FU-20U); fresh Ulva – 0% Ulva (FU-0U); 20% Ulva – fresh Ulva (20U-FU) and 0% Ulva – fresh Ulva (0U-FU). Somatic growth was largely effected by the presence of Ulva within a diet. Similar growth, in diameter, of juvenile urchins was achieved using either an artificial diet containing Ulva (20U) or fresh Ulva (FU), during the somatic growth phase.An artificial diet with the same nutritional properties but without Ulva supplementation (0U) produced urchins that were significantly (p > 0.05) smaller. Gonad production in the somatic growth phaseof the trial was higher for urchins fed with artificial diets (0U & 20U), but the reduced size of urchins in the 0U diets significantly reduced gonad mass. After the diets were changed from artificial feeds (0U & 20U) to fresh Ulva (FU) and vice versa (week 20), both gonad size and colour were affected, with artificial diets promoting gonad growth, while FU improved gonad colour. At the end of the study, all feeding regimes produced similar amounts of gonad, except for those individuals that were fed the 0U feed during the somatic growth phase (which were significantly (p > 0.05) smaller). Gonad colourationof all treatments at the end of the study was of marketable quality. From these results it is recommendedthat FU be fed inthe somatic growth phase, while the 20U artificial diet should be used to increase gonad size, and optimise gonad colour, in the gonad enhancement phase. Through the use of stable isotope mass spectrometry and IsoSource, a mixing and mass balance model, the relative contribution and importance of specific feed ingredientsto gonad production was determined. Ulva was shown to be an important isotopic source for gonad production, accounting for an average of 33% of the isotopic signal across all Ulvacontaining, diets at the end of the trial. The final section of work focused on efforts to manipulate the gametogenic cycle of T. gratilla, by altering daylength, to attempt to reduce the production of large amounts of gametes, which would decrease gonad value. Histology indicated that urchins exposed to a Short day (8:16 h) were significantly more advanced reproductively, with the majority of urchins in a mature or spent state compared to urchins exposed to a Long day (16:8 h), which were mostly premature. Nutritive phagocyte (NP) density within the gonads supported the findings from histology, as gonads from urchins exposed to a short day had significantly less NP's (21.58 ± 4.35%), compared to the Long day treatment (65.26 ± 3.09%). The results from this study suggest that urchins of this species exposed to Long days progress through gametogenesis more slowly than those exposed to Short days, which, appeared to mature more rapidly. These findings could allow for the production of a high quality product for longer periods of the year, without the onset of gonad maturation. The research in this thesis clearly shows that the use of the macroalga Ulva as a feed, or feed additive, to artificially formulated, high protein feeds can have a number of significant benefits in echinoculture. The use of the artificial feeds and feeding regimes developed in this work, along with the ability to manipulate daylenth to suspend gametogenisis, could greatly facilitate the success of the newly developing T. gratilla industry, both in South Africa and worldwide.