Browsing by Subject "Mariculture"

Now showing 1 - 4 of 4
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    An assessment of the suitability of the galjoen, Coracinus capensis cuvier, for mariculture in South Africa
    (1991) Van der Lingen, Carl David; Cook, Peter
    The suitability of the galjoen, Coracinus capensis, for mariculture in South Africa has been assessed from both an economic and a biological viewpoint. In terms of economic criteria galjoen shows a high potential for culture, being widely known and highly regarded as a table fish. The restaurant trade in the southwestern Cape has been identified as a possible market showing a high demand for this species. Adult galjoen are readily available, hardy, and are easily maintained in captivity. A biochemical technique to determine the sex of live fish has been elucidated and allows sexual identification to be conducted for several months prior to and during the spawning season. Natural serial spawning with high fertilization occurs readily in captivity, with galjoen producing large numbers of good quality eggs during a single season. However induced spawning using two mammalian gonadotropins resulted in the production of poor quality eggs. The relationship between temperature and development time for fertilized galjoen eggs has been determined, and the lower lethal temperature for developing eggs was found to lie between 14° and 16°C. Newly-hatched larvae exhaust their endogenous food reserves rapidly and show a short time to irreversible starvation, with first-feeding beginning from 110 hours after hatching at 18°C. Galjoen larvae proved to be extremely difficult to rear. Although successful first-feeding on a few live food organisms was observed, mass mortality at 4-8 days and again at 12-15 days after first-feeding resulted in exceptionally poor survival. It is surmised that galjoen larvae have very stringent nutritional requirements which cannot be met by employing commonly-used live food organisms. Growth rate estimates for galjoen that survived past metamorphosis indicate that growth under culture conditions is similar to that in the natural environment. Certain biological attributes of the galjoen such as simple broodstock maintenance, ease of natural spawning in captivity and high fecundity select this species for culture. However the inability to mass rear larvae through to metamorphosis drastically reduces the suitability of this species, especially since larval rearing is the key to successful mariculture. In addition, the slow growth rate under culture conditions observed also selects against this species. Because of these last two factors, it is concluded that the galjoen is not a suitable species for mariculture in South Africa.
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    Bioenergetics and growth of white steenbras, Lithognathus lithognathus, under culture conditions
    (1991) Harris, Shael Anne; Cook, Peter
    The bioenergetics and growth of white steenbras, Lithognathus lithognathus, under culture conditions were determined to assess its suitability for mariculture. Fish were captured by seine netting, from nearby estuaries and transported to the laboratory where they were successfully kept for the duration of the experimental period. The fish were initially fed on white mussels and then weaned onto a diet of commercial trout pellets. The bioenergetics of L.lithognathus was examined using a large, simple closed system respirometer in which nitrogen excretion and oxygen consumption were measured simultaneously. This system permitted the use of groups of fish for experiment which simulated aquaculture conditions. The effects of fish size, ration size and temperature on faecal and nonfaecal excretion, and on oxygen consumption of L.lithognathus were examined.
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    Do we have the vision to integrate our marine aquaculture?
    (2006) Bolton, John J
    The article focuses on the author's views on marine aquaculture in South Africa. He discussed the draft policy for the development of a sustainable aquaculture industry in South Africa released by the Department of Environmental Affairs and Tourism. Statistics on African aquaculture production, geographical spread and species exploitation in acquaculture, and marine aquaculture consumption are provided. The author also gives reasons why aquaculture production is low in the country.
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    The potential of Grateloupia filicina (Lamouroux) J. Agardh. for mariculture: culture experiments and observations on shore phenology
    (1996) Vetter, Susanne; Bolton, John J; Anderson, Robert J
    Grateloupia filicina is a carrageenophytic red alga which is in demand as a carrageenan raw material and for use in food. There is therefore interest in developing a technique for mariculturing this species. Since vegetative propagation from thallus fragments has not been successful, the present study was initiated to determine suitable conditions for spore liberation and growth of G. filicina from spores. It was also attempted to propagate G. filicina sporelings from crust and thallus fragments. In addition, the proportions of plants in different life history phases were determined in August and September to test for seasonal differences in shore phenology, and whether G. filicina is monoecious or dioecious, since there is disagreement on this in the literature. Spore release was easy to achieve, even without stressing the parent plant. Growth of crusts was found to be fastest at 50 μM.m⁻².s⁻¹ and at 20°C. Carposporelings (i.e. young tetrasporophytes) grew slightly but significantly faster than tetrasporelings (i.e. young carposporophytes). Crust fragments were able re-attach to the substrate and gave rise to new upright thalli within 1-2 weeks, compared to 4-5 weeks between spore release and thallus initiation. Attachment was weak, however, and only a small proportion of the crust fragments placed into culture regenerated. Thallus regeneration was not successful. There were seasonal differences in shore phenology during the study period: while two thirds of the plants collected in August were carposporophytes, only tetrasporophytes were found in September. No male gametophytes or spermatangia were found. It did not emerge from this study whether G. filicina in an annual, or what phenotypic differences are found throughout the year. Information of this kind is important for mariculture as it affects the supply of parent plants (and therefore spores) and the growth of young plants on ropes if these are released into the sea. The culturing experiments look promising; techniques (seeding ropes directly with spores or using regenerated crust fragments) still need to be refined.