Browsing by Author "Rousseau, Meghan"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Open Access
    Enrichment of rotifers (Branchionus plicatilis), Artemia nauplii and artificial dry feed with live yeast (Debaryomyces hansenii) for the growth of cultured dusky kob (Argyrosomus japonicus) larvae
    (2013) Rousseau, Meghan; Bolton, John J; Macey, Brett M
    Aquaculture has expanded dramatically over the last fifty years and now contributes almost half of the global total fish production. Since fish are a very important source of protein for humans, aquaculture is an important food source and economic practice. It is therefore important to minimise and manage any factors that may negatively impact on aquaculture operations. One of the major problems in marine fish aquaculture is the high rate of larval mortality in captivity. One way of combatting this problem is by improving overall health of larvae. Probiotics, especially yeasts, can be used as immune boosters, disease control agents and a source of additional nutrients to help minimise this problem. These probiotics can be effectively administered to larvae using live feeds, such as rotifers and Artemia, and formulated feeds. The dusky kob, Argryosomus japonicus, is emerging as a commercially viable marine aquaculture species in South Africa. However, commercial production of this species is being hindered by parasitic disease. Therefore, this study tested the efficacy of (1) incorporating live culturable Debaryomyces hansenii (yeast) cells into rotifers (Branchionus plicatilis), Artemia nauplii and a formulated feed (Nutroscience Pre-starter Crumble), and (2) investigated the effects of the probiotic supplemented feeds on growth and survival of dusky kob larvae. We demonstrated that live culturable yeast cells, incubated at a period of 0.5 hours, delivered significantly more yeast cells per rotifer than the longer incubation periods (p<0.001). For Artemia, the incubation period of 0.5 hours delivered more yeast cells per Artemia, but this incubation period was not significantly better than the longer incubation periods (p=0.204). The starting yeast concentration of 1 x 1012 yeast cells.ml-1 resulted in significantly more yeast cells per rotifer (p=0.042) and Artemia (p<0.001) than the lower starting yeast concentrations. The proliferation of Debaryomyces hansenii on the formulated (dry) feed is significantly higher at a storage temperature of 4 °C than it is at a storage temperature of 20 °C (p<0.001). This could however, be causing a deterioration in the stability of the feed. The number of yeast cells per g of feed significantly decreases after 14 days, indicating a possible loss of culturability and stability of the yeast in the feed, regardless of the storage temperature (p<0.001 for 4 °C; p<0.05 for 20 °C). Drying the feed after coating it in yeast also causes a significant reduction in the number of yeast cells per g of feed (p<0.001). With more replication and more cautionary experimental design, this experiment could be repeated in the future. Unfortunately, the mortality rate of the larvae was so high that the results obtained for the larval growth trials could not be statistically analysed, even though rotifer and Artemia (live feed) incubations were performed.
  • Thumbnail Image
    Item
    Open Access
    Modelling the effect of alternative management strategies on the catch and effort in the carpenter (Argyrozona argyrozona) linefishery
    (2013) Rousseau, Meghan; Attwood, Colin
    In South Africa, linefishing increased in the mid-1800s and eventually reached a peak in the 1980s/90s. A legal linefishery emergency was declared in 2000 in accordance with the Marine Living Resources Act of 1998. This was a large blow for the commercially important industry. Nonetheless, the carpenter stocks had already been overexploited to such a high degree by linefishing, and also as part of trawling bycatch, that even at an effort less than half of the effort that produces a maximum sustainable yield, carpenter stocks were still found below the biomass found at the maximum sustainable yield. In order to explore three different management strategies for the carpenter stock on the offshore Central Agulhas Bank, an agestructured, non-stochastic model was set up. The influences of the following strategies - Total Allowable Catch (TAC), as well as revised minimum size limit and closed season – on a stock found at a dismal 19.2% of carrying capacity, are projected using this model on a monthly time-step. The objectives of this fishery are to achieve a biomass in the final year equal to the biomass found at a maximum sustainable yield (7243 t) and to maximise effort (employment) and catch. The overall recommendation for this stock was a reduction in minimum size limit from 35 cm to 30.48 cm in combination with a flexible TAC starting at 790 t. It is also recommended that even though models are important for fisheries management, no model should be taken in isolation without first considering life history traits and other important information about a stock.