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
Bachelor Thesis
2013
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University of Cape Town
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Abstract
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.
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Rousseau, M. 2013. 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. University of Cape Town.