Thesis (MSc)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: The ocean’s fish resources are declining mainly because of irresponsible exploitation.
Fish is a vital source of protein for humans and growing world populations are threatening
the sustainability of commercial fisheries. This has led to the rapid growth of aquaculture
worldwide. In South Africa, aquaculture of both fresh and marine species is expanding
and is now practised in all nine provinces of the country.
One of the major problems in aquaculture is the economic losses as a result of diseases.
Viruses, bacteria, fungi and parasites are well known to infect fish, with bacteria causing
the majority of diseases. Antibiotics were commonly used to control diseases, however,
due to their negative impact on the environment, the use of these agents is questioned.
This has led to the search for probiotics as an alternative way to control bacterial diseases
in aquaculture. Probiotics used in aquatic environments can be defined as live microbial
supplements which have beneficial effects on the host by altering the microbial
communities associated with the host and the immediate environment. Probiotics have a
variety of different mechanisms of action, including competition with pathogens, production
of beneficial compounds, enhancement of host immune response and antiviral effects. This study aimed to isolate potential probiotic bacteria from the gastrointestinal tract (GIT)
of the South African abalone (Haliotis midae). Nine different bacterial species were
isolated and identified as Corynebacterium variabilei, Staphylococcus carnosus,
Staphylococcus equorum, Staphylococcus cohniii, Vibrio aestuarianus, Vibrio
nigripulchritudo, Vibrio cyclitrophicus, Photobacterium leiognathi, and Paracoccus marcusii
(Chapter 2). One of these isolates, P. marcusii (isolate 6.15), showed promising probiotic
properties together with the potential to be used as a pigmentation source due to its
production of the carotenoid astaxanthin. Aquatic animals are not able to synthesize
astaxanthin and under aquaculture conditions do not come into contact with natural
pigment sources. This results in dark grey meat which is unappealing for consumers.
Therefore, astaxanthin is included in the feed of a variety of aquaculture species such as
salmon, trout, red see bream and shrimp to give the meat a pink/orange colour.
Astaxanthin also plays an important role in other essential biological functions of fish such
as increasing the defence potential against oxidative stress and enhancing sexual
maturity, embryo development, and egg survival. Mozambique tilapia (Oreochromis mossambicus) and rainbow trout (Oncorhynchus
mykiss), two important aquaculture species in South Africa, were used to evaluate the
probiotic and pigmentation effect of P. marcusii (isolate 6.15). Fish feed was coated with
freeze dried bacterial cells (107 CFU/kg feed) and administrated to tilapia and trout.
Because tilapia cannot incorporate astaxanthin into their meat, no pigmentation effect of P.
marcusii (isolate 6.15) was evaluated for this species. However, tilapia showed significant
improvement in growth and immune parameters. Fish supplemented with P. marcusii
(isolate 6.15) had a higher percentage increase in body weight and a better feed
conversion ratio for the duration of the trial. Enhanced lysozyme activity in the blood
serum of the fish was also seen (Chapter 3). In contrast, P. marcusii (isolate 6.15) did not
have any probiotic or pigmentation effect on rainbow trout. A possible reason for this may
be that the concentration of P. marcusii (isolate 6.15) added to the feed was too low. More
probably, it is suspected that no pigmentation was observed due to the destruction of the
astaxanthin before being ingested by the trout, because astaxanthin is a very unstable
molecule. Furthermore, the GIT microbial communities of trout were investigated over the
duration of the trial for the different treatments. No similarities in community structures
were observed betwee the different treatments, however, bacterial communities in the GIT
of fish sampled at the same time were very similar (Chapter 4). / AFRIKAANSE OPSOMMING: Die oseaan se vis hulpbronne is besig om af te neem as gevolg van die
onverantwoordelike gebruik daarvan. Vis is ‘n belangrike bron van proteïene vir mense en
die toenemende wêreld populasie bedreig die volhoubaarheid van kommersiële visserye.
As gevolg hiervan is daar ‘n drastiese toename in die akwakultuur industrie wêreldwyd.
Ook in Suid Afrika brei die akwakultuur van beide vars water en mariene vis spesies uit.
Een van die grootste probleme in akwakultuur is ekonomiese verliese as gevolg van
siektes wat veroorsaak word deur virusse, bakterieë, fungi en parasiete. Bakterieë
veroorsaak die meerderheid van die siektes en antibiotika word algemeen gebruik vir die
beheer van bakteriële siektes. Die gebruik van antibiotika word egter bevraagteken omdat
dit verskeie negatiewe implikasies vir die omgewing inhou Daarom word probiotika
oorweeg as ‘n alternatief tot antibiotika om bakteriële siektes te voorkom en te behandel.
Probiotika wat in akwatiese omgewings toegedien word kan gedefinieer word as a
lewende mikrobiese aanvulling wat ‘n positiewe effek op die gasheer het, deur die
mikrobiese gemeenskappe geassosieer met die gasheer en die ommidellike omgewing te
verander. Hierdie mikrobiese aanvulling verbeter die gesondheid van die visse deur
verskeie meganismes wat insluit kompetisie met patogene, produksie van voordelige
chemiese verbindings, verhoging van die gasheer se immuniteit en antivirale effekte. Die doel van hierdie studie was om potensiële probiotika te isoleer uit die spysverterings
kanaal (SVK) van die Suid Afrikaanse perlemoen spesie, Haliotis midae. Tydens die
studie is daar nege verskillende bakteriële spesies geïsoleer en geidentifiseer as stamme
verteenwoordegend van Corynebacterium variabilei, Staphylococcus carnosus,
Staphylococcus equorum, Staphylococcus cohniii, Vibrio aestuarianus, Vibrio
nigripulchritudo, Vibrio cyclitrophicus, Photobacterium leiognathi en Paracoccus marcusii
(Hoofstuk 2). Een van die isolate, P. marcusii, het belowende probiotika en potensiële
pigmentering eienskappe getoon a.g.v. die produksie van die karotenoïed astazantien.
Akwatiese diere is nie daartoe instaat om hierdie pigment te produseer nie en onder
akwakultuur toestande kom die visse ook nie in kontak met natuurlike bronne van hierdie
pigment nie. Dit lei daartoe dat die vleis van visspesies soos forel en salm grys word wat
dit onaantreklik vir verbruikers maak. Daarom word astazantien bygevoeg by visvoer om sodoende ‘n pienk/oranje kleur te verseker.Daar benewens speel astazantien ook ‘n rol in
belangrike biologiese funksies van visse. Dit sluit in die verhoging in beskerming teen
oksidatiewe stres, bevordering van seksuele volwassenheid, embrio ontwikkeling en eier
oorlewing.
Twee belangrike akwakultuur spesies in Suid Afrika, Mosambiek tilapia (Oreochromis
mossambicus) en reënboog forel (Oncorhynchus mykiss), was in hierdie studie gebruik.
Die probiotiese en pigmentasie effek van P. marcusii op reënboog forel was gëevalueer
terwyl slegs die probiotiese effek op tilapia geëvalueer weens die onvermoeë van tilapia
om die pigment in hul vleis te inkorpereer. Visvoer korrels was omhul met gevriesdroogde
bakteriële selle (107 CFU/kg kos) en vir die visse gevoer. Daar was ‘n duidelike
verbetering in groei en immuun parameters van tilapia. Visse toegedien met P. marcusii
het ‘n hoër persentasie vermeerdering in liggaamsgewig en ‘n beter voedsel omsettings
verhouding gehad tydens die verloop van die proef in vergelyking met die kontroles
(Hoofstuk 3). In kontras hiermee kon daar geen probiotiese of pigmenterings effekte
waargeneem word by die reënboog forel nie. ‘n Moontlike rede hiervoor kon wees dat die
konsentrasie van P. marcusii wat by die kos gevoeg is te laag was. Dit is egter ook
moontlik dat die astazantien vernietig was voordat dit deur die forel opgeneem is
aangesien astazantien ‘n baie onstabiele molekuul is. Verder het ons die impak van
verskillende visvoer behandelings op die mikrobiese gemeenskappe in die
spysverteringskanaal (SVK) van forel tydens die verloop van die proef bestudeer. Geen
ooreenkomste in mikrobiese gemeenskap strukture in die forel SVK is waargeneem tussen
die verskillende voer behandelings nie, maar daar is wel ooreenkomste gevind tussen die
mikrobiese gemeenskappe van visse by spesifieke tyd intervalle (Hoofstuk 4).
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/79852 |
| Date | 03 1900 |
| Creators | De Bruyn, Anneke |
| Contributors | Jacobs, Karin, De Wet, Lourens, Stellenbosch University. Faculty of Science. Dept. of Microbiology. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | ix, 139 p. : ill. |
| Rights | Stellenbosch University |
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