Thesis (PhD)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: This study investigated the “Effect of Phytogenic Feed Additives on Gonadal Development in Mozambique tilapia
(Oreochromis mossambicus). Aquaculture remains the fastest growing animal food-producing sector and it is set to
overtake capture fisheries as a source of food fish, and also to outpace population growth. This rapid growth can be
attributed to the increasing demand for aquaculture products, and an urgent need for a sustainable food resource and
the safe production of food. Globally, fish provides over 3.5 billion people with up to 15 percent of their average per
capita intake of animal protein.
The introduction of aquaculture to sub-Saharan African (SSA) took place during the 1940s and 1950s, and the main
objectives were to improve nutrition in rural areas, allow for the diversification of activities to reduce the risk of crop
failures, to generate additional income, and to create employment opportunities. Aquaculture was seen as a viable option
for rural development in SSA, and substantial resources were invested to support its development. Poor results were
however, recorded in terms of production and sustainability.
Tilapia is the most widely cultured of all fish species farmed, and the second most important group of freshwater and
brackish water fish after carps. Tilapia has all the necessary traits that makes it an excellent species to culture, but costefficient
production is hampered by the animals attaining sexual maturity at a an early age, which then result in
precocious breeding in aquaculture systems. The production of single-sex populations (i.e. all male) is a potential means
to address the problem of precocious breeding, but the technologies used to establish single-sex populations are not
readily available to resource-poor communities that farm with tilapia for food purposes.
Phytochemicals, also known as phytoestrogens, are plant-derived compounds that structurally or functionally mimic
mammalian estrogens that affect the sexual differentiation of fish. Phytochemicals occur in plants like Pawpaw (Carica
papaya) and Moringa (Moringa oleifera). The study thus had a threefold objective. Firstly, the study investigated the
potential of Pawpaw seed meal (P) and Moringa seed meal (M), as part of a commercial tilapia diet, to be used as
endocrine disrupting compounds (EDC’s) to control the reproduction of sexually mature Mozambique tilapia (20-45g).
Secondly, assess the potential of P and M to inhibit the attainment of sexual maturity in immature tilapia (2-8g). Finally,
P and M to determine its influence on sexual differentiation of tilapia fry (9-12 days posthatch) to produce all-male
populations.
The study indicated that both P and M seeds contain bio-active chemicals that are capable of disrupting the gonad
function, differentiation and sexual maturation of Mozambique tilapia. Sperm production was affected, evident in the
degeneration of the testicular tissue samples. Egg production, ovulation and spawning were all affected, as evident in the
difference in colour of the degrading eggs, as well as the absence of spawning. Ovo-testes were observed in cases
where diets containing 10.0g P and 10.0g M /kg basal diet were fed. Eggs were observed in the ovaries of sexually
immature fish, but spawning did not occur. The study also presents the first report on the isolation of Oleanolic acid in
Moringa seeds.
The evident of antifertility properties of both Pawpaw and Moringa seeds can be exploited to control or prevent
reproduction of Mozambique tilapia in SSA aquaculture systems. This could be of particular importance to aquaculture
development in rural areas of Sub-Saharan African countries, given the abundant year round availability of these
compounds. Further studies are required to optimise the preparation of the experimental compounds; as well as
determining the optimal inclusion level of the phytogenic compounds, as well as how their efficacy to manipulate the
reproductive potential and ability of Mozambique tilapia are influenced by environmental factors such as water
temperature. / AFRIKAANSE OPSOMMING: Akwakultuur is die vinnigste groeiende dierlike voedsel-sektor. Daar word verwag dat dit visserye sal oortref as ʼn bron
van voedsel en dat groei in dié bedryf selfs die bevolkingsgroei sal verbysteek. Die vinnige groei in die sektor kan
toegeskryf word aan die toenemende vraag na akwakultuur produkte en 'n dringende behoefte vir 'n volhoubare voedsel
hulpbron, wat ook die veilige produksie van voedsel sal verseker. Wêreldwyd voed vis meer as 3.5 miljard mense en dra
tot 15% van die gemiddelde hoeveelheid dierlike proteïen per kapita ingeneem, by.
Die bekendstelling van akwakultuur in sub-Sahara Afrika (SSA) het gedurende die 1940's en 1950's plaasgevind, met die
belangrikste doelwitte om voeding in landelike gebiede te verbeter, geleenthede vir diversifisering te skep wat die risiko
van misoeste verminder, om bykomende inkomste te genereer en werksgeleenthede te skep. Akwakultuur is gesien as
'n lewensvatbare opsie vir die ontwikkeling van die landelike gebiede in SSA en aansienlike hulpbronne is belê om die
ontwikkeling daarvan te ondersteun. Swak resultate is egter in terme van produksie en volhoubaarheid behaal.
Tilapia is die mees algemene spesies wat gekweek word en is die tweede mees belangrike groep van varswater en brak
water vis soesies, na Karp. Tilapia beskik oor al die nodige eienskappe wat dit ʼn uitstekende spesie vir voedselproduksie
maak, maar koste-doeltreffende produksie daarvan word gekortwiek deur die feit dat die spesie seksuele volwassenheid
op 'n vroeë ouderdom bereik, wat dan lei tot vroeg-rype teling en die gevolglike oorbevolking en swak groei van tilapia in
ʼn akwakultuur sisteem. Die produksie van enkel-geslag bevolkings (d.i. slegs manlike vis) is ʼn potensiële oplossing vir
dié probleme, maar die tegnologie wat gebruik word om enkel-geslag bevolkings te produseer is nie geredelik toeganklik
vir hulpbron-arme gemeenskappe wat met Tilapia vir kosdoeleindes boer nie.
Fitochemikalieë, anders ook bekend as fito-estrogene, is verbindings wat in plante voorkom en wat struktureel of
funksioneel die werking van die natuurlike soogdier estrogene/androgene naboots, met die fitochemikalieë wat die
seksuele differensiasie van vis beïnvloed. Fitochemikalieë kom in plante soos papaja (Carica papaya) en Moringa
(Moringa oleifera) voor. Die studie het dus gepoog om die potensiaal van papaja saad meel (P) en Moringa saad meel
(M), as deel van 'n kommersiële tilapia dieet, om as endokriene ontwrigters (EDC's) gebruik te word om die reproduksie
van seksueel volwasse Mosambiek tilapia (20-45g) te beheer, om te voorkom dat onvolwasse tilapia (2-8g)
geslagsrypheid te vroeg bereik en ook om die geslagsdifferensiasie van tilapia vingerlinge (9-12 dae na uitkom) te
manipuleer om enkel-geslag (manlike) produksiegroepe te produseer.
Die studie het aangedui dat beide papaja en Moringa sade bio-aktiewe chemikalieë wat die werking van die
gonadotrofien hormone, geslagsdifferensiasie die stadium waarop Mosambiek tilapia geslagsrypheid bereik, kan
beïnvloed. Spermproduksie is negatief beïnvloed, soos waargeneem in die degenerasie van die testisweefsel.
Eierproduksie, ovulasie en die vrystelling van eiers is almal negatief beïnvloed, soos duidelik waargeneem in die
kleurverskil (van normale eiers) van eiers wat ʼn mate van reabsorbsie aandui en die feit dat geen eiers vrygestel is nie.
Ovo-testes is waargeneem in gevalle waar diëte met 10.0g papaja en / of Moringa / kg basale dieet gevoer is. Eiers is
waargeneem in die eierstokke van seksueel onvolwasse vis, maar vrystelling het nie plaasgevind nie. Die studie is die
eerste verslag oor die isolasie van Oleanoliese suur in Moringa sade.
Die duidelike reproduksie-beperkende (anti-vrugbaarheid) eienskappe van beide papaja en Moringa sade kan benut kan
word om reproduksie in Mosambiek tilapia te voorkom of te manipuleer in SSA akwakultuur stelsels. Dit is veral van
besondere belang vir akwakultuur ontwikkeling in die landelike gebiede van SSA lande, gegewe dat beide sade regdeur
die jaar geredelik beskikbaar is.
Verdere studies word benodig om protokolle vir die voorbereiding van die eksperimentele verbindings te optimaliseer,
sowel as die bepaling van die optimale insluitingsvlakke van die fitogeniese verbindings, asook hoe die doeltreffendheid
van hierdie verbindings deur omgewingsfaktore soos water temperatuur beïnvloed word. / The University for Development Studies (UDS), Ghana, particularly Prof S.K. Nokoe, and Ghana
Education Trust Fund (GETFund), for the initial financial support that enabled me to enrol for the
programme.
The Division of Aquaculture, together with the Postgraduate and International Office (Postgraduate
Funding Section), Stellenbosch University (SU) for financial support during my studies.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/79976 |
| Date | 03 1900 |
| Creators | Ampofo-Yeboah, Akwasi |
| Contributors | Brink, Danie, Lambrechts, Helet, Stellenbosch University. Faculty of AgriSciences. Dept. of Animal Sciences. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | xiii, 240 p. : col. ill. |
| Rights | Stellenbosch University |
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