ENGLISH ABSTRACT: The first successful captive spawning of the South African abalone Haliotis midae occurred in
the 1980’s and subsequently the commercial abalone industry in South Africa has
developed, with an estimated investment of US$ 12 million and annual output of 500 to 800
tons by 2001, making South Africa the biggest abalone producer outside of Asia. Natural
kelp is currently the major feed and the development of a suitable substitute, and improved
disease management in abalone culture are seen as the primary factors limiting expansion of
the industry in South Africa. Further, abalone growth rates are very slow and improvements
in growth rate will lead to shortened production times with benefits to producers. Diseases in
aquaculture have traditionally been combated using antibiotics as treatment (therapeutic
usage) and preventative measure (prophylactic usage). In terrestrial livestock management,
antibiotics are also used as growth promoters. The use of antibiotics in aquaculture has
recently sparked concerns about the development of antibiotic resistance in pathogens of
humans and aquaculture organisms, and alternative strategies to using antibiotics mainly
focus on manipulating the microbial composition in the host organism, in order to establish a
beneficial microbial population to prevent disease.
The role that organic acids and their salts can play as growth promoters in the South African
abalone Haliotis midae, and as manipulators of the gut microflora of this species of abalone
was investigated and compared to the effects of antibiotics. Three different treatments were
tested against a negative control and a positive control containing 30ppm avilamycin, a
commercial antibiotic growth promoter (AGP) used in the pig and poultry industry. The 3
treatments consisted of 1% acetic and 1% formic acid (treatment AF), 1% sodium benzoate
and 1% potassium sorbate (treatment SBPS), and 1% benzoic and 1% sorbic acid
(treatment BS). Three different experiments were conducted to test the effects of the different
acids and salts. The first experiment was under controlled optimum water temperature
conditions (16.5ºC), another at elevated water temperature (20.5ºC) in order to test response
during temperature stress conditions, and the final trial was conducted under uncontrolled
practical production conditions. In an attempt to establish the mechanism by which the
treatments have their effects (if any), the composition of the gut microflora of the abalone
was monitored. It was found that the organic acids and salts investigated can enhance the growth rate of
Haliotis midae in the size class 23 mm to 33 mm mean length significantly when compared to
both control treatments. It was further found that the tested AGP had no effect on growth
rate. None of the treatments had a significant effect on feed conversion ratio (FCR),
Incidence cost (IC) or feed intake. It could also not be shown that the treatments affected the
intestinal microflora of the abalone, although this might be due to inadequate microbiological
methods. The mechanism by which the acids and salts have their effects could not be
established.
It was found that the animals in the controlled system underwent an initial adaptation period,
which led to improvement in specific growth rate (SGR), FCR and IC as the experiment
progressed during the controlled optimal conditions experiment. Large differences in FCR
and IC was seen for controlled optimal conditions and production conditions which means
that there is still a large scope for developing methods to improve practical on-farm feed
utilisation by abalone.
SGR, FCR and IC were negatively influenced by raising water temperature from 16.5ºC to
20.5ºC. The composition of the gut microflora of the abalone also changed significantly after
the water temperature was raised. It appears that animal weight gain and shell growth
respond differently to changing water temperatures, which is reflected in a change in Fulton
condition factor.
A relationship between the length and weight of abalone between 15 mm and 47 mm was
established and it was found that Haliotis midae does not follow an isometric growth
relationship. This relation can be used as a tool to improve farm management and therefore
also profitability.
Various micro-organisms were isolated from Haliotis midae during the trial, but their
relationship and interaction with abalone is not clear. Clear dominance by specific species of
bacteria was observed during certain periods.
The current research has clearly showed the potential of organic acids and their salts to act
as growth promoters in the South African abalone Haliotis midae, with application in both the
local aquaculture and feed manufacturing industries. The possibility further exists that some
aspects of the current research can be adapted to be applicable in other abalone species
and even in other aquaculture species. / AFRIKAANSE OPSOMMING: Die eerste suksesvolle aanteel van die Suid-Afrikaanse perlemoen Haliotis midae in
gevangeskap is in die 1980’s gerapporteer, waarna ‘n suksesvolle akwakultuur industrie
ontwikkel het met ‘n geskatte produksievermoë van 500 tot 800 ton en kapitaalbelegging van
US$ 12 miljoen in 2001. Suid-Afrika is tans die grootste perlemoen-produserende land wat
buite Asië geleë is. Die ontwikkeling van ‘n geskikte alternatiewe voedselbron vir natuurlike
kelp (tans die algemeenste voedselbron wat gebruik word in die kweek van perlemoen),
sowel as verbeterde siektebestryding word tans gesien as die hooffaktore wat verdere
uitbreiding in die Suid-Afrikaanse industrie beperk. Perlemoen het verder baie stadige
groeitempo’s en enige verbetering in hierdie verband sal produksietye verkort en dus
produsente bevoordeel. Siektes in akwakultuur word tradisioneel bestry deur gebruik te
maak van antibiotiese behandeling (terapeutiese bestryding) of van voorkomende
behandeling (profilaktiese bestryding). In gewone diereproduksie-sisteme (bv. varke en
hoenders) word antibiotika ook gebruik as groeistimulante. Die gebruik van antibiotika in
akwakultuur het onlangs die bekommernis laat ontstaan dat sekere menslike en dierepatogene
weerstand kan ontwikkel teen sommige middels, wat die behoefte laat ontstaan het
om siektebestryding sonder die gebruik van antibiotika te ontwikkel. Alternatiewe strategieë
fokus grootliks daarop om die samestelling van die mikrobiese bevolking van die gasheer te
manipuleer en sodoende ‘n voordelige bevolking in die gasheer te vestig, wat dan siektes
voorkom.
Daar is ondersoek ingestel na die rol van organiese sure en hul soute as groeistimulante en
manipuleerders van die mikrobiese bevolking in die Suid-Afrikaanse perlemoen Haliotis
midae. Drie verskillende behandelings is getoets en vergelyk met beide ‘n negatiewe- en
positiewe kontrole (wat 30 dele per miljoen van ‘n kommersiële antibiotiese groeistimulant
bevat het). Die drie formulasies het onderskeidelik bestaan uit ‘n mengsel van 1% etanoëen
1% metanoësuur (behandeling AF), 1% bensoë- en 1% sorbiensuur (behandeling BS) en
1% natriumbensoaat en 1% kaliumsorbaat (behandeling SBPS). Om die effekte van hierdie
formulasies te toets, is daar 3 proewe gedoen. Een proef is gedoen onder temperatuurbeheerde
toestande teen ‘n optimum watertemperatuur van 16.5ºC terwyl ‘n ander gedoen is
onder onbeheerde, praktiese produksie-omstandighede. ‘n Verdere beheerde proef is
gedoen teen ‘n watertemperatuur van 20.5ºC om die effek van die verskillende formulasies te
toets wanneer die diere aan temperatuur-spanning blootgestel word. Die samestelling van
die mikrobiese bevolking in die dunderm van die perlemoen is deurentyd gemonitor in ‘n poging om die meganisme vas te stel waarvolgens die sure en soute hul effek het, indien
daar enige effek waargeneem word.
Daar is gevind dat die onderskeie sure en suursoute die groeitempo van Haliotis midae met
‘n gemiddelde lengte van 23 mm tot 33 mm beduidend kan verhoog in vergelyking met die
groeitempo’s van beide kontroles. Daar is gevind dat die antibiotiese groeistimulant geen
effek het op die groei van die diere nie en dat geen behandelings ‘n beduidende effek op
voeromsetting, voerkoste of voerinname gehad het nie. Daar kon nie bewys word dat enige
van die formulasies of die antibiotika ‘n effek gehad het op die mikrobes in die
spysverteringskanaal van die perlemoene in die sisteem nie, alhoewel die gebrek aan ‘n
effek moontlik toegeskryf kan word aan die onakkurate en onvoldoende mikrobiologiese
metodes wat gebruik is tydens die studie. Die meganisme waarvolgens die sure werk kon
nie vasgestel word nie.
Daar is verder gevind dat die diere in die temperatuur-beheerde eksperiment aanvaklik deur
‘n aanpassingsperiode gegaan het, wat tot gevolg gehad het dat die spesifieke groeitempo,
voeromsetting en voerkoste verbeter het met die verloop van die eksperiment. Daar is groot
verskille gevind in die voeromsetting van beheerde optimale toestande en onbeheerde
produksietoestande, wat impliseer dat daar nog baie ruimte en geleenthede is om metodes
te ontwikkel wat beter voeromsetting bewerkstellig tydens perlemoenproduksie.
Spesifieke groeitempo, voeromsetting en voerkoste is nadelig beïnvloed toe die
watertemperatuur verhoog is vanaf 16.5ºC na 20.5ºC. Die samestelling van die mikrobiese
bevolking in die spysverteringskanaal van die perlemoen het ook beduidende veranderinge
ondergaan tydens hierdie temperatuur verhoging. Dit wil voorkom asof die lengtegroei van
die dop en die toename in massa verskillend reageer op ‘n verandering in watertemperatuur
en hierdie effek word weerspieël in die verandering in Fulton-kondisiefaktor.
‘n Verwantskap tussen totale doplengte en totale gewig van Haliotis midae kon vasgestel
word vir diere tussen 15 mm en 47 mm en daar is gewys dat H. midae nie ‘n isometriese
groeipatroon volg nie. Hierdie verwantskap kan aangewend word tydens produksiebestuur
om produksie te verbeter en daardeur ook winsgewendheid te verhoog.
Verskeie mikrobes is tydens die verloop van die proef geïsoleer, maar die rol van en
interaksie tussen hierdie mikrobes en die Suid-Afrikaanse perlemoen is nie duidelik nie.
Sekere bakterieë het die mikrobiese bevolking in die spysverteringskanaal van die
perlemoen in hierdie proef oorheers tydens sekere groeiperiodes. Die huidige navorsing het duidelik aangetoon dat organiese sure en hul soute as
groeistimulante kan optree in die Suid-Afrikaanse perlemoen Haliotis midae, met toepassings
in die plaaslike akwakultuur- en voervervaardigins-industrieë. Dit beskik verder oor die
potensiaal om aangepas te word sodat dit toepaslik is in ander perlemoenspesies en selfs
ander akwakultuur organismes.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/16416 |
| Date | 12 1900 |
| Creators | Goosen, Neill Jurgens |
| Contributors | Gorgens, J. F., De Wet, L. F., Aldrich, C., University of Stellenbosch. Faculty of Engineering. Dept. of Process Engineering |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | 118 p. : ill. |
| Rights | Stellenbosch University |
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