Thesis (MSc)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: Haliotis midae (locally also known as perlemoen) is the largest of five endemic species found along the coast of South Africa. It is the only species with commercial value contributing to the exploitation of these animals. Due to declines of natural stocks, farming practices were established during the early 1990s in order to supply the international demand. To facilitate efficient breeding methods and ensure the sustainability of these commercial populations, genetic management, which can be accomplished with the use of molecular markers such as single nucleotide polymorphisms (SNPs), is necessary. Single nucleotide polymorphisms have become the markers of choice in various applications in aquaculture genetics due to their abundance in genomes, reduction in developmental costs and increased throughput of genotyping assays. Identification of SNPs in non-model species such as H. midae can be achieved by in silico approaches. In silico methods are suitable for de novo SNP identification and are both cost- and time-efficient. It is based on the analysis of multiple alignments where mismatches may be reported as candidate SNPs. Various medium-throughput genotyping methods are available to confirm putative SNPs, but the ideal method depends on factors such as cost, accuracy and multiplexing capacity. Although SNP markers can have various applications within the aquaculture environment the focus for this current study was saturating the linkage map of H. midae with additional markers. This would assist in the identification of quantitative trait loci associated with economically important traits, which in turn could ultimately be employed for marker-assisted selection and improved molecular breeding programs. In order to identify in silico SNPs, sequenced transcriptome data from a previous study was used and subjected to a series of criteria: minor allele frequency 10%, minimum coverage 80, 60 bp flanking regions. Selected loci were genotyped using a 192-plex assay with the Illumina GoldenGate genotyping assay with the VeraCode technology on the BeadXpress platform, in individuals from six mapping families. A conversion rate of 69.35% and global success rate of 76.34% was achieved. Polymorphic loci were subjected to linkage analysis using JoinMap® v.4.1 to create sex-average and sex-specific maps and to saturate the current linkage map for H. midae. Along with previously developed markers, 54% of the newly developed SNPs could be successfully incorporated into the linkage map of H. midae. A total of 18 linkage groups were observed with an average marker spacing of 6.9 cM and genome coverage of 79.1%. Bioinformatic analyses and setting stringent criteria to identify SNPs from sequenced transcriptomic data proved to be an efficient way for SNP discovery in the current study. Genotyping of the identified loci with the GoldenGate genotyping assay demonstrated a high success rate; providing a genotyping assay adequate for species with little genomic information. The linkage map created in this study illustrated the utility of SNP markers in conjunction with microsatellite markers for linkage map construction and the adequate marker spacing obtained provides a step closer to quantitative trait loci mapping in this species. / AFRIKAANSE OPSOMMING: Haliotis midae (plaaslik ook bekend as perlemoen) is die grootste van vyf inheemse spesies wat langs die kus van Suid-Afrika aangetref word. Dit is die enigste spesie van kommersiële waarde wat bydraend is tot die uitbuiting van hierdie diere. As gevolg van die afname in hierdie natuurlike hulpbron het boerdery praktyke gedurende die vroeë 1990's ontstaan om in die internasionale aanvraag te voorsien. Ten einde doeltreffende teelmetodes te beoefen en die volhoubaarheid van hierdie kommersiële populasies te verseker is genetiese bestuur, wat bewerkstellig kan word deur die gebruik van molekulêre merkers soos enkel nukleotied polimorfismes (ENPs), baie belangrik. Enkel nukleotied polimorfismes is gewilde merkers in verskeie toepassings in akwakultuur genetika as gevolg van hul oorvloed in genome, verlaagde ontwikkelingskoste en verhoogde deurset van ENP-genotiperingstoetse. Identifisering van ENPs in nie-model spesies soos H. midae kan uitgevoer word deur in siliko benaderings te gebruik wat geskik is vir de novo ENP identifisering en ook tyd- en koste-effektief is. Dit word gebaseer op die analise van veelvuldige inlynstellings waar nukleotiedes wat nie ooreenstem nie as kandidaat ENPs gerapporteer kan word. Om kandidaat ENPs te bevestig, kan verskeie medium-deurset genotiperingsmetodes uitgevoer word, maar die ideale metode word bepaal deur faktore soos koste, akkuraatheid en multipleks kapasiteit. Alhoewel ENP merkers in verskeie toepassing binne die akwakultuur omgewing gebruik kan word was die fokus van die huidige studie om die koppelingskaart van H. midae te versadig. Dit sal bydrae tot die identifisering van kwantitatiewe eienskap lokusse wat gekoppel kan word aan ekonomies belangrike eienskappe wat dan op die beurt weer vir merkerbemiddelde seleksie gebruik kan word en uiteindelik ten opsigte van die verbetering van molekulêre teelprogramme aangewend kan word. Ten einde in siliko ENPs te identifiseer is transkriptoomdata van 'n vorige studie gebruik en onderwerp aan 'n reeks kriteria: geringste alleelfrekwensie 10%, minimum dekking 80, 60 bp gebiede weerskante van polimorfisme. Geïdentifiseerde lokus-genotipering is met behulp van 'n 192-pleks toets uitgevoer met die Illumina GoldenGate genotiperingstoets met die VeraCode tegnologie op die BeadXpress-platform, in individue afkomsitg vanaf ses karteringsfamilies. 'n Omskakelingskoers van 69.35% en 'n algehele sukseskoers van 76.34% is bereik. Polimorfiese lokusse is onderwerp aan koppelings-analise met behulp van JoinMap® v.4.1 om geslags-gemiddelde en geslags-spesifieke kaarte te skep asook om die kaart wat beskikbaar is vir H. midae te versadig. Saam met voorheen ontwikkelde merkers is 54% van die nuut ontwikkelde ENPs suksesvol opgeneem in die kaart van H. midae. 'n Totaal van 18 koppelingsgroepe is verkry met 'n gemiddelde merker-spasiëring van 6.9 cM en 'n genoomdekking van 79.1%. Die gebruik van bioinformatiese analises en streng kriteria om ENPs vanaf transkriptoomdata te identifiseer blyk doeltreffend te wees in hierdie studie. Genotipering van die geïdentifiseerde lokusse met die GoldenGate genotiperingstoets dui op 'n hoë suksessyfer en verskaf 'n voldoende genotiperingstoets aan spesies met min genomiese inligting. Die koppelingskaart in hierdie studie het geïllustreer dat die ENP merkers suksesvol saam met mikrosatelliet merkers gebruik kan word vir koppelingskaart konstruksie en dat die voldoende merker-spasiëring verkry 'n stap nader aan kwantitatiewe eienskap lokus kartering in hierdie spesie bied.

Thesis (MScAgric)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: Abalone production is the largest financial contributor to aquaculture in South Africa and practically all of the abalone produced is exported to Asia. This means that the product must be globally competitive and many technologies have been applied to this cause. One that specifically shows great promise for bivalve mollusc production is triploidy; more precisely, sterility due to the induction of aneuploidy. Under normal maturation, energy is diverted from somatic growth through sexual maturation, therefore inhibiting or retarding gametogenesis through a process such as aneuploidy is expected to increase growth and decrease the time to marketing. Two studies preceding this one investigated the induction of triploidy through hydrostatic shock (De Beer, 2004) and the comparative growth rate of triploid genotypes from 8 to 24 months, prior to the onset of sexual maturation (Schoonbee, 2008). During this comparative growth stage, no convincing statistical evidence of faster growth or of seasonal environmental effects could be obtained. It was recommended that growth between triploid and diploid variants be compared during the age period when sexual maturity becomes a factor to determine whether triploidy in Haliotis midae is a useful biotechnological tool to improve biological productivity and global competiveness of the abalone industry. The growth measured as shell length and wet weight in the period from 29 to 62 months showed a statistically significant difference in mean weight and mean length with diploids showing a superior growth rate compared to their triploid siblings. This difference of 1.99 mm and 5.13 g was however not perceived as being commercially significant. Important production parameters including canning yield percentage and gonadosomatic index were also measured during this trial. For both these parameters, the triploid genotype showed statistically and commercially significant improvement of 10.68% increased canning yield and 28.42% reduction in gonadosomatic index when compared to their diploid counterparts. Triploid abalone was found to be not completely sterile; gametes and even mature gonads were observed in some instances. Even though complete sterility was not achieved there appeared to be a retarded gonadosomatic development in triploid variants. The delay in sexual maturation, together with the improvement in canning yield, may justify triploidy’s commercial application, despite its reduced growth rate. / AFRIKAANSE OPSOMMING: Perlemoen produksie lewer die grootste finansiële bydra tot akwakultuur in Suid Afrika en feitlik al die Perlemoen word uitgevoer na Asië. Dit beteken dat die produk moet kompeteer op die wêreld mark en verskeie tegnologieë word reeds aangewend vir die spesifieke doel. Een so tegnologie wat potensiaal toon ten opsigte van akwakultuur produksie is triploïedie; meer spesifiek, sterieliteit veroorsaak deur aneuploïedie induksie. Onder normale volwassewording, word energie weggeneem van somatiese groei wanneer geslagsrypheid intree en daarom kan groeitempo verhoog word deur gametogenese te inhibeer of te vertraag deur ‘n proses soos aneuploïedie en, word korter tydperk benodig om bemarkingsgrootte te bereik. Twee voorafgaande studies het gehandel oor die induksie van triploïedie deur hidrostatiese druk skok (De Beer, 2004) en die vergelykende groeitempo van triploïede genotipes vanaf ouderdom 8 tot 24 maande (Schoonbee, 2008) alvorens geslagsrypheid intree. Tydens hierdie vergelykende groeifase kon geen statisties betekenisvolle aanduidings van vinniger groei of seisoenale omgewingseffekte aangetoon word nie. Die studie handel vervolgens oor die uitbreiding van die vergelykende groeistudies tussen triploïede en diploïede genotipes tot ouderdom van 62 maande wat die intrede van geslagsrypheid insluit, ten einde te bepaal of die induksie van triploïedie in Haliotis midae voordele inhou ten opsigte van produksiedoeltreffendheid en mededingendheid op wêreldmarkte. Groei gemeet in terme van skulplengte en lewende massa oor die tydperk van 29 tot 62 maande het statisties betekenisvolle verskille getoon in gemiddelde massa en lengte van diploïede genotipes bo die van triploïede verwante individue. Die verskille van 1.99 mm en 5.13 g kan egter nie as kommersieel betekenisvol beskou word nie. Belangrike produksie eienskappe waaronder persentasie opbrengs van eindproduk en die gonadosomatiese indeks is ook bepaal. Vir beide die produksie eienskappe het die triploïede genotipe statisties sowel as kommersieel betekenisvolle verbetering van 10.68% getoon vir opbrengs en 28.42% verlaging in gonadosomatiese indeks in vergelyking met die diploïede genotipe. Triploïede genotipes was nie volledig steriel nie, gegewe die aanwesigheid van gonades en gamete in sommige individue. Selfs al is totale steriliteit nie bereik nie, het dit wel voorgekom asof daar vertraging in gonadosomatiese ontwikkeling plaasgevind het in triploïede genotipes. Die vertraging in geslagsrypheid tesame met die verhoogde persentasie opbrengs van die eindproduk hou voordele in bo die andersins effense stadiger groei van triploïede genotipes.

Thesis (MSc)--University of Stellenbosch, 2007. / ENGLISH ABSTRACT: The indigenous abalone Haliotis midae is one of the most remarkable and highly exploited species of marine molluscs in South Africa. It is the only species of southern African Haliotidae to be commercially reared and has been successfully cultured for almost two decades. Its short history of domestication along with market demands and the need to develop efficiency in the production process has resulted in an increased interest in the possible genetic improvement of this species. The unhurried growth rate associated with H. midae is a cause of particular concern to the industry, predominantly with regards to profitability and competitiveness in the market place. A modest amount of work has so far been directed at establishing a means of enhancement for selective breeding on the commercial level. Genetics plays a key role in the establishment of successful improvement programmes in various aquaculture species. The aim of this study was to develop species-specific microsatellite markers for the abalone and subsequently perform parentage assignment on farm produced animals entered into a growth performance recording scheme. Animals were obtained from the hatcheries of three commercial abalone farms situated in the Walker Bay region in the Western Cape. Microsatellites were isolated using the enrichment-based FIASCO method, and characterised into perfect, imperfect and compound repeats according to the structural nature of their repetitive units. From the partial gDNA libraries obtained and 365 screened colonies, a total of 54 loci were located. PCR primers were designed for 36 markers and the 15 primer pairs that displayed loci with the highest level of polymorphism were subsequently chosen for fluorescent labelling. The markers were tested on a subset of 32 wild H. midae individuals to determine their usefulness and efficiency in genotyping. Five markers, along with five others that were previously designed, were chosen for assigning parentage to the animals submitted to the performance recording scheme. Three thousand offspring from each of the three participating farms were equally divided and reared at five different locations. From each location 20 fast growing and 20 slow growing juveniles, as well as the broodstocks, were sampled and genotyped using the ten chosen microsatellite loci. Two farms had 60% of offspring unambiguously assigned to a single parental couple. Assignments showed patterns of dominant male and female brooders, but no trend in brooders specifically contributing to fast or slow growing offspring. Parentage assignment for the third farm was, however, unsuccessful due to lack of broodstock data. In future, screening of all available broodstock will ensure acquisition of relevant pedigree information. The results obtained in this study are an initial step in the development of a genetic improvement programme for commercial Haliotis midae. / AFRIKAANSE OPSOMMING: Die inheemse skulpvis Haliotis midae is een van die mees merkwaardige en hoogs oorbenutte mariene slakspesies in Suid-Afrika. Dit is die enigste suidelike Afrika Haliotidae spesie wat kommersieel benut word en dit word al meer as twee dekades suksesvol geteel. Die spesie se kort domestiseringsgeskiedenis, toenemende mark aanvraag en die behoefte om meer effektiewe produksie daar te stel, het gelei tot toenemende belangstelling in die moontlike genetiese verbetering van die spesie. Die stadige groeitempo geassosieer met H. midae is veral ‘n punt van kommer vir die industrie, veral in terme van winsgewendheid en kompetering in die markplek. Minimale werk is sover gedoen in die daarstelling van verbetering deur selektiewe teling op ‘n kommersiële skaal. Genetika speel ’n sleutelrol in die daarstelling van suksesvolle verbeteringsprogramme van verskeie akwakultuur spesies. Die doel van hierdie studie was om spesie-spesifieke mikrosatelliet merkers vir perlemoen te ontwikkel en vervolgens ouerskapsbepaling van kommersiële diere, wat deelneem aan ‘n groeiprestasie aantekenstelsel, uit te voer. Diere is voorsien deur die teelstasies van drie kommersiële perlemoenplase geleë in die Walker Bay omgewing in die Wes-Kaap. Mikrosatelliete is geïsoleer deur die verrykings-gebaseerde FIASCO metode, en gekarakteriseer as perfekte, onderbroke of saamgestelde herhalings gebaseer op die strukturele aard van die herhalings eenhede. Vanaf die gedeeltelik gDNA biblioteke wat bekom is en 365 gesifte kolonies, is ‘n totaal van 54 loki opgespoor. PKR inleiers is ontwerp vir 36 merkers en die 15 inleierpare, wat loki met die hoogste polimorfisme geamplifiseer het, is vervolgens geselekteer vir fluoreserende merking. Die merkers is getoets op ’n kleiner groep van 32 natuurlike H. midae individue om hulle bruikbaarheid en genotiperingseffektiwiteit te bepaal. Vyf merkers is saam met vyf reeds ontwikkelde merkers gekies vir ouerskapsbepaling van die diere in die prestasie aantekenstelsel. Drieduisend nageslag diere vanaf elkeen van die drie deelnemde plase is gelykop verdeel en grootgemaak op die vyf verskillende lokaliteite. ‘n Monster van 20 vinnig groeiende en 20 stadig groeiende jong perlemoen, sowel as broeidiere, is vanaf elke lokaliteit geneem en gegenotipeer deur middel van die 10 geselekteerde mikrosatelliet loki. Sestig persent van twee van die plase se nageslag is onteenseglik toegesê aan ‘n enkele ouerpaar. Ouerskapstoekenning het patrone van dominante vroulike en manlike broeidiere getoon, maar geen tendens in terme van bydrae tot vinnig en stadig groeiende nageslag kon gevind word nie. Ouerskapstoekenning vir die derde plaas was onsuksesvol as gevolg van ’n gebrek aan data vir die broeidiere. In die toekoms sal genotipering van alle beskikbare broeidiere die daarstelling van relevante stamboominligting verseker. Die resultate verkry in hierdie studie verteenwoordig ‘n eerste stap in die ontwikkeling van ’n genetiese verbeteringsprogram vir kommersiële Haliotis midae.

The inclusion of soya as a dietary protein source in the formulated feed, Abfeed® S34 (Marifeed Pty (Ltd), Hermanus) for farmed abalone, Haliotis midae has resulted in larger gonads during reproductive seasons compared to the gonads of abalone fed kelp or diets that included fishmeal as the only main protein source. The aim of this study was to determine if the isoflavones present in the soya were responsible for this increase in gonad size and the subsequent effects on farmed abalone growth. Animals weighing between 40-50 g were fed one of seven isonitrogenous and isoenergetic diets containing either 0, 25, 50 or 100 percent of the soya component of the commercial feed (Abfeed® S34, Marifeed Pty (Ltd), Hermanus) from September 2013 to March 2014. An additional three diets were formulated to include crystalline isoflavone (ISO). These diets were identical to the 0 percent soya diet (i.e. the fishmeal only diet - FM), only ISO was included at the same rate that ISO occurred in the three soya diets. Data were analysed using a multiple forward stepwise regression analysis (MSR) to test the effects of ISO concentration, soya concentration, time, sex, time by concentration interaction and sex by concentration interaction on growth and gonad development and to identify those variables that most contributed to the model. The inclusion of crystalline ISO failed to promote larger gonads and had no effect on abalone growth, while growth and gonad development was dose dependent on soya inclusion rates with sex and time contributing to the models. Mean monthly weight gain in males correlated with increasing soya concentrations (c) (MSR, y = 3.24 + 0.002c, r2 = 0.23, p = 0.03), ranging from 3.11 ± 0.55 g abalone-1 month-1 to 4.43 ± 0.46 g abalone-1 month-1, while both male and female monthly length gain was not influenced by soya concentration with an overall mean of 1.62 ± 0.05 mm abalone-1 month-1 (MSR, p = 0.05 and p = 0.81, respectively). By December, the whole body mass, meat mass and visceral mass in both males and females decreased with increasing soya levels. However, by February, female whole body mass, meat mass and visceral mass positively correlated with soya levels. At the end of the study, male abalone fed FM with soya equivalent to the commercial feed had the highest whole body mass (69.00 ± 2.48 g abalone-1), meat mass (41.80 ± 1.12 g abalone-1), visceral mass (9.00 ± 2.47 g abalone-1) and gonad bulk index (42.70 ± 9.82 g abalone-1), while females were not influenced by soya concentrations with an overall whole body mass of 63.46 ± 0.79 g abalone-1. Weight loss was observed in all treatments between February and March, probably due to a spawning event. The moisture content in the meat was not influenced by treatment, however, visceral water loss was effected by both ISO and soya concentration with time and sex contributing to the model. The visceral water loss of females fed graded levels of soya decreased as a function of soya from December to March, and from December to February for males, whereas females fed ISO-enriched diets decreased as a function of ISO concentration (c) at the end of the study from 74.98 ± 0.88 to 73.10 ± 0.75 percent (MSR, y = 74.97 – 0.0025c, r2 = 0.20, p = 0.048). The inclusion of crystalline ISO had no significant effect on oogenesis in female farmed Haliotis midae, while the distribution of the predominant oocyte stage, stage 7 (second last stage prior to spawning) was dose-dependent in abalone fed increasing soya concentration (c) (MSR, y = 33.38 + 0.03c, r2 = 0.32, F(1, 18) = 8.52, p = 0.01). The increase in stage 7 oocytes in abalone fed FM with soya did not reduce the number of oocytes (44.96 ± 3.01 oocytes mm-2) present within the lumen, while the number of oocytes (o) in abalone fed the FM-only based diets decreased with increasing abundance of stage 7 oocytes (MSR, y = 58.28 – 0.48c, r2 = 0.38, F(1, 18) = 12.51, p = 0.002), possibly due to the increase in size of the oocytes with thicker jelly coats. This study provided evidence that crystalline isoflavone had no influence on abalone gonad development over five months, while soya had a dose-dependent effect on growth, gonad mass and oogenesis in farmed Haliotis midae. Formulated abalone feed could be manipulated at certain times of the year to obtain maximum growth. These implications and further studies were discussed.

Physiological stress in farmed abalone can lead to immunosuppression and increase the susceptibility to bacterial, viral and parasitic disease, often followed by mortality. Thus, handling and poor water quality can reduce farm production efficiency. Probiotics in aquaculture have been effective in a wide range of species in enhancing immunity, survival, improving feed utilisation and growth. Three putative probionts identified as a result of in vitro screening had been beneficial to laboratory-reared abalone in a previous study. The aim of this study was to produce an abalone feed that contains a suite of probionts that may promote abalone growth and health under farming conditions. The objectives were to compare growth and physiological responses (i.e., haemocyte and phagocytosis counts) of abalone fed a commercial feed (Abfeed®S 34, Marifeed, Hermanus) supplemented with probiotics (i.e., the probiotic diet) to abalone fed the commercial feed without probiotic supplementation as a control treatment in a factorial design with handling method as an independent variable. This experiment was conducted at HIK Abalone Farm (Pty Ltd) for a period of eight months with initial weight and length 36.1 ± 0.05 g and 58.6 ± 0.06 mm abalone-1. Another experiment was carried out at Roman Bay Sea Farm (Pty) Ltd with initial weight and length 34.7 ± 0.17 g and 62.3 ± 0.18 mm abalone-1, but this experiment included one factor only, i.e. the presence and absence of the probionts in the feed. At HIK there was no significant interaction between diet and handling on average length and weight gain month-1 after four (p=0.81 and p=0.32) and eight (p=0.51 and p=0.53) months, respectively. Average length (additional handling = 73.9 ± 0.52 mm, normal farm handling = 75.8 ± 0.57 mm) and weight gain (mean: additional handling = 68.5 ± 1.20 g, normal farm handling = 74.3 ± 1.86 g) increased significantly in animals that were handled under normal farm procedure and were either fed probiotic or control diet after eight months (p=0.03 and p=0.02, respectively). There was no iii difference in length gain or weight gain of abalone fed the probiotic diet and those fed the control diet (ANOVA: F(1,16)=0.04, p=0.84; F(1,16)=0.14, p=0.71, respectively). After four months phagocytotic count was significantly different between dietary treatments with mean values of 74.50 ± 10.52 and 63.52 ± 14.52 % phagocytosis count per sample for the probionts and control treatment, respectively (p=0.04), there was no difference after eight months at HIK Abalone Farm. There was no effect of stressor application (p=0.14) and no interaction between dietary treatment and stressor application for this variable i.e., phagocytosis count (p=0.61). There was no difference in feed conversion ratio between treatments with values ranging from 2.9 to 3.8. At Roman Bay Sea farm, there was no significant difference in mean length gain between abalone fed the probiotic and control diet after eight months (repeated measures ANOVA: F(4,28)=16.54. Mean weight gain of abalone fed the probiotic diet was significantly greater than those fed the control diet after eight months (repeated measures ANOVA: F(4,28)=39.82, p(0.00001). There was no significant difference in haemocyte counts between animals fed either probiotic or control diet after four and eight months at Roman Bay Sea farm (p>0.05).

Thesis (MSc)--University of Stellenbosch, 2003. / ENGLISH ABSTRACT: The genetic status of H. midae broodstock in the South African aquaculture industry reflects that of random samples originating from undomesticated wild populations. The nature of growth in abalone is very slow, taking between three and four years to reach a marketable size of between 60 to 100 grams. It is therefore of paramount importance to improve this trait in order to ensure global competitiveness and economic viability within the industry. Improving this negative characteristic through conventional selection methods is a long-term venture and alternative means that would yield instantaneous results had to be considered. Crossbreeding was identified as an alternative, short-term strategy to improve growth rate. A crossbreeding experiment was performed between two populations of the abalone, Haliotis midae, from the East (E) and West (W) Coast of South Africa. This was done to investigate the occurrence of heterosis for growth among the crossbred genotypes (East x West, West x East). Fifteen males and females from both the East and the West Coast populations were mated in a complete dialelle crossbreeding experiment to produce four progeny groups (WW, EE, EW and WE). Progeny groups were evaluated for weight (bW) and length gain (bL) over a specific growth period of 9 months. The results provided no evidence of significant differences in weight (P = 0.085) or length gain (P = 0.244) between the four progeny groups, giving no indication of significant heterosis for weight and length gain among the crossbred progenies of these East and West Coast populations. It is recommended that further efforts to obtain improved growth rate in the abalone, Haliotis midae, through crossbreeding only be considered in light of clear evidence of substantial genetic differentiation between such populations. / AFRIKAANSE OPSOMMING: Die huidige status van perlemoen, soos dit voorkom in akwakultuur bedrywighede in Suid Afrika, weerspieël dié van ‘n ewekansige monster vanuit wilde, natuurlike populasies. Perlemoen is inherent ‘n stadig groeiende organisme wat tussen drie en vier jaar neem om tot ‘n bemarkbare grote van 60 tot 100 gram te groei. Dit is dus uiters noodsaaklik om hierdie eienskap te verbeter ten einde die bedryf ekonomies lewensvatbaar en mededingend op wêreld markte te maak. Konvensionele seleksie as ‘n metode om hierdie negatiewe eienskap te verbeter is ‘n langtermyn onderneming wat die identifisering van ‘n korttermyn metode, wat ondmiddellike resultate lewer, noodsaak. Kruisteelt is geïdentifiseer as geskikte korttermyn oplossing aangesien dit onmiddellike resultate lewer. ‘n Kruisteel eksperiment is uitgevoer tussen twee populasies van die perlemoen, Haliotis midae, van die Ooskus (E = East) en die Weskus (W = West) van Suid Afrika. Dit is gedoen om die omvang van heterose vir groeitempo in die gekruisde nageslag (East x West, West x East) te bepaal. Fyftien mannetjies en wyfies van beide die Oos- en Weskus populasies is met mekaar gepaar in ‘n volledige dialleel kruising om vier nageslag groepe (WW, EE, EW en WE) te vorm. Die nageslag is geëvalueer ten opsigte van massa (bW) en lengte (bL) toename oor ‘n spesifieke groei tydperk van 9 maande. Die eksperimentele resultate dui daarop dat die vier nageslag groepe nie betekenisvol van mekaar verskil het ten opsigte van massa (P = 0.085) en lengte (P = 0.244) toename nie en dat daar dus geen aanduiding van heterose vir massa en lengte toename in die nageslag van kruisings tussen die Ooskus en Weskus populasies bestaan nie. Daar word aanbeveel dat kruisteling as ‘n metode van genetiese verbetering van groeitempo in Haliotis midae slegs oorweeg word in die lig van nuwe molekulêre bewyse van genoegsame genetiese differensiasie tussen sulke populasies.