Graduation date: 2003

Thesis (MScAgric)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: The species Haliotis midae is of great commercial value to the South African abalone industry and is mainly exported to Asian markets, specifically China. Up to 50% is sold as canned products with H. midae registering an average canning yield of approximately 35%. The species is presently genetically undomesticated and breeding programmes are being introduced to improve a range of production traits of which growth and yield is of primary importance. The objective of the study was to determine genetic parameters such as heritability, genotypic and phenotypic correlations of yield-related traits to assess the potential genetic improvement through selective breeding. A series of yield-related parameters were identified that is of relevance to the standard abalone canning procedure. Low to moderate heritabilities where recorded for most traits, including pre-shuck/live weight (0.20 ± 0.06), post-shuck weight (0.15 ± 0.05), post-gut weight (0.15 ± 0.05), post-brine weight (0.19 ± 0.06), pre-canning weight (0.19 ± 0.06), post-canning weight (0.21 ± 0.06), shell weight (0.16 ± 0.05), canning yield percentage (0.08 ± 0.03) and shell weight to post-gut weight ratio (SW: PGW) (0.09 ± 0.04). Weight related parameters are phenotypically highly correlated (0.86 ≤ r ≤ 0.99) but show negative correlation with canning yield percentage (-0.38 ≤ r ≤ 0.04). The nett yield of abalone shows a relatively strong positive correlation with the live weight (r = 0.66). Shell length is highly heritable (h2 ≈ 0.48) and show a strong positive correlation with live weight (r = 0.94). Shell weight is also highly correlated with live weight (r = 0.80) and the SW: PGW ratio does not show a significant correlate with live weight (r = 0.03). Weight-related traits show heritability values ranging from 0.15 to 0.20 that could allow a positive genetic response. Shell length (as a linear growth parameter) shows a high heritability (h2 ≈ 0.48) and a strong positive correlation with live weight (r = 0.94) which also makes it suitable for use as a selection criterion in breeding programmes for improved growth rate. Direct selection for canning yield is compromised by the destructive nature of measurement and the low heritability (h2 < 0.10). The negative correlations between yield as a percentage and growth traits (-0.38 ≤ r ≤ 0.04) further complicate its use as a direct breeding objective. Although the canning yield as a percentage shows a decrease with an increase in live weight, the nett canning yield increases (r = 0.66) with the live weight. It is therefore recommended to use shell length as a criterion for selection for increased growth rate and nett yield, thereby optimising profitability. / AFRIKAANSE OPSOMMING: Die spesie Haliotis midae is van groot kommersiёle waarde tot die Suid-Afrikaanse perlemoenindustrie en word meestal uitgevoer na markte in Asiё, spesifiek China. Tot 50% van die perlemoen wat in Suid-Afrika geproduseer en uitgevoer word, word verblik en huidiglik is die verblikkingsopbrengspersentasie ongeveer 35%. Haliotis midae is tans geneties onderontwikkeld en die gebruik van teelprogramme word nou geimplementeer met die doel om 'n verskeidenheid eienskappe te verbeter, waarvan groei en opbrengs van primêre belang is. Die doelwit van die studie was om genetiese parameters soos oorerflikheid en ook die genotipiese en fenotipiese korrelasies van obrengsverwante eienskappe te bepaal om sodoende die potensiёle genetiese verbetering as gevolg van selektiewe teeling te assesseer. 'n Reeks obrengsverwante eienskappe is geidentifiseer wat relevant is binne bestaande en standaard kommersiёle perlemoenverblikkingsprotokolle. Lae tot matige oorerflikheidswaardes is waargeneem en sluit in lewende, of voor-ontskulpingsgewig (0.20 ± 0.06), na-ontskulpingsgewig (0.15 ± 0.05), na-oopvlekkingsgewig (0.15 ± 0.05), na-pekelgewig (0.19 ± 0.06), voor-verblikkingsgewig (0.19 ± 0.06), na-verblikkingsgewig (0.21 ± 0.06), skulpgewig (0.16 ± 0.05), verblikkingsopbrengspersentasie (0.08 ± 0.03) en 'n skulpgewig tot na-oopvlekkingsgewig verhouding (SW: PGW) (0.09 ± 0.04). Gewigsverwante parameters is fenotipies hoogs gekorreleerd met mekaar (0.86 ≤ r ≤ 0.99) maar toon 'n negatiewe korrelasie met die verblikkingsopbrengspersentasie (-0.38 ≤ r ≤ 0.04). Die netto opbrengs van perlemoen dui op 'n relatiewe sterk positiewe korrelasie met lewende gewig (r = 0.66). Skulplengte is hoogs oorerflik (h2 ≈ 0.48) en toon 'n sterk positiewe korrelasie met lewende gewig (r = 0.94). Skulpgewig is ook hoogs gekorreleerd met lewende gewig (r = 0.80) en die SW: PGW verhouding toon geen beduidende korrelasie met lewende gewig nie (r = 0.03). Gewigsverwante eienskappe toon oorerflikheidswaardes wat varieer tussen 0.15 en 0.20 en kan 'n moontlike genetiese respons lewer. Skulplengte (as 'n liniêre groeiparameter) toon 'n hoё oorerflikheid (h2 ≈ 0.48) en 'n sterk positiewe korrelasie met lewende gewig (r = 0.94) wat dit gepas maak vir gebruik as 'n seleksiekriterium in 'n teelprogram met verbeterde groeitempo as doel. Direkte seleksie in terme van verblikkingsopbrengs word ingeboet danksy die destruktiewe natuur van die metingsmetodiek asook 'n lae oorerflikheid (h2 < 0.10). Die negatiewe korrelasies tussen verblikkingsopbrengs (uitgedruk as 'n persentasie) en groeieienskappe (-0.38 ≤ r ≤ 0.04) dien as 'n verdere komplikasie in die gebruik van dié eienskap as direkte teeldoelwit. Alhoewel die verblikkingopbrengs 'n afname toon soos lewende gewig toeneem, is daar steeds 'n positiewe korrelasie tussen die netto verblikkingsopbrengs en die lewende gewig (r = 0.66). Dit word dus aangeraai om skulplengte as seleksiekriterium vir verbeterde groeitempo en netto opbrengs te gebruik om sodoende wins te maksimaliseer.

Thesis (MSc)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: Cultured abalone in South Africa is undomesticated. For the local industry to remain competitive on the international markets it is essential to improve production. This study is part of a selective breeding component of a larger genetic programme that aims to enhance productivity of the local industry by genetic improvement of growth rates. Selective breeding programmes are based on genetic variation and correlations. Molecular studies proved genetic differentiation exist between the broodstock- and offspring populations and among the offspring populations used in this study. Five commercial abalone farms from the Walker bay region each entered 3000 randomly selected animals obtained from synchronised mass spawning of conditioned broodstock into a Performance Recording Scheme (PRS). Microsatellite marker analysis proved these broodstock populations to be representative of the wild populations. The five cohorts were assessed over the five locations represented by three replicates per location with 200 randomly assigned animals per replicate. The average growth rate was used as growth performance parameter by measuring shell length and body weight at three month intervals over a period of 24 months. Interaction was observed between cohort and location effects when analysing the full data set. This was unexpected as the cohorts were constructed from parent stick that was randomly sampled from the same geographical area, the larger Walker bay. The factors suspected of causing this observed interaction were considered in a stepwise analysis. Initial and progressive tag loss, differences in initial size of animals entered into the study and on-farm management errors were considered as possible causes of the observed interaction in a stepwise analysis. Statistically significant differences were observed between the five cohorts and between the five locations in terms of length and weight growth rates. Based on these findings it is advised that a central facility is used to effectively compare the growth rates of different cohorts or populations. Any future research in selective breeding to follow this study should involve the integration of molecular techniques and biotechnologies. / AFRIKAANSE OPSOMMING: In Suid-Afrika is gekweekte perlemoen wild. Vir die plaaslike bedryf om op die internasionale markte kompeterend te bly, is dit noodsaaklik om produksie te verbeter. Hierdie studie vorm deel van ’n selektiewe telingskomponent van ‘n groter genetiese program met die doel om die produktiwiteit van die plaaslike bedryf deur die genetiese verbetering van groeitempo’s te verbeter. Selektiewe teelprogramme word gebaseer op genetiese variasie en korrelasies. Molekulêre studies het bewys dat daar genetiese differensiasie bestaan tussen die teel- en nageslagpopulasies en onder die nageslagpopulasies wat in hierdie studie gebruik is. Vyf kommersiële perlemoenplase in die Walkerbaaistreek het elk 3000 ewekansig geselekteerde diere vanaf gesinkroniseerde massa broei van gekondisioneerde teelpopulasies aan ‘n Performance Recording Scheme (PRS) bygedra. Mikrosatelliet merker-analise het bewys dat hierdie teelpopulasies verteenwoordigend is van die wilde populasies. Die vyf kohorte is oor die vyf liggings geassesseer, elkeen waarvan verteenwoordig is deur drie replikate bestaande uit 200 ewekansig toegedeelde diere per replikaat. Die gemiddelde groeitempo is gebruik as die groeiprestasieparameter deur skulplengte en liggaamsgewig elke drie maande oor ‘n tydperk van 24 maande te meet. Daar is interaksie waargeneem tussen kohort- en liggingseffekte toe die volledige datastel geanaliseer is. Hierdie was onverwags, aangesien die kohorte gekonstrueer is uit teelouers waarvan monsters ewekansig vanuit dieselfde geografiese gebied, naamlik die groter Walkerbaai, geneem is. Die faktore wat vermoedelik hierdie waargenome interaksie veroorsaak het, is in ‘n stapsgewyse analise beskou. Aanvanklike en progressiewe merkerverlies, verskille in die aanvanklike grootte van die diere wat in die studie ingesluit is en bestuursfoute op die plaas is as moontlike oorsake van die waargenome interaksie voorgestel. Statisties betekenisvolle verskille is tussen die vyf genotipes en tussen die vyf liggings in terme van lengte en gewigsgroeitempo’s waargeneem. Op grond van hierdie bevindings word daar voorgestel dat ‘n sentrale fasiliteit gebruik word om die groeitempo’s van die verskillende genotipes of populasies doeltreffend te vergelyk. Enige toekomstige navorsing oor selektiewe teelt wat op hierdie studie sou volg, moet die integrasie van molekulêre tegnieke en biotegnologieë behels.

Since the discovery of a new species of sabellid worm in 1993, the Californian and South African abalone industries have experienced increasing shell breakage and reduced growth rates of abalone, resulting in reduced market value of product. This polychaete worm can reach very high infestation levels. It was described as Terebrasabella heterouncinata in 1999, having originated from the South African coastline where it had been observed on several wild mollusc species. Although not a shell borer, it occupies tubes on the growing edge which are formed by deposition of nacreous shell over sabellid larvae by the host abalone. Heavy sabellid infestation levels have placed the economic viability of several South African farms under threat. Past research methods have not been successful in establishing effective means of eradication or control, partly due to the lack of knowledge of basic biological information on this species. This study forms the first part of an ongoing research project into the biology of terebrasabella heterouncinata. Abalone farms in South African utilise two main diets in abalone culture. An artificial formulated feed, Abfeed, is produced in South Africa and is used by the majority of farms as it increases abalone growth rate. Kelp, a natural diet of abalone, is harvested and also used as a feed. Farmers have observed higher sabellid infestation levels on Abfeed-fed abalone and suspect that diet may be an important factor influencing sabellid infestation. Abalone stocking density has also been identified as a potential factor influencing sabellid population growth on commercial farms. In order to better understand sabellid nutrition, the feeding behaviour of the sabellid in response to suspended solids of various particle size classes from both abalone diets were investigated. Both the effect of abalone diet and stocking density and their effects on sabellid morphometrics were quantified. The proximate composition and particle size distribution of suspended-solids present within kelp and Abfeed abalone raceways were also quantified. Results indicate that sabellid feeding follows no structured behavioural pattern for both abalone diets. The quantity of suspended solids in kelp raceways was greater than in Abfeed raceways (p<0.02) while there was no difference in particulate level between three abalone stocking densities (p>0.05). Protein (p<0.0001) and energy (p<0.0.1) levels of suspended solids were significantly greater in raceways dedicated to feeding Abfeed. The infestation level (number of tubes/centimetre on the grwoing edge) was significantly higher (p<0.001) in Abfeed-fed abalone. The morphometrics of the sabellids indicated that sabellids from Abfeed-fed abalone were larger in various body measurements: length (p<0.00001); neck width (p<0.001); base width (p<0.001); and surface area (p<0.001). This study suggests that abalone diet has an important influence on the infestation level and size of sabellids and that this is likely to be due to the fragmentation and leaching of nutrients from the artificially enriched commercial abalone diet.

The largest abalone in South Africa, the perlemoen, Haliotis midae, occurs along approximately two-thirds of the country's coastline, but has only been the target of an extensive commercial fishery in the south-western part of South Africa. Large-scale illegal fishing has however proliferated throughout its entire range over the last 10–15 years, which has had serious effects on stock abundance and once productive populations are facing economic collapse. Abalone stock enhancement has been put forward as an addition or alternative to traditional fisheries management practices, which can potentially rehabilitate overfished abalone populations and enhance natural production. The aim of this project was to investigate the potential of abalone stock enhancement for managing an area in the Eastern Cape Province, which was being subjected to intense illegal fishing pressure. A research approach was adopted to investigate the scale and effects of this poaching and to investigate the survival of artificially cultured abalone seed in the natural environment. A model of a commercial-scale ranching operation was investigated to assess the economic feasibility of such a scheme. Analysis of poaching cases and research samples from Cape Recife indicated high levels of fishing effort that appeared to be causing the observed declines in emergent abalone abundance and average size. Poaching cases from Cape Recife contributed 32% of the total number of cases of known origin in the Eastern Cape Province from 1998–2002, with the majority of the cases (82%) originating from within the Port Elizabeth metropole. There was an exponential increase in the number of poaching cases in the Eastern Cape Province (r²=0.967) and Port Elizabeth over this period but actual annual total catch stabilized, particularly at Cape Recife, where estimates of CPUE declined significantly from 2000–2002 (p<0.001). The annual proportion of emergent abalone under the MLS from Cape Recife was always >85% in confiscations and research collections, and did not change significantly over the period of examination. Comparison of illegal catches with an adjacent site indicated that the emergent abalone population at Cape Recife had a significantly higher proportion of undersized emergent animals (p<0.001) and they were significantly smaller than the abalone from the closest site, Noordhoek, and other areas in Port Elizabeth from 2000–2002 (p<0.001). The apparent declines in emergent abalone abundance indicated by the poaching data were corroborated by sampling of emergent abalone abundance at Cape Recife. Numbers of abalone declined significantly from 125.6 to 53.8 per 20min count (p<0.001), from April 1998–October 2001 and density declined from 1.3 to 0.8m⁻² over a similar period (p<0.001). Juvenile density did not change over this period, although there were significant differences in density observed between two different habitats (p<0.001). Initial releases of cultured juvenile abalone showed that they could be distinguished from their wild counterparts for at least a year after release, by their different shell colouration. Short-term, small-scale trials (7–10 days) using animals between 17 and 30mm SL had mean survival rates of 64–82% (mean 70.4%) and the effect of size on survival was not significant in most cases, although the power to detect differences was low. Attempts to measure the effect of habitat on survival were not conclusive, although refuges under sea urchins appeared to be favoured by both seed and wild abalone, although urchins were not an absolute requirement for survival. Similar medium-term trials (31–74 days) in sheltered sites yielded mean returns of 53.1% using 25mm SL animals and similar trials in a more exposed area had more variable survival rates of between 18.4 and 73.6%, after 25–27 days. A comparison between careful hand-seeding and surface-scattering seed release methods in the open-ocean habitat showed no significant differences in survival rate after 41 days. Larger seed survived significantly better than the smaller seed when scattered on the surface (p<0.0001) and the smaller seed survived significantly better when seeded carefully by hand onto the substrate (p<0.028). Further medium-term releases of large numbers of seed abalone, released using the surface-scattering method in open-ocean habitat, gave mean survival rates of 32.8% over periods of 83–114 days. Assessment of a seeding trial using release modules to seed juvenile animals in the open-ocean was hampered by poor sea conditions and difficult to search substrates, and a mean recovery rate of 3.1% was obtained for the sites that were sampled. Movement of seed was low in the more sheltered sites, and also appeared to be affected by the amount of available habitat. Growth of seed was measured using changes in shell colouration and there were significant differences between areas. An average growth of 1.6mm.month⁻¹ shell length was calculated for all areas. The potential for commercial scale abalone ranching to be used to enhance a territorial user right fishery was investigated using a model of economic feasibility. Internal rates of return of 30.3 and 36.9% were obtained from two harvest regimes using different harvest sizes. There was a high degree of risk associated with these figures owing to a lack of consistent seed survival rate estimates, and the input parameters, which are subject to variation, showed a significant effect on profitability. The operation of this type of ranching scheme is probably not economically feasible as a stand-alone operation but could probably be operated effectively in conjunction with an existing abalone farm. By adding a small wild catch component the profitability of a ranching scheme could be significantly improved. The results of the present study indicate that high levels of poaching at Cape Recife have led to declines in emergent abalone abundance, which will probably lead to stock collapse in the near future. This implies that fisheries managers have failed to fulfil the provisions of fisheries policy in South Africa. The present results from seeding trials show that cultured juveniles can survive and make a contribution to overall stock abundance. Furthermore, while there are obstacles to economic feasibility, commercial ranching has the potential to be a valuable addition to current abalone management strategy.

Terebrasabella heterouncinata is a small K-selected sabellid polychaete. It is a simultaneous hermaphrodite with a semi-continuous mode of reproduction, producing relatively few large eggs that are brooded within the parental burrow until the larvae emerge, to settle on the growing edge of the abalone shell. Despite its low fecundity, this worm has become problematic on abalone farms in South Africa. The present study was conducted to gain an understanding of the life history patterns of T. helerouncinata to determine how they contributed to the success of these worms under altered conditions. This study demonstrated that conditions prevalent on abalone farms were conducive to enhancing the reproductive success of this worm, and suggests that larger, more fecund worms may have been selected for in the decade that these worms have been present on the farms. Increased nutrient availability, and possibly the increased stability of the farm environment relative to its natural environment, has led to a 1.5-fold increase in the average size of the worms. Body size was found to be positively correlated with brood size, and this resulted in worms on farms brooding 3 to 4.5 times more offspring at a time than worms from wild abalone. The ability to increase the number of eggs produced at a time may have been limited by the fact that these worms have only two ovaries. Thus, the increase in fecundity may have been related primarily to the increase in the rate at which the eggs were laid by the worms on the farms, and the increase in the coelomic space available for the storage of these rapidly developing eggs. The ability to increase the rate at which oocytes develop may be related to the vitellogenic mechanisms employed by these worms. Vitellogenic oocytes are able to incorporate high molecular weight yolk precursors from the surrounding coelomic fluid through endocytotic activity. This may allow the oocytes to increase the rate at which they incorporate yolk material under conditions of nutrient enrichment. The increase in fecundity did not occur at the expense of offspring size and, presumably, quality. The increased reproductive output on the farms was compounded by a proportionate increase in the number of reproducing worms within the population. In addition, these worms are long-lived (worms from farmed abalone reached a maximum age of approximately 40 months) and exhibit negligible senescence. Thus, their reproductive output did not change significantly with an increase in age. Furthermore, the proportion of the reproductive worms did not decrease with an increase in age. Thus, within the age range tested, worms of all ages have the potential to make equal contributions to population growth. While diet and abalone stocking density could not be identified as having a significant effect on reproductive output and infestation rate under intensive culture conditions, it was demonstrated that in a naïve abalone population, the total intensity of infestation increased exponentially with time. This increase may be a consequence of an increase in fertilisation success. These worms continuously produce entaquasperm that are released into the water column. The sperm are collected by other individuals that then store the sperm in a single spermatheca. The ability to store sperm relieves individuals of a dependence on the synchronisation of spawning of eggs and sperm. As the population size and density increases, there could be more individuals releasing sperm into the water column, resulting in a continuous supply of sperm. The increased production of eggs would therefore not be constrained by a lack of sperm. The stored sperm are released into the brood chamber to fertilise eggs as they are laid, and this would probably increase the fertilisation success in the species. This study also provides evidence to suggest that reproduction in this worm has a seasonal component. Future studies should concentrate on measuring fertilisation success in greater detail, measuring the effect of season on reproduction, determining whether there are genetic differences between worms on farmed and wild abalone and determining whether wild worms have similar life-spans and age-related fecundity as worms on farms.

Thesis (MPhil (Animal Sciences. Aquaculture))--University of Stellenbosch, 2006. / T. heterouncinata is a sabellid polychaete endemic to South Africa and found primarily in the shells of the abalone Haliotis midae. With the intensification of abalone aquaculture around the world, T. heterouncinata has become a problematic pest by causing shell deformities, reducing abalone growth rates and, in some instances, high abalone mortalities. The problem of this sabellid was first noticed in Californian in the early 1980’s in Red abalone (Haliotis rufescens) production facilities. Many mitigation methods have been tested over the years and this paper investigates another two methods; a reduction in particulate load in the tank to reduce the food source of the sabellid which perhaps will reduce fecundity, and to use ultrasound as a possible mitigation method. This study found that filtration and reduction in suspended particles did not have a significant effect, but that ultrasound did have a significant effect in reducing T. heterouncinata populations.

Investigations were carried out on aspects of the biology of the vetigastropod Turbo sarmaticus. Studies included: 1) the distribution and standing stock of this animal at four sites along the coast of the Eastern Cape Province of South Africa; 2) the growth rate of animals on a wave-cut platform; 3) the reproductive cycle of an intertidal population; and 4) aspects of the feeding biology examining the ability of this mollusc to consume and digest six macroalgae, the influence of algal diet on growth rate and reproductive fitness and the polysaccharolytic activity of the digestive enzymes. On eastern Cape shores, T. sarmaticus had a size related distribution, with smaller animals being found towards the upper mid-shore and larger animals being found in a downshore direction. The mean shore densities of T. sarmaticus at three sites where exploitation of animals was minimal, were very similar (1.2 - 1.7 individuals/m²). The largest animals (up to 110 mm shell length) were found on an offshore island. This may have been a result of animals not being exploited, as well as a possible increase in primary productivity and food availability. The lowest density (0.2 individuals/m²) and animal size (<70 mm shell length) was recorded at a site (Kelly's beach - Port Alfred) where exploitation was more intense. It is probable that intense overexploitation was threatening the populations at this site. The growth rate of T. sarmaticus was determined by means of the von Bertalanffy growth model and expressed by the equation L[subscript]t = 81.07(l-e⁻°·⁵⁴⁴[superscript](t)). The initial growth rate of T. sarmaticus (up to ≈ 80 mm shell length) was similar on shores with different geomorphologies (i.e. boulder shores and wave-cut platforms). Growth rates of individuals were variable, which means that individuals within a population reached exploitable size (3 - 6 years old) and sexual maturity (1.5 - 2 years old) at different ages. Seasonality of reproduction of T. sarmaticus was determined using gonad index, egg diameters and spermatozoa content within the gonad. Turbo sarmaticus was dioecious and had a sex ratio in favour of males (1.2: 1). Animals attained sexual maturity at a size of about 52.5 mm shell length. There was little variation in the reproductive cycle over time with gametogenesis occurring from March/April until August/September, whilst maturity (Gonad Index = 15%) was maintained until the spawning event from December to March. After spawning the gonad regressed. Field and laboratory observations of the feeding biology of T. sarmaticus confirmed that this mollusc was a generalist grazer capable of consuming and digesting algae from the Rhodophyta, Chlorophyta and Phaeophyta. The consumption rates (juveniles: 1.45 - 9.50% body weight/day, adults: 1.06 - 6.08%) and digestibility (9 - 75% apparent dry matter) of six macroalgae was found to vary. For most algae, juvenile T. sarmaticus had higher consumption rates (1.6 - 2.8 times higher) and digestibility values (12 - 24% higher) than adults. It is suggested that consumption rates were dependent on the digestibility of the algae. In addition, it is suggested that the consumption rates of the different algae were not related to the nutritional content, but rather the energetic content of the algae. In both juvenile and adult animals, temperature had a positive influence on consumption rates, resulting in an increase at higher temperatures. However, in both juvenile and adult T. sarmaticus, algal digestibility was not affected by temperature. Finally, it was proposed that Viva rigida, Codium extricatum, Ecklonia radiata and Gelidium pristoides would provide the best nutritional value for growth and reproductive fitness in T. sarmaticus, whilst Jyengaria stellata and Corallina spp. would provide the poorest. Experiments on the effects of four algal diets on the biology of T. sarmaticus showed that the best growth rate (up to 13.8 mm shell length increase per annum), reproductive fitness (Gonad Index up to 33%) and energy levels (up to 4.76% glycogen in the foot) were achieved when T. sarmaticus was fed G. pristoides, U. rigid a or a mixed diet. Turbo sarmaticus fed Corallina spp. showed reduced growth (2.4 mm shell length increase), reproductive fitness (Gonad Index up to 4.4%) and energy levels (up to 3.42% glycogen in the foot). A study of the polysaccharolytic enzyme activity of T. sarmaticus indicated that this mollusc possesses enzymes that can, at least partially, digest most of the storage and structural polysaccharides found in the Chlorophyta, Rhodophyta and Phaeophyta. This further supported the findings that T. sarmaticus was a generalist grazer. Two levels of activity were detected: 1) high levels of enzyme activity (up to 328.2 Ilglmglmllhr)occurred on the storage polysaccharides that occur in the Rhodophyta and Chlorophyta, and 2) lower levels of activity were detected on the storage polysaccharides (up to 44.8 μg/mg/ml/hr) of the Phaeophyta and on all the structural polysaccharides tested (<45.5 μg/mg/ml/hr). It was suggested that T. sarmaticus did not rely heavily on structural carbohydrates as a source of carbon. Finally, the results of this study were discussed in relation to the future management of T. sarmaticus stocks, the possible role of this macro algal grazer in the intertidal zone and the effects of over-exploitation of this animal. The potential aquaculture of this mollusc was also addressed briefly.

The profitability of abalone farms is heavily influenced by their production per unit of grow-out space. With farms having physically expanded to the maximum, and with increasing production costs, one of the most realistic ways for farms to increase their production is through optimizing stocking densities. The effect of stocking density on Haliotis midae performance is undocumented and optimal stocking densities for this species have not been determined. Experiments were conducted under farm conditions to investigate the effects of four different stocking densities (16 %, 20 %, 22 % and 24 % of available surface area) on growth, production and health of three different size classes of abalone (15-35 g, 45-65 g, and 70-90 g start weight). Each treatment was replicated four times and trials ran over a period of eight months with measurements being made at four month intervals. Abalone behaviour was observed during the trials in the experimental tanks. Weight gain per abalone decreased with an increase in density for all tested size classes (5.04 ± 0.18 to 2.38 ± 0.17; 5.35 ± 0.21 to 4.62 ± 0.29; 7.97 ± 0.37 to 6.53 ± 0.28 g.abalone-1.month-1 for the 15-35, 45-65 and 70-90 g classes respectively, with an increased density of 16 to 24 %). Individual weight gain of 15-35 g abalone was similar at stocking densities of 16 % and 20 % while weight gain of 45-65 g and 70-90 g abalone decreased when density was increased above 16 %. Biomass gain (kg.basket-1.month-1) was not affected by stocking density in the 15-35 g and 45-65 g size classes (1.29 ± 0.02 and 0.97 ± 0.02 kg.basket-1.month-1 respectively). However, the biomass gained by baskets stocked with 70-90 g abalone increased with stocking density (1.08 ± 0.02 to 1.33 ± 0.02 kg.basket-1.month-1) with an increased density of 16 to 24 %) and did not appear to plateau within the tested density range (16 to 24 %). Food conversion ratio did not differ significantly between densities across all size classes. Stocking density did not have a significant effect on abalone condition factor or health indices. The proportion of abalone above the level of the feeder plate increased with density (7.26 ± 1.33 to 16.44 ± 1.33 with an increased density of 16 to 24 %). As a proportion of abalone situated in the area of the basket, the same proportions were situated on the walls above the feeder plate and on the feeder plate itself irrespective of stocking density (p > 0.05). Higher proportions of animals had restricted access to feed at higher stocking densities (p = 0.03). The amount of formulated feed available on the feeder plate did not differ between stocking densities throughout the night (p = 0.19). Individual abalone spent more time above the feeder plate at higher stocking densities (p < 0.05). The percentage of time above the feeder plate, spent on the walls of the basket and on the feeding surface was not significantly different at densities of 20 %, 22 % and 24 % (p > 0.05) but abalone stocked at 16 % spent a greater percentage of time above the feeder plate on the feeding surface (83.99 ± 6.26 %) than on the basket walls (16.01 ± 6.26 %). Stocking density did not affect the positioning of abalone within a basket during the day or at night. Different size H. midae are affected differently by increases in stocking density in terms of growth performance. Findings from this research may be implemented into farm management strategies to best suit production goals, whether in terms of biomass production or individual weight gain. The fundamental mechanisms resulting in reduced growth at higher densities are not well understood, however results from behaviour observations suggest that competition for preferred attachment space and feed availability are contributing to decreased growth rates. With knowledge of abalone behaviour at different densities, innovative tank designs may be established in order to counter the reduction in growth at higher densities.

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).