The available literature on abalone nutrition was synthesised and the prospects for developing a complete pelleted dry feed for Haliotis midae evaluated. The similar body compositions, digestive structures, enzyme activity, acceptance of a wide variety of feed ingredients and comparable growth performance on formulated diets of various abalone species suggests that they have similar nutritional requirements. Abalone also appear to be similar to other farmed monogastric animals in that digestion is primarily extracelluar and they possess a large, muscular crop and stomach. Abalone energy metabolism is carbohydrate based. They are capable of digesting high levels of dietary protein but their ability to utilise fat is limited. Abalone have been shown to consume predictable amounts of dry feed which is efficiently converted into body weight. Efficiency indices of utilisation of formulated feeds, such as feed conversion ratio, protein efficiency ratio, net protein utilisation and apparent digestibility have been successfully applied to abalone. It was concluded that the prospects for developing complete diets for H. midae using a conventional animal feed science model were good. The ability of H. midae to utilise a range of proteins which had potential for inclusion in practical diets was investigated. Five protein rich ingredients, namely, casein, fishmeal, soya oil cake, Spirulina, and torula yeast, were fed to H. midae in semi-purified diets. Two algal diets, fresh Plocamium corallorhiza and dried Ecklonia maxima were fed as controls. Abalone fed on fishmeal and Spirulina based diets displayed significantly higher growth rates than diets containing soya oil cake, torula yeast, casein and E. maxima. Growth rates of abalone fed with P. corallorhiza were significantly lower than all other diets. All artificial diets yield lower feed conversion ratios (0.7-1.8) and higher protein efficiency ratios (3.3-6.5) ratios than the seaweed control diets (FCR = 2.8-3.4; PER = 2.2-3.0). The results indicated that fishmeal and Spirulina were the most suitable proteins for inclusion in practical diets for H. midae. The effect of protein level on growth rate and nutritional indices was evaluated by feeding starch bound, fishmeal based diets containing 27, 32, 37, 42 and 47% protein to juvenile H. midae. Weight gain was positively related to the level of dietary protein, increasing by 18% between 27% and 47% protein. Protein efficiency ratio declining from 3.2 to 2.3 with an increasing dietary protein content. Feed consumption rate was approximately 1% of body weight per day for all diets. Post-weaning abalone (ca. lOmm shell length, 0.2g) differed from larger juveniles (ca. 35mm, 8g) in their response to varying proportions of dietary protein and energy. The smaller animals appeared to have a lower protein requirement and poorer ability to utilise lipid than the larger juveniles. Proximate analyses revealed that the levels of protein, lipid and carbohydrate in abalone soft tissue increased with increasing dietary levels of these nutrients. Larger juveniles contained significantly higher levels of protein and carbohydrate, but lower levels of lipid, ash and moisture, than the smaller post-weaning abalone. The assimilation efficiency of [U-¹⁴C]-arginine by H. midae fed diets enriched with [U-¹⁴C]-arginine was only 0.45%. Furthennore, supplementation of diets with graded levels of crystalline arginine did not have any effect on growth rates. It was concluded that the prospects for defining the quantitative amino acid requirements of H. midae using crystalline amino acids are not promising. Rates of gastric evacuation and enzyme secretion were monitored in juvenile H. midae fed an extruded, fishmeal based dry feed. Gut fullness peaked 6h after feed was offered and the bulk of feed consumed was digested within 24 h. Enzyme secretion appeared to begin with the onset of feeding and continued for at least 6h after peak gut fullness was attained. Protease activity increased significantly following ingestion but amylase activity was maintained at a more or less constant level. A low level of lipase activity was observed suggesting that the ability of H. midae to digest fat is limited. The growth rate of H. midae fed an extruded, fishmeal based feed increased with increasing temperature between 12°C and 20°C. Between 20°C and 24°C a marked decline in growth rate accompanied by a deterioration in feed conversion and increased mortality was observed. Consumption of a dry pelleted feed was shown to be a function of body size and temperature. Based on these data a model which predicts a daily ration for H. midae was developed. The present study showed that H. midae efficiently utilises extruded dry feeds containing conventional feed ingredients. Although technical difficulties were encountered in measuring apparent digestibility, it was concluded that the prospects for developing practical diets according to established nutritional principles are promising.

The evaluation of potential alternative protein sources for the formulation of least-cost optimal diets to satisfy the nutrient requirements of South African abalone (Haliotis midae) has been hampered by the absence of a suitable, practical, replicable and reliable digestibility technique. A suitable lowcost faeces collection technique was developed in this study to obtain suitable quantities of excreta for analysis from this species. Acid-insoluble ash was identified as a reliable, replicable and safe internal marker in comparison to chromic oxide and crude fibre for use in nutrient digestibility studies with H. midae. This was validated by the consistency and repeatability of the results and by comparison to total collection of faeces. The traditional substitution method used in digestibility studies with fish to evaluate protein digestibility of feed ingredients was found to be unsuitable for H. midae. Apparent protein digestibility values exceeding 100 % derived through this method could be attributed to associative effects between feed ingredients, differential diet and faecal nutrient leaching, and mathematical artifacts in calculations when using substitution versus single protein diets. An ingredient particle size of less than 450 μm in comparison to particle size classes of above 450 μm was shown to enhance nutrient (dry matter, organic matter, protein, fat) digestibility and minimise dry matter leaching from diets. The dietary inclusion level of both pre-gelatinised maize starch and a-cellulose did not influence (P > 0.05) apparent nutrient (protein, fat, fiber, starch) digestibility. Using the above digestibility protocol amino acid availability of all plants ingredients currently used in the South African animal industry was evaluated for H. midae. Soybean meal (96.86 %) and lupins (96.51 %) presented the highest apparent mean amino acid availability of all plant protein ingredients evaluated with H. midae. Canola meal (94.21 %), faba beans (92.87 %) sunflower meal (92.77 %), peanut meal (87.39 %) and cottonseed meal (85.15 %) presented higher apparent mean amino acid availability values than fish meal (82.75 %). Apparent protein digestibility was highly correlated (r = 0.99) with mean apparent amino acid availability, while true amino acid availability was 1.88 % units higher than apparent amino acid availability for all ingredients tested. Predicted apparent protein digestibility in compound diets was within 1.1-6.5 % of determined values. Calcium phosphate mono dibasic presented the lowest (P < 0.05) dietary phosphorus leaching (51.51 % maximum) and highest apparent phosphorus digestibility (66.27 %) in comparison to other inorganic phosphorus sources. Based on the method of direct experimentation to determine the optimal dietary protein level using graded levels of dietary protein 28.1-35.9 % dietary protein from good quality sources is recommended for maximum growth of juvenile H. midae. This study provides a scientifically sound research tool including a faecal collection technique, suitable marker and assay technique that could be use in further studies to improve least-cost diet formulation for H. midae. Future nutritional studies in H. midae should primarily concentrate on reducing dietary nutrient leaching and improving the intake of nutrients in order to properly evaluate responses of this species to different dietary regimes.

The potential to reduce feed formulation costs by the replacement of existing proteinsources in artificial feeds for Haliotis midae was assessed. A comparison between the efficacy of the direct method and chromic oxide marker techniques in determining apparent protein digestibility coefficients, revealed that while the former was not a suitable methodology for use with this species, the latter produced replicable and reliable results. It was established that the chromic oxide marker is inert, is not absorbed by the abalone, does not interfere with the digestive processes and moves through the intestine at the same rate to the protein. However, as this method was time consuming and expensive to implement, a multienzyme pH-stat in vitro protein digestibility technique using a three enzyme system was employed to rapidly assess the protein quality of 34 protein sources. The efficacy of the technique was established by correlating the in vitro digestibility estimates with in vivo digestibility coefficients obtained using the chromic oxide marker technique. The highest degree of in vivo predictability was attained when protein sources were separated according to origin, and significant correlations between either animal (r²=0.89, P<0.004) or plant (r²=0.79, P<0.04) protein sources were found. The effect of animal size on the qualitative protein requirements of two size classes of H.midae was assessed by feeding 12 isonitrogenous and isoenergetic single protein diets to juvenile and young adult animals (10-20 and 40-50mm shell length). The criteria for protein source selection were their bioavailability as determined using the pH-stat in vitro digestibility technique, and their cost and availability within South Africa. The protein sources identified for the trial comprised four fishmeals, casein, spirulina, abalone viscera silage, brewery waste, torula yeast, carcass, sunflower and cotton meals. The results indicated that in terms of growth and feed efficiency, the fishmeals and spirulina were the most suitable candidates as primary protein sources in formulated feeds for H.midae, and with the exceptions of the carcass meal and brewery waste, the remaining protein sources demonstrated promise as partial primary protein source replacements. The smaller size class of abalone displayed significantly reduced growth, feed and protein efficiency than their larger counterparts. In terms of feed conversion and growth response, two-way analysis of variance revealed significant interactions between protein source and animal size, suggesting that qualitative differences exist between the dietary protein requirements of the juvenile and young adult abalone. The commercial implication of thisfinding was discussed. An evaluation was undertaken to determine the effects of the partial and total replacement of dietary fishmeal with selected plant protein sources on growth and nutritional indices of juvenile H.midae. A commercial “Abfeed” formulation in which 100% of the protein component comprised LT-fishmeal was employed as a control. Fifteen isonitrogenous experimental diets were formulated in which the LT fishmeal was substituted at either 10, 15, 30, 50, 75 or 100% with either spirulina, semolina, ground maize, torula yeast, soya, sunflower or corn gluten meals or combinations thereof. No significant differences were found in the growth rates between the control diet and those diets in which 30% of the fishmeal component had been replaced by either soya, sunflower meal, or torula yeast. In addition, 50% of the fishmeal component could be substituted with either soya meal or spirulina without affecting growth. Replacement of either 75 or 100% of the fishmeal had a significant negative affect on growth. Pearson product moment correlations between dietary lysine levels and either growth rates or protein efficiency ratios revealed positive correlations (r=0.77, P=0.0005; r=0.52, P=0.04 respectively) suggesting that lysine may have been the first limiting amino acid in these diets. Carcass analysis revealed that dietary protein source had no significant effect on body composition. An assessment of the dietary arginine requirement of juvenile H.midae using whole proteins to supply graded levels of dietary arginine did not promote a growth response. It was concluded that arginine is probably not the first limiting amino acid in formulated feeds for H.midae. An assessment of the dietary lysine requirement of juvenile H.midae using two micro-encapsulation techniques (gelatin/acacia colloid or cellulose acetate phthalate) was not successful. The efficacy of the encapsulation techniques were established and an assessment of the degree of lysine supplementation undertaken. Failure of the crystalline lysine enriched diets to promote growth suggests that the prospects for using crystalline amino acids in essential amino acid requirement studies in H.midae is low. The results of the present study indicate that the prospects for replacing fishmeal with cheaper alternative protein sources in artificial feeds for H.midae is promising. Furthermore, while the technical difficulties such as the determination of the essential amino acid requirements of the abalone precluded the application of “least cost” programming, the prospects for its future application are promising.

In the late 1980's abalone culturalists noticed reduced growth rate and shell deformities in some abalone stocks. These problems were the result of infestations by a shell boring polychaete, Terebrasabella heterouncinata. Under intensive abalone culture conditions the level of infestation can reach epidemic proportions and there are often severe consequences for the host abalone. Heavy sabellid infestation levels have placed the economic viability of several South African farms under threat. This study formed part of an ongoing project that is aimed at investigating the basic biology of Terebrasabella heterouncinata. The majority of abalone farmers in South Africa feed their abalone either naturally occurring kelp (Ecklonia maxima) or the formulated abalone feed, Abfeed. Farmers have suggested that the use of Abfeed is associated with higher sabellid infestation levels and changing the abalone diet from Abfeed to kelp helps reduce sabellid infestation. Speculation has arisen indicating that older, slower growing abalone are more susceptible to sabellid infestation. The effect of host abalone diet history and their growth on sabellid settlement success, morphometries and reproduction was quantified. To better understand the plasticity of the expression of life history traits the variability of morphometric and reproductive characteristics was compared between different farm environments. And more...

Haliotis midae is the cornerstone of the South African abalone fishery. For more than a decade, the wild abalone stock of South Africa has suffered decline due to over-exploitation and illegal activities such as poaching. Prior to 1970, no regulations were in place concerning the annual landings. As a result the fishery was exploited as if it were an infinite resource. It is this initial uncontrolled harvesting (regardless of age) and poaching that has driven the abalone resource decline. Due to the slow growth rate exhibited by abalone as a species, natural replenishment of wild stock following exploitation and poaching was far below the rate of exploitation of this resource. Studies on the growth of abalone have mainly been conducted under laboratory conditions. The purpose of this study was to measure the growth of abalone, fed different diets, under commercial culture conditions. Three food types were used namely; commercial pellets, seaweed (Ulva spp.) and dried kelp bars (Ecklonia maxima). Four diets were obtained from the three food types namely; combination of commercial pellets and seaweed (Diet A), commercial pellets only (Diet B), seaweed only (Diet C) and dried kelp bars only (Diet D). The food types used in this study represent both artificial (Commercial pellets) and natural feeds (seaweed and kelp) used in commercial abalone culture. The growth of two cohorts (40-50 mm and 50-60 mm) was followed over a 426 day period, with data for the first 183 days being used for statistical analysis to determine performance of a given diet. The best growth rates were found in abalone fed Diet A (40-50 mm: 2.64 mm.month-1; 50-60 mm 2.78: mm.month-1) and B (40-50 mm: 2.20 mm.month-1; 50-60 mm: 2.35: mm.month-1). These (Diets A and B) gave higher growth rates when compared to Diets C and D (natural diets), whose growth rates ranged between 0.50 mm.month-1 and 1.71 mm.month-1 for both cohorts. Also observed in this study was that, the mixture of formulated diet and seaweed gave better growth than formulated diet given exclusively.

The abalone (Haliotis midae) culture industry in South Africa is becoming increasingly dependent on the use of formulated feeds, due to limitations in the supply of kelp. The bulk of the feeds that are currently available were developed based on the requirements of juvenile abalone cultured within the optimal temperature range for growth (18 - 20 °C). However, most abalone farming facilities are land-based pump ashore operations and are thus mostly exposed to temperatures outside of this range. In addition, these feeds have been found to be unsuitable for abalone cultured at elevated water temperatures (> 20°C). The aim of the study was to develop size and temperature specific diets for H midoe through optimisation of dietary protein, energy and lipid levels. Abalone were cultured under farm-like conditions in three partially recirculating temperature controlled systems at either 18, 22 or 24°C and fed formulated diets containing graded levels of protein (18,22 and 26 %) and energy (11.6, 13.5 and 16.2 MJ.kg·I ). Abalone were stocked into baskets at 5 % of available of surface area (n=36) and each diet (n=9) was fed to four baskets of abalone at each of the three temperature regimes for ten weeks. Abalone growth was temperature dependent, with growth declining from 4.33 g.month-I for abalone cultured at 18°C to 0.77 g.month-I at 24°C. Dietary protein could be reduced from 26 to 18 % provided dietary energy levels were maintained at 13.5 MJ.kg- l • A dietary energy level of 11.6 MJ.kg-1 was insufficient to meet the energetic requirements of H midae regardless of the protein content of the diet. The effects of water temperature and body size on the protein requirements of H midae were investigated by culturing abalone at temperatures within the optimal range for abalone farming (i.e. 14, 16 and 18°C). Three size classes of abalone (15, 50 and 80 mm) were fed formulated feed containing graded levels of dietary protein (20, 26, 32, 38 and 44 %) under controlled laboratory conditions for 12 weeks, and, in a separate experiment, under commercial farm conditions for 24 weeks. It was not possible to convincingly define the optimal protein levels for abalone of different sizes in this experiment because growth rates fell below average commercial growth rates obtained on farms. Growth was temperature dependent in the laboratory trial, with the rate of weight gain of the 15 mm (ANOV A: p=0.002) and 50 mm abalone (ANOV A: p=0.02) increasing significantly with an increase in temperature from 14 to 18°C. In the farm trial, dietary protein content did not affect the growth rate of the 10-15 or 80 mm abalone (ANOVA: p>0.05), however, the 50 mm abalone displayed significantly higher weight gain on the 32 % (4.72±0.20 g.month-I ) and 38 % (5.01±0.34 g.month-I ) protein diets compared to those fed the 20 % protein diet (3.75±0.13 g.month-I ) (ANOVA: p=O.OI). Although definition of optimal dietary protein levels were not possible, the effects of dietary protein content and water temperature on the growth of H midae were independent signifying that the protein requirements of abalone are temperature independent. In addition, there was no evidence to indicate that abalone of the different sizes tested here had different dietary protein requirements. The size specific dietary lipid and protein requirements of H midae were investigated by feeding two size classes of abalone (30 and 60 mm initial shell length) diets containing graded levels of dietary lipid (4, 7, 10, 13 and 16 %) and protein (34 - 39 %) for 12 weeks. The 30 and 60 mm abalone were stocked at 7 (n=200) and 9 % (n=36) of the available basket surface area respectively and each diet was fed to four baskets of abalone of each size class. The protein requirements of H. midae are influenced by the amount of available dietary energy and thus it is possible that the ability of abalone to utilise lipids as a source of energy differs in the presence of varying levels of dietary protein. High levels of dietary lipid negatively affected the growth, condition factor and soft tissue glycogen content of both size classes of abalone. This negative effect was greater in the 30 mm size class compared to the 60 mm abalone. The corresponding increase in feed consumption and feed conversion ratio in response to increasing levels of dietary protein also provides evidence that abalone are unable to utilise dietary lipids as an energy source and high levels of dietary lipid probably inhibit the uptake of carbohydrates and protein. High dietary lipid levels did however appear to promote gonad maturation. It was possible to reduce dietary protein from 34 to 20 % without negatively affecting growth through the maintenance of dietary energy levels and thus it is recommended that future experiments on the energy content of formulated feeds should focus on the improved use of carbohydrates. Reductions in the protein portion of formulated feeds for H. midae are possible provided the diet contains sufficient levels of energy supplied from carbohydrates. As the ability of abalone to utilise dietary lipid is limited, lipids are unlikely to play a significant role as an energy source in abalone feeds. Further investigations should focus on the utilisation of various carbohydrate sources in abalone feeds.

An understanding of species specific water quality requirements is essential for efficient production of aquaculture products, an aspect not well documented for the land-based culture of the South African abalone, Haliotis midae. In order for the industry to remain competitive in international markets, efficient use of water supplies and the development of water reuse technology is needed. This study assessed the changes in water quality between tanks in a tiered serial-use raceway in relation to accumulated biomass and water flow and estimated the flow index (FI) (L h⁻¹ kg⁻¹) at which growth becomes significantly affected. The effect of dietary protein level, supplementation of pure oxygen and addition of sodium hydroxide (NaOH⁻) on water quality and fundamental production parameters in the serial-use raceways was also assessed. The serial-use raceways were used as a tool to create a range of water quality conditions at which the growth, feed conversion ratio (FCR) and condition factor (CF) of "cocktail" size (60 – 70 mm) H. midae could be monitored. The metabolic activity of the abalone resulted in a deterioration in water quality between tanks in series. pH (r² = 0.99; p < 0.001) and dissolved oxygen concentration (r² = 0.99; p < 0.001) were positively correlated with flow index (pH = 7.38 FI°·°² ; dissolved oxygen = 6.92 FI°·°⁴), while free ammonia nitrogen (FAN) (r² = 0.99, p < 0.001) and nitrite (NO²⁻ - N) (r² = 0.93, p < 0.001) were negatively correlated with flow index (FAN = 8.02 FI⁻°·⁷¹). Nitrite concentrations increased over time indicating colonisation of Nitrosomonas bacteria on the basket surfaces. A flow index of 7.2 – 9.0 L h⁻¹ kg⁻¹ was estimated as the minimum to avoid significant reductions in weight and shell length gain and increases in FCR values. Total ammonia nitrogen (TAN) and FAN concentrations were significantly correlated to dietary protein (P) (t = 6.63, p < 0.0001 and t = 6.41, p < 0.0001, respectively) and flow index (t = 5.42, p < 0.0001 and t = 3.9, p < 0.0002, respectively) and could be estimated using the models TAN = 9.73 P – 110.3 log (FI), and FAN = 0.132 P – 1.10 log (FI). Mean FAN concentrations were 67 and 41 % lower in tanks fed a diet containing 22 and 26 % protein respectively, when compared to tanks fed a 33 % protein diet. Supplementation with pure oxygen (103 ± 8 % saturation) improved shell length gain (t = 3.45, p = 0.026) in abalone exposed to high FAN (2.43 ± 1.1 μg L⁻¹) and low pH (7.6 ± 0.13), relative to a treatment with no oxygen supplementation (92 ± 6 % saturation). Addition of a sodium hydroxide solution resulted in elevated mean pH in treatment raceways when compared to control raceways. The increased pH resulted in significantly higher weight gain (g abalone⁻¹) (F₁·₁₂ = 4.51; p = 0.055) and shell length gain (mm abalone⁻¹) (F₁·₁₂ = 4.56; p = 0.054) at an α-error level of < 5.5 %. In two trials, weight gain and shell length gain were significantly correlated to pH (p < 0.001), and multiple regression of pH, dissolved oxygen and FAN consistently revealed pH to be the best predictor of growth. It is therefore suggested that decreasing pH is the first limiting water quality variable for abalone in serial-use raceways. As a decrease in water pH is linked to respiration by the abalone and subsequent increase in dissolved carbon dioxide (CO₂) concentration, future studies should examine the effects of CO₂ on H. midae metabolic rate, calcification rate and health. The results of this study will contribute toward our understanding of the specific water quality requirements for H. midae in commercial aquaculture systems, and influence the design and management procedures for abalone water reuse systems.