Optimum dietary crude protein level for growth in South African abalone (Haliotis midae L.)

A 95‐day feeding trial was conducted to evaluate the effects of dietary crude protein level on total body weight gain and protein gain of juvenile (4.89 ± 0.57 g) South African abalone (Haliotis midae). Six semi‐purified diets containing casein, fish meal and cottonseed meal as protein sources, and with crude protein levels ranging from 54.8 to 479.2 g kg^?1 dry matter (DM), were fed to four tanks containing 30 abalone each in a continuous flow system. No differences (P > 0.05) were found in moisture, ash or lipid content of soft‐body tissue as dietary crude protein level increased, indicating that differences (P < 0.05) in soft‐body protein content were solely due to dietary crude protein level. The relationships between dietary crude protein level and total body weight gain and protein gain were analysed by broken‐line and second‐order polynomial regression models. Based on total body weight gain, 358.7 g kg^?1 DM dietary protein from good quality sources is recommended for maximum growth of juvenile H. midae, while, if dietary protein is reduced to 280.7 g kg^?1 DM, growth will be depressed with 5 g kg^?1.     

An assessment of the efficacy of two lysine microencapsulation techniques to determine the quantitative lysine requirement of the South African abalone, Haliotis midae L.

The quantification of the essential amino acid requirements of a species is a prerequisite to the formulation of biologically optimized diets. In this study, crystalline L -lysine was used in an attempt to determine the quantitative lysine requirement of juvenile Haliotis midae . Two microencapsulation techniques [gelatine/acacia and cellulose acetate phthalate (CAP)] were used to retard leaching of crystalline L -lysine incorporated into semipurified test diets. An assessment of the efficacy of the encapsulation techniques, revealed that despite effective lysine supplementation, H. midae fed semipurified test diets containing encapsulated crystalline L -lysine failed to promote significant improvements in either growth, feed or protein efficiency ( P  > 0.05). The failure of the crystalline L -lysine to illicit growth and nutritional responses is discussed.     

Dietary phosphorus leaching and apparent phosphorus digestibility from different inorganic phosphorus sources for South African abalone (Haliotis midae L.)

The objective of this study was to determine phosphorus leaching of diets supplemented with various inorganic phosphorus sources [mono basic sodium phosphate (MSP), mono basic calcium phosphate (MCP), a 3 : 1 mixture of mono and dibasic calcium phosphate (MDCP), dibasic calcium phosphate (DCP)], and the apparent phosphorus digestibility of these sources in Haliotis midae. A trend of increased dietary phosphorus leaching from diet pellets with increased water solubility of sources was observed. MSP presented the highest (P < 0.05) phosphorus leaching (58.8%), while a value of 14.9% was obtained with DCP. Unexpectedly high phosphorus leaching (48.7% maximum) was obtained for a reference diet consisting of commercial feed ingredients (fish meal, soya bean meal, cottonseed meal) without any phosphorus supplementation. DCP presented a lower (P < 0.05) apparent phosphorus digestibility (27.9%) than MSP (66.5%), MCP (72.6%) and MDCP (66.3%). When dietary phosphorus leaching and apparent phosphorus digestibility were take into account, MDCP seems to be the most promising inorganic phosphorus source for inclusion in abalone diets. Further research should concentrate on minimizing dietary phosphorus leaching through feed preparation techniques.     

Research on abalone (Haliotis midae L.) cultivation in South Africa

Although abalone fisheries in South Africa have existed since 1949, cultivation started by successful spawning of captured specimens in 1981 to produce spat and juveniles. Twelve abalone farms, with an estimated investment of US$12 million, have since been established on the coast of South Africa, with a projected production of 500–800 tons. While Haliotis midae could reach a maximum size of about 200 mm shell length at an age of over 30 years in the wild, farm production is concentrating on an average size of 100 mm after 5 years. Growth rates of 0.08–4.5% body weight day ^?1 for abalone of 10–17 mm shell length have been found under stimulated farming conditions on formulated diets, while the corresponding feed conversion ratio (FCR) was 0.9–2.4. Growth rate, FCR and protein efficiency ratio decline at water temperatures above 20 °C. Anaesthetics, for example magnesium sulphate, are used to prevent injury during removal from tanks. Prostrate diatoms, such as Cocconeis sublittoralis (Hendey), Amphora proteoides (Hustedt) and Achnanthes brevipes (Agardh) are preferred after the larval stage (5–7 days, depending on temperature) are finished. South Africa abalone growers prefer formulated feeds in pellet form, which is convenience and cost favourable to farm operations and management. Although fish meal has been found to be the most suitable protein source for inclusion in formulated diets, plant proteins such as soy bean meal, cottonseed meal and sunflower meal presented good growth and apparent protein digestibility. The parasite sabellid polychaete, Terebrasabella heterouncinata, recently named by Australian and American researchers, is indigenous to a variety of South African intertidal molluscs and impedes growth by causing irritation beneath the mantle in abalone. Prevention to some degree is possible by high standards of hygiene and husbandry of abalone in the tanks, but new techniques to control large infestations now include ultrasound. In spite of a reputation for toughness, abalone meat frozen immediately after shucking is tender relative to red meat. The success of abalone farming in South Africa has been as a result of a high degree of cooperation between the private sector and government‐backed research institutions, and it is anticipated that this collaboration will continue.     

The effect of animal size on the ability of Haliotis midae L. to utilize selected dietary protein sources

The effect of animal size on the qualitative protein requirements of two size classes of Haliotis midae L. was assessed by feeding 12 semi‐purified single protein test diets (20% protein, 6% lipid) to juvenile and young adult animals (10–20‐ and 40–50‐mm initial shell length). The protein sources selected for the trial comprised four fishmeals, casein, spirulina, abalone viscera silage, brewery waste, torula yeast, carcass, sunflower and cotton seed meals. The results indicated that in terms of growth and feed efficiency, the fishmeals and spirulina were the most suitable candidates for use as primary protein sources in formulated feeds, and with the exceptions of the carcass meal and brewery waste, the remaining protein sources demonstrated promise as partial primary protein source replacements. Mean growth rates for the large and small abalone over the experimental period were 1.45 and 1.24 mm month^?1 respectively. With respect to the larger size class of abalone, the smaller abalone displayed significantly reduced growth (F = 64.7, P < 0.0001), feed conversion ratio (F = 16.6, P < 0.0001) and protein efficiency (F = 26.8, P < 0.0001). Two‐way analysis of variance revealed significant interactions between protein source, animal size and feed conversion ratio (F = 2.4, P < 0.01) and growth (F = 5.4, P < 0.05), thus indicating that qualitative differences exist between the dietary protein requirements of the juvenile and young adult abalone.     

Parentage assignment in Haliotis midae L.: a precursor to future genetic enhancement programmes for South African abalone

The establishment and evaluation of family lines using pedigree information provides an advanced understanding of the variability that exists for complex, economically valuable traits and is a necessary step in the execution of an effective breeding programme. The aim of this study was to assign parentage to mass‐spawned Haliotis midae juveniles using species‐specific microsatellite markers. Screening of wild abalone individuals revealed that the nine loci selected complied with the minimum requirements for parentage analyses: a null allele frequency <5% as well as a high number and frequency of alleles per locus. A total of 598 individuals were genotyped (198 breeding individuals and 400 F1 progeny) from two farms, with parentage results yielding 91% and 90% successful assignment for Farms A and B respectively. This study, therefore, provided the necessary pedigree information required for controlled breeding of individual adult abalone and indicated the usefulness of the panel of microsatellite markers selected for parentage assignment.     

Apparent and true availability of amino acids from common feed ingredients for South African abalone (Haliotis midae L.)

Apparent (APD) and true (TPD) protein digestibility and apparent (AAAA) and true (TAAA) amino acid availability of fish meal and plant protein ingredients utilized in the South African animal feed industry (corn gluten meal, soya bean meal, cottonseed meal, sunflower meal, canola meal, peanut meal, lupins and faba beans), incorporated at 450 g kg^?1 into single protein diets, were determined with juvenile South African abalone (Haliotis midae). Soya bean meal (96.34%) and lupins (96.51%) presented the highest APD values, with corn gluten meal (76.08%) the lowest value, while values for sunflower meal (92.21%), canola meal (93.94%) and faba beans (93.17%) were above 90%. APD values for cottonseed meal (86.28%) and peanut meal (86.73%) were comparable with that of fish meal (82.94%). A correlation coefficient (r) of 0.99 was found between ADP and mean AAAA. Furthermore, amino acid availabilities were relatively consistent within various feed ingredients. The mean amino acid secretion from a protein‐free diet was 19.08 mg 100 g^?1 dry diet, resulting in a mean increase of 1.88% units over all feed ingredients when comparing TAAA with AAAA. Calculated APD according to APD coefficients determined with single protein diets underestimated determined APD in several compound diets by 1.10–6.50%, while mean AAAA was underestimated by 6.93%.     

Optimal protein level in a semipurified diet for juvenile greenlip abalone Haliotis laevigata

To optimize dietary protein level in relation to growth, semipurified diets with an essential amino acid profile similar to that of the soft body profile were fed for 59 days to young greenlip abalone, Haliotis laevigata (initial shell length, 15–25 mm). Animals were housed in 10-L acrylic tanks, with flow-through seawater supplied at 1 L min^–1 (20 °C, salinity= 36 g L^–1). Protein level of feeds ranged from 122 g kg^–1 to 461 g kg^–1 crude protein (CP) on an 'as is' basis. Second-order polynomial regression analysis of specific growth rate indicated that maximal growth occurs at 270 g kg^–1 CP. The protein and energy components of the feed were estimated to have a digestibility of 71.7% and 55.6%, respectively.     

Induction of triploidy in the South African abalone using cytochalasin B

An investigation into triploidy induction in the South African abalone, Haliotis midae, was conducted. It was found that 0.5 mg l–1 of Cytochalasin B (CB) in seawater induced triploidy when administered to coincide with the normal timing of the release of either polar body one (PB1) or two (PB2). This concentration of CB produced 70.9% triploid induction in the PB2 treatment and 48.4% induction at PB1. Significant numbers of tetraploid larvae were found in the PB1 treatment. These resulted from the presence of excess sperm (polyspermy) but only when CB was present. Although larval survival after triploid induction was lower than the control animals, it was considered high enough for use in commercial hatcheries. © Rapid Science Ltd. 1998     

Comparative performance of juvenile red abalone, Haliotis rufescens, reared in laboratory with fresh kelp and balanced diets

Juvenile Haliotis rufescens were reared in the laboratory in order to investigate the extent to which fresh kelp and formulated feeds with 250 g kg⁻¹ (25P) and 380 g kg⁻¹ protein content (38P) affected their growth rate, gut residence time (GRT), food consumption ( C ), food conversion ratio (FCR) and digestibility. Abalone from 38P attained the highest growth rate (70.5 ± 4.2 μm day⁻¹; 98.3 ± 6.95 μg day⁻¹), followed by 25P (47.9 ± 2.79 μm day⁻¹; 67.4 ± 2.82 μg day⁻¹) and kelp (23.6 ± 3.36 μm day⁻¹; 28.2 ± 4.11 μg day⁻¹). No significant differences were observed in consumption rate among treatments (0.61–0.68% body weight per day), yet kelp-fed abalone exhibited higher FCR (2.44), protein efficiency ratio (4.42), and apparent digestibility of dry matter (69.5%), protein (69.8%) and gross energy (79.2%) than 38P organisms (59.8, 62.4 and 62.2%, respectively). They also showed longer GRT (23.1 ± 0.93 h). This study demonstrated that formulated diets with 250 g kg⁻¹ and 380 g kg⁻¹ protein inclusion can sustain higher growth rates of juvenile H. rufescens than fresh algae. These differences seem to be due to the amount of dietary protein. Kelp meal appears to improve the consumption and digestibility of balanced diets, and its inclusion in formulated diets is recommended.     

Effect of dietary lipid level on growth and feed utilization in cultured South African abalone Haliotis midae L. fed diets with a constant protein‐to‐energy ratio

The aim was to test whether abalone growth and feed conversion ratio (FCR) could be maintained at increased dietary lipid levels if the protein:energy ratio (P:E) was kept constant. Two size classes (25–30 and 65–70 mm) of Haliotis midae were fed diets with graded levels of lipid (4–16%), in which total protein varied (34–39%) to maintain a constant P:E (22 g protein MJ^?1). For both size classes, overall performance was best on diets containing 4% and 7% lipid. Above 7% lipid, specific growth rate, shell length increment and protein efficiency ratio decreased while feed consumption and FCR increased significantly. The observed deterioration in growth and nutritional performance in diets with >7% dietary lipid was more marked in the 65–70 mm size class than in the 25–30 mm class, indicating that the smaller size class were better equipped to metabolize higher levels of dietary lipid. We concluded that the observed decrease in growth and feed utlization with the increasing dietary lipid was not due to an imbalance of dietary protein relative to energy, but rather that H. midae is unable to effectively utilize lipids as an energy source at levels in excess of 7% due to inherent physiological constraints.     

Evaluation of cytochalasin B (CB) treatments for triploidy induction in the blacklip abalone, Haliotis rubra (Leach, 1814)

The effectiveness of cytochalasin B (CB) treatments for inducing triploidy was evaluated in the blacklip abalone Haliotis rubra (Leach, 1814) in two orthogonal design experiments. The first experiment employed three dosages (DSs) of 0.25, 0.5 and 1.0 mg CB L^?1, three starting times (STs) of 5, 15 and25 min post fertilization and three treatment durations (TDs) of 10, 20 and 40 min, for a total of 27 treatments. The second experiment comprised of two DSs of 0.25 and 0.5 mg CB L^?1, five STs of 5, 15, 20, 25and 30 min post fertilization, and three TDs of 10, 20 and 40 min, for a total of 30 treatments. Water temperature was held at 17.5–18.5°C. Day 3 larvae were sampled for triploidy using flow cytometry (FCM) and survival. Optimal inductions were treatments starting at 15 or 20 min post fertilization and continuing for 40 min, and those initiated 25 or 30 min post fertilization for 20 or 40 min, using 0.5 mg CB L^?1. These treatments were all targeted at inhibition of the second polar body (PB2) formation and yielded triploidy rates of 84.8–89.5% coupled with (relative) survival rates of 20.1–52.1% in the first experiment, and corresponding rates of 86.5–96.5% and 33.0–74.1%, respectively, in the second experiment. A common and essential feature of these optimal conditions is that treatment must fully span the period of time for most of the eggs to extrude PB2. Treatments that resulted in suppression of the first polar body (PB1) formation induced triploidy levels below 71.5% and 57.6% in experiments 1 and 2 respectively. Treatments that had overlapping effects on both PB1 and PB2 extrusion led to triploidy rates above 80% but very low survival rates of 1.8% and 5.4% in experiments 1 and 2 respectively.     

The protein and energy requirements of farmed South African abalone Haliotis midae L. cultured at optimal and elevated water temperatures

Formulated abalone feeds used by the culture industry are believed to be unsuitable for use at elevated water temperatures (>20 °C). The aim of this study was to develop a feed that could safely be fed to abalone cultured at elevated water temperatures by optimizing dietary protein/energy levels. Abalone (54.90 ± 0.08 mm; 28.99 ± 0.16 g) were cultured at either 18, 22 or 24 °C, and fed diets containing graded levels of protein (18–26%) and energy (11.6–16.2 MJ kg^?1). Abalone growth was temperature dependent, declining from 4.33 g month^?1 at 18 °C to 0.77 g month^?1 at 24 °C. Shell length and weight gain were independent of dietary protein, provided that the digestible energy content of the diet was not lower than 13.5 MJ kg^?1. Dietary energy levels below 13.5MJ kg^‐1 resulted in significant reductions in shell growth, weight gain and increased mortality from 5% to 27%. Feed consumption of the 22% and 26% protein diets with 11.6 MJ kg^?1 was significantly higher (0.53 ± 0.04 and 0.55 ± 0.04% bd. wt. day^?1 respectively) compared with abalone fed the 16.2 MJ kg^?1 diets at the same protein levels (combined mean of 0.45 ± 0.04% bd. wt. day^?1) indicating that consumption was linked to energy requirement. The growth and mortality results suggest that abalone cultured at these temperatures have a dietary digestible energy requirement of at least 13.5 MJ kg^?1.