Haliotis Midae Research Articles

Bacterial microbiome dynamics in commercial integrated aquaculture systems growing Ulva in abalone effluent water

In South Africa, the green seaweed Ulva lacinulata is grown in land-based integrated multi-trophic aquaculture (IMTA) farms with the abalone Haliotis midae. The Ulva serves as a biofilter and the co-produced Ulva is often used as feed for the abalone. To better understand the potential benefits and risks associated with this practice, this study characterised the bacterial microbiome associated with the seawater and Ulva raceways receiving abalone effluent (IMTA system) and compared this to Ulva tanks supplied with fertilised seawater (non-IMTA; control). Ulva samples were collected from each Ulva system, and water samples were collected at the inlet and outlet of each system. Bacterial communities were assessed using a culture-based approach and next-generation sequencing (NGS) of the V3-V4 16S rDNA region. It was observed that Ulva has the potential to reduce the bacterial load of abalone effluent, with the total number of potential culturable Vibrio species declining from 150×103 cells mL-1 in the inlet to 37×103 cells mL-1 in the outlet of the Ulva system. The NGS dataset supported these findings, with a reduction observed in Vibrio and Pseudoalteromonas from the inlet to outlet samples. A lower number of genera (p < 0.05) were observed on Ulva when compared with water samples, indicating that Ulva has a beneficial, modulatory effect on bacteria. These findings contribute towards the growing body of evidence for the benefits of seaweeds in IMTA and addresses the biosecurity concerns of abalone farmers wishing to improve the circularity of their farming activities by incorporating seaweeds.

Construction of a high-density linkage map and QTL detection for growth traits in South African abalone (Haliotis midae).

Haliotis midae is one of the most important molluscs in South African commercial aquaculture. In this study, a high-resolution integrated linkage map was constructed, and QTL identified using 2b-RADseq for genotyping SNPs in three families. The final integrated linkage map was composed by merging the individual family maps, resulting in 3290 informative SNPs mapping to 18 linkage groups, conforming to the known haploid chromosome number for H. midae. The total map spanned 1798.25 cM with an average marker interval of 0.55 cM, representing a genome coverage of 98.76%. QTL analysis, across all three families, resulted in a total of five QTL identified for growth-related traits, shell width, shell length, and total body weight. For shell width and total body weight, one QTL was identified for each trait respectively, whilst three QTL were identified for shell length. The identified QTL respectively explained between 7.20% and 11.40% of the observed phenotypic variance. All three traits were significantly correlated (r = 0.862-0.970; p < 0.01) and shared overlapping QTL. The QTL for growth traits were mapped back to the H. midae draft genome and BLAST searches revealed the identity of candidate genes, such as egf-1, megf10, megf6, tnx, sevp1, kcp, notch1, and scube2 with possible functional roles in H. midae growth. The constructed high-density linkage map and mapped QTL have given valuable insights regarding the genetic architecture of growth-related traits and will be important genetic resources for marker-assisted selection. It remains, however, important to validate causal variants through linkage disequilibrium fine mapping in future.

Coculture of abalone (Haliotis midae) and sea cucumber (Neostichopus grammatus) to reduce tank cleaning frequency in abalone farming

Abalone farming produces nutrient-rich sludge, and the frequent cleaning and removal of sludge from abalone tanks is labour and capital-intensive. This study aimed to assess the effect of culture methods and tank cleaning frequency on abalone growth, water quality, and sludge characteristics. The study was conducted for 16 weeks. Four treatments were used, namely, abalone cocultured with sea cucumber cleaned once (AS1) and twice weekly (AS2); abalone monoculture cleaned once (A1) and cleaned twice weekly (A2). Abalone (initial avg weight = 40.9 g) were maintained under commercial stocking conditions in flow through systems at a salinity of 35 ppt and fed a commercial formulated diet (Abfeed™) and fresh seaweed (Ulva lacinulata and Gracillaria gracilis). The stocking densities were 200 abalone m−2 and 50 sea cucumbers m−2. The sea cucumbers (initial average weight = 12.5 g) fed on the abalone faeces and leftover feed, which settled at the abalone tank's bottom (sludge). There was a significant interaction between the type of culture and the frequency of cleaning on abalone weight (F (1,476) = 12.41, p < 0.001). Abalone in the A2 treatment group showed higher growth (p = 0.006) than those of the A1 treatment group, while abalone in AS1 had significantly higher growth (p < 0.001) than those in the AS2 treatment group. Also, abalone in AS1 showed higher growth (p = 0.026) than abalone in the A1 treatment. However, abalone in AS1 had growth similar (p = 0.53) to those in A2. The survival rate of the sea cucumbers was high, however, the sea cucumbers experienced a reduction in weight regardless of the treatment. This study showed that growth optimisation in abalone farming can be achieved by cleaning tanks twice instead of once weekly. However, when abalone are cocultured with sea cucumber, tanks need only be cleaned once a week without compromising abalone growth or water quality. The coculture of abalone and sea cucumber results in an additional aquacultured product, a significant reduction in labour and other associated costs of cleaning, without an additional cost of production.

Mitigating the Impact of Harmful Algal Blooms on Aquaculture Using Technological Interventions: Case Study on a South African Farm

Seafood, especially from the ocean, is now seen as a greener and more sustainable source of protein, causing an increase in its demand. This has also led to people making choices towards seafood as a replacement for carbon-intensive protein sources. As a result, the demand for seafood is growing, and as the aquaculture industry looks to increase production, keeping products safe and sustainable is imperative. There are many challenges faced by the aquaculture industry in meeting these increased demands. One such challenge is the presence of harmful algal blooms (HABs) in the ocean, which can have a major impact on aquatic life. In this paper, we look at the impact of this challenge on aquaculture and monitoring strategies whilst illustrating the potential for technological interventions to help mitigate the impact of an HAB. We will focus on Abagold Limited, a land-based marine aquaculture business that specialises in the large-scale production of abalone (Haliotis midae) based in Hermanus, South Africa. HABs are considered a threat to commercial-scale abalone farming along the South African coastline and require continuous monitoring. The most recent HAB was in February–April 2019, when the area experienced a severe red-tide event with blooms of predominantly Lingulodinium polyedrum. We present some of the monitoring strategies employing digital technologies to future-proof the industry. This article presents the development of a novel hybrid water quality forecasting model based on a TriLux multi-parameter sensor to monitor key water quality parameters. The actual experimental real water quality data from Abagold Limited show a good correlation as a basis for a forecasting model which would be a useful tool for the management of HABs in the aquaculture industry.

Staining of larval abalone (haliotis midae) shells using two epifluorescent dyes

ABSTRACT A nontoxic method that results in distinct and persistent marks in Haliotis midae juveniles is fundamental for field-based studies, abalone ranching, and stock enhancement programs. Developed (6 days after fertilization) H. midae larvae were batch-tagged with 25 and 50 mg L−1 of calcein and xylenol orange for 24 and 48 h to determine the effect on survival, settlement, and the persistence of the mark on the shell. Epifluorescence was detected in the shell spire of larvae tagged with either 25 mg L−1 or 50 mg L−1 of calcein for 24 and 48 h immediately after the staining (t0) and was visible after 51 days when the experiment was terminated. Survival of calcein stained larvae was higher after 24 h compared to 48 h immersion. However, percentage settlement was higher in the 48 h treatments when compared to 24 h treatments for both concentrations and dyes. Therefore, bright and persistent epifluorescence marks can be induced in H. midae shells using calcein (25 mg L−1 for 24 h) without negatively affecting the survival and settlement of larvae, post-immersion.

A first annotated genome sequence for Haliotis midae with genomic insights into abalone evolution and traits of economic importance.

Haliotis midae or "perlemoen" is one of five abalone species endemic to South Africa, and being palatable, the only commercially important abalone species with a high international demand. The higher demand for this abalone species has resulted in the decrease of natural stocks due to overexploitation by capture fisheries and poaching. Facilitating aquaculture production of H. midae should assist in minimising the pressure on the wild populations. Here, the draft genome of H. midae has been sequenced, assembled, and annotated. The draft assembly resulted in a total length of 1.5 Gb, contig N50 of 0.238Mb, scaffold N50 of 0. 238Mb and GC level of 40%. Gene annotation, combining ab initio and evidence-based pipelines identified 52,280 genes with protein coding potential. The genes identified were used to predict orthologous genes shared among the four other abalone species (H. laevigata, H. rubra, H. discus hannai and H. rufescens) and 4702 orthologous genes were shared across the five species. Among the orthologous genes in abalones, single copy genes were further analysed for signatures of selection and several molecular regulatory proteins involved in developmental functions were found to be under positive selection in specific abalone lineages. Furthermore, whole genome SNP-based phylogenomic assessment was performed to confirm the evolutionary relationship among the considered abalone species with draft genomes, reaffirming that H. midae is closely related to the Australian Greenlip (H. laevigata) and Blacklip (H. rubra). The study assists in the understanding of genes related to various biological systems underscoring the evolution and development of abalones, with potential applications for genetic improvement of commercial stocks.

The use of chemical and biological settlement cues in enhancing the larval settlement of abalone (Haliotis midae): Implications for hatcheries and ocean ranching

AbstractReducing the time to settlement and metamorphosis of abalone larvae is critical for ensuring that abalone larvae settle within the seeding site for ocean ranching or to increase production in hatcheries. This study investigated the effect of biological (planktonic Nitzschia sp.) and chemical (potassium chloride) cues in inducing settlement and metamorphosis of abalone larvae Haliotis midae on diatom‐coated plastic sheets. Larvae were exposed to different concentrations of KCl (10–20 mM), with settlement being highest at 10 mM in the first 20 h. Settlement of larvae exposed to a combined KCl and Nitzschia treatment for 24 h was highest, followed by larvae exposed to KCl for 12 h, while larvae exposed to KCl for 24 h, and both controls (12 and 24 h) had the lowest settlement. However, in both experiments, larval settlement in all treatments declined after 24 h of exposure, while that of the controls (no added settlement cues) increased and surpassed the other treatments after 24 h. Finally, the settlement was very low on uncoated sheets, compared to diatom‐coated sheets, regardless of exposure to different combinations of KCl and Nitzschia. The exposure period's results should be interpreted with caution when drawing biological conclusions for field studies. This is due to the dramatic decrease in mean settlement post‐exposure to the cue. Therefore, we hypothesize that exposure of H. midae larvae to 10 mM KCl and Nitzschia sp. will not enhance settlement in the ocean, as the inducers are primarily only effective at a KCl concentration level equal to 10 mM for 12 h. However, long‐term exposure to KCl and Nitzschia over 24 h could be used in hatcheries to improve the settlement of H. midae larvae.

Fisheries restoration: Lessons learnt from four benefit-cost models

Globally, fisheries are in decline and in many parts of the world illegal fishing is a major cause of these declines. Ecological restoration of fisheries needs to be promoted, inter alia through improved enforcement, but, which method is the most successful at improving fish stocks, as well as having the highest economic returns? We compare one open-loop (without feedback) and three closed-loop (with feedback) benefit–cost models representing different restoration interventions aimed at promoting compliance. The hybrid systems methodology has been utilized, combining system dynamics, systems archetypes, mathematical differential equations and economic benefit–cost methodologies. The model is tested with reference to a case study of abalone (Haliotis midae) biomass restoration in the Table Mountain National Park marine area (Zone E), Cape Town. Stocks in Zone E have dropped to below the government’s management threshold for sustainable fisheries of 20 percent of the pre-fished levels, and urgent action is required to restore the stocks. According to the model, all proposed restoration interventions produce stock recovery to 100 percent of carrying capacity, well in excess of government targets of 40 percent. Also, all four models had a net present value of greater than zero, indicating substantial positive net benefits to restoration. Each model had specific management recommendations associated with it- greater involvement by the state, capital investment in restoration, changing poacher behavior and entrepreneurship. Although the Post Keynesian and Institutional model produced the highest net returns to restoration over 80 years (Net present value = US$12.66 million at a 6 % discount rate, 2021 prices), all the models are essentially co-evolutionary models, and have merit over different time periods, compliance rates and assumptions around discount rates. While the case study is developed for abalone the findings of the model are likely to be applicable in a wide range of fishery restoration contexts.

Gonad development in farmed male and female South African abalone, Haliotis midae, fed artificial and natural diets under a range of husbandry conditions

Growth rate is one of the most important factors in the farming of Haliotis midae, and somatic growth rates decline after abalone reach sexual maturity. Artificial diets are suspected to accelerate maturation, in particular when soya meal is used as a protein source, because of this plant’s high concentration of phytoestrogens. The effect of diet on the gonad development of 27-month-old farmed Haliotis midae, raised at two stocking densities, was analysed. We fed two artificial diets and a natural diet, kelp, to cultured abalone. The first artificial diet had fishmeal as its main source of protein, while in the other, Abfeed® S34, 32% of the fish meal was replaced with soya meal. For each gonad sample, the development phase was determined based on both histological criteria and the gonad bulk index (GBIn). The hypothesised link between dietary protein source and gonad development could not be established by either morphological criteria or GBIn. Similarly, stocking density did not have a significant effect on GBIn-values. GBIn values were significantly correlated to the results from the histological analyses in males and females. The results from this study suggest that artificial diets including those using soya meal are a valid alternative in the feeding of abalone. The research provides a database for future research on factors influencing gonad development in this species.

Feeding indicators and bioremediation ability of warty sea cucumber Neostichopus grammatus fed potential wastes from abalone Haliotis midae farming

The reuse of aquaculture waste to produce valuable sea cucumber biomass promises to reduce environmental impacts of aquaculture and increase incomes. This study aimed to assess the suitability of potential waste from abalone farming as feed for the warty sea cucumber Neostichopus grammatus and infer bioremediation effects from sea cucumber feeding. Four diets: abalone waste, fermented algae (sea lettuce Ulva lacinulata) mixed with sand (U+S), abalone pelleted feed, and sand, were fed to N. grammatus under controlled conditions for 6 wk. Sea cucumbers fed sand exhibited a significantly higher (p &lt; 0.001) ingestion rate (1.35 ± 0.04 g ind..-1 d-1) than other diets. Those fed U+S (1.03 ± 0.02 g ind..-1 d-1) had a significantly higher ingestion rate (p &lt; 0.001) than those fed abalone waste and pellet. However, the ingestion rate was similar for pellets (0.67 ± 0.07 g ind..-1 d-1) and abalone waste (0.54 ± 0.02 g ind..-1 d-1) (p = 0.138). Ingestion and faecal production rates were inversely influenced by the diet’s total organic matter content (TOM). The faecal TOM of sea cucumber fed abalone waste, pellet, and U+S decreased from the TOM of the diet by 37.53 ± 1.63% (p &lt; 0.001), 31.39 ± 0.53% (p &lt; 0.001), and 48.83 ± 9.81% (p = 0.03), respectively. There was a decrease (37.74 ± 0.12%, p &lt; 0.001) in the carbon content of sea cucumber faeces fed pellet compared to the feed, while there was no difference in nitrogen (p = 0.08) content. The carbon content of sea cucumber faeces fed U+S was not significantly different (p = 0.11) from that of the feed. However, the nitrogen content decreased by 63.00 ± 8.27% (p = 0.03). This study shows that wastes from abalone farming are acceptable food for N. grammatus, affirms the bioremediation potential of N. grammatus through integrated multitrophic aquaculture, and recommends its coculture trial with abalone.

A proteomic analysis of the effect of ocean acidification on the haemocyte proteome of the South African abalone Haliotis midae

As a result of increasing CO2 emissions and the prevalence of global climate change, ocean acidification (OA) is becoming more pervasive, affecting many trophic levels, particularly those that rely on succinctly balanced ocean chemistry. This ultimately threatens community structures, as well as the future sustainability of the fishing/aquaculture industry. Understanding the molecular stress response of key organisms will aid in predicting their future survivability under changing environmental conditions. This study sought to elucidate the molecular stress response of the South African abalone, Haliotis midae, an understudied organism with high economic value, utilising a high throughput iTRAQ-based proteomics methodology. Adult abalone were exposed to control (pH 7.9) and experimental (pH 7.5) conditions for 12, 72 and 168 h, following which protein was isolated from sampled haemocytes and subsequently processed. iTRAQ-labelled peptides were analysed using mass spectrometry, while an array of bioinformatics tools was utilised for analysing the proteomic data. COG analysis identified “Cytoskeleton”, “Translation, ribosomal structure and biogenesis”, “Post-translational modification, protein turnover, chaperones”, and “Intracellular trafficking, secretion and vesicular transport” to be the most enriched functional classes, while statistical analysis identified a total of 33 up-regulated and 23 down-regulated effectors of OA stress in abalone. Several of the up-regulated proteins that were identified function in central metabolism (ENO1, PGK, DUOX1, GPD2), the stress/immune response (CAMKI, HSPA5/GRP78, MAPKI), and cytoskeleton, protein sorting and signal transduction (IQGAP1, MYO9B, TLN1, RDX, TCP-1/CCT, SNX6, CHMP1a, VPS13a). Protein-protein interactions were predicted using STRING DB, Cytoscape and Ingenuity Pathway Analysis, providing a model of the effects of OA on the H. midae haemocyte proteome. The data indicated that H. midae underwent a metabolic shift under OA conditions to utilize more energy-efficient mechanisms of ATP generation, while attempts at restoring haemocyte stabilisation and homeostasis were reflected by up-regulation of oxidative stress and cytoskeletal proteins. Our results support other molluscan studies that report a complex array of overlapping functions of both the stress and immune response systems. This interplay of the mounted stress and immune response is maintained and observed through the up-regulation of proteins involved in protein synthesis and turnover, as well as intracellular signalling and transport. The data presented in this study highlight the value of employing sensitive and robust -omics technologies for assessing the effects of changing environmental conditions on marine organisms.

Effect of Temperature on the Development and Settlement of the Abalone Larvae Haliotis midae: Considerations for Abalone Hatchery Management and Stock Enhancement

Abalones are poikilotherms, and their rate of development is intrinsically linked with temperature. Understanding the effect of temperature on development is key for the successful production planning in abalone hatcheries and the reseeding of cultured abalone larvae for stock enhancement. This study investigates the effect of temperature on the development of the abalone larvae Haliotis midae. Newly hatched trochophore larvae were raised at temperatures of 14°C, 16°C, 18°C, 20°C, and 22°C until settlement. The temperature had a significant effect on the larval development—most rapid at 22°C [3 days and 65 degree-days (DD), °C day] and slowest at 14°C (6.7 days and 95 DD). Larval settlement was highest at 22°C (43.44% ± 3.73%, larvae). Larvae should preferably be seeded at temperatures between 20°C and 22°C as this will potentially increase settlement, thereby reducing larval dispersion outside of the seeding area.

Modelling regional and local-scale larval seeding strategies for abalone (H. midae) ranching in South Africa

Understanding connectivity between abalone populations and residence times for pelagic larvae within suitable settlement habitats is critical for sustainable management of wild abalone stocks and ranching schemes. In the Eastern Cape region of South Africa, poaching has severely depleted wild abalone Haliotis midae populations. Rebuilding stock through larval seeding is being considered as a potentially viable method, though is hampered by a limited understanding of abalone habitat connectivity through larval dispersal, both at a regional and local scale. To address this shortcoming, we apply a multi-scale approach to investigate potential larval dispersal along the coastline of Eastern Cape, South Africa, examining both intra- and inter-site connectivity, with the primary focus at the local nearshore scale (< 40 m water depth) where surf zone processes have a strong influence. Delft3D is applied at a regional scale (400-km domain) and XBeach is used at a local scale (5-km domain) to model a known abalone habitat at Cape Recife at high-resolution (5-m cell size). Models were validated using field observations. Complex topo-bathymetry data for the local-scale model domain around Cape Recife were obtained using a state-of-the-art low-cost multi-method surveying approach. At a regional scale, sites with abalone habitat have the potential to be connected across distances of 50–100 km. However, a large sandy embayment (Algoa Bay; 100-km arc length) is likely to present an obstacle to larval transport in all but the most extreme and sustained wind and wave forcing conditions. The central Cape Recife abalone ranching area has the potential to act either as a self-seeding or meta-population connected site, depending on forcing conditions. At the local scale around Cape Recife, a zone of shallow gullies, under lower-energy waves, was determined to be the optimal release point to maximise residency times within the preferred rocky, shallow subtidal habitat of H. midae. Competent larvae released in this zone are predicted to have an order of magnitude greater residency than randomly seeded larvae. This study provides site-specific connectivity and residence time information for the Eastern Cape abalone fishery, but more generally it provides a novel multi-scale method to aid in planning and managing of abalone larval seeding for ranching and stock enhancement programs that could be applied in other locations.

Macrocystis (Laminariales, Phaeophyceae) in South Africa: potential for cultivation through holdfast fragmentation and use as feed for the aquacultured abalone, Haliotis midae

Macrocystis pyrifera (Linnaeus) C. Agardh, known in some regions as ‘giant kelp’, occurs along temperate coastal rocky reefs throughout the southern hemisphere, as well as along the north-east Pacific coastline. In Chile, it serves as a major source of abalone feed within the abalone industry, with considerable literature on cultivation of the species. Here we attempt to cultivate South African M. pyrifera through vegetative propagation and investigate its use as a feed for the abalone, Haliotis midae. Kelp holdfasts were attached to a rope-raft system in Saldanha Bay, South Africa, and monitored over 3 months. In addition, a 6-month H. midae feed inclusion trial was carried out, which compared the use of M. pyrifera with the predominant commercial kelp feed species, Ecklonia maxima. Young M. pyrifera grew well on the culture system, with mean upright length nearly doubling over the culture period (55.6–102.2 cm) and displayed mean upright relative growth rates between 0.99 and 1.22% day-1. Additionally, holdfasts developed new uprights and holdfasts increased in size, growing around culture lines. Simulated partial harvesting of samples stopped upright elongation, but samples survived, whereas complete removal of uprights caused mortality. Haliotis midae fed with M. pyrifera + formulated feed (SAF 3000®) displayed comparable growth rates to the E. maxima + SAF 3000® diet. No significant differences in mean specific growth rate (M. pyrifera 0.19, E. maxima 0.18% body weight day-1), daily increment in shell length (M. pyrifera 31.19, E. maxima 24.64 μm day-1), condition factor (M. pyrifera 1.37, E. maxima 1.40 g mm-1) and mortality rate were identified between the two diets. Additionally, H. midae consumed significantly less M. pyrifera than E. maxima, suggesting potential differences in feed conversion ratio/kelp nutritional composition among the kelp species. These findings provide baseline information for the potential cultivation and use of M. pyrifera as a new source of fresh seaweed feed in the South African abalone industry.

Localisation of probiotic Vibrio midae K811 within the gastrointestinal tract of post-larval abalone, Haliotis midae

An artificial biofilm probiotic-supplemented diet was shown to enhance the growth and survival of post-larval South African abalone, Haliotis midae. To ensure the effectiveness of the probiotic bacterium Vibrio midae K811 in an aquaculture environment, we wished to investigate whether V. midae K811 reaches the abalone intestinal tract where it is expected to exert its probiotic effect. Thus, the aim of this study was to investigate the colonization potential of V. midae K811 and to localise the probiotic within the gastrointestinal tract of post-larval H. midae. The Tn9 cat gene incorporated in V. midae K811 was PCR amplified from total DNA isolated from whole abalone homogenates up to 10 days following the cessation of feeding abalone with the probiotic-supplemented diet, while viable V. midae K811 was detected in abalone homogenates up to 25 days after the post-larval abalone had been switched from an alginate surface supplemented with V. midae K811 to a surface supplemented with Cocconeis sp. Furthermore, in situ hybridization using two Tn9 cat gene-specific DIG-labelled oligonucleotide probes detected V. midae K811 in the intestine of post-larval H. midae, confirming that the probiotic reaches the digestive tract of post-larval abalone placed on an alginate biofilm supplemented with the probiotic, and that the bacterium can persist in the abalone digestive tract for a period of at least 3 weeks.

Genome-wide linkage disequilibrium in South African abalone, Haliotis midae, and implications for understanding complex traits

The abalone, Haliotis midae, is the most import aquaculture species in South Africa. Nonetheless, genetic improvement of the species is hindered by late maturity and long generational intervals. The application of marker assisted- and genomic selection is one strategy to accelerate genetic gains for production traits. However, with limited understanding of linkage disequilibrium, it is unclear how such a molecular-driven selective breeding approach should be implemented. The aim of this study was therefore to characterise LD in two wild and two cultured populations of the South African abalone and to investigate how their respective population histories have shaped LD across the genome and on a locus-specific scale. One hundred and twelve mapped microsatellite markers were used to genotype the four population cohorts. Levels of genetic diversity were similarly high for all cohorts, although significant population structure was evident. The decay of LD with genetic distance was present in both cultured cohorts, but almost absent within the wild cohorts. Levels of LD were high in comparison with other aquaculture species, but could be explained by various population demographic events related to the over-exploitation of the species in the wild, domestication, and the reproductive strategy of abalone. A number of interesting patterns were observed surrounding candidate loci under selection, including possible hitch-hiking events and epistatic interactions between loci. In terms of the potential for association studies, the persistence of significant LD over relatively long distances within these cohorts suggested that fewer markers would be sufficient to ensure marker-QTL co-segregation, although the use of generationally discrete cohorts is advised.

ITRAQ-based quantitative proteomic profiling of the immune response of the South African abalone, Haliotis midae

The South African abalone Haliotis midae is a commercially important species farmed at high densities in land-based aquaculture systems. Disease outbreaks have had a severe financial impact on the abalone industry yet the molecular mechanisms underlying the immune response of H. midae remain obscure. In this study, a comparative shotgun proteomics approach using iTRAQ coupled with LC-MS/MS was employed to investigate H. midae proteome changes in response to Vibrio anguillarum challenge. A total of 118 non-redundant, unique haemocyte proteins were identified and quantified, with 16 proteins significantly regulated. Hierarchical clustering and pathway analysis uncovered a coordinated response dominated by calcium and cAMP signalling via activation of MAPK cascades. Early up-regulated biological processes involve phagocytosis, nitric oxide production and ATP-synthesis, whilst down-regulated responses were predominantly involved in the regulation of apoptosis. The late up-regulated response involved protein kinase activity and detoxification processes. Expression of selected proteins was validated by Western blot. A putative allograft inflammatory factor-1 protein was further selected to establish its functional molecular role in haemocytes. Confocal imaging revealed that allograft inflammatory factor-1 regulates phagocytosis via a functional interaction with filamentous actin. This is the first time a high-throughput proteomics approach has been used to investigate the immune response of H. midae.

Improved growth and survival of post-larval Haliotis midae in response to probiotic biofilm diets

The bacterium Vibrio midae SY9, shown to enhance the nutrition and health of juvenile Haliotis midae, was investigated as a probiotic for H. midae during the post-larval phase of development. Using a randomized box design, we conducted three independent laboratory-scale experiments in which post-larval H. midae (mean shell length 2.7 mm) were fed three different artificial biofilm diets. The diets consisted of alginate and either the probiotic V. midae K811 only (diet 1), a mixture of the benthic diatom Cocconeis sp. and Vibrio midae K811 (diet 2) or Cocconeis sp. only (diatom control diet). Abalone survival was monitored over 25 days, and growth was quantified by measuring abalone shell length. Results confirmed that V. midae K811 has a probiotic effect on post-larval H. midae by significantly improving survival and promoting a three-fold increase in the growth rate of these animals. This study also demonstrated that post-larval H. midae can survive and grow on a bacterial biofilm diet lacking diatom cells which might suggest that bacteria could replace diatoms as the principle food source for post-larval H. midae.

An approach to determine the extinction risk of exploited populations

We propose a method for assessing the persistence of species where the resource is harvested. Four sustainability measures are employed, namely a population measure, a harvest measure, a profitability measure and a catchability measure. These are used to assess the sustainability of two natural resources representing terrestrial and aquatic species, namely White Rhino (Ceratotherium simum) and South African abalone (Haliotis Midae) species, respectively. The framework is used to evaluate these two resources against relevant local and international protected species listings. The results show that the proposed framework produces a more conservative approach to listing threatened species, consistent with the precautionary principle. The framework provides a way of conducting a precautionary assessment of extinction risk under conditions of exploitation, across a range of aquatic and terrestrial species. Once developed, we also apply this framework to seven additional species using a scenario analysis. The results highlight the importance of taking into consideration institutional factors under conditions of overexploitation.

A first study on the effect of dietary soya levels and crystalline isoflavones on growth, gonad development and gonad histology of farmed abalone, Haliotis midae

Soya in formulated diets for abalone, Haliotis midae, can improve somatic growth. However, it may also influence gonad development, thereby limiting the potential benefit of including soya in feed. This is the first study to determine both the effect of dietary soya level on growth and reproduction of abalone and the role of crystalline isoflavones (ISO) at concentrations occurring in soya diets. Abalone (40–50 g individual−1) were fed seven isonitrogenous and isoenergetic diets. Three diets contained 5, 10 or 19% soya, while an additional three diets included graded levels of ISO. A fishmeal (FM)-only diet was included. The inclusion of ISO did not influence gonad development or abalone growth while soya inclusion level had an effect on both reproductive development and abalone growth. After 180 days, male abalone fed FM with soya inclusion had the highest whole body mass (69.0 ± 2.48 g abalone−1), meat mass index (60.5 ± 1.88%), visceral mass index (13.0 ± 0.27%) and gonad bulk index (42.7 ± 9.82 g abalone−1). Weight loss was observed in all treatments probably due to spawning events. The frequency distribution of the predominant oocyte stage, stage 7 was influenced by soya concentration. The increase in the frequency of stage 7 oocytes in abalone fed FM with soya did not reduce the number of oocytes (45.0 ± 3.01 oocytes mm−2), while the number of oocytes (o) in abalone fed the FM-only diets decreased with increasing abundance of stage 7 oocytes, possibly due to an increase in oocyte size.