Abalone Aquaculture Research Articles

Use of a gene encoding zona pellucida 4 as a female-specific marker for early stage sexual differentiation and size dimorphism in the pacific abalone Haliotis discus hannai

Growth rates of Pacific abalone Haliotis discus hannai are an important trait affecting the economic value in the abalone aquaculture industry. A reverse-transcription polymerase chain reaction (RT-PCR) analyses of tissues from H. discus hannai was conducted for sexually mature gonads to determine male- and female-specific target gene expression, including genes encoding zona pellucida domain 4 (zp4), sperm protein (sp) and lysin (lys), respectively. Sex-specific expression patterns of these gene expression, even in sexually immature abalone, indicate these genes can be used as sensitive and robust sex-specific molecular markers. The RT-PCR procedure was also performed to analyze tissues collected at various developmental stages (50-day intervals) beginning at fertilization to determine when sex differentiation and expression of sex-specific genes was initiated. Detection of zp4 transcript in tissues collected at 200 days post-fertilization (dpf) indicated egg-specific development starts at 150–200 dpf. To evaluate possible sex-specific differences in growth rate, there was conducting of a molecular marker-based sex identification of abalone from a population selected for rapid growth rate. In a group of large H. discus hannai, females were more prevalent than males. To assess the correlation between growth and sex, there was comparison of weights of 3-year-old Pacific abalone in specimens where there had been sex determinations by visual examination and molecular methods. The results indicated females weighed more (55.92 ± 9.38 g, n = 15) than males (43.64 ± 15.55 g, n = 6, P = 0.037), indicating females had a more rapid growth rate than males.

The effects of depth and diet on red abalone growth and survival in cage mariculture at San Jeronimo Island, Baja California, Mexico

In recent decades, global abalone aquaculture has significantly increased, while wild abalone fishery landings have decreased drastically, shifting production from fishing to farming. In California (USA) and Baja California (Mexico), overfishing and climate changelinked diseases are thought to be responsible for mass mortalities and significant declines in abalone fisheries landings. Conservation aquaculture is an option for enhancing abalone populations through captive propagation and cage mariculture with subsequent restockings into the wild. To test, inform, and promote innovative sustainable seafood production strategies in the Northeastern Pacific, we designed an experimental mariculture system at San Jeronimo Island, Baja California. We explored the feasibility of rearing juvenile red abalone, Haliotis rufescens, in a near-shore mariculture cage-based production system to supply individuals for local restoration programs. We tested the effects of 2 different depths, surface and bottom (5 m), and 3 macroalgal diets (Macrocystis pyrifera, Eisenia arborea, and a mixed diet of Pelagophycus porra with M. pyrifera) on the survival and growth of juvenile red abalone (32 ± 3.33 mm in shell length) inside cages attached to a long-line system. Over the 90-d experiment, survival was 99% for the surface treatment and 95% for the bottom treatment. Mean daily increment in shell length was 93 ± 12 µm·d–1 in surface cages and 82 ± 13 µm·d–1 in bottom cages. Depth did not affect growth or survival. Growth was highest using the E. arborea diet (99 ± 7 µm·d–1) but not significantly different from the M. pyrifera and mixed diets (88 ± 10 and 74 ± 13 µm·d–1, respectively). High survivorship and growth indicate that San Jeronimo Island can support cage-based mariculture of red abalone and that this strategy may be a useful tool in developing climate-resilient abalone restoration solutions aimed at bolstering seafood production.

The intestinal microbiome of Australian abalone, Haliotis laevigata and Haliotis laevigata × Haliotis rubra, over a 1-year period in aquaculture.

The digestive tract microbiome aids its host in food digestion, immune system function, development, and health. In marine organisms and habitats, microbiome research is limited. In Australia, abalone aquaculture is an economically important industry; however, little is known about the relationship between abalone and their microbiome. This study investigated the intestinal microbiomes of hybrid, or Tiger, (Haliotis laevigata x H. rubra) and greenlip (Haliotis laevigata) abalone over a one-year production period, grown at two commercial farms. Abalone samples (n = 30 for each species) were collected every three months, for a total of five sampling periods, mimicking seasonal change (i.e. Autumn, Winter, Spring, Summer, Autumn) for each farm. The intestinal samples were sequenced (16S rRNA gene, Illumina MiSeq) and the intestinal microbiomes were analysed. The intestinal microbiomes of hybrid and greenlip abalone were dominated by four genera: Psychrilyobacter, Vibrio, Mycoplasma, and to a lesser extent Formosa. The dominance of the digestive tract by four genera (≥88%) indicates that the abalone gut is a niche environment with unique selective pressures. The intestinal microbiomes were significantly impacted by the sampling date, which is associated with seasonal changes and abalone age.

Growth Performance and Transcriptomic Response of Warm-Acclimated Hybrid Abalone Haliotis rufescens (♀) × H. corrugata (♂).

Along the Pacific coast of the Baja California Peninsula (Mexico), abalone represents one of the most lucrative fisheries. As wild populations are currently depleted, abalone farm production aims to balance the decreasing populations with the increasing demand. The Mexican abalone aquaculture is almost entirely based on red abalone (Haliotis rufescens). However, the increasing frequency of extreme temperature events is hampering this activity. The use interspecific hybrids can potentially improve abalone culture, as species have differences in their thermal tolerance. Therefore, the hybrid progeny between H. rufescens (♀) and pink abalone H. corrugata (♂), a temperate and a warmer water abalone species, respectively, will naturally support higher temperature. To test this hypothesis, growth rate, mortality and metabolic rate of both pure (RR) and hybrid abalone (RP) were assessed under the H. rufescens' optimum (18°C) and thermally stressed (22°C) conditions. To unveil the molecular pathways involved in the heat response, transcriptional profiling of both crosses was also investigated. At high temperature, we observed constrained growth and survival in RR while RP showed a significant increase in both rates, supporting the improved performance of the hybrid compared. These results match with the transcriptional profiling of hybrids showing higher expression of genes involved in growth and calcification, whereas in the pure red progeny, the transcriptional profile was mainly associated with the regulation of necroptosis process. Our results may contribute to propose new management plans to increase farm abalone production in Baja California.

Evolved differences in energy metabolism and growth dictate the impacts of ocean acidification on abalone aquaculture

Ocean acidification (OA) poses a major threat to marine ecosystems and shellfish aquaculture. A promising mitigation strategy is the identification and breeding of shellfish varieties exhibiting resilience to acidification stress. We experimentally compared the effects of OA on two populations of red abalone (Haliotis rufescens), a marine mollusc important to fisheries and global aquaculture. Results from our experiments simulating captive aquaculture conditions demonstrated that abalone sourced from a strong upwelling region were tolerant of ongoing OA, whereas a captive-raised population sourced from a region of weaker upwelling exhibited significant mortality and vulnerability to OA. This difference was linked to population-specific variation in the maternal provisioning of lipids to offspring, with a positive correlation between lipid concentrations and survival under OA. This relationship also persisted in experiments on second-generation animals, and larval lipid consumption rates varied among paternal crosses, which is consistent with the presence of genetic variation for physiological traits relevant for OA survival. Across experimental trials, growth rates differed among family lineages, and the highest mortality under OA occurred in the fastest growing crosses. Identifying traits that convey resilience to OA is critical to the continued success of abalone and other shellfish production, and these mitigation efforts should be incorporated into breeding programs for commercial and restoration aquaculture.

Transcriptome expression profiles between diploid and triploid Pacific abalone (Haliotis discus hannai) juveniles in response to acute heat-stress and hypoxia treatments.

With an increasing interest for the use of triploids in abalone aquaculture, it is crucial to understand their physiological responses to environmental stress, particularly such as heat-stress and hypoxia, which are significant factors that cause adverse effects on the efficiency and capacity of farming practice in abalone production. However, nothing is known about gene expression of triploid abalone to modulate physiological responses under different environmental stresses. Transcriptomic response to the acute heat-stress and hypoxia were explored in hepatopancreas of diploid and triploid Pacific abalone (Haliotis discus hannai) juveniles. A total of 316 million clean reads were de novo assembled into 271,039 contigs, of which a transcriptome with 209,974 non-redundant transcripts was produced. Using generalized fold change (GFOLD) algorithm with a cut-off │GFOLD value│>4, we identified differentially expressed transcripts (DETs) from diploid and triploid abalone in responses to acute heat-stress and hypoxia treatments, respectively. Comparative analysis of the identified DETs revealed alteration of transcript expression profile, level, and process in triploid abalone compared to their diploid siblings. Thus, our study will provide not only comprehensive insight into understanding of the transcriptional regulation to environmental stresses in triploid abalone but a framework for efficient management of triploid abalone aquaculture.

Microbiota of the Digestive Gland of Red Abalone (Haliotis rufescens) Is Affected by Withering Syndrome.

Withering syndrome (WS), an infectious disease caused by intracellular bacteria Candidatus Xenohaliotis californiensis, has provoked significant economic losses in abalone aquaculture. The pathogen infects gastroenteric epithelia, including digestive gland, disrupting the digestive system and causing a progressive wilting in abalone. Nonetheless, our knowledge about WS implications in digestive gland microbiota, and its role in diseases progress remains largely unknown. This study aims to determine whether digestive gland-associated microbiota differs between healthy red abalone (Haliotis rufescens) and red abalone affected with WS. Using high-throughput sequencing of the V4 region of the 16S rRNA gene, our results revealed differences in microbiota between groups. Bacterial genera, including Mycoplasma, Lactobacillus, Cocleimonas and Tateyamaria were significantly more abundant in healthy abalones, whilst Candidatus Xenohaliotis californiensis and Marinomonas were more abundant in WS-affected abalones. Whilst Mycoplasma was the dominant genus in the healthy group, Candidatus Xenohaliotis californiensis was dominant in the WS group. However, Candidatus Xenohaliotis californiensis was present in two healthy specimens, and thus the Mycoplasma/Candidatus Xenohaliotis californiensis ratio appears to be more determinant in specimens affected with WS. Further research to elucidate the role of digestive gland microbiota ecology in WS pathogenesis is required.

전복 해상가두리 양식업의 품종별 경제성 비교 분석

This study aimed to analyze the economic feasibility of hybrid abalone aquaculture production performance in Wando region, Korea. Hybrid abalones formed from two species were produced. Comparative analyses on income and cost of production based on experimental results for growth and survival rates of the hybrid abalone were conducted. Also, sensitivity analyses for very uncertain survival rate, a price of the juvenile abalone, and selling prices were performed. This study identified the highest value of NPV for hybrid abalone. Although the result of economic evaluation for existing species was good, considering higher profits abalone aquaculture specialized in hybrid species was considered to be advantageous.

Trends in seaweed resource use and aquaculture in South Africa and Namibia over the last 30 years

Abstract The seaweed industry of temperate Southern Africa was last reviewed in 2003. Since then there have been considerable changes. There are three main uses of kelp (mostly Ecklonia maxima, with some Laminaria pallida) in South Africa. The collection of wash-up for drying and exporting for alginate extraction has drastically reduced to very small amounts in recent years. The boat harvest of fresh kelp for abalone feed in land-based farms has reached a plateau of between 4000 and 5000 t fresh per annum. The diver harvest of E. maxima for agricultural liquid plant growth enhancer shows a constant increase over several years, is still growing, and is currently over 3000 t fresh per annum. The small intertidal collection of Gelidium pristoides as export for agar production has maintained a small, sustainable production of around 100 t dry for many years. Former Gracilaria industries in sheltered bays in both South Africa and Namibia have collapsed, and there is currently no commercial collection. There was commercial raft aquaculture production of Gracilaria in Lüderitz Bay, Namibia for a number of years, but this is no longer practised. Currently, the only commercial seaweed use in Namibia is of L. pallida. Annually, ca. 150 t of fresh wash-up is collected, in Lüderitz, to be used as feed in land-based abalone aquaculture. There are a number of small start-up companies experimenting with seaweed products for cosmetics and nutritional products in both countries, some involving species of Ulva and Porphyra. The former species is a major aquaculture product, with around 2000 t fresh yr–1 being produced in integrated land-based systems with abalone.

Shelter selection by juvenile Pacific abalone ( Haliotis discus hannai Ino) as a function of food distribution and water flow velocity

Juvenile Pacific abalone (Haliotis discus hannai Ino) are currently reared in land-based aquaculture systems until they reach the necessary size for seeding in the sea. One problem that this industry faces is that an uneven distribution of juveniles in tanks can lead to variations in the growth rate. Understanding the cues that affect the sheltering behaviours exhibited by juvenile Pacific abalone—namely, the food distribution and the water flow velocity—will help optimize abalone culture settings. In this study, a group of 1,000 juvenile Pacific abalone (distributed across three tanks) was visually observed and enumerated during six experiments that were conducted over a 5-month study period. It was found that juvenile Pacific abalone preferred to shelter close to food sources when the food was unevenly distributed. When the food was evenly distributed, the juveniles tended to avoid areas of rapid water flow and distributed evenly across the sheltered areas receiving the equal water velocity. This distribution might be the confounding effects between water flow velocity and food stimulus. Based on these findings, it was recommend that the food and water velocity be evenly distributed in an abalone aquaculture system.

The survival and respiration response of two abalones under short-term hypoxia challenges

Anthropogenically increased occurrence of hypoxic conditions in the aquatic environment, combined with climate change-induced temperature increase, is causing increased concern for aquaculture species. In this study, the survival of the Pacific abalone Haliotis discus hannai (DD) and its hybrid offspring (H. discus hannai ♀ × H. fulgens ♂, DF) were observed under 96 h hypoxia at both optimum temperature (20 °C) and high temperature (28 °C). The respiration rates (MO2) of DD and DF facing acute hypoxia at three temperatures (20 °C, 25 °C, and 28 °C) and progressive hypoxia at three different sizes (2 cm, 4 cm, and 6 cm) were compared. At 20 °C, there was no significant (p > .05) difference between median lethal concentrations (LC50) of DD and DF while considering all time intervals; however, at 28 °C, 96 h DO LC50 of DF (3.18 mg/L) was lower than that of DD (4.82 mg/L), indicating that DF displayed stronger hypoxia tolerance ability than DD at 28 °C. MO2 of DD and DF increased with rising temperature and larger sizes under acute and progressive hypoxia tests, while DF showed higher MO2 than DD, indicating its better plasticity of oxygen uptake. These results suggest that DD might be more vulnerable to a combination of thermal and hypoxia stress than DF, revealing that hybridization could be a useful way to improve stress-resistance for the abalone aquaculture industry.

Immune response in probiotic-fed New Zealand black-footed abalone (Haliotis iris) under Vibrio splendidus challenge

Vibriosis disease is a major constraint for sustainable molluscan aquaculture. Development of strategies to enhance disease resistance during grow out would greatly reduce stock mortality and boost production yields. In this study, New Zealand black-footed abalone (Haliotis iris) were fed a commercial diet enhanced with multi-strain probiotics (Exiguobacterium JHEb1, Vibrio JH1 and Enterococcus JHLDc) for four months, then challenged with an injection of pathogenic Vibrio splendidus. Host immune responses in haemocytes were characterized using flow cytometry by measuring total haemocyte counts (THC) and viability, degree of apoptosis, and production of reactive oxygen species (ROS) 48 h post-challenge. Probiotic-fed abalone had significantly higher survival rates compared to control animals after the bacterial challenge. Infected probiotic-fed abalone also had significantly higher haemocyte viabilities, slightly lower proportions of haemocytes undergoing early apoptosis, and lower proportions of ROS-producing haemocytes compared to infected control-fed abalone. In addition, metabolite profiles of muscle tissues generated via gas chromatography–mass spectrometry (GC-MS) delivered complimentary evidence to support a perturbed ROS-regulatory system in infected abalone through changes in key metabolites associated with glutathione biosynthesis. The results of this study provide valuable information to assist in farm management practices, leading to enhance production and sustainability of the New Zealand abalone aquaculture industry.

Review Vibriosis Management in Indonesian Marine Fish Farming

Vibriosis is a bacterial disease that has been reported in Indonesian marine fish culture since the 1990s. The disease was reported mostly in grouper and shrimp (monodon and vanname) farming, although the infections in snapper (Lates calcarifer)and abalone (Haliotis squamata)aquaculture were also occurred. Causative agents of vibriosis in Indonesia marine fish is involving 14 species of vibrio namelyVibrio harveyi, V. anguillarum, V. alginoluticus, V. parahaemolyticus, V. fluvialis, V. furnisii, V. methcnikovii, V. vulnificus, V. ordalii, V. cincinnatiensis, V. carchariae, V. azureus, V. mimicus and V. damsela. Control of vibriosis is conducted with water quality management, applications of vaccines, antibiotics, probiotics and immunostimulants. Most vaccines developed and commercially available in Indonesia are in the form of inactive-whole cell types. The vaccine product is effective enough to protect fish from vibriosis. Probiotics have been widely studied since the 2000s and have been shown to increase fish and shrimp growth and resistances against vibriosis. Immunostimulants began to be developed since 2010 based on the extracts of terrestrial plants, seaweeds and chitosan. It is therefore concluded that the continuous existence of pathogenic strains in aquaculture farm requires further development of the control methods, including periodic updating of the vaccines, probiotics and immunostimulant formulas for more potent efficacies.

A new indicator of hypoxia tolerance in abalone, developed based on heart rate fluctuations

China is the largest producer and consumer of abalone worldwide, harvesting nearly 140,000 tons in 2016. Due to rising temperatures, intensive culture patterns, and other factors, hypoxia has become a serious problem for Chinese abalone aquaculture, especially in Fujian Province. A hypoxia-tolerant strain is needed for the sustainable development of abalone farming. However, it is problematic to evaluate hypoxia tolerance in abalone. Usually, the traditional analyses cause severe damages to the sampled individuals, possibly including disorders in gonad development or death and these samples could hardly be used for breeding. Here, it was found that abalone heart rates characteristically exhibited a sharp decline below a certain DO threshold, which can be referred to as the breakpoint of dissolved oxygen (BPDO). The BPDOs were sensitive to temperature – the higher acclimation temperature or experimental temperature would increase BPDO. To verify the utility of BPDO as an indicator of hypoxia tolerance in abalone, an acute stress test was conducted with 32 abalone individuals under severe hypoxia (~0.5 mg/L) and significant negative correlations between BPDO and attachment duration, and between BPDO and survival time were found. The BPDO method was advantageous, as it supported individual detection and survival, which allows the selection and retention of hypoxic-tolerant individuals for further genetic breeding. BPDOs at different temperatures also provide important references for abalone aquaculture.

Growth enhancement of tropical abalone, Haliotis asinina L, through probiotic supplementation

The use of probionts has been considered to be an effective technology in enhancing growth performances and survival rate of aquaculture species. This study examined the effect of three probiotic candidates (Bacillus amyloliquefaciens MA228, Enterobacter ludwigii MA208, and Pediococcus acidilactici MA160) on the growth and survival rates of juvenile abalone, Haliotis asinina L). The three probionts were incorporated as a mixture of two or three onto Gracilaria sp. and fed to juvenile abalone for 62 days. Then, specific growth rate (SGR), feed conversion ratio (FCR), and survival rate (SR) were measured. The results showed that the increments in weight and length were significantly higher (P 72% among the treatments and control. Our study shows that the growth of juvenile abalone could be improved through probiotic supplementation. Thus, E. ludwigii MA208 and B. amyloliquefaciens MA228 are considered potential probionts which can be used to shorten culture period of abalone aquaculture.

Greenlip Abalone (Haliotis laevigata) Genome and Protein Analysis Provides Insights into Maturation and Spawning.

Wild abalone (Family Haliotidae) populations have been severely affected by commercial fishing, poaching, anthropogenic pollution, environment and climate changes. These issues have stimulated an increase in aquaculture production; however production growth has been slow due to a lack of genetic knowledge and resources. We have sequenced a draft genome for the commercially important temperate Australian ‘greenlip’ abalone (Haliotis laevigata, Donovan 1808) and generated 11 tissue transcriptomes from a female adult abalone. Phylogenetic analysis of the greenlip abalone with reference to the Pacific abalone (Haliotis discus hannai) indicates that these abalone species diverged approximately 71 million years ago. This study presents an in-depth analysis into the features of reproductive dysfunction, where we provide the putative biochemical messenger components (neuropeptides) that may regulate reproduction including gonad maturation and spawning. Indeed, we isolate the egg-laying hormone neuropeptide and under trial conditions induce spawning at 80% efficiency. Altogether, we provide a solid platform for further studies aimed at stimulating advances in abalone aquaculture production. The H. laevigata genome and resources are made available to the public on the abalone ‘omics website, http://abalonedb.org.

Effects of the probiotic Bacillus amyloliquefaciens on the growth, immunity, and disease resistance of Haliotis discus hannai

The effects of a diet containing the probiotic Bacillus amyloliquefaciens on the survival and growth of Haliotis discus hannai were evaluated by measuring growth and hematological parameters and the expression levels of nonspecific immune genes. In addition, the abalone's response to Vibrio parahaemolyticus infection was assessed. H. discus hannai (shell length: 29.35 ± 1.81 mm, body weight: 4.28 ± 0.23 g) were exposed to an 8-week culture experiment in indoor aquariums and a 2-week V. parahaemolyticus artificial infection experiment. In each experiment, the control group (C) was fed daily with the basal feed; the experimental groups were fed daily with the experimental feed, prepared by spraying B. amyloliquefaciens onto the basal feed at final concentrations of 103 (group A1), 105 (A2), and 107 (A3) cfu/g. The survival rate, body weight specific growth rate, and food conversion efficiency in A2 and A3 were significantly higher than those in A1 and C (P < 0.05). The total number of blood lymphocytes, the O2− and NO levels produced from respiratory burst, the activities of acid phosphatase, superoxide dismutase, and catalase, and the expression levels of catalase and thiol peroxidase in A2 were not significantly different from those in A3, but these factors were significantly higher in A2 compared to A1 and C (P < 0.05). The total antioxidant capacity and expression levels of glutathione S-transferase in A1, A2 and A3 were significantly higher than those in C (P < 0.05). At day 9 after infection with V. parahaemolyticus, all abalone in C were dead; at the end of the experiment, the cumulative mortality of abalone in A2 was significantly lower than that in any other group (P < 0.05). Thus, the experimental feed containing 105 cfu/g B. amyloliquefaciens not only facilitated the food intake and growth of abalone, but also effectively enhanced their non-specific immunity and resistance to V. parahaemolyticus infection. In this regard, B. amyloliquefaciens may be a useful probiotic strain for abalone aquaculture.

Intraindividual Variation in Nuclear DNA Content in Durvillaea Antarctica (Chamisso) Hariot, Macrocystis pyrifera (Linnaeus) C. Agardh and Lessonia spicata (Suhr) Santelices (Phaeophyceae)

Macrocystis C. Agardh, Durvillaea Bory and Lessonia Bory are three brown seaweeds genera of commercial importance for Chilean fishermen. Macrocystis pyrifera (Linnaeus) C. Agardh (Laminariales, Laminariaceae) is one of the world's most ecologically and economically important seaweed collected in Chile for alginate extraction; and as food for abalone aquaculture, Lessonia spicata (Suhr) Santelices (Laminariales, Lessoniaceae) represents more than 70% of the total brown seaweeds annual landing in Chile; and Durvillaea antarctica (Chamisso) Hariot (Fucales, Durvillaeaceae) is consumed as food, being considered very healthy because of its iodine content. Despite the economic importance of these species their nuclear DNA content is unknown until this moment. The present research was initiated to determine the nuclear DNA content and the intraindividual ploidy level variation in these seaweeds. The DNA-localizing fluorochrome DAPI (4′,6-diamidino-2-phenylindole) and red blood cell (chicken erythrocyte) standard were used to estimate the nuclear DNA contents by image analysis. Durvillaea antarctica presented lower 2C DNA (1.2 pg) content and narrower range of DNA contents (1C-2C) than the Laminariales, which showed higher 2C DNA contents (1.4 -1.5 pg) and a wider range of ploidy level, achieving up to 4C in L. spicata and up to 8C in M. pyrifera. This higher ploidy levels observed would be related with the more complex cortical organization in the Laminariales than D. antarctica. 1C nuclei were only found in mature antheridia (D. antarctica) and sporangia (M. pyrifera and L. spicata). The 2C values observed for the taxa assessed were in the range of other previously published Fucales and Laminariales.

The prevalence of abalone herpesvirus in two Haliotis species in South China during 2002–2013

Abalones (Haliotis spp.) are economically important seafoods. However, the appearance of lethal diseases since 1999, such as those caused by low-temperature viruses, have led to the near collapse of the aquaculture industry of small abalone (H. diversicolor) in southern China. The abalone herpesvirus (AbHV) is one of these suspected low-temperature viral pathogens, but the absence of epidemic data of AbHV in abalone species in China has hampered in-depth studies of AbHV and the identification of the pathogen(s) causing abalone viral disease(s). Here, we performed the first epidemiological study on AbHV in China, using quantitative PCR. The first batch of abalone individuals (n = 1082) was collected monthly from April 2012 to October 2013 at seven sites along the coast of the South China Sea. Analyses revealed the presence of AbHV in cultured abalone in China, with a detection rate of 27.73%. Most individuals were healthy and showed a viral DNA load below 103 copies per ng host DNA. No effect of the culture method (artificial pond culture or open sea raft culture), shell length, or host species (H. diversicolor and H. discus hannai) on the viral load was detected. In the second batch of samples (n = 500), collected between 2002 and 2012, AbHV was detected at a detection rate of 29.20%. Ultra-high viral DNA loads (105 to 107 copies/ng host DNA) were detected in the diseased abalone samples. Artificial infection results confirmed the pathogenicity of AbHV to H. diversicolor, suggesting that AbHV is probably the pathogen responsible for the abalone low-temperature viral disease. These findings will benefit the abalone aquaculture industry, as it provides data that can be used to improve the control of viral diseases, and facilitate further AbHV-related studies.

Hemolymph and transcriptome analysis to understand innate immune responses to hypoxia in Pacific abalone

Hypoxia was thought to inhibit immune responses, causing severe mortality to marine organisms. The Pacific abalone, Haliotis discus hannai, is the most widely cultured abalone species in China, but suffering from “summer mortality” in which hypoxia has been one of the main reasons. The effect of hypoxia exposure on immune responses in H. discus hannai was investigated, including cellular immune response using flow cytometry and transcriptome profiles. The influence of hypoxia treatment on the total hemocyte count (THC) of H. discus hannai was rather limited but the hemocyte survival rate of abalone increased during 48 h exposure. There was an initial rise in the production of phagocytes and reactive oxygen species (ROS) shortly (3 h) after hypoxic stimulation, but finally decreased after 48 h. This indicates that hypoxia inhibited redox activity of abalone. RNA-seq studies of gill tissues also revealed immune response mechanism in abalone after 24 h of hypoxia. Totally 954 differentially expressed genes (DEGs) were detected under different degrees of deoxygenation. Though oxidation-reduction turbulence was a result of both up- and down-regulated DEGs, cell death/apoptosis induction resulted from up-regulated DEGs, whilst DNA metabolic and immunity suppression resulted from down-regulated DEGs. In summary, our data provides evidence that deoxygenation greatly affects abalone immunity, probably making it more vulnerable. The present study also lays the foundation for further research in hypoxia-associated conditions in abalone aquaculture.