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Introduction: The Pacific abalone, Haliotis discus hannai, is one of the most commercially important marine shellfish in China. Cell engineering breeding is an important tool in abalone genetic breeding, and the triploids obtained through this method have high commercial value. However, current research mainly focuses on establishing induction methods and evaluating the growth traits of triploids, while there is a lack of basic research on triploid cytogenetics. Method: In this study, Cytogenetic analysis of triploid Haliotis discus hannai larvae (produced by chemical treatment) and diploid larvae was performed. Result: The results showed that triploid H. discus hannai had a chromosome number of 3n = 54, consisting of 30 metacentric (m) and 24 submetacentric (sm) chromosomes, while the diploids had a chromosome number of 2n = 36, consisting of 20 metacentric (m) and 16 submetacentric (sm) chromosomes. Notably, both triploids and diploids displayed variation in the number of NORs and/or their diameter. The average number of NORs in triploid was significantly higher than that in diploids (p <0.05), but the average diameter of NORs of triploid was no significant different from that of diploid (p> 0.05). Additionally, 5S rDNA localization to 3 submetacentric chromosomes was observed in triploids, compared to 2 submetacentric chromosomes in diploids. The number of 18S rDNA sites displayed positional conservancy and quantitative variability in both diploids and triploids. Specifically, 18S rDNA was found at the end of the chromosome in both groups, with triploids exhibiting a significantly higher number of loci than diploids (p <0.01). Conclusion: This study provides valuable insights into the cytogenetic characteristics of triploid H. discus hannai, which could facilitate further research on the stability of the chromosome set in this species. [ABSTRACT FROM AUTHOR]

The cost of reproduction is the core driver of life history evolution in animals. This paper demonstrates that the cumulative distance moved and the duration of movement of sexually immature abalones, Haliotis discus hannai, kept in various male and female groups, were significantly higher than those of sexually mature individuals, except when kept in mixed cultures of mature males and females. After mixed‐culture, sexually mature males moved significantly further and for a longer duration than mature female abalones, and even more so than mature male abalones of any other group. Examination of the LC‐MS metabolomics of mature males cultured with sexually mature females (AM) and those cultured with sexually immature females (JM) showed that cyclic adenosine monophosphate (cAMP) acted as a differential metabolic biomarker. After 24‐h uninterrupted sampling, the concentration of 5‐HT and the expression levels of the 5‐HT2 and 5‐HT6 receptors in AM were significantly higher than those in JM. After further injection of 5‐HT2 and 5‐HT6 receptor antagonists, the concentrations of cAMP and PKA rose again, but the cumulative movement duration and distance of male abalones decreased significantly, showing that 5‐HT was involved in the regulation of movement behavior of male abalones through the 5‐HT2 and 5‐HT6 receptor‐activated cAMP‐PKA pathways. The results demonstrated a significant increase in the movement endurance of mature male abalones cultured with mature females, providing a theoretical basis for understanding the adaptive life history strategies of abalones and suggesting ways to protect diverse benthic resources for abalones during the reproductive stage. [ABSTRACT FROM AUTHOR]

Dietary antioxidant supplementation, especially astaxanthin, has shown great results on reproductive aspects, egg quality, growth, survival, immunity, stress tolerance, and disease resistance in aquatic animals. However, the effects of dietary astaxanthin supplementation from different sources are still unknown. A comprehensive comparison of survival, growth, immune response, antioxidant activity, thermal resistance, disease resistance, and intestinal microbial structure was conducted in dietary antioxidant supplementation from the sources of Gracilaria lemaneiformis (GL), industrial synthetic astaxanthin (80 mg/kg astaxanthin actual weight, named as group 'SA80'), Phaffia rhodozyma (80 mg/kg astaxanthin actual weight, named as group 'PR80') and Haematococcus pluvialis (120 mg/kg astaxanthin actual weight, named as group 'HP120') at their optimal supplementation amounts. Furthermore, the SA80, PR80, and HP120 groups performed better in all aspects, including survival, growth, immune response, antioxidant activity, thermal resistance, and disease resistance, compared with the GL group. The PR80 and HP120 group also had a better growth performance than the SA80 group. In terms of heat stress and bacterial challenge, abalone in the PR80 group showed the strongest resistance. Overall, 80 mg/kg astaxanthin supplementation from Phaffia rhodozyma was recommended to obtain a more effective and comprehensive outcome. This study contributes to the discovery of the optimum dietary astaxanthin supplementation source for abalone, which is helpful to improve the production efficiency and economic benefits of abalone. Future research can further explore the action mechanism and the method of application of astaxanthin to better exploit its antioxidant role. [ABSTRACT FROM AUTHOR]

Bone morphogenetic proteins (BMPs) play important roles in a lot of biological processes, such as bone development, cell proliferation, cell differentiation, growth, etc. However, the functions of abalone BMP genes are still unknown. This study aimed to better understand the characterization and biological function of BMP7 of Haliotis discus hannai (hdh-BMP7) via cloning and sequencing analysis. The coding sequence (CDS) length of hdh-BMP7 is 1251 bp, which encodes 416 amino acids including a signal peptide (1–28 aa), a transforming growth factor-β (TGF-β) propeptide (38–272 aa), and a mature TGF-β peptide (314–416 aa). The analysis of expression showed that hdh-BMP7 mRNA was widely expressed in all the examined tissues of H. discus hannai. Four SNPs were related to growth traits. The results of RNA interference (RNAi) showed that the mRNA expression levels of hdh-BMPR I, hdh-BMPR II, hdh-smad1, and hdh-MHC declined after hdh-BMP7 was silenced. After RNAi experiment for 30 days, the shell length, shell width, and total weight were found to be reduced in H. discus hannai (p < 0.05). The results of real-time quantitative reverse transcription PCR revealed that the hdh-BMP7 mRNA was lower in abalone of the S-DD-group than in the L-DD-group. Based on these data, we hypothesized that BMP7 gene has a positive role in the growth of H. discus hannai. [ABSTRACT FROM AUTHOR]

Pacific abalone (Haliotis discus hannai) is one of the most valuable aquaculture species in China. However, the rapid development of the aquaculture industry has caused problem of germplasm degeneration. It is important to carry out genetic improvement of economic traits for H. discus hannai. This study was conducted to estimate genetic parameters of growth traits in Pacific abalone to provide a database for selective breeding programs. Data of 10 growth‐related traits—shell length (SL), shell width (SW), shell height (SH), shell weight (SWT), wet weight (WW), foot muscle weight (MW), soft tissue weight (STW), visceral mass weight (VW), foot muscle weight/wet weight ratio (MWR) and soft tissue weight/wet weight ratio (SWR)—were collected from 1059 adults sampled from 115 families. Significant growth differences existed between abalone under different culture modes. Abalone with red shell colour presented poorer growth performance than the normal shell colour group, and their hybrids displayed mid‐parent heterosis. The heritability values of SL, SW, SH, SWT, WW, MW and STW were 0.65 ± 0.06, 0.63 ± 0.06, 0.51 ± 0.08, 0.59 ± 0.09, 0.54 ± 0.05, 0.43 ± 0.08 and 0.43 ± 0.08, respectively, indicating high heritability. The heritabilities of VW and MWR were moderate, with estimates of 0.36 ± 0.07 and 0.21 ± 0.06, respectively, and SWR had low heritability with value of 0.17 ± 0.06. Genetic and phenotypic correlations among the growth traits were positive, in the ranges 0.24–0.99 and 0.12–0.99 respectively. Genetic correlation coefficients among most of the growth traits were close to or higher than 0.9. The results of this study demonstrate the genetic improvement potential of Pacific abalone in selective breeding. Traits such as SL, SW, SH and WW could be selected and improved simultaneously. [ABSTRACT FROM AUTHOR]

Feed efficiency (FE) is critical to the economic and environmental benefits of aquaculture. Both the intestines and intestinal microbiota play a key role in energy acquisition and influence FE. In the current research, intestinal microbiota, metabolome, and key digestive enzyme activities were compared between abalones with high [Residual feed intake (RFI) = −0.029] and low FE (RFI = 0.022). The FE of group A were significantly higher than these of group B. There were significant differences in intestinal microbiota structures between high- and low-FE groups, while higher microbiota diversity was observed in the high-FE group. Differences in FE were also strongly correlated to variations in intestinal digestive enzyme activity that may be caused by Pseudoalteromonas and Cobetia. In addition, Saprospira , Rhodanobacteraceae , Llumatobacteraceae , and Gaiellales may potentially be utilized as biomarkers to distinguish high- from low-FE abalones. Significantly different microorganisms (uncultured beta proteobacterium , BD1_7_clade, and Lautropia) were found to be highly correlated to significantly different metabolites [DL-methionine sulfoxide Arg-Gln, L-pyroglutamic acid, dopamine, tyramine, phosphatidyl cholines (PC) (16:0/16:0), and indoleacetic acid] in the high- and low-FE groups, and intestinal trypsin activity also significantly differed between the two groups. We propose that interactions occur among intestinal microbiota, intestinal metabolites, and enzyme activity, which improve abalone FE by enhancing amino acid metabolism, immune response, and signal transduction pathways. The present study not only elucidates mechanisms of variations in abalone FE, but it also provides important basic knowledge for improving abalone FE by modulating intestinal microbiota. [ABSTRACT FROM AUTHOR]

Settlement and metamorphosis is the key stage during which Haliotis discus hannai larvae change from planktonic to benthic life. Larvae tend to be highly sensitive to changes in the external environment, which can result in increased mortality. In the aquaculture industry, increasing the metamorphosis rate of larvae is considered to be a critical factor for increasing yield. In this study, we modified a recirculating aquaculture system (RAS) for dense rearing of abalone larvae. We set up five density groups (1, 5, 10, 20 and 40 ind/ml) and compared the effects of traditional aquaculture (TA) and the RAS on the hatching success rate, metamorphosis rate and the expression levels of metamorphosis‐related genes. At stocking densities of 1, 5 and 10 ind/ml, the survival rate, metamorphosis rate and expression levels of MIRP, α2ADR and DopR2 in both culture modes were significantly higher than those in the 20 and 40 ind/ml densities (p < 0.05). The metamorphosis rate and survival rate of larvae in the RAS groups were significantly higher than those in the TA groups (p < 0.05). Under TA at the 40 ind/ml stocking density, the dissolved oxygen concentration in the water declined and the TAN concentration significantly increased (p < 0.05). As the stocking density increased, the size of metamorphosed larvae under each mode tended to increase in both culture modes. In particular, when the density was highest, the time required for metamorphosis was significantly extended (p < 0.05). Based these results, use of the RAS with stocking density of 10 ind/ml would maintain a stable aquaculture water environment, prevent fertilized eggs from hatching or becoming densely aggregated before larval metamorphosis, and significantly increase the stocking density per unit water. These results provide an important reference for scaling up reproduction of larval abalone and further developing the culture mode for this economically important shellfish. [ABSTRACT FROM AUTHOR]

Phenotypic plasticity is an adaptive mechanism used by organisms to cope with environmental fluctuations. Pacific abalone (Haliotis discus hannai) are large-scale farmed in the temperate area of northern China and in the warmer waters of southern China. RNA-seq and comparative transcriptomic analysis here were performed to determine if the northern and southern populations have evolved divergent plasticity and if functional differences are associated with protein synthesis and growth-related biological progress. The DNA methylation (5mC) landscape of H. discus hannai from the two populations using whole genomic bisulfite sequencing (WGBS), exhibited different epigenetic patterns. The southern population had significant genomic hypo-methylation that may have resulted from long-term acclimation to heat stress. Combining 790 differentially expressed genes (DEGs) and 7635 differentially methylated genes (DMGs), we found that methylation within the gene body might be important in predicting abalone gene expression. Genes related to growth, development, transduction, and apoptosis may be regulated by methylation and could explain the phenotypic divergence of H. discus hannai. Our findings not only emphasize the significant roles of adaptive plasticity in the acclimation of H. discus hannai to high temperatures but also provide a new understanding of the epigenetic mechanism underlying the phenotypic plasticity in adaptation to climate change for marine organisms. [ABSTRACT FROM AUTHOR]

In recent years, suboptimal environmental conditions have been frequently reported to negatively impact on aquaculture organisms. Salinity is an important environmental factor, and its fluctuation will affect survival, growth and, potentially, the meat quality of the organisms with narrow salt tolerance cultured in coastal and inner bay. The aim of the study was to ascertain and report the influence of sub‐low salinity (28 and 30) on the production traits and nutrient composition of the Pacific abalone Haliotis discus hannai (DD), and two of its hybrids (DF and SD). In view of this, 360 abalones were subjected to four salinity levels (28, 30, 32 and 34) for ninety days. The data showed that the weight gain and the specific growth rates in wet weight between the groups followed the trend of DF > SD > DD. DF recorded the highest meat yield, which was significantly higher than SD and DD (p <.05). The sub‐low salinities tested did not influence moisture content, crude protein, total lipid and total carbohydrate (p >.05). Whilst lipid levels were fairly higher in SD and DF than in DD, at sub‐low salinities, the opposite was true for carbohydrate content. Total minerals (ash), however, were influenced by salinity (p <.05). Individuals reared at 28 significantly differed from those of the other three treatments, but there was no significant difference between the groups (p >.05). Further analysis showed sodium and potassium as the predominant minerals—with a higher concentration of sodium at higher salinities, though no significant difference was found between individuals treated at 30, 32 and 34. Zinc was the only mineral not affected by salinity (p >.05), and the accumulation of discrete minerals by the species significantly differed from one mineral to the other and proved to be species‐specific. Notwithstanding, SD demonstrated superior content of most essential minerals over DF and DD. The results in this paper infer that the Pacific abalone and its hybrids could maintain good meat quality and survival under a range of 28–34 of salinity, promoting the growth of cultured abalone under the sub‐low salinity of 28. [ABSTRACT FROM AUTHOR]

Background: The Pacific abalone, Haliotis discus hannai, is the most important cultivated abalone in China. Improving abalone muscle growth and increasing the rate of growth are important genetic improvement programs in this industry. MicroRNAs are important small noncoding RNA molecules that regulate post-transcription gene expression. However, no miRNAs have been reported to regulate muscle growth in H. discus hannai. Results: we profiled six small RNA libraries for three large abalone individuals (L_HD group) and three small individuals (S_HD group) using RNA sequencing technology. A total of 205 miRNAs, including 200 novel and 5 known miRNAs, were identified. In the L_HD group, 3 miRNAs were up-regulated and 7 were down-regulated compared to the S_HD specimens. Bioinformatics analysis of miRNA target genes revealed that miRNAs participated in the regulation of cellular metabolic processes, the regulation of biological processes, the Wnt signaling pathway, ECM-receptor interaction, and the MAPK signaling pathway, which are associated with regulating growth. Bone morphogenetic protein 7 (BMP7) was verified as a target gene of hdh-miR-1984 by a luciferase reporter assay and we examined the expression pattern in different developmental stages. Conclusion: This is the first study to demonstrate that miRNAs are related to the muscle growth of H. discus hannai. This information could be used to study the mechanisms of abalone muscle growth. These DE-miRNAs may be useful as molecular markers for functional genomics and breeding research in abalone and closely related species. [ABSTRACT FROM AUTHOR]

The temperate-water Pacific abalone, Haliotis discus hannai , has replaced the local subtropical species Haliotis diversicolor , as the main cultured abalone species in southern China in recent years. Although the ability to tolerate high temperature has increased for Pacific abalone, summer mortality still has a serious effect on cultivation success, as the temperature in southern China is significantly higher than the temperature in natural habitats. Hybridization has been demonstrated as an effective way to improve adaptability to particular environmental conditions. In this study, we introduced green abalone, Haliotis fulgens , from North America into China and successfully conducted hybridization trials with Pacific abalone. Fertilization rate for H. discus hannai ♀ × H. fulgens ♂ was at an acceptable level for commercial production. The hybrids exhibited hybrid vigor for growth and survival, as well as a higher temperature tolerance, showing great potential for application in the abalone aquaculture industry in southern China. Moreover, two-step PCR methods using three primers were developed, which can be used for quick genetic identification of green abalone, Pacific abalone and their reciprocal hybrids. Statement of relevance Summer mortality still has a serious effect on cultivation success of abalone farming in China. In this study, green abalone, H. fulgens were introduced and successfully conducted hybridization trials with Pacific abalone. The hybrids exhibited exciting hybrid vigor and adaptation to the higher temperature tolerance, which showed great potentials on application to the abalone aquaculture industry in southern China. [ABSTRACT FROM AUTHOR]

In natural environments, the spectral composition of incident light is often subject to drastic changes due to the abundance of suspended particles, floating animals, and plants in coastal waters. In this study, after four months of culturing under blue light (NB), orange light (NY), dark environment (ND), and natural light (NN), the shell length and weight-specific growth rate in Pacific abalone, Haliotis discus hannai , were ranked in the following order: NY > NN > ND > NB. To understand the growth differences in abalone under these different light environments, we first performed 24-h video monitoring and found that the cumulative movement distance and duration were lowest in group NB, whereas the cumulative movement distance and duration were significantly higher in group ND than in any other group (P < 0.05). In group NB, the time spent hidden underneath the attachment substrate accounted for 81% of the resting time, but this ratio was lowest in group ND, at only 37% (P < 0.05). Next, LC-MS metabolomics identified 201 and 105 metabolites in NB vs. NN, ND vs. NN, and NY vs. NN under the positive and negative ion modes, respectively. According to the fold changes and annotations for differential metabolites in the KEGG enrichment pathways, adenosine, NAD+, cGMP, and arachidonic acid were used as differential metabolism markers, and the AMPK signaling pathway was enriched in every comparison group, and thus investigated further. The gene sequences of three subtypes of AMPK were obtained by cloning and we found that the expression levels of AMPKα and AMPKγ , and the AMP content were significantly higher in group NB than in any other group (P < 0.05). In addition, the ATP contents and adenylate energy charge values were ranked in the following order: NY > NN > ND > NB. According to in situ hybridization analysis, the three subtype genes were widely expressed in the hepatopancreas. Finally, the contents of many lipid metabolites differed significantly among groups and the expression levels of the triglyceride hydrolysis-related gene hormone sensitive lipase and fatty acid oxidation-related gene carnitine palmitoyltransferase 1 were higher in groups ND and NB than in groups NN and NY according to fluorescence quantification PCR (P < 0.05). The expression levels of fatty acid synthase and acetyl-CoA carboxylase were significantly lower in groups ND and NB than in groups NN and NY (P < 0.05). These findings indicated that differences in the spectral composition of incident light could reshape the behavior and physiological metabolism in abalone by influencing the "energy switch" AMPK, thereby providing some insights into the mechanisms that allow nocturnal marine organisms to adapt to different lighting environments. • The movement behavior characteristics of abalones under different spectral compositions were quantified. • Energy homeostasis was evaluated based on differences in the ATP, ADP, and AMP contents. • The impact of AMPK on the switching of energy utilization modes by abalones was identified. • Lipolysis was shown to be the main energy source for abalones under blue light and in darkness. [ABSTRACT FROM AUTHOR]

The prevalence of juvenile Pacific abalone disease without apparent external lesions in the Chinese province of Fujian has led to mass mortality in 2018. A novel method for screening abalone pathogen was developed based on the importance of mucus in innate immunity. We identified the pathogenic bacterial strain of abalone by bacterial isolation, sequence analysis, and experimental challenges in vitro and in vivo. We verified that the abalone mortality rates were high when exposed to Pseudoalteromonas shioyasakiensis strain SDCH87 at 28 °C. This opportunistic pathogen had an outstanding growth ability in mucus and disrupted the first line mucosal immunity in the pedal within three days. To our knowledge, this is the first report that P. shioyasakiensis is a severe opportunistic pathogen of abalone, which indicated pedal was the lesion, in the context of a heatwave. • A novel method was developed for screening abalone pathogens, based on the important role of mucus in the innate immunity. • P. shioyasakiensis strain SDCH87 is a significant opportunistic pathogen of abalone during a record-breaking heatwave. • Histopathology and the distribution of bacterial strains indicated pedal was the lesion. [ABSTRACT FROM AUTHOR]

Circadian rhythm is the most important and universal biological rhythm in marine organisms. In this research, the movement behaviour of abalone (Haliotis discus hannai) was continuously monitored under a light cycle of 12 L:12D. It was found that the cumulative movement distance and cumulative movement time of abalone reached was highest from 00:00–03:00 h. The minimum values of maximum movement velocity occurred between 21:00–00:00 h, and a significant circadian cosine rhythm was exhibited during these periods (P < 0.05). Metabolomic analysis of cerebral ganglions of abalone was conducted at 06:00 h (6 M), 14:00 h (14 M), and 22:00 h (22 M) and 380, 385, and 315 metabolites with significant differences were identified in 6 M vs 14 M, 14 M vs 22 M, and 6 M vs 22 M, respectively (P < 0.05). With the alternation of day and night, the expression levels of phosphatidylcholine, 5-HT, N -acetyl-5-hydroxytryptamine, indole-3-acetaldehyde, hypoxanthine, and deoxyinosine declined significantly, while those of Lysophosphatidylcholines (lysoPC) (20: 5 (5Z, 8Z, 11Z, 14Z, 17Z)), lysoPC (22: 4 (7Z, 10Z, 13Z, 16Z)), lysoPC (16: 1 (9Z) / 0: 0), phosphatidylethanolamine (PE) (18: 1 (11Z) 22: 2 (13Z, 16Z)), and guanosine 5′-phosphate rose significantly. These 11 metabolites can be used as differential metabolic markers. These findings not only quantitatively describe the circadian movement behaviours of abalone, but also provide an initial analysis of the circadian mechanism of the physiological metabolic conversion of abalone, which in turn provides guidelines for light control and feeding strategy for use in aquaculture production. • A specific method and unit for studying the behavioral ecology of abalone was established. • A quantitative description of the characteristics of movement behaviours of abalone was performed for the first time. • The circadian physiological adaptation mechanism of abalone was revealed by metabolomics. • Certain references were provided for lighting control and feeding strategy during the aquaculture production of abalone. [ABSTRACT FROM AUTHOR]

Marine environments harbor a growing number of stressors brought about by global climate change, local human activities and the urbanization of coastal areas. The Pacific abalone, Haliotis discus hannai , is a nocturnal animal that avoids strong light and prefers darkness. Previous research showed that the abalone mortality rate under short-wavelength blue light was remarkably greater than that under darkness, natural light and orange light. In this study, the temporal variations in the dopamine content of abalone hemolymph under various light conditions were compared, and the dopamine content after exposure to blue light for 6 h was remarkably higher than that in any other group. The full-length monoamine oxidase (MAO) gene sequence for the catecholamine metabolism-related MAO enzyme was obtained by cloning. This gene encoded 545 amino acids, in which the predicted sequence contained a domain that was characteristic for monoamino oxidase. The MAO expression levels were highest in the hepatopancreas and in situ hybridization further revealed that MAO was widely localized around the hepatic nerve cord. The in vitro recombinant MAO protein could catalyze the degradation of epinephrine and dopamine. After 3 h exposure to blue light, the expression levels of MAO , Mn-superoxide dismutase (Mn-SOD), and catalase (CAT) genes were remarkably greater than those in any other group, but the lysozyme (LYZ) and sigma-glutathione-s-transferase (GST s) expression levels began to increase at 12 h and 6 h, respectively. After the MAO expression levels were knocked-down by RNAi technology, the dopamine concentration significantly increased, but the phagocytic activity, nitric oxide concentration, and the Mn-SOD , CAT , GST s and LYZ expression levels were remarakbly lower than in the control group and the enhanced green fluorescent protein (GFP) group, suggesting that the normal dopamine metabolism process played a vital role in maintaining the immune response. The above results show that monoamine oxidase may act as an immunomodulator in abalone when responding to adverse light conditions. These results could also be useful when drawing up conservation measures for preserving nearshore benthic biodiversity, such as optimizing urban night lighting schemes. • The impacts of light pollution on the NEI of nocturnal Mollusca was examined. • Full-length sequence of the MAO gene in H. discus hannai was obtained by cloning. • Recombinant MAO protein catalyzed the degradation of epinephrine and dopamine in vitro. • Knockdown of MAO expression inhibited the expression of immune-related enzyme genes. • MAO mediated NEI regulation of the abalone immune process in response to blue light. [ABSTRACT FROM AUTHOR]

Genetic improvement of feed efficiency (FE) in Pacific abalone (Haliotis discus hannai) can improve farming efficiency and reduce costs. Temperature has important effects on the feeding and growth of abalone, and genotype by environment (G × E) interactions should be considered in selecting breeding programs for genetic gain. To improve the selection strategy, FE performance, genetic parameters, and G × E interactions of abalone were measured and evaluated at 17 °C, 21 °C, and 27 °C. The feed efficiency ratio (FER) showed a similar degree of phenotypic variation at all three temperatures, with the best phenotypic performance at 17 °C. The heritability of FER was high (0.55–0.72) and relatively stable at different temperatures, while the heritability of residual feed intake (RFI) changed with temperature and was 0.21 at 27 °C. The FER had a high positive genetic correlation (0.68–0.75) with specific growth rates (SGRs) and a genetic correlation ranging from 0.32 to 0.81 with food intake (FI). RFI had a low genetic correlation with growth (−0.43 to 0.03) and a high genetic correlation (0.42–0.82) with FI. The between-environment genetic correlations for FI, weight gain (WG), and FER were high (0.78–0.94). However, the RFI showed significant G × E interactions at different temperatures. By combining the performance results, genetic parameters, and G × E interactions, it was found that FER was the most suitable trait for improving abalone FE at variable temperatures in breeding programs. This study provides guidance on selective breeding strategies to improve abalone FE. • FER showed a similar degree of phenotypic variation at three temperatures. • FER was more associated with increased growth, while selection for the RFI favored reduced feeding. • When selecting for FE at different temperatures, G × E interactions should be considered for RFI. [ABSTRACT FROM AUTHOR]

In natural aquatic environments, the spectral composition of incident light often changes abruptly in response to the abundance of suspended particulate matter and zooplankton and plankton in nearshore waters. Understanding these responses is important for the aquaculture of various species, including the abalone Haliotis discus hannai. The current study investigated the metabolic regulatory mechanisms leading to growth differences of H. d. hannai under different spectral compositions [blue light (NB), orange light (NY), dark environment (ND) and natural light (NN)]. Overall, the cumulative distance moved, and duration and average speed of movement were significantly higher under NB than under ND or NY following an abrupt change from natural light to blue light. There was a significant increase in reactive oxygen species (ROS) content, with glutathione S -transferase (GST) activity and glutathione (GSH) content being significantly higher in Group NB than in Groups ND and NY, suggesting that the blue light environment causes oxidative stress to which the abalones respond by moving away. Based on LC-MS metabolomics, 201 and 105 metabolites were identified in NB versus NN, ND versus NN, and NY versus NN groups under positive and negative ion mode, respectively. Based on fold changes and annotations in the KEGG enrichment pathway, methionine, AMP, D-mannose 6-phosphate, phenylpyruvic acid, L-tyrosine, L-histidine, NAD+, and 5-hydroxytryptophan were used as metabolic biomarkers. Only Group NB had a significant increase in 5-HT concentration and 5 -HT1A receptor expression levels, suggesting that this receptor is involved in the endocrine response of abalones to blue light stress. These results quantify the characteristics of the movement behavior of abalones under different light conditions, and preliminarily identify the physiological adaptation mechanisms of abalones under abrupt light change. Such data provide guidance for the optimization and regulation of environmental light factors in the aquaculture of H. d. hannai. [Display omitted] • A comparative study of the movement behavior of abalone was conducted to determine effect of changing the light environment. • It was found that abalone antioxidant system became activated following a change from natural to blue light. • 5-Hydroxytryptophan was identified as a differential metabolic marker following an abrupt change in the lighting conditions. • The 5-HT1 receptor was shown to be active in regulating the endocrine system and movement behavior of abalone. [ABSTRACT FROM AUTHOR]

The hybrid abalone Haliotis discus hannai ♀ × H. fulgens ♂ (DF) shows obvious growth advantages compared with one of its parents, H. discus hannai (DD); however, the reasons for these advantages are not fully understood. Using a video surveillance system, the current study showed that the feeding behaviors of DD and DF exhibited an obvious circadian rhythm, with significantly more feeding at night by DD and DF than during the day. In addition, the amount of time feeding by DF during the day and at night was significantly higher compared with that of DD, especially at ZT8 (20:00), ZT12 (24:00), ZT16 (04:00), and ZT20 (08:00), with the proportion of time feeding by DF increasing 2.22-, 1.60-, 2.71-, and 2.40-fold compared with those of DD, respectively. The maximum values of pepsase activity in DD and DF, of α-amylase activity in DD, and of alginate lyase activity in DF coincided with the peak feeding period. Relative to the changes in expression levels of neuropeptide Y receptor (NPYR) in the intestine, diurnal changes in NPYR expression levels in cerebral ganglia were consistent with the changes in feeding behavior, being highest at 24:00 h in both DD and DF and then declining. There was no significant difference in the circadian expression levels of cholecystokinin receptor (CCKR) in the cerebral ganglia, whereas, in the intestinal tract, peak CCKR expression levels coincided with its anorexigenic effect; the expression levels of CCKR in the intestinal tract exhibited a significant circadian rhythm in DD. These results explain the growth advantage of DF over DD in terms of feeding behavior and digestive physiology, and support the hypothesis that diurnal changes in feeding-related genes in the nervous and digestive systems are correlated with the initiation of abalone feeding behavior. Our findings also provide guidance for developing a suitable feeding strategy for, and improving the efficiency of, the production of abalone. • The movement behavior parameters of abalone Haliotis discus hannai ♀ × H. fulgens ♂ hybrids and parental H. discus hannai were quantified. • The digestive and physiological characteristics of abalone H. discus hannai ♀ × H. fulgens ♂ hybrids were compared with those of parental H. discus hannai. • The correlation between the feeding behaviors of two abalones and the expression levels of feeding-related hormone receptors was revealed. [ABSTRACT FROM AUTHOR]

Pacific abalone (Haliotis discus hannai) is the dominant farmed abalone species in China. Feed efficiency is an important economic trait for abalone, but little attention has been paid to this trait in breeding programs of Pacific abalone. In this study, the growth and feed efficiency traits of 648 abalone were measured during two time periods (days 1–36 and days 37–72), while an individual-based accurate measurement method of feed efficiency for abalone was established. The residual feed intake (RFI) was first evaluated in abalone; this was significantly correlated between the two periods, while the feed efficiency ratio (FER) was not significantly correlated between the two periods. Genetic analysis showed that RFI exhibited moderate or high heritability, with respective scores of 0.32 and 0.40 in the two periods, and there was a strong positive genetic correlation between the two periods (0.892 ± 0.042). RFI showed weak negative genetic correlations with average daily gain (ADG) during the two growth periods (−0.144 and − 0.008), and a positive genetic correlation with daily feed intake (DFI) (0.901 and 0.794). In addition, a group-feeding experiment were carried out on 12 families. It was found that the body growth and feed intake of abalone were highly correlated with the results of individual-feeding experiment. The results demonstrated that RFI could be used as a suitable trait for indicating the feed efficiency of abalone in future breeding programs. • An individual-based method for feed efficiency measurement was established and accurate measurement of individual feed intake was achieved for the first time in abalone. • It is proved that RFI can be used as an index to evaluate feed efficiency of abalone, and the first systematic genetic evaluation of RFI in abalone was carried out. • The consistency of feed intake and growth traits of abalone in different breeding modes showed that the results of individual-feeding experiment are largely suitable for abalone industrialized farming. [ABSTRACT FROM AUTHOR]

Considerable research has been conducted on the induction of triploids in Haliotis discus hannai. However, very few studies have focused on the performance of triploids. In this study, we present the first report of a comprehensive comparative field study on triploids of H. discus hannai and their diploid siblings cultivated for up to 30 months on a sea-based suspended system in a subtropical environment. Two types of triploids were created using cytochalasin-B (CB) and 6-dimethylaminopurine (6-DMAP). The triploid percentages were 89.10% (CB group) and 100.00% (6-DMAP group) at the larval stage, which fell to 28.58% (CB group) and 86.91% (6-DMAP group) at 30 months post-fertilization (mpf). The survival rates in both treatments were similar to that of the control group, except for the 6-DMAP group at 9 mpf and both treated groups during the first high-temperature period (Jun-Dec), when significant decreases in survival were observed (P < 0.05). Surprisingly, there was no difference in thermal tolerance between triploids and diploids through the assessment of heat adhesion duration (P > 0.05). The growth of the triploids differed across the two ploidy levels. The triploids within the CB group did not differ from control diploids throughout the observation period (P > 0.05), whereas triploids in the 6-DMAP group showed superior growth in body weight at 20 mpf (P < 0.05). After the end of the maturation season (30 mpf), a significant increase (19.57%) in foot muscle weight was found in the 6-DMAP group triploids, and a significant increase (7.22%) in the foot muscle-soft tissue index (FMSI) was found in the CB group triploids in comparison to diploid individuals (P < 0.05). The advantage of meat yield may be attributed to the hypothesis of the diversion of energy from gonadal to somatic growth. Despite the normal sex ratio (1:1) of triploids, their reproductive potential was significantly reduced, showing infertility in the females with highly reduced numbers of oocytes or abnormal oogonia and sterility in the males with an absence of spermatozoa. Our study confirms a definite advantage in the meat yield of triploid H. discus hannai and provides insights for the commercial promotion of triploid strains in the abalone aquaculture industry in southern China. • The first field study on the Pacific abalone triploids cultured in subtropical area by the sea-based suspended systems. • Triploids at 20 mpf in the 6-DMAP group exhibited greater body weight than diploids; the CB group was not. • Triploids had obvious advantages in meat yield after the end of the maturation season. [ABSTRACT FROM AUTHOR]

The abalone Haliotis discus hannai is a typical nocturnal animal. It generally feeds and moves at night but evades light by hiding in the shade during the day. However, the effects of different light cycles on the feeding physiology and potential molecular mechanisms responsible for such effects in H. discus hannai have not yet been reported. We examined the feeding patterns of abalones under different light (L)/dark (D) cycles (0 L:24D, 12 L:12D, 24 L:0D) using an infrared camera and analyzed the relationships between circadian digestive enzyme activities, gene expression levels of neuropeptide Y (NPY) and its receptor (NPYR), which can promote appetite, and feeding rhythms. Feeding in abalones, including searching for food and, food capture and intake, was examined by observation of videos. The percentage of abalones feeding under different light/dark cycles had two peaks, at 20:00–22:00 and 02:00–04:00. The ingestion rate was significantly higher in abalones maintained under 12 L:12D compared with 24 L:0D conditions. The percentage of feeding individuals and food intake were significantly lower in the "daytime" compared with at "night" irrespective of the light/dark cycle, suggesting the existence of an independent internal timing mechanism and the possible involvement of circadian clock genes in the regulation of periodic feeding activity in abalones. In abalones maintained under 12 L:12D and 24 L:0D cycles, protease, cellulase, and α-amylase activities started to increase from 18:00, 2 h before the first peak of food intake. Expression levels of NPY peaked at 20:00 and expression levels of NPYR increased again at 04:00, suggesting that NPY and NPYR might be induced before and after the two peak periods of food intake in abalones, respectively. These findings demonstrate the feeding rhythm and ingestion rate of abalones under different light/dark cycles, as well as the relationships among digestive enzyme activities, gene expression levels of NPY and NPYR , and feeding activity, which in turn provides a useful reference for the development of optimal feeding strategies and improved food utilization in abalone aquaculture production. • Feeding behavior in abalones consists of searching, followed by food capture and intake. • The feeding rhythms of abalones maintained under different light/dark cycles were identified. • Digestive enzyme activities started to increase 2 h before the feeding peak in abalones. • We elucidated the internal relationships among NPY, NPYR, and feeding rhythm in abalones. • The results provide the basis for regulating the light/dark cycle in relation to feeding strategies in aquaculture. [ABSTRACT FROM AUTHOR]

The abalone Haliotis discus hannai is a typical nocturnal marine invertebrate. In this study, a quantitative analysis was performed on the motion behaviour characteristics of abalones exposed to different light cycles (0 L:24D, 12 L:12D, 24 L:0D) using infrared camera and behavioural analysis software. A preliminary analysis of the intrinsic correlations between melatonin secretion and abalone behaviour rhythms was also conducted. The results showed that the cumulative moving distance and duration of movement for abalone in the 0 L:24D group were significantly higher than those in the 12 L:12D and 24 L:0D groups (P < 0.05). The mean and maximum moving velocities of abalones in the 12 L:12D group were significantly higher than those in the 0 L:24D group (P < 0.05). The maximum cumulative moving distance and duration of movement for abalone in the 12 L:12D and 24 L:0D groups occurred between 00:00–03:00. In the 0 L:24D group, peak cumulative moving distance and duration movement were recorded between 00:00–03:00 and 15:00–18:00. According to the results of cosine analysis, melatonin content and expression levels of aralkylamine N -acetyl transferase (AANAT) and N -acetylserotonin O -methyltransferase (ASMT) in the 12 L:12D and 24 L:0D groups showed significant circadian cosine rhythms (P < 0.05) and tended to be higher during the day and lower at night. Compared with the variation trend of melatonin, the expression levels of melatonin receptor (MTR) in each group showed significant circadian cosine rhythms (P < 0.05). Especially in the 0 L:24D group, the expression levels of MTR also tended to be higher during the day and lower at night, indicating that MTR may mediate other factors which participate in the regulation of abalone circadian rhythms. The results of this study provide a quantitative description of the motion behaviour characteristics of abalone exposed to different light cycles. The intrinsic correlation between melatonin secretion and abalone motion behaviour rhythms was also examined in this study, which in turn provides a reference for light regulation and feeding strategies in aquaculture production. • A specific method and unit for studying the behavioural ecology of abalone was established. • This study provided an initial quantitative description of abalone diurnal behaviour characteristics under different light cycles. • The intrinsic correlation between melatonin secretion and abalone behavioural rhythms was further investigated. • Certain references were provided for lighting control and feeding strategy during the aquaculture production of abalone. [ABSTRACT FROM AUTHOR]