Discus Hannai Research Articles

Haemolymph pH of two important mollusc species is susceptible to seawater buffering capacity instead of pH or pCO2

The acid-base status and balance of molluscs are considered to be susceptible to environmental changes, especially in the context of ocean acidification (OA). Here, we studied the effects of manipulated seawater carbonate chemistry on the acid-base status of scallop Chlamys farreri and abalone Haliotis discus hannai. The haemolymph pH of the tested individuals showed a fast response to acidified seawater incubation, and the pH level was restored to a normal value within 1 h of recovery in control seawater. However, no significant correlation (P > 0.05) was found between haemolymph pH and seawater pCO2 or pH, while the squared Pearson correlation coefficient (R2) ranged from close to zero to 0.41. In addition, although the pCO2 level of total alkalinity (TA)-lowered seawater was lower than half of that in the control, molluscs eliminated less CO2 (less than 80%) to TA lowered waters than to the control waters. These findings seem to disagree with the crucial role of seawater pCO2 in influencing the acid-base balance of molluscs. CO2 elimination occurs in the microenvironment, and CO2 first diffuses to limited amounts of seawater that tightly surround the gills, causing dissolved inorganic carbon (DIC) accumulation in the ventilation sites, which leads to a sharp increase in the pCO2 of the surrounding seawater. Moreover, in this microenvironment, the pCO2 level increases much faster and more greatly if the environmental seawater is acidified or contains a lower level of TA. Therefore, mollusc acid-base status is influenced by rapidly varying pCO2 levels at the ventilation site, which is largely independent of that of the rest of the incubating seawater. In summary, CO2 elimination by molluscs relies heavily on the carbonate chemistry of environmental seawater, and seawater buffering capacity should be taken into consideration instead of considering only pCO2 or pH in studying the acid-base balance of marine molluscs.

Acoustic Characterization for The Feeding Activities of Haliotis discus Hannai

In order to analyze the sound production mechanism and the acoustic characteristics of Haliotis discus hannai during feeding, this paper proposes a multi-source information fusion approach combining passive acoustics with videos. In the experiments, abalones with a shell length of 60 ± 2.7 mm were divided into two groups: Group A was fed with fresh macro algae Gracilaria lemaneiformis as food once each day; Group B was placed on a small amount of sand as impurities at the bottom of the tank. As control groups, Group C did not have abalone or food and Group D did not have abalones but food was added. The eating acoustic signals of abalone were mainly concentrated in the frequency range between 9.49 kHz and 44.36 kHz, wherein the peak frequency is 37.86 ± 2.55 kHz, with the maximum energy −66.43 ± 5.17 dBm/Hz. Each pulse sequence is with a duration of 119.12 ± 70.51 ms and consists of several sub-pulses. Nearly 70% of the pulse sequences consist of 1~2 sub-pulses and the duration of the pulse containing one sub-pulse is 42.62 ± 19.72 ms. The eating rate was kept at 0.61 ± 0.04 times/min at the beginning and was decreased significantly to 0.48 ± 0.08 times/min after 60 min. Note that the characteristic analysis of abalone acoustic signals during feeding are first reported in this manuscript to the best of our knowledge, and this paper also demonstrates that the sound of abalone is produced by scraping and grinding food with radula. Because the eating rate decreases with the reduction in the abalone’s level of hunger, the results may be used as an acoustic indicator of feeding strategy for the abalone aquaculture industry.

Oxidative Stress and Apoptosis in Disk Abalone (Haliotis discus hannai) Caused by Water Temperature and pH Changes.

Ocean warming and acidification can induce oxidative stress in marine species, resulting in cellular damage and apoptosis. However, the effects of pH and water temperature conditions on oxidative stress and apoptosis in disk abalone are poorly understood. This study investigated, for the first time, the effects of different water temperatures (15, 20, and 25 °C) and pH levels (7.5 and 8.1) on oxidative stress and apoptosis in disk abalone by estimating levels of H2O2, malondialdehyde (MDA), dismutase (SOD), catalase (CAT), and the apoptosis-related gene caspase-3. We also visually confirmed apoptotic effects of different water temperatures and pH levels via in situ hybridization and terminal deoxynucleotidyl transferase dUTP nick end labeling assays. The levels of H2O2, MDA, SOD, CAT, and caspase-3 increased under low/high water temperature and/or low pH conditions. Expression of the genes was high under high temperature and low pH conditions. Additionally, the apoptotic rate was high under high temperatures and low pH conditions. These results indicate that changes in water temperature and pH conditions individually and in combination trigger oxidative stress in abalone, which can induce cell death. Specifically, high temperatures induce apoptosis by increasing the expression of the apoptosis-related gene caspase-3.

Chicken by‐product meal as a replacement to fish meal in juvenile abalone (Haliotis discus hannai Ino 1952) feed

AbstractThis study aims to assess the effect of replacing anchovy meal with chicken by‐product meal (CBM) in juvenile abalone (Haliotis discus hannai) feed. Five diets were formulated to contain 0 (CBM0), 25 (CBM25), 50 (CBM 50), 75 (CBM75), and 100% (CBM100) CBM in replacement to 24% fish meal (FM). Dried Saccharina japonica, which is the natural food for this species of abalone was also prepared. Each diet was fed to triplicate groups of abalone. 1260 abalone assigned into eighteen cages were fed for 16 weeks. After the 16‐week feeding trial, 30 abalones from each cage were exposed to air for 24 h, and survival was monitored for 7 days. Results showed that weight gain and specific growth rate of abalone fed the CBM0 (185.4 ± 12.83% and 0.93 ± 0.040%/day, respectively) diet were significantly (p < 0.04 for both) higher than those of abalone fed the CBM100 (139.0 ± 6.36% and 0.78 ± 0.024%/day, respectively) diet. Shell length and width of abalone fed the CBM0 diet were significantly (p < 0.003 and p < 0.02, respectively) longer and wider than those of abalone fed the CBM75 and CBM100 diets. Survival of abalone during the 7‐day post‐observation period after the 24‐h air exposure exhibited no remarkable (p > 0.1 for Log Rank and Wilcoxon tests) difference among all formulated diets according to the analysis of the Kaplan–Meier survival curve. In conclusion, CBM can replace FM up to 50% in an abalone diet without compromising growth performance and survival.

Identification and dimorphic expression of sex-related genes in Pacific abalone (Haliotis discus hannai)

Sex determination is a hot topic in evolutionary biology. The mechanism of sex determination is complex and diverse in shellfish, while no sex chromosomes have been found in mollusks. The Pacific abalone (Haliotis discus hannai) is one of the most economically important cultured shellfish species in China, and its sex determination mechanism is still unclear. Here, we identified the sex-determination region (SDR) of Pacific abalone and developed five stable sex-specific markers through genome-wide association studies (GWAS) based on re-sequencing data from 803 abalones. These markers can be used for sex discrimination in polyploid and sexually immature individuals in abalone breeding projects. In addition, haplotype analysis and quantitative expression of candidate sex-related genes showed that RhoGAPp190, Skp1, Cul2, and Otulin were potentially involved in the sex determination of Pacific abalone by the ubiquitin-mediated proteolysis pathway. Our study could help to better understand the molecular mechanisms that underpin sex determination and reproductive regulation in mollusks.

Purification of phenoloxidase from Haliotis discus hannai and its anti-inflammatory activity in vitro

Haliotis discus hannai, a food with a high protein content, is widely consumed in Asian countries. It is known to have antioxidant, anticancer, and antibacterial effects. Since the biological significance of H. discus hannai hemolymph has not been widely studied, the objective of the present study was to purify phenoloxidase (PO) and investigate its immunological effects on human colonic epithelial cells. PO was purified through ammonium sulfate precipitation and one step column chromatography. The molecular weight of the protein was about 270 kDa. When PO was mixed with Gram-negative bacteria-derived lipopolysaccharide (LPS) at various ratios (10:1–1:10, w/w), the amount of residual LPS was reduced. PO at concentrations up to 200 μg/mL was not cytotoxic to HT-29 cells. The inflammatory response induced by LPS in HT-29 cells was regulated when the concentration of PO was increased. With increasing concentration of PO, production levels of pro-inflammatory cytokines, cytokines associated with hyperimmune responses such as IL4, IL-5, and INF-γ, and prostaglandin 2 (PGE2) were regulated. It was thought that simultaneous treatment with PO and LPS anti-inflammatory effects in HT-29 cells showed by regulating the ERK1/2-mediated NF-κB pathway. Results of this study suggest that H. discus hannai hemolymph is involved in the regulation of Gram-negative bacteria-related inflammatory immune responses in human colonic epithelial cells.

Dietary phospholipids improve growth performance and change the lipid composition and volatile flavor compound profiles in the muscle of abalone Haliotis discus hannai by affecting the glycerophospholipid metabolism

A 106-day feeding trial was conducted to investigate the effects of dietary phospholipids on growth performance, volatile flavor compounds as well as the lipid composition in abalone Haliotis discus hannai. Abalones (initial weight: 16.19 ± 0.16 g) were fed with graded levels of dietary phospholipids (0.10 %, 0.30 %, 0.69 %, 1.30 %, 1.83 % and 2.48 %). Results showed that weight gain rate (WGR) were highest in 1.83 % dietary phospholipids level. Based on the quadratic regression analysis for WGR, the optimal dietary phospholipids level for abalone was estimated to be 1.57 %. The contents of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in abalone muscle increased gradually with the increase of dietary phospholipids levels. A total of 25 volatile flavor compounds were detected in the muscle of abalone by gas chromatograph-ion mobility spectrometry (GC-IMS), including 9 aldehydes, 6 esters, 4 ketones, 3 alcohols and 3 hydrocarbons. The content of some volatile flavor compounds with pleasant aroma in the muscle of abalone increased significantly when fed with diets containing 1.83 % and 2.48 % of phospholipids. Lipidomics analysis showed that dietary phospholipids could affect the lipid composition in the muscle by reducing the synthesis and promoting the decomposition of phospholipids. Among 244 differential lipids identified by lipidomics, phosphatidylcholines (PCs) and phosphatidylethanolamines (PEs) were the main species, accounting for more than 50 % of them. Partial least squares regression (PLS-R) analysis showed that the changes of volatile flavor compounds in the muscle of abalone was strongly related to PCs and PEs. Altogether, the present study suggested that dietary phospholipids can not only improve the growth performance and nutritional value of abalone, but also have the potential to improve the flavor quality of abalone.

Genome-wide association screening and MassARRAY for detection of high-temperature resistance-related SNPs and genes in a hybrid abalone (Haliotis discus hannai ♀ × H. fulgens ♂) based on super genotyping-by-sequencing

High seawater temperatures in summer often lead to high mortality in farmed abalone, which greatly increases the cost of farming. The hybrid abalone (Haliotis discus hannai ♀ × H. fulgens ♂, DF), is one of the main varieties of abalone cultured in Fujian Province, China, to resist the high temperature. In this study, the high-temperature resistance of DF abalones was assessed under 28 °C - 32 °C. 31 °C was applied in the subsequent screening experiments of high-temperature resistant individuals. A total of 614,321 single nucleotide polymorphisms (SNPs) were identified via super genotyping-by-sequencing (S-GBS), and 69 SNPs involved in 42 candidate genes were identified by genome-wide association study (GWAS). In addition, according to gene functional annotation, the locus with the lowest P value was screened within the threshold range (−log10P = 4.98296). The genotyping was verified by Sequenom MassARRAY, and 7 SNPs were proved to be related to high temperature resistance in DF population of 100 individuals. 7 candidate genes (fabp, e3rglg4, rgs2, tanc2x6, osbp1, arsb, and uch1) were identified near these SNPs. Finally, these candidate genes were further proved to be associated with the high-temperature resistance trait of DF by the analysis of differential expression genes between sensitive and tolerant individuals. These candidate genes involved regulatory mechanisms such as cell stability, protein repair, lipid metabolism and immune regulation. Notably, the mechanism by which the e3rglg4 gene was involved in the degradation of abnormally folded proteins of abalone under heat stress, corroborating the reliability of the results of GWAS and Sequenom MassARRA. These results complement the shortage of molecular markers for heat resistance of hybrid abalone, provide a reference for marker-assisted selection (MAS) and accelerate the development of heat-resistant abalone varieties.

Effect of dietary protein, vitamin E, and vitamin C levels on the growth and gonad development of hybrid male abalone (Haliotis fulgens ♂ × H. discus hannai ♀) by the orthogonal array design

Effect of dietary protein, vitamin E, and vitamin C levels on the growth and gonad development of hybrid male abalone (Haliotis fulgens ♂ × H. discus hannai ♀) by the orthogonal array design

Analysis of the physiological responses of Pacific abalone (Haliotis discus hannai) to various stressors to identify a suitable stress indicator

AbstractThe Pacific abalone (Haliotis discus hannai) is the most economically valuable shellfish species in Northeast Asia, accounting for most of the shellfish production in South Korea. Despite the continuous improvement in the productivity of domestic abalone aquaculture, rapid seawater temperature changes caused by global warming have led to mass mortality in coastal abalone farms. Therefore, research on environmental stressors is urgently needed to prevent abalone production losses. This study analyzed the expression of heat shock protein (HSP) genes in foot muscles of H. discus hannai and metabolic parameters including glucose, lysozyme, catalase, D‐lactate, and trehalose levels in the hemolymph under acute high temperature, low temperature, low salinity, and air exposure. Quantitative reverse‐transcription polymerase chain reaction analysis showed that HSP20 expression was downregulated in all experimental groups, whereas HSP70 expression increased immediately in all experimental groups except for the low‐temperature stress group. Hemolymph analysis showed that glucose and lysozyme levels increased significantly immediately after treatment in all groups, and decreased during the recovery period. Together, the results indicate that low water temperature stress had the smallest effect on abalone among the treatments. We conclude that the other treatments acted as stressors of abalone and that HSP genes, glucose, and lysozyme can be used as stress indicators in H. discus hannai.

Interaction between dietary lipid and bile acids on the growth performance and lipid metabolism in abalone Haliotis discus hannai Ino

A 105-day feeding trail was conducted to evaluate the effects of dietary lipid and bile acids levels as well as their interactions on the growth, digestion and lipid metabolism in abalone Haliotis discus hannai (initial weight: 5.29 ± 0.02 g). Eight isonitrogenous diets with two levels of lipid (4.3% and 6.3%) and four levels of bile acids (0, 15, 60 and 240 mg/kg) were formulated in a 2 × 4 two-factor design. The results showed that 6.3% of dietary lipid decreased the weight gain rate (WGR) of abalone, which increased as the dietary bile acids level increasing from 0 mg/kg to 60 mg/kg. The treatment with the highest WGR contained 4.3% of dietary lipid and 60 mg/kg of dietary bile acids. In the groups with 4.3% of dietary lipid, the expression of genes involved in lipid transport and lipolysis was increased (P < 0.05). And dietary bile acids increased the expression of genes involved in lipid transport and lipolysis while decreased the expression of genes involved in lipogenesis (P < 0.05). The expression of genes involved in lipid metabolism, such as cluster of differentiation, fatty acid transport protein, microsomal triglyceride transfer protein and peroxisome proliferator-activated receptor α, revealed the interactions between dietary lipid and bile acids (P < 0.05). In conclusion, the growth and digestion of abalone were negatively impacted by an excessively high dietary lipid content (6.3%). Appropriate supplemented level of dietary bile acids (60 mg/kg) significantly enhanced the growth and digestion of abalone. Dietary lipid and bile acids had an interactive effect on the lipid metabolism in abalone, including lipid transport, lipolysis and lipogenesis.

Interactions between dietary protein level and water temperature on the growth performance, innate immunity and disease resistance of juvenile abalone Haliotis discus hannai Ino

A 100-day feeding trial was performed to examine the effects of dietary protein level, water temperature and their interactions on the growth performance, innate immunity and disease resistance of abalone Haliotis discus hannai with an initial body weight of 12.20 ± 0.1 g and an initial shell length of 42.64 ± 0.29 mm. With graded levels of dietary protein (9.33%, 27.53% and 40.42%, respectively), three isolipidic and isoenergetic diets were made and used in two water temperatures (17 °C and 23 °C) in a form of a 3 × 2 factorial design. The results indicated that the weight gain rate (WGR) and daily increment in shell length of abalones (DISL) were significantly higher in 27.53% of dietary protein level at both 17 °C and 23 °C water temperatures. At 17 °C and 23 °C of water temperatures, 27.53% of dietary protein significantly increased the trypsin and α- amylase as well as decreased the malondialdehyde content and glutamate dehydrogenase activities of abalone. Dietary protein and water temperature interact significantly with WGR and α-amylase. The histological analysis of abalone’s digestive gland showed that 27.53% of dietary protein caused normal development at both water temperatures. The mRNA levels of tumor necrosis factor alpha, toll-like receptor 2 and 4, inhibitor κBα, iκb kinase α, myeloid differentiation primary response gene 88, interleukin1 receptor-associated kinase 4, caspase 3 and B-cell lymphoma protein-2-associated X protein were significantly down-regulated by 27.53% of dietary protein at 17 °C of water temperature. The total hemocyte counts (THC), respiratory burst (RB) and B-cell lymphoma 2 (Bcl-2) were significantly increased by 27.53% of dietary protein at 17 °C water temperature. Dietary protein and water temperature interact significantly with THC, RB and Bcl-2. The use of 27.53% of dietary protein at 17 °C of water temperature showed no mortality when challenged with V. parahaemolyticus. In conclusion, 27.53% of dietary protein level at 17 °C of water temperature activated the innate immunity by reducing inflammation and apoptosis response, hence increasing disease resistance in abalones after the Vibrio challenge test.

Genome-wide identification and characterization of Toll-like receptors (TLR) genes in Haliotis discus hannai, H. rufescens, and H. laevigata

Toll-like receptors (TLRs) play essential roles in the innate immune system and have been extensively studied in mollusks. In this study, through a genome-wide search, TLR genes were identified as 29 in Haliotis discus hannai, 33 in H. rufescens, and 16 in H. laevigata. Domain analysis indicated that these TLR genes contain leucine-rich repeat (LRR) and Toll/IL-1 receptor (TIR) domains and exons ranging from 1 to 5. Polymorphism analysis showed that the TLRs in abalones did not have high diversities with 143 SNPs and no Indel in H. discus hannai, 92 SNPs and 3 Indels together with 6 missense mutations in H. rufescens, and no SNP or Indel in H. laevigata. The expression of 8 TLR genes in H. discus hannai was confirmed in the hepatopancreas, gill, hemolymph, gonads, intestine, muscle, and mantle. The expression of five TLR genes (out of 8) in gills (p < 0.05), three in hepatopancreas (p < 0.05), and three in hemolymph (p < 0.05) was upregulated separately in response to the infection caused by Vibrio parahaemolyticus. The findings in this study would contribute to a better understanding of the molecular immune mechanism of H. discus hannai against stimulation by V. parahaemolyticus and provide a basis for the study of TLRs in abalones.

Development of organic-inorganic hybrid antimicrobial materials by mechanical force and application for active packaging

The loading and delivery of nanomaterials have attracted considerable interest. In this study, the organic-inorganic hybrid antimicrobial materials of clove essential oil (CEO) intercalated organic montmorillonite (MMT) were prepared using a facile and novel cryogenic ball milling technology and characterized. Fourier transform infrared spectroscopy, powder X-ray diffraction, and transmission electron micrograph analysis confirmed the successful preparation of the hybrid antimicrobial materials, and thermogravimetric analysis further demonstrated the thermal stability. In a novel application, hybrid antimicrobial materials were extruded with thermoplastic starch (TPS), polylactic acid (PLA), and poly (butylene adipate-co-terephthalate) (PBAT) to prepare active packaging films. The film release experiments showed that the CEO in the film, containing hybrid antimicrobial materials, was in a sustained release state, and its equilibrium release was higher than that of other films. The prepared films were used to preserve fresh abalone （Haliotis discus hannai Ino）, physicochemical changes and microbiological counts were determined. The results showed that the shelf life of fresh abalone packed in films containing hybrid antimicrobial materials was extended by 3–5 days, indicating that cryogenic ball milling is a simple and effective method for preparing organic-inorganic hybrid antimicrobial materials for active packaging.

Seawater carbonate parameters function differently in affecting embryonic development and calcification in Pacific abalone (Haliotis discus hannai)

pH or pCO2 are usually taken to study the impact of ocean acidification on molluscs. Here we studied the different impact of seawater carbonate parameters on embryonic development and calcification of the Pacific abalone (Haliotis discus hannai). Early embryonic development was susceptible to elevated pCO2 level. Larvae hatching duration was positively and hatching rate was negatively correlated with the pCO2 level, respectively. Calcium carbonate (CaCO3) deposition of larval shell was found to be susceptible to calcium carbonate saturation state (Ω) rather than pCO2 or pH. Most larvae incubated in seawater with Ωarag = 1.5 succeeded in shell formation, even when seawater pCO2 level was higher than 3700 μatm and pHT was close to 7.4. Nevertheless, larvae failed to generate CaCO3 in seawater with Ωarag ≤ 0.52 and control level of pCO2, while seawater DIC level was lowered (≤ 852 μmol/kg). Surprisingly, some larvae completed CaCO3 deposition in seawater with Ωarag = 0.6 and slightly elevated DIC (2266 μmol/kg), while seawater pCO2 level was higher than 2700 μatm and pHT was lower than 7.3. This indicates that abalone may be capable of regulating carbonate chemistry to support shell formation, however, the capability was limited as surging pCO2 level lowered growth rate and jeopardized the integrity of larval shells. Larvae generated thicker shell in seawater with Ωarag = 5.6, while adult abalone could not deposit CaCO3 in seawater with Ωarag = 0.29 and DIC = 321 μmol/kg. This indicates that abalone may lack the ability to directly remove or add inorganic carbon at the calcifying sites. In conclusion, different seawater carbonate parameters play different roles in affecting early embryonic development and shell formation of the Pacific abalone, which may exhibit limited capacity to regulate carbonate chemistry.

Metabolic and transcriptional responses demonstrating enhanced thermal tolerance in domesticated abalone

Global warming threatens aquatic systems and organisms. Many studies have focused on the vulnerability and stress responses of aquaculture organisms to future thermal conditions. However, it may be of more practical significance to reveal their acclimation potential and mechanisms. In this study, the physiological, metabolic, and transcriptional responses to long-term temperature acclimation of northern and southern populations of Pacific abalone Haliotis discus hannai, a commercially important gastropod sensitive to environmental changes, were compared. This study conducted two common-garden experiments, including a thermostatic experiment in the lab and an aquaculture experiment on the farm. The abalone population cultured in warmer southern waters was tolerant of ongoing high temperatures, whereas the abalone population originally cultured in cooler northern waters exhibited vulnerability to high temperatures but could enhance its thermal tolerance through the process of natural selection in warmer southern waters. This difference was linked to divergence in the metabolic and transcriptional processes of the two populations. The tolerant population exhibited a greater capacity for carbohydrate and amino acid metabolism regulation and energy redistribution to cope with heat stress. This capacity may have been selected for, and accumulated, over many generations because the tolerant population originated from the intolerant population over two decades ago. This work provides insight into the vulnerability and acclimation potential of abalone to heat stress and discloses the molecular and metabolic traits underlying this phenomenon. Future research on the ability of abalone and other commercial shellfish species to acclimate to global warming should take this potential into account.

Dietary replacement of Undaria pinnatifida by Sargassum horneri in feed formulation for abalone Haliotis discus hannai: Effect on growth, gut microbiota, and taste sensory profile

The necessity for additional macroalgal biomass is warranted amid the ongoing expansion of abalone aquaculture. In the current study, an in-depth investigation of the food value of Sargassum horneri as a replacement for Undaria pinnatifida on growth, body composition, body histology, gut microbiota, and the taste sensory profile of abalone Haliotis discus hannai was carried out. After a 12-week feeding trial, the results indicated that 25% replacement (SH25) induced the highest shell-growth performance and best feed utilization values, although there was no significant difference in weight-related growth parameters with the basal (no inclusion of S. horneri) and 50% replacement (SH50) diets. Interestingly, the highest protein content was detected in abalone fed the basal diet followed by SH25 and SH50. The high replacement of S. horneri in the diet showed signs of structural integrity loss in the digestive gland. The results from the pyrosequencing of the genomic DNA from the gut of the abalone indicated an insignificant difference in α-diversity parameters and only a clear boundary was observed between SH0 and SH100 diets based on principal coordinate analysis. The bacterial genera Psychrilobacter, Vibrio, and Mycoplasma predominantly occupied the gut of the abalone, although there is a difference in their relative abundance. The taste screening experiment through the use of an electronic tongue showed a comparable taste profile of the abalone and is independent of the diets given. The findings of the present study showed that S. horneri, up to 50% replacement of macroalgal ingredients, can be utilized in feed formulation for H. discus hannai. These, in turn, contribute to the expanding knowledge on the utilization of biofouling and non-traditional macroalgae for sustainable abalone aquaculture practices.

Reproduction strategy of nocturnal marine molluscs: running for love.

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.

Interactive effects of diet and water temperature on the nutritional value, flavor, and sensory quality in hybrid abalone (Haliotis. discus hannai ♀ × H. fulgens♂) meat

In commercial aquaculture, the phenomena of diet conversion and water temperature fluctuation commonly occur in abalone farming. The meat quality of abalone is affected by diet and temperature, and this in turn directly influences consumer acceptance of abalone products and financial returns to producers. The aim of this study was to investigate the impacts of diet (Gracilaria lemaneiformis vs artificial feed) and water temperature (low, 19 °C and high, 27 °C) on growth performance, nutritional value, flavor, and sensory quality of abalone. The results showed that artificial feed led to increases in growth, content of body protein, total free amino acids (TAA), delicious amino acids (DAA), volatile compounds (alcohols, acids, aromatic compounds, and esters), and sensory quality (hardness) of abalone meat. High temperature significantly decreased the growth, body moisture, n-3 polyunsaturated fatty acids, and hardness but increased the contents of DAA, TAA, alcohols, acids, and aromatic compounds in abalone meat. Our study suggests that high temperature significantly decreases the growth and nutritional value of abalone muscle but does provide a different mouthfeel and flavor for consumers, and nutrition-balanced artificial feed as the diet at a low water temperature maximizes the growth of abalone without sacrificing meat quality. The results may help to formulate an optimal feed strategy for farming industries throughout the abalone culture period, thereby allowing farmers to harvest premium quality abalone and elevate the market value of abalone products.

Identification and Characterization of Hdh-FMRF2 Gene in Pacific Abalone and Its Possible Role in Reproduction and Larva Development.

FMRFamide-related peptides are neuropeptides involved in a wide range of biological processes, including reproduction and larval development. To characterize the involvement of FMRFamide in the reproduction and larval development of Pacific abalone Haliotis discus hannai, an FMRFamide cDNA (Hdh-FMRF2) was cloned from the cerebral ganglion (CG). Fluorescence in situ hybridization and qRT-PCR were performed for functional characterization. The Hdh-FMRF2 cDNA encoded 204 deduced amino acids that contained a putative signal peptide and four FaRP domains. The major population of Hdh-FMRF2 neuronal cell bodies was localized in the cortex of CG. Hdh-FMRF2 mRNA expression was significantly upregulated in CG during the mature stage of gonadal development and effective accumulative temperature (EAT) exposed abalone in both sexes. In the induced spawning event, Hdh-FMRF2 expression was significantly upregulated during spawning in males. However, no upregulation was observed in females, suggesting Hdh-FMRF2 might inhibit gamete release in female abalone. These results revealed Hdh-FMRF2 as a reproduction related peptide. Furthermore, mRNA expression in larval development suggested that this peptide was also involved in larval development during development of Pacific abalone. Collectively, this study provides evidence of possible involvement of an FMRFamide neuropeptide in the reproduction and larval development of Pacific abalone.