The role of hybridization in improving the immune response and thermal tolerance of abalone

Exposure to polystyrene nanoplastics causes immune damage, oxidative stress and intestinal flora disruption in salamander (Andrias davidianus) larvae

The toxic effects of nanoparticles have been increasingly investigated, but there has been limited research on amphibians, especially those of conservation value. This study examined the effects of different concentrations (0, 0.04, 0.2, 1, 5 mg/L) of polystyrene nanoplastics (PS-NPs, 80 nm) on the short-term exposure (7 d) of Andrias davidianus. Results demonstrated the concentration-dependent enrichment of PS-NPs in the intestine. Histological lesions displayed increased hepatic macrophages with cellular rupture, broken intestinal villi, decreased cuprocytes and crypt depression. Antioxidant- and inflammation-related enzyme activities were analysed, and it was found that hepatic and intestinal MDA content and CAT activity were highest in the N-1 group and SOD activity was highest in the N-0.2 group (p < 0.05). AKP activity continued to decline, and iNOS activity was highest in the N-0.2 group (p < 0.05). il-10, tgf-β, bcl-w and txnl1 were significantly downregulated in the N-0.2 group, while il-6 and il-8 were markedly upregulated in the N-0.2 group (p < 0.05). Exposing to PS-NPs decreased probiotic bacteria (Cetobacterium, Akkermansia) and increased pathogenic bacteria (Lachnoclostridium). Our results suggest that NPs exposure can have deleterious effects on salamanders, which predicts that NPs contamination may lead to continued amphibian declines. Therefore, we strongly recommend that attention be paid to amphibians, especially endangered species, in the field of NPs.

Vitamin C as a functional enhancer in the non-specific immune defense, antioxidant capacity and resistance to low-temperature stress of juvenile mud crab, Scylla paramamosain

This experiment was conducted to explore the effects of dietary vitamin C supplementation on non-specific immune defense, antioxidant capacity and resistance to low-temperature stress of juvenile mud crab (Scylla paramamosain). Mud crabs with an initial weight of 14.67 ± 0.13 g were randomly divided into 6 treatments and fed diets with 0.86 (control), 44.79, 98.45, 133.94, 186.36 and 364.28 mg/kg vitamin C, respectively. The experiment consisted of 6 treatments, each treatment was designed with 4 replicates and each replicate was stocked with 8 crabs. After 42 days of feeding experiment, 2 crabs were randomly selected from each replicate, and a total of 8 crabs in each treatment were carried out 72 h low-temperature challenge experiment. The results showed that crabs fed diets with 186.36 and 364.28 mg/kg vitamin C significantly improved the activities of alkaline phosphatase (AKP) and acid phosphatase (ACP) in hemolymph and hepatopancreas (P < 0.05). Crabs fed diet with 133.94 mg/kg vitamin C significantly decreased the concentration of nitric oxide (NO) and the activity of nitric oxide synthase (NOS) in hemolymph (P < 0.05). Diet with 133.94 mg/kg vitamin C was improved the activity of polyphenol oxidase (PPO) and the concentration of albumin (ALB) in hemolymph. Crabs fed diet with 133.94 mg/kg vitamin C showed lower concentration of malondialdehyde (MDA) in hemolymph and hepatopancreas than those fed the other diets. Meanwhile, crabs fed diet with 98.45 mg/kg vitamin C showed higher activity of total superoxide dismutase (T-SOD) in hemolymph, and crabs fed diet with 133.94 mg/kg vitamin C showed higher activity of T-SOD in hepatopancreas. Crabs fed diet with 186.36 mg/kg vitamin C significantly decreased the concentration of reduced glutathione (GSH) and the activity of glutathione peroxidase (GSH-PX) in hepatopancreas (P < 0.05). In normal temperature, crabs fed diets with 133.94 mg/kg vitamin C significantly up-regulated the expression levels of gpx (glutathione peroxidase) and trx (thioredoxin) in hepatopancreas compared with the control treatment (P < 0.05). The highest expression levels of relish, il16 (interleukin 16), caspase 2 (caspase 2), p38 mapk (p38 mitogen-activated protein kinases) and bax (bcl-2 associated x protein) in hepatopancreas were found at crabs fed control diet (P < 0.05). Moreover, crabs fed diet with 133.94 mg/kg vitamin C showed higher expression levels of alf-3 (anti-lipopolysaccharide factor 3) and bcl-2 (B-cell lymphoma 2) in hepatopancreas than those fed the other diets (P < 0.05). Under low-temperature stress, crabs fed diet with 133.94 mg/kg vitamin C significantly improved the expression levels of hsp90 (heat shock protein 90), cat (catalase), gpx, prx (thioredoxin peroxidase) and trx in hepatopancreas (P < 0.05). In addition, dietary with 133.94 vitamin C significantly up-regulated the expression levels of alf-3 and bcl-2 (P < 0.05). Based on two slope broken-line regression analysis of activity of PPO against the dietary vitamin C level, the optimal dietary vitamin C requirement was estimated to be 144.81 mg/kg for juvenile mud crab. In conclusion, dietary 133.94-144.81 mg/kg vitamin C significantly improved the non-specific immune defense, antioxidant capacity and resistance to low-temperature stress of juvenile mud crab.

MiR-214_L-1R+4 regulate gossypol-induced immune response through MyD88-dependent signaling pathway in Cyprinus carpio

MicroRNAs (miRNAs) have been demonstrated to act as crucial modulators with considerable impacts on the immune system. Cottonseed meal is often used as a protein source in aqua feed, cottonseed meal contains gossypol, which is harmful to animals. However, there is a lack of research on the role of miRNAs in fish exposed to gossypol stress. To determine the regulatory effects of miRNAs on gossypol toxicity, Cyprinus carpio were given to oral administration of 20 mg/kg gossypol for 7 days, and the gossypol concentration in the tissues was tested. Then, we detected spleen index, histology, immune enzyme activities of fish induced by gossypol. The results of miRNA sequencing revealed 8 differentially expressed miRNAs in gossypol group, and miR-214_L-1R+4 was found involved in immune response induced by gossypol. The potential targets of miR-214_L-1R+4 were predicted, and found a putative miR-214_L-1R+4 binding site in the 3'UTR of MyD88a. Furthermore, dual-luciferase reporter assays displayed miR-214_L-1R+4 decreased MyD88a expression through binding to the 3'UTR of MyD88a. Moreover, miR-214_L-1R+4 antagomir were intraperitoneally administered to C. carpio, down-regulated miR-214_L-1R+4 could increase MyD88a expression, as well as inflammatory cytokines and anti-inflammatory cytokines expression. These findings revealed that miR-214_L-1R+4 via the MyD88-dependent signaling pathway modulate the immune response to gossypol in C. carpio spleen.

Protective effects of butyric acid during heat stress on the survival, immune response, histopathology, and gene expression in the hepatopancreas of juvenile pacific shrimp (L. Vannamei)

This study looked at the effects of adding butyric acid (BA) to the diets of juvenile Pacific shrimp and how it affected their response to survival, immunity, histopathological, and gene expression profiles under heat stress. The shrimp were divided into groups: a control group with no BA supplementation and groups with BA inclusion levels of 0.5 %, 1 %, 1.5 %, 2 %, and 2.5 %. Following the 8-week feeding trial period, the shrimp endured a heat stress test lasting 1 h at a temperature of 38 °C. The results showed that the control group had a lower survival rate than those given BA. Interestingly, no mortality was observed in the group receiving 1.5 % BA supplementation. Heat stress had a negative impact on the activities of alkaline phosphatase (AKP) and acid phosphatase (ACP) in the control group. Still, these activities were increased in shrimp fed the BA diet. Similar variations were observed in AST and ALT fluctuations among the different groups. The levels of triglycerides (TG) and cholesterol (CHO) increased with high temperatures but were reduced in shrimp-supplemented BA. The activity of an antioxidant enzyme superoxide dismutase (SOD) increased with higher BA levels (P < 0.05). Moreover, the groups supplemented with 1.5 % BA exhibited a significant reduction in malondialdehyde (MDA) content (P < 0.05), suggesting the potential antioxidant properties of BA. The histology of the shrimp's hepatopancreas showed improvements in the groups given BA. Conversely, the BA significantly down-regulated the HSPs and up-regulated MnSOD transcript level in response to heat stress. The measured parameters determine the essential dietary requirement of BA for shrimp. Based on the results, the optimal level of BA for survival, antioxidant function, and immunity for shrimp under heat stress is 1.5 %.

Ginger polysaccharide alleviates the effects of acute exposure to carbonate in crucian carp (Carassius auratus) by regulating immunity, intestinal microbiota, and intestinal metabolism

Alkaline stress poses a significant challenge to the healthy growth of fish. Ginger polysaccharide (GP) is one of the main active substances in ginger and has pharmacological effects, such as anti-oxidation and immune regulation. However, the physiological regulatory mechanism of GP addition to diet on alkalinity stress in crucian carp remains unclear. This study aimed to investigate the potential protective effects of dietary GP on antioxidant capacity, gene expression levels, intestinal microbiome, and metabolomics of crucian carp exposed to carbonate (NaHCO3). The CK group (no GP supplementation) and COG group (NaHCO3 stress and no GP supplementation) were set up. The GPCS group (NaHCO3 stress and 0.4% GP supplementation) was stressed for seven days. Based on these data, GP significantly increased the activities of total antioxidant capacity (T-AOC), superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GSH-PX), acid phosphatase (ACP), and alkaline phosphatase (AKP) in carp under alkalinity stress (p < 0.05) and decreased the activity of malon dialdehyde (MDA) (p < 0.05). GP restored the activity of GSH-PX, ACP, and AKP to CK levels. The expression levels of tumor necrosis factor β (TGF-β), tumor necrosis factor-alpha (TNF-α), interferon-gamma (IFN-γ), and interleukin 8 (IL-8) genes were decreased, and the expression levels of determination factor kappa-B (NF-κB) and interleukin 10 (IL-10) genes were increased (p < 0.05). Based on 16 S rRNA high-throughput sequencing, GP improved the changes in the intestinal microbial diversity and structural composition of crucian carp caused by NaHCO3 exposure. In particular, GP increased the relative abundance of Proteobacteria and Bacteroidetes and decreased the relative abundance of Actinobacteria. The metabolic response of GP to NaHCO3 exposed crucian carp guts was studied using LC/MS. Compared to the COG group, the GPCS group had 64 different metabolites and enriched 10 metabolic pathways, including lipid metabolism, nucleotide metabolism, and carbohydrate metabolism. The addition of GP to feed can promote galactose metabolism and provide an energy supply to crucian carp, thus alleviating the damage induced by alkalinity stress. In conclusion, GP can mitigate the effects of NaHCO3 alkalinity stress by regulating immune function, intestinal flora, and intestinal metabolism in crucian carp. These findings provide a novel idea for studying the mechanism of salt-alkali tolerance in crucian carp by adding GP to feed.

Black soldier fly pulp in the diet of golden pompano: Effect on growth performance, liver antioxidant and intestinal health

Black soldier fly (Hermetia illucens) has been widely researched as a protein source for fish meal replacement in aquaculture, but few studies have focused on its potential as a feed additive for growth and immune enhancement. We conducted a 56-day culture experiment to determine the impact of feed addition of black soldier fly pulp (BSFP, with 86.2% small peptides in dry basis) on growth performance, plasma biochemistry, liver antioxidant levels, intestinal immunity, digestion and microbiota of juvenile golden pompano (Trachinotus ovatus, 5.63 ± 0.02 g). BSFP was added to the basal diet at 0%, 1%, 3%, 5%, 7% and 9% (named Control, BSFP-1, BSFP-3, BSFP-5, BSFP-7, BSFP-9), respectively. BSFP increased the weight gain rate, specific growth rate, protein efficiency ratio and reduced the feed conversion rate of juvenile T. ovatus, the optimal growth performance was reached at BSFP-1, after which a negative feedback phenomenon was observed. Low levels of BSFP upregulated the expression of hepatic antioxidant, intestinal tight junctions, anti-inflammatory related genes and enhanced antioxidant, immune and intestinal digestive enzyme activities, which simultaneously reduced hepatic malondialdehyde and plasma aspartate transaminase and alanine aminotransferase concentrations. However, at BSFP-7, catalase activity was significantly reduced, while NF-κB p65 and pro-inflammatory cytokines transcription was significantly enhanced (P < 0.05). The results suggest that high doses of BSFP addition may damage fish health by inhibiting small peptide uptake, decreasing the activity of antioxidant enzyme and activating the canonical NF-κB pathway. Conversely, low doses of BSFP enhanced intestinal tight junction protein transcription, digestive enzyme activity and immune performance, inhibited pathogenic microbiota, while enhancing liver antioxidant capacity, which was associated with activated Nrf2-Keap1 pathway and suppressed NF-κB pathway, showing its potential as a feed additive to aquafeeds.

Infection burdens and virulence under heat stress: ecological and evolutionary considerations

As a result of global change, hosts and parasites (including pathogens) are experiencing shifts in their thermal environment. Despite the importance of heat stress tolerance for host population persistence, infection by parasites can impair a host's ability to cope with heat. Host-parasite eco-evolutionary dynamics will be affected if infection reduces host performance during heating. Theory predicts that within-host parasite burden (replication rate or number of infecting parasites per host), a key component of parasite fitness, should correlate positively with virulence-the harm caused to hosts during infection. Surprisingly, however, the relationship between within-host parasite burden and virulence during heating is often weak. Here, we describe the current evidence for the link between within-host parasite burden and host heat stress tolerance. We consider the biology of host-parasite systems that may explain the weak or absent link between these two important host and parasite traits during hot conditions. The processes that mediate the relationship between parasite burden and host fitness will be fundamental in ecological and evolutionary responses of host and parasites in a warming world. This article is part of the theme issue 'Infectious disease ecology and evolution in a changing world'.

A Potential Negative Regulatory Function of Myostatin in the Growth of the Pacific Abalone, Haliotis discus hannai

Myostatin, also known as GDF8, is a member of the transforming growth factor-β (TGF-β) superfamily. In vertebrates, myostatin negatively regulates the growth of skeletal muscle. In invertebrates, it has been reported to be closely related to animal growth. However, knowledge concerning the molecular mechanisms involved in the myostatin regulation of molluscan growth is limited. In this study, we found that the hdh-myostatin open reading frame (ORF) comprised 1470 base pairs that encoded 489 amino acids and contained structural characteristics typical of the TGF-β superfamily, including a C-terminal signal peptide, a propeptide domain, and TGF-β region. Gene expression analysis revealed that hdh-myostatin mRNA was widely expressed at different levels in all of the examined tissues of Haliotis discus hannai. Nine single nucleotide polymorphisms (SNPs) were associated with the growth traits. RNA interference (RNAi) against hdh-myostatin mRNA significantly downregulated hdh-myostatin at days 1, 15, and 30 post injection, and the pattern was correlated with downregulation of the genes TGF-β receptor type-I (hdh-TβR I), activin receptor type-IIB (hdh-ActR IIB), and mothers against decapentaplegic 3 (hdh-Smad3). After one month of the RNAi experiment, the shell lengths and total weights increased in the abalone, Haliotis discus hannai. The results of qRT-PCR showed that the hdh-myostatin mRNA level was higher in the slow-growing group than in the fast-growing group. These results suggest that hdh-myostatin is involved in the regulation of growth, and that these SNPs would be informative for further studies on selective breeding in abalone.

Effects of one-year exposure to ocean acidification on two species of abalone

Ocean acidification (OA) resulting from the absorption of excess atmospheric CO₂ by the ocean threatens the survival of marine calcareous organisms, including mollusks. This study investigated the effects of OA on adults of two abalone species (Haliotis diversicolor, a subtropical species, and Haliotis discus hannai, a temperate species). Abalone were exposed to three pCO₂ conditions for 1 year (ambient, ~ 880, and ~ 1600 μatm), and parameters, including mortality, physiology, immune system, biochemistry, and carry-over effects, were measured. Survival decreased significantly at ~ 800 μatm pCO₂ for H. diversicolor, while H. discus hannai survival was negatively affected only at a higher OA level (~ 1600 μatm pCO₂). H. diversicolor exhibited depressed metabolic and excretion rates and a higher O:N ratio under OA, indicating a shift to lipids as a metabolism substrate, while these physiological parameters in H. discus hannai were robust to OA. Both abalone failed to compensate for the pH decrease of their internal fluids because of the lowered hemolymph pH under OA. However, the reduced hemolymph pH did not affect total hemocyte counts or tested biomarkers. Additionally, H. discus hannai increased its hemolymph protein content under OA, which could indicate enhanced immunity. Larvae produced by adults exposed to the three pCO₂ levels were cultured in the same pCO₂ conditions and larval deformation and shell length were measured to observe carry-over effects. Enhanced OA tolerance was observed for H. discus hannai exposed under both of the OA treatments, while that was only observed following parental pCO₂ ~ 880 μatm exposure for H. diversicolor. Following pCO₂ ~ 1600 μatm parental exposure, H. diversicolor offspring exhibited higher deformation and lower shell growth in all pCO₂ treatments. In general, H. diversicolor were more susceptible to OA compared with H. discus hannai, suggesting that H. diversicolor could be unable to adapt to acidified oceans in the future.

Transcriptomic responses to thermal stress in hybrid abalone (Haliotis discus hannai ♀ × H. fulgens ♂)

China is the world’s largest abalone producing country. Currently, summer mortality caused by high temperature, is one of the biggest challenges for abalone aquaculture industry. The hybrid abalone (Haliotis discus hannai ♀ × H. fulgens ♂) was conferred on the “new variety”. It has heterosis for thermal tolerance and has been cultured at large-scale in southern China. In this study, a transcriptome analysis was performed to identify the related genes in this hybrid abalone under thermal stress and recovery stage. Compared to control group (18°C), a total of 75, 2173, 1050, 1349, 2548, 494, and 305 differentially expressed genes (DEGs) were identified at 21°C, 24°C, 27°C, 30°C, 32°C, 29°C, and 26°C, respectively. In this study, 24°C is the critical temperature at which the abalone is subjected to thermal stress. With the temperature rising, the number of stress-responsive genes increased. During the temperature recovering to the optimum, the number of stress-responsive genes decreased gradually. Thus, this hybrid abalone has a rapid response and strong adaptability to the temperature. Under the thermal stress, the abalone triggered a complicated regulatory network including degrading the misfolded proteins, activating immune systems, negative regulation of DNA replication, and activating energy production processes. The more quickly feedback regulation, more abundant energy supply and more powerful immune system might be the underlying mechanisms to fight against thermal stress in this hybrid abalone. These findings could provide clues for exploring the thermal-response mechanisms in abalone. The key genes and pathways would facilitate biomarker identification and thermal-tolerant abalone breeding studies.

Transcriptome analysis reveals fluid shear stress (FSS) and atherosclerosis pathway as a candidate molecular mechanism of short-term low salinity stress tolerance in abalone

Background

Transcriptome sequencing is an effective tool to reveal the essential genes and pathways underlying countless biotic and abiotic stress adaptation mechanisms. Although severely challenged by diverse environmental conditions, the Pacific abalone Haliotis discus hannai remains a high-value aquaculture mollusk and a Chinese predominantly cultured abalone species. Salinity is one of such environmental factors whose fluctuation could significantly affect the abalone’s cellular and molecular immune responses and result in high mortality and reduced growth rate during prolonged exposure. Meanwhile, hybrids have shown superiority in tolerating diverse environmental stresses over their purebred counterparts and have gained admiration in the Chinese abalone aquaculture industry.

The objective of this study was to investigate the molecular and cellular mechanisms of low salinity adaptation in abalone. Therefore, this study used transcriptome analysis of the gill tissues and flow cytometric analysis of hemolymph of H. discus hannai (DD) and interspecific hybrid H. discus hannai ♀ x H. fulgens ♂ (DF) during low salinity exposure. Also, the survival and growth rate of the species under various salinities were assessed.

Results

The transcriptome data revealed that the differentially expressed genes (DEGs) were significantly enriched on the fluid shear stress and atherosclerosis (FSS) pathway. Meanwhile, the expression profiles of some essential genes involved in this pathway suggest that abalone significantly up-regulated calmodulin-4 (CaM-4) and heat-shock protein90 (HSP90), and significantly down-regulated tumor necrosis factor (TNF), bone morphogenetic protein-4 (BMP-4), and nuclear factor kappa B (NF-kB).

Also, the hybrid DF showed significantly higher and sustained expression of CaM and HSP90, significantly higher phagocytosis, significantly lower hemocyte mortality, and significantly higher survival at low salinity, suggesting a more active molecular and hemocyte-mediated immune response and a more efficient capacity to tolerate low salinity than DD.

Conclusions

Our study argues that the abalone CaM gene might be necessary to maintain ion equilibrium while HSP90 can offset the adverse changes caused by low salinity, thereby preventing damage to gill epithelial cells (ECs).

The data reveal a potential molecular mechanism by which abalone responds to low salinity and confirms that hybridization could be a method for breeding more stress-resilient aquatic species.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08611-8.

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.

Effects of dietary asafoetida (Ferula sinkiangensis K. M. Shen) levels on feeding attraction activity, growth performance, healthiness, and digestive enzyme activity in juvenile Lateolabrax japonicus

The study was to investigate effects of asafoetida (Ferula sinkiangensis K. M. Shen) powder on feeding attraction activity (FAA), growth performance, healthiness, and digestive enzyme activity of juvenile Lateolabrax japonicus. Six concentration levels (0, 5, 10, 15, 20, and 25 g/kg diets) were formulated for luring and feeding experiment. Results showed that asafoetida could stimulate the appetite of L. japonicus at the dietary levels from 10 to 25 g/kg; reduce the feed conversion ratio (FCR) and feed intake (FI) at 10-20 g/kg; increase the weight gain (WG) and specific growth rate (SGR) at 5-10 g/kg; increase the hepatosomatic index (HSI), body crude lipid content, serum total protein (TP) content, and lysozyme activity at 10-15 g/kg; decrease the moisture at 10-15 g/kg; and increase the serum total superoxide dismutase (T-SOD) activity at 5-15 g/kg, when compared with the control group (p < 0.05). Digestive enzyme activities including amylase (AMS) and trypsin in the intestine were significantly affected by the asafoetida powder (p < 0.05). Regression analyses between the FAA, FCR, WG, SGR, HSI, LZM, T-SOD, AMS, trypsin, and the dietary asafoetida powder levels showed that the optimal additional amount was 16.95, 13.65, 8.36, 8.15, 15.45, 9.94, 8.75, 11.77, and 7.07 g/kg, respectively, indicating that the optimal amount of asafoetida powder was located in 7.07-16.95 g/kg diet. However, combined with the significant difference analyses obtained from the current study, we would suggest the additive suitable dosage was 10 g/kg.

Effect of acclimated temperature on thermal tolerance, immune response and expression of HSP genes in Labeo rohita, Catla catla and their intergeneric hybrids

The ability of a species and population to respond to a decrease or an increase in temperature depends on their adaptive potential. Here, the critical thermal tolerance (CTmax and CTmin) of four populations: Labeo rohita, Catla catla, and their reciprocal hybrids L. rohita♀× C. catla♂ (RC) and C. catla♀ × L. rohita♂ (CR) being acclimatized at four acclimation temperatures (22, 26, 30 and 34 °C) were determined. All populations indicated substantial variations (P < 0.05) in CTmax and CTmin values. L. rohita displayed, comparatively the highest CTmax with largest total and intrinsic polygon zones as well as the upper and lower acquired thermal tolerance zones followed by RC and CR hybrids, while C. catla showed significantly the highest CTmin value and the smallest intrinsic and acquired thermal tolerance zones. Both hybrids illustrated low parent heterosis (≤11%). Additionally, the highest expression of Hsp70 and Hsp90 (heat shock proteins) genes, serum lysozyme level, respiratory burst activity and lowest lipid peroxidation level under lower and higher temperature shock further illustrated strong physiological mechanism of L. rohita in contrast to C. catla, to deal with acute temperature, while hybrids, especially F1 RC hybrid appeared as a good option to replace C. catla in relatively higher and lower temperature areas.

Metabolomics Adaptation of Juvenile Pacific Abalone Haliotis discus hannai to Heat Stress

Temperature fluctuation is a key abiotic factor for the growth and survival of Pacific abalone Haliotis discus hannai, particularly during climate change. However, the physiological mechanism underlying the abalones’ response to heat stress remains unknown. We sought to understand the metabolic adaptation mechanism of Pacific abalone to heat stress for further analyzing its heat tolerance capacity. For two groups experienced different acclimate temperature (10 °C and 30 °C for 62 days), the Pacific abalone juveniles displayed significantly different survival rates under 31 °C acute heat treatment. A total of 1815 and 1314 differential metabolites were identified from the 10 °C and 30 °C acclimate groups respectively, by comparing mass spectrometry data of the samples before and after heat stimulation. Heat stress led to mitochondrial failure, resulting in incomplete oxidative metabolism of amino acids and fatty acids in the mitochondria, and massive accumulation of unstable metabolic intermediates in cells. The 10 °C acclimated group accumulated more harmful substances after heat stimulation, provoking further stress responses and pathophysiological processes. In comparison, the 30 °C acclimated group showed stronger regulation capacity to produce beneficial substances for metabolic homeostasis. The findings provided insight into the heat response of marine animals, especially concerning mitochondrial metabolism.

Comparative immune response during the juvenile and adult stages of two abalones under Vibrio harveyi challenge

Mass mortality of juvenile hybrid (Haliotis discus hannai ♀× H. fulgens ♂, DF) and adult H. discus hannai (DD) occurs in south China during the summer. This study showed that the juvenile DF and adult DD exhibited significantly lower survival rates than juvenile DD and adult DF under 72 h pathogenic bacteria (Vibrio harveyi) challenge at different temperatures (20 °C and 28 °C). Phenoloxidase (PO) and superoxide dismutase (SOD) activities were significantly higher in juvenile DD compared to juvenile DF, whereas that in adult abalone was the opposite. Juvenile DD and adult DF also exhibited advantages in terms of immune-related gene expression (TRAF, TLR, MIF, Lys, Spi, Cat, TNF, and SOD) compared to juvenile DF and adult DD. The data reveals immunocompetence differences in DD and DF at the juvenile and adult stages.

Survival, retention rate and immunity of the black shell colored stocks of pearl oyster Pinctada fucata martensii after grafting operation

We have developed a black shell colored selected line observed to have higher survival ability. In this study, to understand its immune capacity, total carotenoid content (TCC) of the black shell colored line (BG) and the control group (CG) were compared. Survival and retention rates, immunity and antioxidant capacity of BG were compared relative to CG at different times after grafting operation. The results showed that BG had significantly larger TCC than CG (P < 0.05). BG had significantly higher survival and retention rates than CG on days 7, 30 and 360 after grafting (P < 0.05). On days 360, BG had significantly larger pearl thickness than CG (P < 0.05). BG exhibited increased ACP, AKP, SOD, CAT, TAOC and LZ activity than the CG on 0 h, 12 h, 1 d, 3 d, 5 d, 7 d and 30 d after grafting. BG had higher expression levels of Fascin, SOD, CDK-7, CDAP-1, IRAK-1, α2m, GST-1, TRAF-3 and Caspase-2 than CG. The results suggested that BG had higher immune competence and pearl production performances, which is promising to improve pearl quality and production.

MicroRNA-155 and microRNA-181a, via HO-1, participate in regulating the immunotoxicity of cadmium in the kidneys of exposed Cyprinus carpio

Cadmium (Cd) is a nonessential metal that is a contaminant in aquatic ecosystems. Cd can accumulate in aquatic animals, leading to detrimental effects in tissues, and Cd exposure can induce immunotoxicity in fish. MicroRNAs (miRNAs) play critical roles in immune responses, yet the participation of miRNAs in Cd-induced immunotoxicity remains poorly understood. The present study evaluated the effects of Cd exposure on the immune responses and the mRNAs and miRNAs expressions of immune-related genes in Cyprinus carpio (C. carpio). Then, microRNA-155 (miR-155) was overexpressed and microRNA-181a (miR-181a) was knocked down to determine which miRNA plays a key role in the immune response to Cd. The results showed that 0.5 mg/L Cd²⁺ significantly decreased the activity of alkaline phosphatase (AKP) and acid phosphatase (ACP) in the kidneys of C. carpio. Cd exposure upregulated the mRNA expressions of interleukin (IL)-1β, IL-8, nuclear factor-kappa B (NF-κB), tumour necrosis factor-α (TNF-α), and Toll-like receptor 4(TLR-4) and downregulated those of IL-10 and heme oxygenase-1 (HO-1) in C. carpio kidneys. Cd exposure also led to upregulation of miR-155 and miR-181a expressions. Furthermore, AKP and ACP activity in the kidneys was markedly changed after intraperitoneal injection of C. carpio with miR-155 agomir and miR-181a antagomir. All detected mRNA expressions were significantly decreased after injection of miR-155 agomir, and IL-10, NF-κB, TNF-α, and HO-1 mRNA expressions were markedly increased after injection of miR-181a antagomir. The results of this study demonstrate that Cd exposure can immunocompromise C. carpio by targeting HO-1 through miR-155 and miR-181a. This is the first study to reveal that Cd exposure induces immunotoxicity through miR-155 and miR-181a in the kidneys of C. carpio.

Effect of vitamin D3 on immunity and antioxidant capacity of pearl oyster Pinctada fucata martensii after transplantation: Insights from LC-MS-based metabolomics analysis

Postoperative care is a critical step of pearl culture that ultimately determines culture success. To determine the effect of dietary vitamin D3 (VD3) levels on immunity and antioxidant capacity of pearl oyster Pinctada fucata martensii during postoperative care and explore the mechanisms behind this phenomenon, five isonitrogenous and isolipidic experimental diets were formulated by adding different levels of dietary VD3 (0, 500, 1000, 3000, and 10000 IU/kg), and the diets were fed to five experimental groups (EG1, EG2, EG3, EG4, and EG5) in turn and cultured indoors. The control group (CG) was cultured in the natural sea. Pearl oysters that were 1.5 years old were subjected to nucleus insertion. After culturing for 30 days, EG3 exhibited significantly higher survival rates than those in CG and EG5 (P < 0.05). Moreover, EG3 exhibited the highest activities of alkaline phosphatase, acid phosphatase, catalase, superoxide dismutase, and lysozyme. However, EG5 achieved the highest activities of glutathione peroxidase. Metabolomics-based profiling of pearl oysters fed with high levels of dietary VD3 (EG5) and optimum levels of dietary VD3 (EG3) revealed 76 significantly differential metabolites (SDMs) (VIP > 1 and P < 0.05). Pathway analysis indicated that SDMs were involved in 21 pathways. Furthermore, integrated key metabolic pathway analysis suggested that pearl oysters in EG5 regulated the pentose phosphate pathway, glutathione metabolism, sphingolipid metabolism, and arachidonic acid metabolism in response to stress generated from excessive VD3. These findings had significant implications on strengthening the future development and application of VD3 in aquaculture of pearl oyster P. f. martensii.

Mannan oligosaccharide increases the growth performance, immunity and resistance capability against Vibro Parahemolyticus in juvenile abalone Haliotis discus hannai Ino

This trial was conducted to investigate the effect of mannose oligosaccharides (MOS) on the growth performance, antioxidation, immunity and disease resistance of Vibro Parahemolyticus in juvenile abalone Haliotis discus hannai Ino. Four formulated diets were produced to contain 0.00 g/kg, 0.40 g/kg, 0.80 g/kg and 1.60 g/kg Actigen®, with functional ingredients of MOS, respectively. Accordingly, the experimental diets were named as A0, A4, A8 and A16. After 120-days feeding trial, the best growth performance was observed in A8 group (P < 0.05) and there was no significant difference in A0, A4 and A16 groups. With the increase of dietary MOS, the activity of the total antioxidant capacity in hepatopancreas is increasingly elevated (P < 0.05) while no significant difference was observed on activity of glutathione S-transferase (P > 0.05). The activities of superoxide dismutase and glutathione peroxidase were firstly increased and then decreased, with the highest values in A8 group (P < 0.05). Immune-related parameters were significantly affected by dietary MOS inclusion. Specifically, the activities of alkaline phosphatase and acid phosphatase in hepatopancreas and serum of abalone fed diets containing MOS were significantly higher than those of control A0 group (P < 0.05). Moreover, the highest values of both enzymes were observed in hepatopancreas of A8 group but in serum of A16 group, respectively. The lysozyme activities in hepatopancreas and serum of A4 group were significantly higher than those of other groups (P < 0.05) and there was no significant difference in A0, A8 and A16 groups (P > 0.05). The activities of cytophagy and respiratory burst in serum of abalone were not significantly affected by dietary MOS content (P > 0.05). The mRNA levels of focal adhesion kinase and integrin-linked kinase were gradually elevated with the increase of dietary MOS, with the highest value recorded in A16 group (P < 0.05). The gene expression of caspse-3 in A8 group was dramatically higher than those of other groups (P < 0.05) and there was no significant difference in A0, A4 and A16 groups (P > 0.05). The mRNA level of nuclear factor-κB was not significantly affected by dietary MOS (P > 0.05). During 56 h of V. Parahemolyticus challenge period, the accumulated mortality rate of abalone fed diets containing MOS were significantly lower than that of control A0 group in each time point (P < 0.05). Overall, the lowest rate was happened in A8 group (P < 0.05). In conclusion, MOS inclusion in diet has obviously positive effect on growth, immunity and disease resistance capability of abalone, with the optimal level of Actigen® at 0.80 g/kg in diet.

Resilience of a harvested gastropod, Turbo militaris, to marine heatwaves

Marine heatwaves (MHW) are predicted to occur with increased frequency, duration and intensity in a changing climate, with pervasive ecological and socioeconomic consequences. While there is a growing understanding of the ecological impacts of warming and marine heatwaves, much less is known about how they influence the underlying physiology and health of species, and the nutritional properties of tissue. We evaluated the effects of different heatwave scenarios and ocean warming on the nutritional properties and immune health of the harvested gastropod Turbo militaris. Neither heatwave scenarios nor elevated temperatures had significant impacts on morphometrics, proximate composition or inorganic content of T. militaris. However, an increased moisture content and non-significant trends, such as elevated amount of lipids, and an increased number of hemocytes in the blood of T. militaris in the heatwave treatments were suggestive of mild stress. Overall, our study suggests that T. militaris is resilient to marine heatwaves and warming, although delayed, additive or synergistic stress responses cannot be ruled out. Understanding the possible effects of ocean warming and heatwaves on fisheries species could improve management actions to avoid species impacts, socioeconomic losses and negative effects to ecosystem service provision in a changing climate.

MAVS of triploid hybrid of red crucian carp and allotetraploid possesses the improved antiviral activity compared with the counterparts of its parents

Triploid hybrid (3n = 150) of red crucian carp (♀, 2n = 100) and allotetraploid (♂, 4n = 200) presents the obviously stronger disease resistance than its parents. To elucidate the innate immunity of triploid hybrid, the MAVS homologues of triploid hybrid (3nMAVS), red crucian carp (2nMAVS) and allotetraploid (4nMAVS) have been identified and characterized separately in this study. 2nMAVS and 4nMAVS were evolutionarily conserved; however, 3nMAVS showed lower amino acid similarity and differently predicted structure to 2nMAVS or 4nMAVS. 3nMAVS transcription increase rate in host cells were obviously higher than 2nMAVS or 4nMAVS in response to different stimuli, which included spring viraemia of carp virus (SVCV), grass carp reovirus (GCRV) and poly (I:C). The reporter assay in EPC cells showed that 3nMAVS owned much stronger ability to induce the production of DrIFNφ1 and eIFN than either 2nMAVS or 4nMAVS. Accordingly, EPC cells transfected with 3nMAVS presented obviously stronger antiviral activity against both GCRV and SVCV than the cells expressing 2nMAVS or 4nMAVS. All the data support the conclusion that 3nMAVS-mediated antiviral signaling during innate immune activation was stronger than those of 2nMAVS and 4nMAVS, which provided us the new insight on the innate immune system of triploid hybrid.

Different Transcriptomic Responses to Thermal Stress in Heat-Tolerant and Heat-Sensitive Pacific Abalones Indicated by Cardiac Performance

The Pacific abalone Haliotis discus hannai is one of the most economically important mollusks in China. Even though it has been farmed in southern China for almost 20 years, summer mortality remains the most challengeable problem for Pacific abalone aquaculture recently. Here, we determined the different heat tolerance ability for five selective lines of H. discus hannai by measuring the cardiac performance and Arrhenius breakpoint temperature (ABT). The Red line (RL) and Yangxia line (YL) were determined as the most heat-sensitive and most heat-tolerant line, respectively. Heart rates for RL were significantly lower than those of the YL at the same temperature (p < 0.05). The differentially expressed genes (DEGs), which were enriched in several pathways including cardiac muscle contraction, glutathione metabolism and oxidative phosphorylation, were identified between RL and YL at control temperature (20°C) and heat stress temperature (28.5°C, the ABT of the RL) by RNA-seq method. In the RL, 3370 DEGs were identified between the control and the heat-stress temperature, while only 1351 DEGs were identified in YL between these two temperature tests. Most of these DEGs were enriched in the pathways such as protein processing in endoplasmic reticulum, nucleotide binding and oligomerization domain (NOD) like receptor signaling, and ubiquitin mediated proteolysis. Notably, the most heat-tolerant line YL used an effective heat-protection strategy based on moderate transcriptional changes and regulation on the expression of key genes.

Negative impact of the imidazolium-based ionic liquid [C8mim]Br on silver carp (Hypophthalmichthys molitrix): Long-term and low-level exposure

This study aimed to determine the chronic toxicity of the ionic liquid (IL) 1-methyl-3-octylimidazolium bromide ([C₈mim]Br) on silver carp to further study the toxicological mechanism of ILs. For this purpose, 60-d chronic exposure at concentrations of 1.09 or 4.38 mg L^-1 [C₈mim]Br in silver carp was conducted. The results of biochemical assays revealed that [C₈mim]Br-treatment remarkably promoted serum lactate dehydrogenase (LDH), aspartate aminotransferase (AST), alanine aminotransferase (ALT), acid phosphatase (ACP), and alkaline phosphatase (AKP) activities, indicating that [C₈mim]Br-exposure caused fish organ damage. Long-term exposure of [C₈mim]Br also altered the activities of superoxide dismutase (SOD) and catalase (CAT) and the glutathione (GSH) level but increased malondialdehyde (MDA) levels in fish brain, gill, intestine, kidney, liver, and muscle, suggesting that [C₈mim]Br-treatment may cause oxidative stress in fish organs. Further work revealed that [C₈mim]Br-treatment increased the activities of erythromycin-N-demethylase (ERND) and glutathione S-transferases (GST), which may participate in the metabolism of [C₈mim]Br in fish liver. Moreover, chronic [C₈mim]Br-exposure remarkably promoted the expression of inducible nitric oxide synthase (iNOS), interleukin-1β (IL-1β), tumour necrosis factor-α (TNF-α), and nuclear factor-κB (NF-κB) and altered the levels of transforming growth factor-β (TGF-β), suggesting that long-term exposure of [C₈mim]Br might promote the inflammatory response in fish liver. Additionally, [C₈mim]Br-exposure altered succinate dehydrogenase (SDH) activity and promoted caspase-9 and caspase-3 activities in fish liver, suggesting that chronic [C₈mim]Br-exposure also induces hepatocellular apoptosis via the mitochondrial pathway. The results presented here may be helpful to illuminate the chronic toxicity mechanism of imidazolium-based ILs and safe use of ILs in the future.

Serum immune responses in common carp (Cyprinus carpio L.) to paraquat exposure: The traditional parameters and circulating microRNAs

Paraquat (PQ) is a herbicide used worldwide, and it was shown to be a high-risk compound to aquatic organisms. This study was conducted to investigate the effects of PQ on traditional serum parameters and circulating microRNAs (miRNAs) in common carp to further elucidate the mechanism of PQ toxicity in fish. In the current study, a subacute toxicity test of common carp exposed to PQ at 1.596 and 3.192 mg/L for 7 d was conducted under laboratory conditions. The results showed that PQ exposure generally reduced the levels of T-AOC, SOD, CAT, and GST, but significantly increased MDA levels in the serum, indicating that PQ exposure induces oxidative stress and lipid peroxidation in the fish. The results of biochemical assays showed that PQ exposure not only significantly altered the activities of LDH, AST, ALT, ACP, AKP, and lysozyme and the contents of IgM and complement 3 but also promoted the expression of pro-inflammatory cytokines, including IFN-γ, IL-1β, IL-6, IL-8, and TNF-α. Additionally, PQ inhibited the levels of the anti-inflammatory cytokines IL-10 and TGF-β, suggesting that PQ exposure may cause fish tissue injury and promote immune inflammatory responses. Furthermore, we found that serum circulating miRNAs, such as ccr-mir-122, ccr-mir-125b, ccr-mir-146a, and ccr-mir-155, were generally promoted in fish following PQ exposure. Based on our results and reports on miRNA-based diagnosis of tissue damage and inflammatory responses in mammals, we suggest that serum ccr-mir-122, ccr-mir-125b, ccr-mir-146a, and ccr-mir-155 could be new biomarkers of PQ toxicity in fish.

Hybridization improved bacteria resistance in abalone: Evidence from physiological and molecular responses

Hybridization is an effective way of improving germplasm in abalone, as it often generates benign traits in the hybrids. The hybrids of Haliotis discus hannai and H. gigantea have shown heterosis in terms of disease resistance than one or both parental species. In the present study, to elucidate the physiological and molecular mechanism of this heterosis, we analyzed the dynamic changes of several immune indexes including survival rate, total circulating haemocyte count (THC), phagocytic activity, reactive oxygen species level (ROS) and phenoloxidase activity (PO) in two parental species, H. discus hannai (DD) and H. gigantea (GG), and their reciprocal hybrids H. discus hannai ♀ × H. gigantea ♂ (DG), H. gigantea ♀ × H. discus hannai ♂ (GD) challenged with a mixture of Vibrio harveyi, V. alginolyticus and V. parahaemolyticus (which have been demonstrated to be pathogenic to abalone). Besides, we cloned and analyzed three important immune genes: heat shock protein 70 (hsp70), ferritin and cold shock domain protein (csdp) in H. discus hannai and H. gigantea, then further investigated their mRNA level changes in the four abalone genotypes after bacterial challenge. Results showed that these physiological and molecular parameters were significantly induced by bacterial exposure, and their changing patterns were obviously different between the four genotypes: (1) Survival rates of the two hybrids were higher than both parental species after bacterial exposure; (2) DG had higher THC than the other three genotypes; (3) Phagocytosis responded slower in the hybrids than in the parental species; (4) DD's ROS level was lower than the other three genotypes at 48 h post infection; (5) Phenoloxidase activity was lower in DD during the infection compared to the other genotypes; (6) mRNA levels of hsp70 and csdp, were always lower in at least one parental species (DD) than in the hybrids after the bacterial exposure. Results from this study indicate that the hybrids are more active or efficient in immune system function, hence they could effectively defense against a bacterial invasion, leading to higher survival rates after challenge. This study provides physiological and molecular evidences for interpreting the disease resistant heterosis in this abalone hybrid system, which could help us in a better understanding and utilization of heterosis in abalone aquaculture.

Epipodial Tentacle Gene Expression and Predetermined Resilience to Summer Mortality in the Commercially Important Greenlip Abalone, Haliotis laevigata

"Summer mortality" is a phenomenon that occurs during warm water temperature spikes that results in the mass mortality of many ecologically and economically important mollusks such as abalone. This study aimed to determine whether the baseline gene expression of abalone before a laboratory-induced summer mortality event was associated with resilience to summer mortality. Tentacle transcriptomes of 35 greenlip abalone (Haliotis laevigata) were sequenced prior to the animals being exposed to an increase in water temperature-simulating conditions which have previously resulted in summer mortality. Abalone derived from three source locations with different environmental conditions were categorized as susceptible or resistant to summer mortality depending on whether they died or survived after the water temperature was increased. We detected two genes showing significantly higher expression in resilient abalone relative to susceptible abalone prior to the laboratory-induced summer mortality event. One of these genes was annotated through the NCBI non-redundant protein database using BLASTX to an anemone (Exaiptasia pallida) Transposon Ty3-G Gag Pol polyprotein. Distinct gene expression signatures were also found between resilient and susceptible abalone depending on the population origin, which may suggest divergence in local adaptation mechanisms for resilience. Many of these genes have been suggested to be involved in antioxidant and immune-related functions. The identification of these genes and their functional roles have enhanced our understanding of processes that may contribute to summer mortality in abalone. Our study supports the hypothesis that prestress gene expression signatures are indicative of the likelihood of summer mortality.

Serum immune response of pearl oyster Pinctada fucata to xenografts and allografts

The mantle piece from the donor pearl oyster would be rejected by the immune system of recipient oyster in pearl culture practice, especially in the case that the donor and receptor are different species. Thus, investigation of the immune response of recipient oyster to grafted mantle pieces, particularly to xenografts, is of importance in creating xenograft transplantation technology for pearl culture industry. The humoral immune responses of P. fucata to allograft (mantle piece of P. fucata) and xenografts (mantle pieces of P. maxima and P. margaritifera, respectively) were studied in this paper. The oysters receiving no transplantations were served as the control group. The serum was collected from recipient P. fucata at 1 d, 2 d, 3 d, 4 d, 5 d, 7 d, 9 d, 11 d, 13 d, and 15 d, respectively after transplantation, and the serum antibacterial activity, lysozyme activity (LZM), alkaline phosphatase (AKP), acid phosphatase (ACP), total antioxidant capacity (TAC), and agglutination to rabbit red blood cells were investigated. The result indicated that serum of both the experimental groups and the control group can agglutinate rabbit red blood cells, with variation between groups and between time points, respectively. The antibacterial activity in the experimental group was significantly higher than that in the control group at 2-4 d, but lower at 5-11 d and returned back to normal at 15 d, with significant differences among experimental groups (P < 0.05). The LZM in the experimental group was significantly higher than that in the control group at 3-7 d, with significant differences in bacteriolytic activity among various groups (P < 0.05). Both the ACP and AKP activity levels in the experimental groups were higher than those in the control group at 2-9 d, with significant differences among various groups at 3-9 d (P < 0.05). The TAC level in the experimental groups was higher than that in the control group at 1-7 d, with significant differences among various groups at 4-7 d (P < 0.05). The above results indicated that all of the humoral immune factors investigated showed immune responses to both allografts and xenografts, with no specific to any of them. Thus, it is necessary to further screen immune rejection factors specific to xenografts, including cellular immune components.

Mytilus hybridisation and impact on aquaculture: A minireview

The three species in the blue mussel complex (Mytilus edulis, Mytilus galloprovincialis and Mytilus trossulus) show varying levels of hybridisation wherever they occur sympatrically. The spatial variation in hybridisation patterns is potentially governed by environmental conditions, larval dispersal and aquaculture practices. Commercial mussel cultivation has been shown to increase hybridisation through introduction of non-native species or spat transfer. There is evidence that mussel cultivation may promote commercially less desirable phenotypes (e.g. fragile shells), however, to what extent hybridisation impacts aquaculture is currently not clear. The aim of this review is to summarize the available information on Mytilus hybridisation patterns in Europe and their promotion through aquaculture practices in order to shed light on the overall implications for the aquaculture industry.

Thiamin deficiency induces impaired fish gill immune responses, tight junction protein expression and antioxidant capacity: Roles of the NF-κB, TOR, p38 MAPK and Nrf2 signaling molecules

In this study, we investigate the effects of dietary thiamin deficiency on immune responses, tight junctions, antioxidant capacity and related signaling molecules in the gills of young grass carp (Ctenopharyngodon idella). Fish were fed diets that contained 0.12-2.04 mg thiamin kg(-1) for 8 weeks. We found that dietary thiamin deficiency resulted in reduced complement 3 content, lysozyme and acid phosphatase activities, mRNA levels of hepcidin, liver-expressed antimicrobial peptides 2, transforming growth factor (TGF)-β1, interleukin (IL)-10, inhibitor protein-κBα (IκBα), ribosomal S6 protein kinase 1 and target of rapamycin (TOR) and increased expression of interferon-γ2, tumor necrosis factor-α, TGF-β2, IL-1β, IL-8, IκB kinases (IKKβ and IKKγ) and nuclear factor-κB p65 (NF-κB p65). Our findings showed that thiamin deficiency reduced the immune status of fish gills. Furthermore, thiamin deficiency resulted in reduced mRNA transcript levels of claudin b, claudin 3, claudin 12, zonula occludens 1 (ZO-1) and occludin and increased mRNA transcript levels of claudin 15a, myosin light-chain kinase (MLCK) and p38 mitogen-activated protein kinase (p38 MAPK) in fish gill tissues. These data suggested that thiamin deficiency disrupted tight junction-mediated fish gill barrier function. Additionally, reactive oxygen species, malondialdehyde and protein carbonyl levels and both the activities and expression levels of Cu/Zn superoxide dismutase, catalase, glutathione peroxidase, glutathione-S-transferases and glutathione reductase, as well as NF-E2-related factor 2 gene expression in fish gills, were lower in fish fed a thiamin-deficient diet. By contrast, thiamin deficiency increased levels of Kelch-like-ECH-associated protein 1a (Keap1a) and Keap1b mRNA transcript expression in fish gills. Taken together, our findings indicated that thiamin deficiency impaired fish gill health by effects on the expression of genes encoding cytokines, tight junction proteins, antioxidant enzymes, NF-κB p65, MLCK and Nrf2.

Morphology and classification of hemocytes in Pinctada fucata and their responses to ocean acidification and warming

Hemocytes play important roles in the innate immune response and biomineralization of bivalve mollusks. However, the hemocytes in pearl oysters are poorly understood. In the present study, we investigated the morphology and classification of hemocytes in the pearl oyster, Pinctada fucata. Three types of hemocytes were successfully obtained by light microscopy, electron microscopy and flow cytometry methods: small hyalinocytes, large hyalinocytes and granulocytes. The small hyalinocytes are the major hemocyte population. Morphological analyses indicated that these hemocytes have species-specific characterizations. In addition, we assessed the potential effects of ocean acidification (OA) and ocean warming (OW) on the immune parameters and calcium homeostasis of the hemocytes. OA and OW (31 °C) altered pH value of hemolymph, increased the total hemocyte count, total protein content, and percentage of large hyalinocytes and granulocytes, while it decreased the neutral red uptake ability, suggesting active stress responses of P. fucata to these stressors. Exposure to OW (25 °C) resulted in no significant differences, indicating an excellent immune defense to heat stress at this level. The outflow of calcium from hemocytes to hemolymph was also determined, implying the potential impact of OA and OW on hemocyte-mediated biomineralization. This study, therefore, provides insight into the classification and characterization of hemocyte in the pearl oyster, P. fucata, and also reveals the immune responses of hemocytes to OA and OW, which are helpful for a comprehensive understanding of the effects of global climate change on pearl oysters.