Nanoplastics pollution has emerged as a global issue due to its widespread potential toxicity. This study delved in to toxic effects of nanoplastics on juvenile P. clarkii and molecular mechanisms from perspectives of growth, biochemical, histopathological analysis and transcriptome level for the first time. The findings of this study indicated that nanoplastics of different concentrations have varying influence mechanisms on juvenile P. clarkii. Nanoplastics have inhibitory effects on growth of juvenile P. clarkii, can induce oxidative stress. The biochemical analysis and transcriptome results indicated that 10mg/L nanoplastics can activate the antioxidant defense system and non-specific immune system in juvenile P. clarkii, and affect energy metabolism and oxidative phosphorylation. While 20mg/L and 40mg/L have a destructive influence on the immune function in juvenile P. clarkii, leading to lipid peroxidation and oxidative damage, and induce apoptosis, can affect ion transport and osmotic pressure regulation. The findings of this study can offer foundational data for delving further into impacts of nanoplastics on crustaceans and toxicity mechanism.

Abstract Based upon mixed linear model and incomplete diallel cross between different strains of Macrobrachium nipponense, the additive‐genetic correlations of growth and morphometrics with meat yield traits in M. nipponense were estimated using the minimum norm quadratic unbiased estimation procedure. Path analysis method was utilized to investigate the overall additive‐genetic determinations of growth and morphometric traits on the meat yield traits. Results indicated that growth and morphometrics were genetically positively correlated with abdominal meat weight (p < 0.01), but were not genetically correlated with abdominal meat percentage (p > 0.05) in both sexes. Growth and morphometrics were genetically positively correlated (p < 0.01). Abdominal meat weight was genetically positively correlated with abdominal meat percentage (p < 0.01). In terms of the overall additive‐genetic determination, body weight had the greatest impact on abdominal meat weight in both sexes. In contrast, abdominal meat weight, abdominal length, and body weight were most influential on abdominal meat percentage in both sexes. The genetic relationships of growth and morphometrics to meat yield traits were elucidated in M. nipponense for the first time, contributing to formulation of sound improvement plan for the meat yield traits in this commercially important prawn species.

The objective of this study is to explore the effects of light intensity (600 1800 lx) and photoperiod (4 24 h) on the growth performance and ovarian development of red swamp crayfish (Procambarus clarkii). The feeding rate (FR), weight gain rate (WGR), specific growth rate (SGR), condition factor (CF), hepatosomatic index (HSI), gonadosomatic index (GSI), and mature oocyte ratio in the ovary were measured. The results of the study showed that the first-order effect of photoperiod and light intensity has significant impacts on FR, WGR, SGR, CF, HSI, GSI, and mature oocyte proportion of P. clarkii; the second-order effect of photoperiod and light intensity has significant impacts on the FR, SGR, and CF of P. clarkii; and the interaction effect of photoperiod and light intensity has significant impacts on WGR, SGR, CF, HSI, GSI, and mature oocyte proportion of P. clarkii. Within the range of conditions in this study, as the photoperiod extended, the FR, WGR, SGR, CF, HSI, and GSI gradually increased. As the light intensity increased, the FR, WGR, SGR, and CF first decreased and then increased, while HSI and GSI showed a gradually increasing trend. The results indicated that the change of light intensity (enhanced or weakened) and the extension of photoperiod in the range of conditions in this study could promote the growth and ovarian development of P. clarkii. The photoperiod and light intensity have important effects on the growth and ovarian development of P. clarkii. The results in this study provided a theoretical basis for biological research of P. clarkii and basic data for artificial reproduction and intensive culture of P. clarkii.

Abamectin is a globally used pesticide, which is one of 16-member macrocyclic lactones compound. As an environmental contaminant, pesticide residues pose a great threat to the health and survival of aquatic animals. Procambarus clarkii is one of the most important economic aquatic animals in China. It is necessary to explore the toxic mechanism of abamectin to P. clarkii. In this study, the toxic mechanism of abamectin to P. clarkii was investigated by 0, 3 and 6 μg/L abamectin stress for 28 days. The digestive-, antioxidant- and immune- related enzymes activities, genes expression levels, and histological observations were analytical indicators of growth performance, digestive capacity, and defense systems. The results in this study showed that with abamectin concentration increasing, the growth of P. clarkii was stunted significantly, and the mortality rate increased significantly. With exposure time and abamectin concentration increasing, the expression levels of related genes, the activities of digestive-, antioxidant-, and immune- related enzymes decreased ultimately. Moreover, through histological observation, it was found that with abamectin concentration increasing, the hepatopancreas, muscle, and intestine were damaged. As elucidated by the results, once abamectin exists in the environment for a long time, even low doses will threaten to healthy growth and survival of P. clarkii. This study explored the potential toxicity and the toxic mechanism of abamectin to P. clarkii, and provides a theoretical basis for further study on the toxicity of pesticides to aquatic animals.

Procambarus clarkii (Girard, 1852) has important economic value in China and internationally. In this research, the comparative transcriptome analysis was used to reveal molecular mechanisms of influences of photoperiod and light intensity on ovarian development in P. clarkii for the first time. Some genes (such as laminin, collagen, integrin beta, catenin) and pathways (including TGF-beta signaling pathway, focal adhesion, ECM-receptor interaction) associated with ovarian development and oocyte maturation were significantly upregulated. Some genes related to circadian clock (such as CLK, PER) were identified in this research. The results indicated that when light intensity or photoperiod increased, P. clarkii could up-regulate the expression levels of the laminin and collagen, thereby synthesizing related proteins, promoting meiosis of the oocytes, thus increasing the number of oocytes in the ovary. At the same time, P. clarkii could up-regulate the expression levels of integrin beta, integrin alpha 6, and diacylglycerol to synthesize related proteins, thereby promoting the formation of proteins and fats such as triglycerides, these proteins and fats can provide material basis for maturation and development of oocytes, resulting in oocyte maturation and ovarian development. P. clarkii could synthesize related proteins by upregulating expression levels of genes (such as catenin), these proteins or hormones can adhere to other actins (such as integrins), thereby stabilizing the morphology of the oocytes and ensuring normal development. Meantime, the increase in light intensity or photoperiod could cause release GSH and VTG, resulting in oocytes development and maturation. The data in this research can reveal molecular mechanisms of impacts of photoperiod and light intensity on oocyte maturation and ovarian development in P. clarkii, can offer crucial genomic data for studying developmental mechanisms of ovary and oocyte in crustacean.

As an important aquaculture fish in the Heilongjiang River Basin, Pseudobagrus ussuriensis has high economic value, and all-male culture is beneficial to the economic development of this fish. In this study, the transcriptomes of gonads in males and females were analyzed, and some genes related to gonad development were found. A total of 82,931 unigenes were found (average length 1504 bp, N50 1829 bp). In addition, 4689 differentially expressed genes (DEGs; including 1424 genes upregulated and 3265 genes downregulated in males) were identified. Some genes associated with testis development (such as Dmrt1 and Ropn1l) were significantly upregulated in males, while genes related to ovary development (such as Wnt2, PLC, Cyp19a, ZP3) were significantly downregulated in males, demonstrating that these genes have a crucial influence on gonad development in P. ussuriensis. Some signaling pathways related to gonad development were found, such as the Wnt pathway and oocyte meiosis. The results of RNA-seq obtained in this study provide theoretical data for elucidating the potential mechanism of gonad development of P. ussuriensis and reliable genomic data for the establishment of mono-sex breeding of P. ussuriensis.

Breeding programs in oriental river prawn populations would benefit from a knowledge of heritabilities for growth-related traits to assess their potential for genetic improvement. This study reports the results of heritability estimation and evaluation of epistatic interactions for growth-related traits in oriental river prawn ( Macrobrachium nipponense ). The results showed that heritability estimates ( h 2 ) were low to medium in magnitude, ranging between 0.10 (±0.02) and 0.22 (±0.01) for females and between 0.08 (±0.01) and 0.26 (±0.02) for males. The additive × additive epistasis was directional and synergistic for body weight (growth), body length, and two processing traits (abdominal meat weight and abdominal meat percentage). The presence of biallelic epistasis provides additional new information for the formulation of selection programs. Elimination of some sources of nonadditive effects from phenotypes can lead to more accurate genetic evaluations, and more desirable genetic gains could be achieved through the integration of heritability, additive effects (breeding values), and epistasis in oriental river prawns.

The effects of herbicides on non-target organisms in paddy fields have become a popular research topic. As a widely used herbicide, it is necessary to explore the potential toxicity of metamifop in non-target organisms, especially aquatic animals, in co-culture mode. In the present study, we evaluated the effects of metamifop (0, 0.2, 0.4, 0.6, and 0.8 mg/L) on the defense system (antioxidation, immunity, and apoptosis) in Monopterus albus. Reactive oxygen species (ROS) production, malondialdehyde (MDA) content, and protein carbonylation (PCO) increased significantly (p < 0.05) with the increasing metamifop concentration, resulting in oxidative damage. In the antioxidant system, superoxide dismutase (SOD) and catalase (CAT) activities increased significantly (p < 0.05) in the 0.2 mg/L treatment group compared with the control group, and decreased in 0.4, 0.6, and 0.8 mg/L treatment groups. Glutathione peroxidase (GPX) activity decreased significantly (p < 0.05) with the increasing metamifop concentration. In the immune system, white cell number (WCN) increased significantly (p < 0.05) in 0.2 mg/L treatment group, and then decreased with the increase in metamifop concentration. Compared with control group, acid phosphatase (ACP) activity not only increased significantly (p < 0.05) in 0.2 mg/L treatment group, but also decreased significantly (p < 0.05) compared with the increase in metamifop concentration. However, in all treatment groups, alkaline phosphatase (AKP) activity was significantly lower than that in the control group (p < 0.05). In the inflammatory response, TNF-α and IL-1β expression levels in the NF-κB signaling pathway decreased significantly (p < 0.05) with the increase in metamifop concentration, while IL-8 expression level in the same signaling pathway increased significantly (p < 0.05) in treatment groups. The expression levels of genes related to apoptosis showed that apoptosis was promoted after exposure to metamifop. The results of the present study show that metamifop induced oxidative damage via a high level of ROS production, and then inhibited or damaged the defense systems of M. albus.

As important environmental factors, ammonia and temperature have important effects on aquatic crustaceans. The combined effects of ammonia and temperature on the anti-oxidation and immunity of Procambarus clarkii were examined using the factorial experimental design in this study. A total of 9 ammonia-temperature com-binations (3 replicates for each combination) were set up with each factor having 3 regimes. The results showed that most indicators varied quadratically with ammonia concentration and temperature in the ranges of the two factors. The interaction between ammonia and temperature was significant on most indicators, demonstrating that ammonia and temperature affected the anti-oxidation and immunity of P. clarkii in a combined manner. Ammonia accumulation and oxidative stress occurred more likely under the combined influences of ammonia and temperature. The enzymatic activities and gene expressions that are closely related to the antioxidation and immunity were easier to be activated or inhibited due to presence of the interaction between ammonia and temperature. This study provides new insights into the mechanism for adaption of P. clarkii to the combined impacts of ammonia and temperature. The results contribute to increased immunity and resistance of this commercially important species against diseases through improvement of multiple culture conditions.

Abamectin, a pesticide of 16-member macrocyclic lactones, is widely applied in agriculture. As an important environmental factor, pesticides pose a great threat to defense system in aquatic animals. Procambarus clarkii is one of the most important economic aquatic animals in China. It is necessary to explore the defense mechanism of P. clarkii to abamectin. In this study, P. clarkii were exposed to 0, 0.2, 0.4, 0.6 mg/L abamectin, immune-and antioxidant-related enzymes activities, genes expression levels, and histological observations were used to analyze the defense capacity of P. clarkii to abamectin. With increasing abamectin concentration, reactive oxygen species (ROS) level and malondiadehyde (MDA) content increased significantly. Meanwhiile, acid phosphate (ACP), alkaline phosphatase (AKP) activities, total haemocyte counts (THC), and Crustin expression level decreased significantly, superoxide dismutase (SOD), catalase (CAT) activities, total antioxidant capacity (T-AOC), and GPX expression level also decreased significantly. Hematoxylin & eosin (H&E) observation showed that with increasing abamectin concentration, hepatopancreas were damaged, especially membrane structure. Through TUNEL observation and apoptosis-related genes (PcCTSL, Bcl-2, Bax, BI-1, PcCytc, caspase-3) expression levels, with increasing abamectin concentration, apoptosis rate increased significantly. Results of this study indicated that abamectin caused oxidative damage to P. clarkii, resulting in damage to defense system, sup-pression of nonspecific immunity and antioxidation, and promotion of apoptosis. It provided theoretical basis for healthy P. clarkii culture, and for further study on defense mechanism of aquatic animals to pesticides.

Metamifop (MET) is a widely used herbicide. It is likely for it to enter water environment when utilized, thus potential impacts may be produced on aquatic animals. Little information is available about its effects on the endocrine system of fish to date. In the current study, female rice field eels ( Monopterus albus ) were exposed to different MET concentrations (0, 0.2, 0.4, 0.6, 0.8 mg L −1) for 96 h to examine the effect of MET on the hypothalamic-pituitary-gonadal (HPG) axis and sexual reversal. The results showed that high concentrations of MET exposure increased vitellogenin (VTG) levels in liver and plasma, but plasma sex hormone levels were not affected by MET exposure. MET exposure increased the expression of CYP19A1b and CYP17 that regulate sex hormone production in the brain, but the expression of genes (CYP19A1a, CYP17, FSHR, LHCGR, hsd11b2, 3β-HSD) associated with sex hormone secretion in the ovary and the estrogen receptor genes (esr1, esr2a, esr2b) in the liver were all suppressed. In addition, the expression of sex-related gene (Dmrt1) was suppressed. This study revealed for the first time that MET has estrogen-like effects and has a strong interference with the expression of HPG axis genes. MET did not show the ability to promote the sexual reversal in M. albus , on the contrary, the genes expression showed that the occurrence of male pathway was inhibited.

As an important trace element and the accessory factor of many enzymatic processes, heavy metal copper is essential to aquatic animals. The toxic mechanism of copper on gill function of M. nipponense was clarified for the first time in terms of histopathological analysis, physiology, biochemistry and the expression of important genes. The results obtained by present in present research showed that heavy metal copper could affect normal respiratory and metabolic activities in M. nipponense. Copper stress could cause damage to the mitochondrial membrane of gill cells in M. nipponense, and the activity of mitochondrial respiratory chain complex could be inhibited by copper. Copper could affect normal electron transport and mitochondrial oxidative phosphorylation, resulting in the inhibition of energy production. High concentrations of copper could disrupt intracellular ion balance and induce cytotoxicity. The oxidative stress could be induced by copper, leading to excessive ROS. Copper could reduce the mitochondrial membrane potential, lead to the leakage of apoptotic factors, and induce apoptosis. Copper could damage structure of gill, affect normal respiration of gill. This study provided fundamental data for exploring impacts of copper on gill function in aquatic organisms and potential mechanisms of copper toxicity.

The use of herbicides is believed to have an impact on the metabolism, physiology and biochemistry of fish. In this study, we studied the effects of metamifop on the production and metabolism of Monopterus. albus living in the water. According to the semi-lethal concentration of metamifop for 96 h, four MET concentration groups (0.2-, 0.4-, 0.6- and 0.8 mg L-1) were set up for 96 h exposure test. The ammonia discharge rate decreased, hemolymph ammonia content increased significantly, and hemolymph urea nitrogen content decreased at all time periods of metamifop exposure. In liver, the protein content decreased, the neutral protease content increased significantly (p < 0.01), amino acid content increased, and ATP content increased significantly (p < 0.01). In brain, the protein content increased, the activity of acid protease, neutral protease and alkaline protease all decreased, amino acid content decreased significantly (p < 0.01), and the content of ATP decreased. Glutamicpyruvic transaminase (GPT) activity did not change in liver but decreased in brain. Glutamine synthetase (GS) activity decreased in liver and increased in brain. Glutaminase (GLS) activity decreased in liver and increased in brain. In conclusion, the liver and brain tissues of M. albus react differently to MET exposure. The liver mainly synthesizes energy through hydrolyzed protein, while the brain mainly synthesizes protein. Amino acids produced by protein hydrolysis cannot be converted to alanine for storage, and the degraded amino acids lead to the elevation of endogenous ammonia. MET inhibits the removal of ammonia from M. albus. Only liver tissue can detoxify the eel by converting ammonia into glutamine. Brain should have to tolerate high levels of endogenous ammonia.

The copper, as heavy metal has important impacts on the antioxidant and immune defense systems in aquatic organisms, and the toxic effects of copper can be accumulated and magnified with the food chain, thus posing a threat to food safety as well as ecosystems. This study explored the response of the antioxidant system and non-specific immunity in M. nipponense to copper stress. Low concentration of copper (0.05, 0.1 mg L-1) had positive effects on the non-specific immunity in M. nipponense, while the non-specific immunity in M. nipponense could be affect negatively or even be inhibited by high copper concentration (0.15 mg L-1). Even low concentrations of copper could cause oxidative stress, and high copper concentration (0.15 mg L-1) could induce oxidative damage and even apoptosis, and thus causing damage to the antioxidant defense system in M. nipponense. Low concentration of copper could affect the gill and hepatopancreas structure in M. nipponense, but high level oxidative stress caused by high copper concentration could cause oxidative damage to these tissue, resulting in the destruction of gill and hepatopancreas. This study provides the safety concentration for using copper-containing fish drugs in the actual culture of M. nipponense and provides basic data for the toxicity mechanism of copper to M. nipponense.

Macrobrachium nipponense is a crustacean species of economic importance. The dress-out traits in this species cannot be directly selected for improvement due to their failure to be reliably measured. In this study, the path analysis approach was used to make clear how much dress-out traits were determined by growth (body weight at harvest) and morphometrics (body length, chela length, abdominal length, cephalothorax width, second abdominal segment width, second abdominal segment height). Then efforts were made to establish reliable prediction models of dress-out traits in both sexes. Results showed that abdominal meat weight was 0.69 (± 0.17) g for females, and 0.75 (± 0.25) g for males; abdominal meat percentage was 34.67 (± 4.21) %, and 33.94 (± 4.85) %. Body weight was the only determinant of abdominal meat weight in both sexes (P < 0.01), whereas the coefficients of determination of growth and morphometrics on abdominal meat percentage were all nonsignificant in both sexes (P > 0.05). According to the results of path analysis, models of abdominal meat weight on body weight were established, with R2 value reaching 0.952 for females, and 0.949 for males. Residuals analysis showed the adequacy of the abdominal meat weight models. The shrinkage on cross-validation of the abdominal meat weight was 0.004 for females, and 0.006 for males, showing the applicability of the models. Growth and morphometrics were not able to be used for predicting abdominal meat percentage. In practical breeding program of this species, direct selection of abdominal meat weight can be pursued through predictions using the reliable models established in our study, alternatively indirect improvement of abdominal meat weight through direct selection for growth. Abdominal meat percentage is not suggested for the target of improvement in M. nipponense.

Sex-specific markers and sequences are essential tools for sex-determination mechanism analyses and sex-control breeding of fishes. Pseudobagrus ussuriensis is a high-value aquaculture fish with great potential for all-male breeding, as males grow much faster than females. In the present study, reduced restriction site-associated DNA sequencing was performed in five female and five male P. ussuriensis using the 2b-RAD approach to identify sex-specific sequences. A total of 84.52 million clean reads were obtained, with 47.30 million in females and 37.22 million in males. After clustering of clean reads, 2,331,843 clean tags were obtained, with average numbers of 235,472 in females and 230,896 in males. Sexual comparison of these tags resulted in 349 potential male-specific tags, among which 22 were false positive (without differences between sequences of males and females), 46 contained insertions/deletions (InDels), 261 contained single nucleotide polymorphisms (SNPs), and 20 were male specific. A male draft genome containing 689,006 scaffolds with a size of 689.04 million base pairs (bp) was obtained to extend potential male-specific tags. Fourteen sex-specific sequences with lengths ranging from 85 bp to 2494 bp were screened out. The validation results indicated three male-specific markers and seven male-specific sequences, which were further confirmed in 300 individuals from two full-sib families and showed the expected 1:1 sex ratio. Annotation of these sex-specific sequences resulted in 12 candidate genes. Furthermore, at least eight of the sex-specific sequences were deduced to be located on the same chromosome, which may be the sex chromosome of P. ussuriensis. The results obtained in this study will be helpful for studies on mechanism analysis of sex determination and all-male breeding in P. ussuriensis.

The sequence information used in this article has been uploaded to the GenBank with the accession number MT892877. All the authors take responsibility for the integrity and usability of the data uploaded.

The growth and survival of pearl oyster postlarvae (Pinctada martensii) were studied under laboratory conditions. A face-centered central composite experimental design was used with 3 factors, temperature (18―34 °C), algal ration (5―100 cells μL―1) and stocking density (0.2―3.0 in.. mL―1). Pearl oyster postlarvae were fed with a 1: 1 mixture of Isochrysis zhanjiangensis and Pavlova viridis during the experiment. Temperature, algal ration and stocking density exerted significant effects on postlarvae growth and survival. Temperature was the most dominant factor, followed by algal ration. Significant interactions among the 3 factors were inhibitory (negative) to growth and survival. Within the ranges of 3 factors tested, growth and survival increased with 3 factors up to a pinnacle, beyond which they began to decrease. The conditions required for the optimal growth could also ensure the optimal survival. Through simultaneously maximizing the reliable models of postlarvae growth and survival, the optimal trifactor culture conditions of 27.86 °C/50.85 cells μL―1/1.60 in.. mL―1 were obtained. These optimal culture conditions resulted in the greatest specific growth of 8.95 % d―1 (95 % confidence interval, 8.73―9.18 % d―1) and survival of 21.5 % (95 % confidence interval, 21.06―21.94 %), with desirability as high as 99.6 %. Due to practical feasibility, the optimal trifactor culture conditions were recommended to apply to practice to maximize growth and survival of the pearl oyster P. martensii postlarvae martensii. This study provides valuable new insights into refining the production efficiency of the pearl oyster postlarvae.

RNA/DNA ratio (RDR) has been reported to be a feasible biochemical indicator for measuring the growth of numerous aquatic animal species. Nevertheless, its applicability has not been investigated to date in the pearl oyster Pinctada fucata (Gould, 1850). A laboratory experiment was undertaken to determine the relationship between RDR and growth rate in P. fucata postlarvae. The face-centered central composite design was used with three important factors (temperature, algal concentration and stocking density) simultaneously varied to produce a variety of growth rates. Temperature ranged between 18 and 34 °C, algal concentration between 5 and 100 cells μL―1, stocking density between 0.2 and 2.5 in.. mL―1. Postlarvae were fed with a 1: 1 mixture of Isochrysis zhanjiangensis and Pavlova viridis over the course of experiment. Results showed that RDR was affected significantly by the first- and second-order effects of and first-order interactions among three factors, but the interactions were negative to the growth of pearl oyster postlarvae. Within the ranges of three factors examined, algal concentration was most important, followed by temperature in influencing the growth of P. fucata postlarvae. RDR was highly positively correlated with specific growth rate (SGR) and absolute growth rate (AGR). Simple linear regression equations of shell height-based growth rates regarding RDR were established, SGR (% d―1) = ―0.05 + 2.01RDR (R2 = 0.98); AGR (μm d―1) = ―0.02 + 2.82RDR (R2 = 0.96). Lack-of-fit test indicated their high adequacy. The models have greater advantages over conventional means of assessing somatic growth, and can be utilized to reliably evaluate recent growth of P. fucata postlarvae under concurrent variations of three factors examined in the present study.

As a non-essential and toxic element, cadmium poses an important threat to aquatic organisms and human food safety. In this study, the effects of cadmium on antioxidant and non-specific immunity of Macrobrachium nipponense were studied from the physiological and biochemical indexes, histology and expression of related genes. These results showed that low concentrations (0.01, 0.02 mg/L) of cadmium have a positive effect on the nonspecific immunity of M. nipponense, but high concentration (0.04 mg/L) of cadmium could inhibit or even damage the non-specific immunity of M. nipponense. The cadmium could induce oxidative stress in M. nipponense, and M. nipponense actived the antioxidant defense system to deal with oxidative stress, but high concentration (0.04 mg/L) of cadmium could inhibit the antioxidant defense system of M. nipponense, leading to oxidative damage, and may induce apoptosis in severe case. At the same time, the results of histology showed that cadmium can damage the structure of gill and hepatopancreas tissues of M. nipponense. This study provides theoretical data for evaluating the influences of heavy metal cadmium on M. nipponense and the toxic mechanism of heavy metal cadmium.