Abstract:There has been much debate on the taxonomy of Schizothoracids. Phylogenetic study provides an effective way to solve taxonomic problems. In this study, mitochondrial genome data from GenBank were analyzed using the maximum likelihood and Bayesian methods to investigate the phylogeny of Schizothoracids. Two data sets were applied: one was composed of 13 protein coding genes (PCGs) and the other of 13 protein coding genes plus two rRNA genes (13 PCGs & 2 rDNAs). Phylogenetic relationships were reconstructed using the multipartition and single-partition strategies, respectively, in adopting nucleotide substitution models to the data sets. The results showed a clear clustering within each of the three grades of Schizothoracids. The “primitive” Schizothoracids and the genus Percocypris of barbine fishes form a monophyletic group, while the “specialized” and “highly-specialized” Schizothoracids form the other evolutionary branch, being paraphyletic to the former. The “highly-specialized” Schizothoracids shared a most recent common ancestor with some “specialized” Schizothoracids. Our results do not support Schizothoracids as a subfamily, but support the combination of “specialized” and “highly-specialized” Schizothoracids into the Schizopygopsini tribe, while “primitive” Schizothoracids and the genus Percocypris are grouped as the Schizothoracini tribe. There was no significant improvement in solving the phylogenetic relationships of Schizothoracids when analyzing with different data sets and different data partition strategies. Time to most recent common ancestor (tMRCA) for main Schizothoracids groups was then estimated using 13 PCGs with a single-partition strategy in adopting nucleotide substitution models to data and the Bayesian method, with the geological evidence and mitochondrial DNA substitution rate as priors. The results showed that the tMRCA of Schizothoracids and Percocypris was about 13.16 Ma, suggesting that these fishes diverged at some point after the middle Miocene. The tMRCA of “primitive” Schizothoracids was about 4.94 Ma, indicating that they originated during the Pliocene. While the tMRCAs of “specialized” and “highly-specialized” groups imply that they began to differentiate from their common ancestor around 9.64 Ma ago, the tMRCA of the “highly-specialized” group suggests it originated approximately 5.40 Ma ago. Considering the geographical history of the distribution range, Schizothoracids may have originated late in the post-collisional period of the Indian and Eurasian plates, and the differentiation of main groups and speciation events in Schizothoracids could closely be related to the stage type evolution and climate fluctuation of the Qinghai-Tibet Plateau.

Abstract:China contains vast areas of saline-alkali waters. Therefore, fish farming in such waters is crucial to ensuring domestic food supply and safety in the future and is also necessary for achieving the strategic goal of “expanding capacity, improving quality, and increasing efficiency” of China’s existing land area. The breeding of saline-tolerant fish species and the establishment of suitable breeding patterns are the key approaches to the efficient utilization of saline-alkali waters. The stability of key metabolic pathways in target organs is necessary for fish to adapt to changes in the external habitat. Gills are the salt-tolerant target organs of fish, and the effect of Rh glycoprotein on the ammonium transporter has been confirmed. However, uncertainty remains around the material basis and mechanism of regulation at the cellular level. This lack of understanding restricts the targeted breeding of salt-tolerant fish, which has become a key bottleneck requiring an urgent solution for the sustainable development of the saline-alkali fish industry. In this study, the saline-alkali tolerant Carassius auratus gibelio variety in China was used as the research object. Specimens were exposed to fresh water in the control group (Con), and three different concentrations of alkali in the stress groups: 20 mmol/L NaHCO₃ (CA20), 40 mmol/L NaHCO₃ (CA40), and 60 mmol/L NaHCO₃ (CA60). Metabolomics were used to screen for endogenous differential metabolites. Statistical analysis of metabolic pathways and multivariate data was used to explore the response mechanism of C. a. gibelio to alkali stress. The results showed that the gill tissue metabolites screened out 89 differential metabolites in the positive and negative ion mode, of which 50 were up-regulated and 39 were down-regulated, mainly enriched in glycerophospholipid metabolism, sphingolipid metabolism, arachidonic acid metabolism, and benzene Alanine metabolism, while the biosynthesis of phenylalanine, tyrosine, and tryptophan was represented by 12 metabolic pathways. This study shows that, after alkali stress, the glycerophospholipid in C. a. gibelio regulates the transport of substances inside and outside the cell membrane, and the pathway to synthesize sphingomyelin and sphingosine is inhibited. As the concentrations of prostaglandins, leukotrienes, and L-phenylalanine in the metabolites increase, the detoxification function increases and inflammatory response decreases. This metabolic mechanism may be a key reason for the tolerance of C. a. gibelio carp to alkali stress. This study explored the toxic effect and physiological regulation mechanism of alkali stress on crucian carp and provided a theoretical basis for further research into the breeding of excellent salt-tolerant fish species.

Abstract:To explore the role of the 5-HT1A receptor in feeding and food consolidation during domestication of Chinese perch, Siniperca chuatsi, we obtained the htr1a gene sequence of the Chinese perch genome using homologous sequence alignment and evolutionary tree analysis. Htr1a has two isoforms, htr1aa and htr1ab, which encode amino acid sequences that have high homology with those of zebrafish (Danio rerio) and medaka (Oryzias latipes), with a similarity of more than 70%. The evolutionary relationship is closest between Chinese perch and wolf perch (Dicentrar chuslabrax). The results indicated that the htr1a gene of Chinese perch is highly conserved in evolution. The expression and methylation of the htr1a gene in mandarin fish were also analyzed. Compared with the first domestication group, the expression of the htr1aa gene and DNA methylation were significantly decreased in the second domestication group (P＜0.05), while htr1ab gene expression was not significantly different between the two groups (P＞0.05). The expression of pomc was related to food intake, which was obviously lower than that of a domesticated animal (P＜0.05). The above results indicated that methylation of the promoter region of the htr1aa gene may change its transcription level during food domestication of Chinese perch, thus affecting the expression of key factors in the learning and memory pathways, inhibiting appetite factor pomc. Therefore, DNA methylation of htr1aa may play an important role in regulating the expression level of feeding related genes in Chinese perch. The results of this study further elucidate the mechanism of learning and memory in the transformation of feeding habits in fish and provide a theoretical solution to the difficult and unstable domestication of Chinese perch.

Abstract:Retinoid X receptor (RXR) belongs to the family of nuclear receptors activated by ligands. In this study, the cDNA sequence of the Sepiella japonica RXR gene was cloned using RT-qPCR; bioinformatics analysis was conducted on the sequence of nucleotide and protein structure in the CDS region of the RXR gene. The results showed that the CDS-domain nucleotide sequence of SjRXR was 1239 bp, encoding a protein composed of 412 amino acids. Moreover, the sequence analysis showed that the CDS region of the S. japonica RXR gene did not contain a signal peptide, possibly indicating that the RXR encoding protein was a non-secretory protein. There is no transmembrane structure in the protein structure, making it a non-transmembrane protein. Hydrophobicity analysis shows that the protein is more hydrophilic than hydrophobic. It also contains a domain of the HOLl family. The phylogenetic tree was constructed using the MEGA6 software employing the ML method. S. japonica is closely related to Octopus bimaculatus, which belongs to the phylum Cephalopoda, gathered into one branch. Thus the molecular evolutionary status of the RXR gene of S. japonica is consistent with its biological classification status. RT-qPCR was also used to analyze the expression characteristics of this gene in eleven tissues of S. japonica during four growth periods. The sjRXR gene was expressed in all tissues, and it was highly expressed in the liver, pancreas, brain, visual lobe, and visual gland. The sjRXR expression changed significantly during the four growth stages, increased in the liver, pancreas, brain, optic lobe, and optic gland, but was followed by a decreasing trend in the brain, optic lobe, and optic gland. These results speculate that SjRXR regulates S. japonica neurodevelopment, reproduction, and aging as an essential factor and provide a vital reference base for in-depth study of the RXR gene in cephalopods.

Abstract:Thymallus arcticus belongs to the Salmonidae family and is a valuable cold-water fish, mainly distributed in the Irtysh River Basin. However, overfishing and habitat destruction have depleted their populations and in 2021, they were classified as national level II protected wild animals. Therefore, basic research is urgently needed to better understand the biological characteristics of T. arcticus. To determine the relationship between the morphological traits and body weight of T. arcticus, individuals with ages 1⁺ , 2⁺ , and 3⁺ were used as the research objects and measured for their body weights (Y) and nine morphological traits, namely body thickness (X₁), eye interval (X₂), body length (X₃), body height (X₄), head length (X₅), eye diameter (X₆), proboscis length (X₇), caudal peduncle length (X₈), and caudal peduncle height (X₉). Relevant analysis, path analysis, and multiple regression analysis were used to screen out the main morphological traits affecting the body weight of T. arcticus and establish regression equations. The results showed that: (1) different types of morphological traits were significantly related (P＜0.05) to the weight of T. arcticus at different ages and the number of traits also decreased as age increased. (2) Path analysis retained 4, 4 and 2 morphological traits for T. arcticus with ages 1⁺, 2⁺, and 3⁺ years, respectively. The body length (X₃) had the greatest direct effect (0.345), while caudal peduncle height (X₉) had the largest indirect effect (0.745) on the body weight of 1⁺ -year-old T. arcticus. Body height (X₄) had the largest direct effect (0.473) and body thickness (X₁) had the largest indirect effect (0.378) in 2⁺ -year-old T. arcticus. Body thickness (X₁) had the largest direct effect (0.635) and caudal peduncle height (X₉) had the largest indirect effect (0.344) in 3+ -year-old T. arcticus. (3) The total determination coefficients of the morphological traits retained by the path analysis, and therefore affecting body weight, were 0.943, 0.778, and 0.997 in T. arcticus with ages 1⁺ , 2⁺ , and 3⁺ , respectively. (4) Through multiple regression analysis, the fitted regression equations of the morphological traits (Xi) and body weight (Y) were found to be Y=?90.510+15.345X₁+3.638X₃+10.473X₄+ 16.884X₉, Y=?142.449+29.023X₁+81.082X₂+27.126X₄?47.376X₇, and Y=?228.922+75.063X1+107.864X9 for T. arcticus with ages 1⁺ , 2⁺ , and 3⁺ , respectively. This study identified the main morphological traits that determine the body weight of T. arcticus at different ages and also established the regression equations, providing fundamental research data for T. arcticus conservation biology, as well as candidate morphological traits for future research on the selection and breeding of T. arcticus.

Abstract:This study estimated the genetic parameters affecting the body weight trait of Litopenaeus vannamei juveniles under low-temperature fluctuation, using the 40K SNP genotyping information of L. vannamei, with the aim of providing fundamental data for the breeding of new L. vannamei varieties tolerant to low temperatures. A total of 4000 L. vannamei juveniles from 40 families were used in a culture experiment. The culture temperature was reduced from 30 ℃ to 20 ℃ by the addition of underground well water, and then stabilized for 4 days after 24 h of natural warming. Continuous cultivation was conducted for 15 days after the cooling-warming-stabilizing process had been repeated 3 times, and the body weight and survival traits of the juveniles were then measured. Compared with that in the control group, low-temperature fluctuation had a significant effect on the growth of L. vannamei larvae (P＜0.05) but not on the survival traits (P＞0.05). An A-matrix was constructed based on individual genealogical information, and the 40K SNP chip was used for SNP genotyping of 159 parents and their SIB individuals. An H-matrix was constructed by combining SNP and pedigree information, estimation of variance components, and the genetic parameters of body weight traits using individual animal models. According to the Aand H-matrices, respectively, the heritability of body weight was 0.37±0.07 and 0.40±0.08 for L. vannamei larvae under low-temperature fluctuation, indicating a high heritability level. This cross-validation shows that there is no significant difference in prediction accuracy and bias between the two matrices. The body weight of L. vannamei under low-temperature fluctuation showed abundant genetic variation, indicating that multi-generation breeding may result in notable genetic gain.

Abstract:Selenium (Se) is an essential trace element for fish, and deficient or excess dietary Se influence their growth. The body growth of fish is mainly influenced by muscle growth, which is mainly determined by the deposition rate of protein in muscle tissue. There is evidence that the autophagic degradation of fish muscle protein is significantly influenced by the level of dietary Se. The autophagy lysosomal pathway is one of the main pathways for muscle protein degradation. Studies have shown that adequate dietary Se (4.0 mg Se/kg diet) inhibited autophagic degradation in rainbow trout (Oncorhynchus mykiss) muscle. However, the effects of deficient or excess dietary Se on the autophagic degradation of rainbow trout muscle requires further exploration. This study aimed to explore the effects and possible mechanisms of dietary Se level on the growth of rainbow trout. Different amounts of Se yeast (as source of Se) were added to the basal diet to reach deficient (DSe, 0 mg Se/kg diet), adequate (ASe, 4.0 mg Se/kg diet), and excessive (ESe, mg Se/kg diet) Se levels. Results showed that DSe and ESe diets were not conducive to the growth performance of rainbow trout. The final body weight and weight gain rate in the rainbow trout fed DSe and ESe diets were significantly lower than those fed ASe diets (P＜0.05). The feed conversion ratio of fish in the ASe group was significantly higher than those in DSe and ESe groups. There was no significant difference in condition factor or feed intake. Furthermore, the diameter of rainbow trout muscle fibers in the DSe and ESe groups was significantly lower than those in the ASe group (P＜0.05). Additionally, dietary Se significantly affected the protein and total Se content of rainbow trout muscle. The autophagy-related gene (Atg) expression and autophagy markers (microtubule-associated protein light chain 3 (LC3) and P62 level are important biomarkers for assessing the level of autophagy. Results showed that mRNA levels of Atg4b, Atg12l, LC3B, Atg13, Atg7, and Atg5 in the muscle of rainbow trout in DSe and ESe groups were significantly higher than those in the ASe group (P＜0.05). The LC3-II level of rainbow trout in DSe and ESe groups was significantly induced, while the content of P62 was significantly reduced (P＜0.05). These results indicate that deficient or excess dietary Se led to increased levels of autophagy in the muscle of rainbow trout. The protein kinase B-target of rapamycin (Akt-TOR) and amp-activated protein kinase (AMPK) pathways are important pathways for autophagy regulation. Both deficient and excessive Se levels significantly inhibited the phosphorylation of Akt and TOR and inhibited the activity of the Akt-TOR pathway. The AMPK activity of rainbow trout muscle was induced in DSe and ESe groups. The malondialdehyde and lipid peroxide contents of rainbow trout muscle were significantly higher in the DSe and ESe groups than that in the ASe group, as revealed through analysis of the oxidation status of rainbow trout muscle. The muscle oxidative stress was intensified, which may have allowed dietary Se to affect the Akt-TOR and AMPK pathways. In summary, this study explored the comprehensive effects of dietary Se on somatic and muscle growth in rainbow trout. The effects and possible mechanisms of dietary Se level on autophagic degradation of rainbow trout muscle protein were also preliminarily revealed. The results can enrich our understanding of the nutritional function of Se and provide a foundation for further research on the mechanism by which Se regulates fish growth.

Abstract:Due to the current low production levels and high price of fish meal, soybean meal has become the best source of protein for replacing fish meal in aquatic feed, as it is rich in crude protein and has a balanced amino acid composition. However, soybeans and their products contain anti-nutritional factors such as trypsin inhibitors, soybean antigen protein, saponins, and oligosaccharides, which cause significant intestinal injury in aquatic animals and are likely to cause intestinal diseases. To maintain the intestinal health of aquatic animals, some functional additives can be added to soybean meal feed to improve intestinal health. Among them, tributyrin (TB), α-ketoglutarate (AKG), and alanyl-glutamine (Ala-Gln) can promote intestinal development and improve intestinal health. This experiment examines the effects of TB, AKG, and Ala-Gln on the growth, digestive enzyme activity, and immune function gene expression of Macrobrachium rosenbergii. Two feeds supplemented with 40% soybean meal and 33.70% peanut meal, respectively, were used as the control groups (named SM group and PM group), while 0.10% and 0.20% TB (TB1 group and TB2 group), 1.00% and 2.00% of AKG (AKG1 group and AKG2 group), 1.00% and 2.00% of Ala-Gln (AGn1 group and AGn2 group) were added to soybean meal feed, respectively, to form 8 kinds of isonitrogenous and isoenergetic feed for M. rosenbergii. A total of 640 M. rosenbergii with an initial weight of (0.10±0.02) g were selected and randomly divided into 8 groups with 4 replicates in each group and 20 tails in each replicate. The trial period was 8 weeks. Compared with the soybean meal group, the TB, AKG, and AGn groups exhibited no significant differences in growth performance, serum superoxide dismutase activity, malondialdehyde content, TOR, or caspase-3 gene expression of M. rosenbergii (P＞0.05). Intestinal and hepatopancreas lipase, trypsin, and α-amylase digestive enzyme activities of the TB, AKG, and AGn2 groups were significantly increased (P＜0.05), and these activities were significantly higher in the AGn2 group than in other experimental groups (P＜0.05). The trypsin activity in the intestine of the AKG2 group was second and was significantly higher than in the other groups (P＜0.05). Although the greatest α-amylase activity in the intestine was seen in the AKG1 group and was significantly higher than that in the other groups (P＜0.05), and the relative expression of caspase-8 was significantly higher in the AKG1 group than in the other groups (P＜0.05), the relative expression of TNF-α was significantly lower in the PM group and the TB group (P＜0.05). The results show that the addition of TB, AKG, and Ala-Gln had no effect on the growth performance and antioxidant function of M. rosenbergii. The addition of TB, AKG, and Ala-Gln can improve digestive enzyme activity and the addition of 2% Ala-Gln significantly improved the activity of digestive enzymes. Soybean meal is more effective than peanut meal for up-regulating the expression of TNF-α. Adding TB can reduce the expression of inflammatory proteins and intestinal cell apoptosis caused by TNF-α in M. rosenbergii.

Abstract:The microorganisms in biofloc play vital roles in ensuring the stable operation of a culture system as a basis for mass conversion and energy flow. The characteristics and associated functions of a microbial community are largely influenced by the type of nutrition provided by the biofloc. The heterotrophic and autotrophic approaches are the two main methods that have been developed for culturing biofloc. However, the former method usually requires large amounts of organic matter, while the latter requires a long period of cultivation to achieve the function of the biofloc. Recently, the “hete-auto” method has been proposed, which involves the cultivation of biofloc using a combination of the heterotrophic and the autotrophic methods. This method avoids the negative effects of the above-mentioned methods when used alone. To date, most studies on this subject have focused on changes in water quality and nitrogen budgets, but the characteristics of the microbial community of such biofloc, compared to that obtained with conventional methods, remains unclear. Specifically, the effect of water quality on the microbial community of the “hete-auto” biofloc has not been reported. To fill this research gap, we constructed three Litopenaeus vannamei culture systems using “hete-auto” biofloc (AUTO), heterotrophic biofloc (HETE), and the flow-through method (CON), respectively. In the HETE group, sugar (i.e., an external carbon source) was supplied throughout the experiment; whereas in the AUTO group, sugar was added at the beginning of the experiment until the water quality had stabilized (i.e., ammonia nitrogen). In CON, no carbon source was added. Microbial characteristics of biofloc in the three culture systems were analyzed using high-throughput sequencing technology (Illumina MiSeq, Pudong, Shanghai), and the interactions between the microbial community and aquaculture water environment were also investigated. The results showed that Proteobacteria (24.2%–70.45%) and Bacteroldota (8.45%–28.09%) dominated in all treatments. At the genus level, no significant differences were observed between the groups in the relative abundance of the filamentous bacterium Leucothrix (essential for biofloc construction) (3.60%–7.29%). Notably, 94 OTUs classified as Nitrospirota (i.e., nitrifying bacteria) only existed in the AUTO biofloc; furthermore, the relative abundance of nitrifying genes such as AmoA and AmoB in the AUTO biofloc (i.e., 0.17% and 0.20%, respectively) were significantly higher than in the HETE biofloc (i.e., 0.10% and 0.09%, respectively). There were no significant differences in the specific growth rates of L. vannamei cultured with different nutrient types of biofloc. Differences in the microbial composition of the biofloc altered the pathways of nitrogen cycling, resulting in different concentrations of ammonia nitrogen, nitrite, and nitrate, which in turn were influenced by differences in water quality. This study demonstrates that changing the nutrient type results in biofloc with a more rational composition and function, which can effectively control water quality and keep the whole culture system balanced and benign.

Abstract:A constructed wetland combines the functions of the substrate, plants, and microorganisms, such as filtration, adsorption, ion exchange, plant absorption, and microbial degradation, to realize the efficient purification of aquaculture tail water. Such a system has the advantages of simple processes, less investment costs, low energy consumption, high anti-shock load capacity, effective water treatment, and remarkable ecological benefits. However, due to the influence of salinity, such systems are rarely used to treat mariculture tail water. High-throughput sequencing technology provides a rapid and affordable method for sequencing millions of DNA molecules simultaneously and has become an important technique for studying the characteristics of a microbial community. To determine the NO₃ ^– -N, NO₂ ^– -N, NH₄ ⁺ -N, and TN removal efficiencies in a constructed wetland for the treatment of mariculture tail water and to evaluate the microbial community characteristics in the plant rhizosphere and different substrate layers, we conducted experiments with an integrated vertical flow constructed wetland containing Spartina alterniflora, fine sand, coal cinder, and crushed stone. We determined the nitrogen removal efficiency of a vertical flow composite constructed wetland using the tail water of grouper culture. The characteristics of the microbial community in the plant rhizosphere and different substrate layers were determined using high-throughput sequencing. In this experiment, water samples were collected at four locations every day from September to November, and the concentrations of COD, NO₃ ^– -N, NO₂ ^– -N, NH₄ ⁺ -N and TN were determined using the national standard method. Subsequently, microbial samples were collected from 16 locations and sequenced using high-throughput sequencing technology. The results of water quality analysis show that the average concentrations of COD, NO3 – -N, NO2 – -N, NH4 + -N, and TN in the outlet water were 4.00 mg/L, 0.15 mg/L, 0.16 mg/L, 0.04 mg/L, and 0.64 mg/L, respectively, yielding removal rates of 48.98%, 92.10%, 94.49% and 78.36%, respectively. High-throughput sequencing revealed a highly abundant and diverse microbial community in the plant rhizosphere and fine sand layer, in contrast to other substrates. This is because plants in a constructed wetland form an oxidative microenvironment in the reducing medium of the root zone through photosynthesis. The co-existence of aerobic and anaerobic zones provides suitable niches for aerobic, facultative anaerobic, and anaerobic microorganisms in the root zone and promotes the growth and reproduction of microorganisms. Additionally, the contact between the fine sand layer and the plant rhizosphere increases the community richness and diversity of the fine sand layer compared to those in other substrate layers. The predominant microbes were in the phyla Proteobacteria, Bacteroidetes, Actinobacteria, Chloroflexi, and Firmicutes with relative abundances of 53.7%, 11.5%, 11.9%, 6.4%, and 3.7%, respectively. The predominant microbes were of the classes Alphaproteobacteria, Gammaproteobacteria, Actinobacteria, and Bacterodia with relative abundance of 30.1%, 20.9%, 11.9%, and 10.3%, respectively. The predominant functional microbes related to nitrogen removal included those in the genera Nitrosomonas, Nitrospira, Bacillus, Pseudomonas, and Acinetobacter. Microbial metabolism function was abundant in the constructed wetland, and all samples had a similar functional composition. Microbial community composition showed little variation within the same substrate layer, indicating that microbial composition remains relatively stable within a consistent environment. The degree of difference between microbial communities in each substrate layer was smaller in the secondary wetland unit than in the primary wetland unit. This is because the majority of tail water purification occurs in the primary wetland, where the change gradient in the concentration of nitrogen, phosphorus, and other pollutants, dissolved oxygen, salinity, and other related factors is greater along the flow direction, resulting in larger changes in the microbial growth environment. Consequently, variation in the microbial community composition is more pronounced. However, the gradient of various influencing factors along the flow direction is smaller in the secondary wetland, and the variation of the microbial growth environment is also limited, resulting in less variation in the microbial community composition in the secondary wetland than in the primary wetland. These results reveal the relationship between nitrogen removal efficiency and microbial community structure. Moreover, they provide a theoretical basis for elucidating the nitrogen removal mechanism of each substrate layer in a constructed wetland, to enable the construction of wetland systems for the efficient treatment of tail water.

Abstract:Giant freshwater prawn Macrobrachium rosenbergii is an important aquaculture species in inland areas of East and South China. In the past decade, prawn disease has occurred frequently during the grow-out stage, mainly due to pathogenic bacteria, which have caused different diseases in different regions. Gaoyou City in Jiangsu Province is the core aquaculture zone of M. rosenbergii in China, however the prawns cultivated in this region suffer from “Dixing disease” during summer. This disease causes prawns to die every day, with lower daily mortality over a long period. Since 2012, another disease has appeared, which causes prawns to grow slowly and develop precocity (commonly known as “iron prawn syndrome” prawn). Both these diseases have caused great economic losses to the prawn industry. In the mid-late grow-out stages, Cyanobacteria blooms have caused the pond water to deteriorate, indirectly affecting prawn production. Microbes in the aquaculture environment are closely related to the health of farmed animals, and the flora structure in the intestinal tract and pond environment of healthy prawn are significantly different from those of a diseased prawn pond. To better understand the composition of dominant bacteria in the aquaculture system of M. rosenbergii and improve the management technology, the composition of cultivable bacteria in the prawn and pond water was investigated in Gaoyou City in July, August, and October 2019. Luria-Bertani medium was used to separate and purify the cultivable bacteria from the hepatopancreas, intestines, gills, and pond water of prawn. Subsequently, the isolated bacteria were identified using 16S rRNA gene sequencing. High-throughput sequencing technology was employed to analyze the microbial community composition in a pond of the prawn affected by “iron prawn syndrome ”and in a pond with a bloom of Microcystis aeruginosa. Additionally, the species of antagonistic bacteria, and their effects on prawn pathogens in the aquaculture system, were screened and analyzed using Aeromonas dhakensis as a test pathogen. A total of 605 cultivable bacteria were isolated and 601 strains were successfully identified, belonging to 37 genera and 119 species. Among them, 76 species in 23 genera were isolated from prawn and 81 species in 28 genera were isolated from pond waters. Investigation results confirmed the existence of potential pathogens in the pond system, belonging to genera such as Aeromonas spp., Enterobacter spp., Lactococcus spp., and Vibrio spp. The species composition and proportion of dominant environmental microorganisms in ponds with “iron shell” prawn are similar to those of healthy prawn ponds, but bacteria in the genera Exiguobacterium and Acinetobacter had higher proportions in disease-affected ponds than those in healthy pond . The blooming of M. aeruginosa could affect the species and structure of environmental microflora and lead to an increase in the proportion of Aeromonas bacteria. Four Bacillus spp., namely B. subtilis, B. methylotrophicus, B. velezensis, and B. amyloliquefaciens, were screened as potential probiotics and were found to have a strong antagonistic effect on Aeromonas spp. These results aid in clarifying the composition of bacterial pathogens in the culture system of M. rosenbergii and provide a theoretical basis for establishing prevention and control technologies for prawn disease.

Abstract:The habitat distribution of chub mackerel Scomber japonicus, an economically important pelagic fish species, is strongly susceptible to climate variability. In this study, we calculated the habitat suitability index (HSI) for the fishing ground of S. japonicus in the East China Sea during 1950?2015, based on the environmental data of vertical water temperature at depths of 2.5 m, 25 m, and 50 m, as well as the Ni?o3.4 index. The spatio-temporal distributions of potential habitats for S. japonicus were compared among La Ni?a years of varying intensity. The habitat suitability was found to be higher during the La Ni?a years than during the years of normal climate conditions. During the weak and moderate La Ni?a years, water temperatures were cold at different depths, leading to a higher proportion of areas with suitable water temperatures and increasing the habitat suitability. However, during the strong La Ni?a years, water temperature at different depths increased, resulting in a decrease in the proportion of areas with suitable water temperatures at different depths. Therefore, the habitat suitability declined. Weak and moderate La Ni?a events resulted in an eastward shift of the longitudinal gravity center of suitable habitat and a southward shift in the latitudinal gravity center relative to its position during strong La Ni?a events. In contrast, the longitudinal gravity center of unsuitable habitat shifted westward, while the latitudinal gravity center of unsuitable habitat shifted northward. During July?September during strong La Ni?a events, the distribution of the most suitable water temperatures at different depths shifted northwestward. Variations in the spatial distribution of S. japonicus habitat under La Ni?a events with different intensities may be due to the monthly difference in distribution of the most suitable water temperature at different depths. Our findings indicated that La Ni?a events with different intensities significantly affected the habitat of S. japonicas in the East China Sea.

Abstract:

Salmo trutta fario is one of the important cold-water economic fishes in Tibet. S. t. fario is delicious; contains no muscle spines; and is rich in amino acids, unsaturated fatty acids, and vitamins. It has become an important local high value-added aquaculture species. Diseases occur frequently in cultured S. t. fario,especially bacterial diseases such as gill rot and furuncle disease and fungal diseases such as saprolegniasis, which has caused huge economic losses to the S. t. fario farming industry. Therefore, disease research is of great significance to the large-scale healthy culture of S. t. fario. To determine the cause of death of S. t. fario, two dominant strains B1 and A3-2 were isolated from diseased S. t. fario and analyzed for virulence gene, animal regression infection, drug resistance gene, and drug sensitivity. The two dominant strains were identified as Aeromonas salmonicida B1 and Aeromonas sobria A3-2. A. salmonicida B1 showed strong pathogenicity to S. t. fario,while A. sobria A3-2 showed no pathogenicity to S. t. fario. Ten virulence genes were detected in A. salmonicida B1, including those of exotoxin (AerA, Act, and hly genes), extracellular enzyme (gcat, ahyB, and Lip genes), secretion system of III type (aexT, aopP, and ascF-G genes), and flagella (Fla gene). Five virulence genes were detected in A. sobria A3-2, including those of exotoxin (Act and Alt genes), exoenzyme (gcat genes), and secretory system III (aexT and aopP genes).A. salmonicida B1 was sensitive to 21 antibiotics, such as ceftriaxone, amoxicillin, florfenicol, ciprofloxacin, tetracycline, and streptomycin, and was only resistant to vancomycin. A. sobria A3-2 was sensitive to 17 antimicrobial drugs, such as ceftriaxone, florfenicol, ciprofloxacin, pipemidic acid, tetracycline, and streptomycin and was resistant to 6 antibiotics, including penicillin, amoxicillin, sulfisoxazole, trimethoprimsulbactam, and vancomycin. Three types of drug-resistant genes (AmpC, gyrA, and parC) were detected in A. salmonicida B1. Four types of drug-resistant genes (AmpC, gyrA, parC, and tetE) were detected in A. sobria A3-2. The drug-resistant genes detected in the two Aeromonas strains were basically consistent with the drug-resistant phenotype. A. salmonicida B1 was found to be an important pathogen causing fulminant death in S. t. fario. This study provides fundamental data on the infection characteristics of A. salmonicida, for vaccine development and disease prevention and control in the breeding process of S. t. fario.

Abstract:To investigate the dynamic change characteristics of Antarctic krill (Euphausia superba) trawling, we conducted sea trials on the krill trawler “Long Fa” of the China Fisheries Corporation from January to April 2020 in subarea 48.2 of Antarctic waters(45°W?48°W, 60°S?61°S). Information was collected on the towing speed, warp length, warp tension, and depth of the net and otter board, and the effects of the warp winding up and releasing speed on the dynamic change of the net were analyzed. The relationships between towing speed, warp length, net mouth opening height, warp tension, and net position were also examined during the stable towing stage. The main results are as follows: (1) the average speed of the shooting net stage was (2.96±0.36) kn and the average speed of the hauling stage was (1.35±0.26) kn. (2) The warp releasing speed was (54.1±5.9) m/min in the natural sinking stage, and the warp winding up speed was (47.15±7.02) m/min in the pursing stage. (3) The warp tension decreased gradually with the increasing of the warp releasing speed, which is proportional to the net position sinking rate. (4) The warp winding up speed was inversely related to the warp tension. The warp tension of the upward adjustment stage was larger than that of the pursing stage. As the warp winding up speed increased, the net mouth opening height increased. (5) During the stable towing stage, the towing speed and the warp length had a significant influence on the net mouth opening heigh. As the towing speed and warp length increased, the net mouth opening height decreased. (6) In the natural sinking stage, when the warp releasing speed was too high and the net sinking speed increased, the phenomenon of “overshoot” occurred. These results can inform adjustments to the net position during Antarctic krill trawling and improve the efficiency of future trawling. They also serve as essential data for the verification model test and numerical simulations of the performance of a mid-water trawl.

Abstract:Marine fisheries are closely related to international food security and the health of marine ecosystems. Due to progress in science and technology, contemporary marine fisheries have developed rapidly but still face a series of problems, such as the decline of fishery resources, the effect of bottom trawling on the seabed, bycatch and discards, ghost fishing and plastic pollution caused by ALDFG (abandoned, lost, discarded fishing gear), climate change, and unbalanced development. This article reviews the progress in the management, technical innovation, and best practices of marine fisheries, which aim to alleviate the above problems. Based on our review, we suggest that stakehoders should: (1) further strengthen basic and applied research into eco-friendly fishing gear and methods, energy efficient technologies, recycling technologies for end-of-life fishing gear, and biodegradable material; (2) identify best practices for energy efficient technology and for reducing by-catch, the impact of bottom trawling on the benthic environment, and the addition of end-of-life fishing gear into the ocean; (3) strengthen exploration and research into incentive mechanisms; increase policy support for the recycling industry for end-of-life fishing gear; improve management systems for marine fisheries and end-of-life fishing gear and enhance governance capacity; (4) strengthen fishery cooperation between countries or regions, share management knowledge and promote balanced development between regions; and (5) strengthen strategic research into adaptation to climate change. Thus, to promote the sustainable development of fisheries, we need to make a long-term plan and adopt all necessary measures.