Abstract:The Jinsha River basin has been marked as an ecological shelter and functional critical region of the upper Yangtze River. It undertakes a variety of important functions, including biodiversity conservation. However, studies on the species composition and community structure of macrozoobenthos in this region are still very limited. To systematically understand the composition and resource status of macrozoobenthos in the lower Jinsha River and to explore the main environmental factors affecting the community structure, the macrozoobenthos of 16 sites in the riparian zone of the mainstream and its tributaries within the four cascade reservoirs along the lower Jinsha River were surveyed three times in 2017?2018. A total of 63 taxa of macrozoobenthos were recorded, and the species composition was mainly aquatic insects, accounting for 66.7% of the total taxa. The number of taxa was between 1 and 22 among the sampling sites. In terms of different reservoir areas, it was the highest within the Wudongde reservoir area and the lowest within the Xiluodu reservoir area. Among different seasons, it was the highest in summer and the lowest in winter. Hydropsyche sp. had the highest dominance among the species, and the dominant species differed across the seasons. The mean density and biomass of macrozoobenthos were (201.6±306.1) ind./m² and (3.2±5.5) g/m² , respectively, with significant differences in different reservoir areas. The CCA (canonical correspondence analysis) results showed that the key affecting factors of macrozoobenthos community composition in the lower Jinsha River were substrate (Sub), water velocity (WV), elevation (Ele), and dissolved oxygen (DO). In general, the macrozoobenthos community structure of the lower Jinsha River was dominated by aquatic insects and Annelida, with lower density and biomass than other rivers in this region. Due to the fast flow velocity and simple habitat bottom in the mainstream, the macrozoobenthos were generally not high in species number or standing crop. However, the rich macrozoobenthos resources in the tributaries of the interval play an important role in maintaining regional biodiversity. Based on the results, several suggestions for the environmental protection of the lower Jinsha River were provided, i.e., meeting the conservation challenges necessitate long-term monitoring of aquatic organisms and impact assessment of aquatic ecology, protecting the riparian zone of rivers to support the river habitat diversities and coordinating the protection of mainstream and tributaries of the lower Jinsha River aimed at maintaining the integrity of the river ecological network. ＜/

Abstract:The process of calcification of shellfish produces CO₂. However, there are large differences in carbonate system compositions among different aquaculture areas. Thus, more rigorous carbonate chemistry modeling, including concurrent changes in seawater carbonate systems, is needed to quantify the CO₂ released into the atmosphere during calcification. In this study, the ratio between the CO₂ emitted into the atmosphere during various biogeochemical processes and the CO₂ produced by these processes is defined as Φ. Therefore, in the calcification process, the Φ_cal value represents the amount of CO₂ emitted from the seawater to the atmosphere when 1 mol of CaCO₃ is formed during shell growth. Results showed that Φ_cal value varied among seasons. The Φ_cal value was lowest during summer in Jiaozhou Bay, Sanggou Bay, and Shenao Bay. Regional differences in the carbonate system in the aquaculture sea area could change the Φ_cal value. In Jiaozhou Bay, 0.79 mol CO₂ was released into the atmosphere for every 1 mol CaCO₃ deposited during shell growth. In Sanggou Bay and Shenao Bay, this value was 0.72. In Jiaozhou Bay, the Φ_cal value decreased in the shellfish's main growing season (from March to July). The result of polynomial fitting further suggested that the Φ_cal value decreased with the temperature rise during this season. The Φ_cal value decreased faster when the water temperature exceeded 18 ℃. Finally, the annual production of 3.2×10⁵ tons of Philippine clams in Jiaozhou Bay was expected to emit about 1.084×10⁵ tons of CO₂ into the atmosphere due to shell growth. This study preliminarily confirmed that Φ_cal, including concurrent changes in the seawater carbonate system in the aquaculture area, could better quantify the CO₂ release caused by shellfish calcification. This study could provide some references for future studies on the topic of the carbon source/sink process of shellfish.

Abstract:Based on the survey data of fishery resources collected from 41 stations in June, July, and September 2019 and May, August, and October 2020 in Liaoning offshore, we analyzed the spatiotemporal distribution of the relative biomass and biological characteristics of Hexagrammos otakii and examined its relationship with environmental variables, including water depth, bottom salinity, bottom water temperature, bottom sediment type, month, and year using a generalized additive model (GAM). The results showed that the relative biomass of H. otakii was higher in summer and autumn than that in spring and varied greatly among different survey stations, and the spatial heterogeneity was high. The body length and body weight of H. otakii increased monthly from May to October, and fatness was higher in summer than that in spring and autumn. These biological indexes showed significant differences (P＜0.05) among different months. The spatiotemporal distribution of relative biomass showed that H. otakii preferred two sediment types, namely reef and sandy bottoms, and lower water temperature. The relative biomass of H. otakii in the northern Yellow Sea was higher than that in Liaodong Bay. GAM analysis indicated that water depth, bottom salinity, bottom water temperature, bottom sediment type, month, and year were the best explanatory variables affecting the distribution of the relative biomass of H. otakii. The relative biomass of H. otakii was significantly positively correlated with a water depth of 4.5?55 m, and the relative biomass in Liaoning Ocean was higher with a salinity of 22.9?31.5 and a bottom water temperature of 12?22.5 ℃. The results of GAM analysis were consistent with the ecological habits of H. otakii. Based on the results, we suggested that the northern Yellow sea, which has a wider range of reef and sandy bottoms and lower bottom water temperature, can be used as a suitable area for the stock enhancement of H. otakii and that the months from May to June can be used as a suitable release time when the bottom water temperature rises to 12 ℃ or higher. These suggested areas and times for stock enhancement of H. otakii may better guarantee the survival rate and quality of the released H. otakii population.

Abstract:The eukaryotic initiation factor 4E protein (4E-BP1) is the main downstream factor of the mTOR signaling pathway. It is phosphorylated by an activated mTORC1 signal and acts as a translation inhibitor. 4E-BP1 plays a key role in the rate-limiting of cap-dependent translation, thus influencing protein synthesis, cell survival, growth, proliferation, and metabolism. Although the regulatory mechanism of 4E-BP1 has been well elucidated in mammals, the knowledge regarding crustaceans is still limited. In this study, we obtained a full-length cDNA of Eriocheir sinensis 4E-BP1 (Es4E-BP1) using the RCAE method. Real-time quantitative PCR (qPCR) was applied to detect the temporal and spatial expression patterns of Es4E-BP1. The double-stranded RNA (dsRNA) silencing method was used to explore the role of Es4E-BP1 in the molting cycle of E. sinensis. Results showed that the length of Es4E-BP1 cDNA was 1678 bp, containing a 134 bp 5′ non-coding region, 1193 bp 3? non-coding region, and 351 bp open reading frame (ORF). The cDNA sequence is composed of three exons (282 bp, 165 bp, and 1209 bp) and two introns (2101 bp and 622 bp). The ORF encodes a putative polypeptide of 116 amino acids with a molecular weight of 12.64 kD and an isoelectric point (PI) of 4.89. The secondary structure of Es4E-BP1 contains a typical eIF4E superfamily conserved domain, a TOR signaling motif, and a Y××××LΦ binding motif (Φ denotes any hydrophobic amino acid), which are unique to the 4E-BPs family. Multiple sequence alignment and phylogenetic tree analysis showed that Es4E-BP1 was clustered with Callinectes sapidus and Portunus trituberculatu, with high identities of 95.69% and 93.16%, respectively. qPCR results showed that Es4E-BP1 was expressed in various tissues of adult crabs. The transcript level in Y organs was significantly higher than that in other tissues, such as muscle, heart, eyestalk, intestine, ovary, testis, hepatopancreas, and gill (P＜0.05). During a complete molting cycle, the expression patterns were distinct among different tissues of juvenile crabs. There is a similar expression pattern in Y-organ and intestine. The highest expression levels were observed in post-molt (stage A-B), followed by intermolt (stage C) and early post-molt (stage D₀ and stage D₁). The expression levels were the lowest in the post-molt (stage D_3-4). The expression level in the eye stalks was the highest in stage A–B. It decreased in stages C and D0 but increased in stage D1 and stage D_3-4. In addition, the expression level of Es4E-BP1 differed among different muscle tissues. The expression levels of Es4E-BP1 in the claw muscle and abdominal muscle reached the peak in stage A–B, was the lowest in stage C (P＜0.05), and increased slightly in stage D_3-4 compared with stage C. In the walking foot muscle, the expression levels were high in stages A–B and C but decreased in stage D_3-4 (P＜0.05). The RNA interference test showed that the mRNA levels of Es4E-BP1 were significantly decreased in the Y-organ and muscle after injection with ds4E-BP1. In the Y-organ, the expression level of Es4E-BP1 in the injected group was 53.77% (24 h post-injection) and 41.99% (48 h post-injection) of that in the control group. Meanwhile, in muscles, the expression level of Es4E-BP1 in the injection group was 44.00% (24 h post-injection) and 27.49% (48 h post-injection) of that in the control group. Furthermore, during the long-term interference experiment, dsEs4E-BP1 was injected every 2 days. The survival rate of the ds4E-BP1 injection group was 38.89%, much lower than 61.11% in the control group and 50.00% in the dsGFP injection group. The average molting interval of the ds4E-BP1 injection group was 38.29 days, much longer than that of the control group (34.45 days) and dsGFP injection group (33.10 days). The weight gain rate of the ds4E-BP1 injection group was 34.32%, higher than that in the control group (28.69%) and dsGFP injection group (26.95%). Overall, our results indicated that Es4E-BP1 might play a crucial role in the molting and growth of E. sinensis.

Abstract:Ghrelin, an appetite-promoting gastrointestinal peptide, is involved in the feeding regulation of vertebrates. Mandarin fish (Siniperca chuatsi) is a typical carnivorous fish. It feeds on live bait throughout its life since its birth and is mainly fed with live bait during its production. In recent years, mandarin fish feed domestication research and experiments on compound food have also made rapid progress. However, compared to live bait feeding, the food intake decreased significantly after compound feed domestication. Ghrelin is the only foodpromoting factor in the periphery. Whether the decrease in food intake after compound feed acclimation is related to the regulation effect of ghrelin remains to be studied. We obtained and analyzed the preproghrelin DNA sequence of Siniperca chuatsi for the first time by transcriptome sequencing and genome data matching and located the secretory cells. At the same time, we detected changes in the ghrelin gene and protein expression in the stomach after being induced and fed. The attraction test simulates the sighting of food before feeding but the inability to feed, while the feeding test simulates the normal feeding of mandarin fish. The results showed that the preproghrelin gene contains four exons and three introns and belongs to type II; 107 amino acids are coded, and the mature peptide ghrelin consists of 20 amino acids with GSSF as the active center. Immunohistochemistry revealed ghrelin-production cells located in the gastric glands. In the attraction test, ghrelin mRNA and protein expression levels were significantly higher in the live-bait group (P＜0.05). In contrast, ghrelin expression levels did not change significantly in the compound food group and were significantly lower than that in the live bait group. At 0h after feeding, ghrelin mRNA and protein levels in the live bait group increased significantly and decreased to normal levels at 2 h after feeding (P＜0.05), with no significant changes in subsequent gastric emptying (P＞0.05). Ghrelin mRNA expression levels in the compound food group did not change significantly throughout the feeding trial (P＞0.05), but fluctuations in protein levels were detected. In summary, ghrelin, located in the gastric glands, is involved in feeding regulation activities and shows a tendency to increase before and decrease after feeding. Additionally, compound food feeding reduced the effect of ghrelin on food regulation.

Abstract:At present, the cultivation of cephalopods mainly relies on natural feeds. The absence of artificial compound feeds is a restrictive factor for the large-scale development of the cultivation of cephalopods. The genes related to glucose metabolism in Octopus sinensis, including glucose phosphate isomerase (GPI), phosphoglycerate kinase (PGK), and pyruvate kinase (PK), were cloned, and their expression levels were examined to study the glucose metabolism pattern of O. sinensis and provide a reference for optimizing the proportion of carbohydrates in its compound feed. The results showed that the open reading frame (ORF) length of OsGPI was 1725 bp encoding 574 amino acids, the ORF length of OsPGK was 1248 bp encoding 415 amino acids, and the ORF length of OsPK was 1683 bp encoding 560 amino acids. The sequence alignment and phylogenetic tree results showed that the identity of O. sinensis GPI, PGK, and PK proteins was the closest to that of Octopus bimaculoides. qRT-PCR results showed that these three genes were expressed in different tissues/organs of O. sinensis, with OsGPI having the highest expression level in the digestive gland and brain, and OsPGK and OsPK in the brain, followed by posterior salivary glands and the digestive glands. This difference in expression distribution may be related to the biological functions performed by different tissues/organs. OsGPI, OsPGK and OsPK were expressed in different developmental stages, with the highest expression at the hatchling stage. During starvation stress in larvae, the expression levels of OsGPI, OsPGK, and OsPK decreased significantly after 2 days (d) of starvation, followed by a significant increase in expression levels after 3 d or 4 d of starvation. Finally, the expression levels started to decrease after 5 d of starvation. In the experiment of feeding compound feeds, Charybdis acuta or Sardina pilchardus, the expression levels of OsGPI, OsPGK, and OsPK in the digestive gland of O. sinensis were increased to varying degrees in the compound feed group and S. pilchardus group after 21 d feeding. The expression levels of OsPGK and OsPK decreased to varying degrees. The expression levels of OsGPI, OsPGK, and OsPK were significantly increased in the C. chinensis group after feeding for 21 d and 42 d, compared to those at 0 d. After 42 d of feeding, the expression levels of OsGPI, OsPGK, and OsPK decreased to varying degrees. The expression levels of OsGPI, OsPGK, and OsPK were significantly increased in the C. acuta group after feeding for 21 d and 42 d, compared to those at 0 d. The expression patterns of OsGPI, OsPGK, and OsPK during different embryonic development stages, starvation, and feeding of different feeds indicated that they were involved in regulating glucose metabolism in O. sinensis. These results may aid in the selection of diets and the addition of carbohydrates in compound feeds.

Abstract:To explore the growth characteristics of Meretrix meretrix in ponds in various months, the shell length (SL), shell width (SW), shell height (SH), and body weight (BW) of M. meretrix at 10, 15, and 20 months of age were measured. The effects of morphological traits on body weight were discussed through correlation, path, and multiple regression analyses. The results showed that the morphological trait with the highest correlation coefficient at 10 and 15 months was SL, and the morphological trait with the highest correlation coefficient of 20 months was SW. Path analysis showed that SL, SH, and SW had the greatest direct impact on the body weight of M. meretrix at the age of 10–20 months. The multiple regression equations established by BW and morphological traits were BW₁₀ = ? 2.976+0.100SL+0.140SW+0.101SH (R² =0.969); BW₁₅ = ?12.176+0.085SL+0.441SW+0.415SH (R² =0.957); and BW₂₀=?21.506+0.255SL+1.098SW+0.152SH (R² =0.920). The allometric growth equation showed that M. meretrix followed different growth laws at different ages: positive allometric growth at 10 months, isokinetic growth at 15 months, and negative allometric growth at 20 months. The results showed that the morphological traits affecting the live weight of M. meretrix changed significantly with the increase in the age of M. meretrix. SL and SH had the greatest impact on BW at 10 and 15 months, respectively. However, with the increase in the age of M. meretrix, the influence of SW on BW increased, which was the quantitative trait index that had the greatest impact on the body weight at the age of 20 months. The results could provide a theoretical reference for the breeding of M. meretrix.

Abstract:Group living is a widespread social phenomenon of animals (e.g., insect swarms, fish shoals, bird flocks, and mammal herds), and collective behavior is affected by ecological contexts and its determination sequence. To investigate the ecological contexts and its determination sequence on the collective behavior of the Cyprinidae fish, the present study used mirror carp (Cyprinus carpio var. specularis) with similar body mass and healthy condition as the experimental fish at (26.3±0.2) ℃. Our study included two treatment groups (i.e., the fixed sequence group and the random sequence group), with each treatment group containing 14 fish shoals of six individuals. The fish stock in each processing group was placed in different ecological contexts (i.e., the open water environment, the food environment, and food plus refuge). We determined the shooting sequence of the random group by drawing lots to simulate environmental changes. Our results showed that the ecological context and determination sequence could reduce the swimming speed and synchronization of Mirror carp individuals. Additionally, the ecological context can increase the distance between the nearest neighbor and the individual. However, the change in the determination sequence reduces the distance between the nearest neighbor in the non-open water environment (the food environment and the food plus shelter environment) of mirror carp. Furthermore, the ecological context and determination sequence could reduce the group swimming speed and percentage time on moving of the group. There was a negative correlation between inter-individual distance and population polarity of the mirror carp. Moreover, the random sequence enhanced this negative correlation between the open water environment and the food plus shelter environment. Our study suggested that ecological context can decrease the coordination and cohesion of fish shoal in the mirror carp. However, the random sequence enhances the coordination and cohesion of fish shoals and reduces the coordination of the open water environment, thus showing the significant cluster behavior of the fish. This positively impacts the information exchange of individual members in the group movement.

Abstract:Mystus macropterus (Bleeker) is a freshwater fish of the Bagrdae family, distributed in the main stream and tributaries of the Yangtze and Pearl rivers with high nutritional value. The author found that M. macropterus displayed aggressive behavior, which led to bites, ulcers, and even death during artificial breeding. Understanding the behavioral characteristics of M. macropterus and its influencing factors and reducing its aggression would help understand the basis of artificial breeding. In the present study, a real-time observation system incorporating indoor pools, cameras, transmitters, and monitors was established to observe the behavioral characteristics of M. macropterus. At the same time, three kinds of caves (tiled, pebble and grass caves) were established in all breeding pools. M. macropterus were divided into three groups based on the proportion of the fish and caves which were free choice group (1 fish), competition-absent group (3 fish), and competition-present group (6 fish). The selection of M. macropterus to shelters under three conditions was recorded by video. The recording started when the fish were put in, and each recording lasted for 72 hours, and all experiments were conducted in triplicate. The results showed that M. macropterus preferred tiled and pebble caves. Not many fish coexisted peacefully in these two caves, but two fish coexisted in grass caves. The attack frequency in the competition-present group was significantly higher than that in the competition-absent group, and the attack frequency at night was significantly higher than that during the day. M. macropterus hid in caves during the day and came out at night. The behaviors included daily activities, such as exploration, patrol, and hunting; attacking behaviors, such as chasing, collision, and biting; and territorial behaviors, such as invasion, driving, and guarding. Social hierarchies were established based on aggression, labeled “strong” and “weak.” The behavioral characteristics of M. macropterus and the selection of hiding places provided an important scientific basis for establishing M. macropterus farming technology. It was suggested that the strategy of night feeding should be adopted in M. Macropterus culture, and an open shelter should be built in the pond for hiding.

Abstract:Costaria costata is a potential economic kelp. Light intensity is one of the key factors that regulates the growth, photosynthesis, and metabolism of seaweeds, and is also the main factor affecting the morphology and vertical distribution of seaweeds. Therefore, it is important to study the tolerance of C. costata to light intensity for commercial farming. The growth, photosynthesis, nutrient composition, and antioxidant capacity of young sporophytes of C. costata were studied under different light intensities of 30–120 μmol/(m² ·s) under laboratory conditions to reveal the adaptability of C. costata sporophytes to light intensity and support the cultivation of this species in marine areas. The results showed that the young sporophytes grew fast at 30–120 μmol/(m² ·s), and both the relative growth rate (RGR) and F_v/F_m were the highest at 60 μmol/(m² ·s). The total photosynthetic rate and the maximum apparent photosynthetic rate increased with light intensity at the early stage (5 d), and reached the highest at 60 μmol/(m² ·s) at the late stage (10 d). The respiration rate (R_d) was significantly lower at 60 μmol/(m² ·s) than at the other light intensities. The contents of chlorophyll a, fucoxanthin, and carotenoid did not differ significantly among the varying light intensities. The content of crude protein, fat, and crude fiber was positively correlated with light intensity, while the content of carbohydrate was negatively correlated with light intensity. The results indicated that light intensity of 60 μmol/(m² ·s) was suitable for the growth of young sporophytes of C. costata. Furthermore, the content of soluble proteins increases under high light intensities while the activities of ASAFR, SOD, APX were higher under low light intensities. Moreover, the alga had the same response mechanism, namely enhanced respiration, under either low light or high light stress.

Abstract:The intestinal flora of fishes has attracted considerable attention in recent years; however, most scholars focus their attention on farmed fish rather than wild coral reef fish. Here, we collected gill and intestinal samples of Gnathodentex aurolineatus from three reefs in the South China Sea to compare the structures of their intestinal bacterial community and carbon source utilization characteristics. MiSeq high-throughput sequencing technology was used to investigate the intestinal bacterial community structure of G. aurolineatus and the Biolog Eco microplate method was used to analyze the carbon source utilization characteristics of bacterial communities in different reef waters. The results showed that the gill tissue and intestinal bacterial communities were highly similar across various seas. Nevertheless, significant differences in relative abundance of phyla and genera were observed. A total of 151 common operational taxonomic units (OTUs) were observed among all samples, and a total of 1022 OTUs were identified from the Yongshu Reef group. A total of 492 OTUs were identified from the Chenhang Island group. At the phylum level, Proteobacteria, Bacteroidetes, and Firmicutes were the dominant phyla in all groups, and the unique dominant phyla were Actinobacteria and Fusobacteria. At the genus level, Escherichia-Shigella, Bacteroides, Bifidobacterium, Phascolarctobacterium, Photobacterium, Marispirillum, and Pandoraea dominated in all gill tissue samples. However, the most common dominant genera were Escherichia-Shigella and Bacteroides in all intestinal samples, and other dominant genera were significantly dissimilar. Metabolic activity and utilization rate of carbon sources of amino acids, carbohydrates, and lipids ranged from high to low in Zhubi Reef group (ZB), Yongshu Reef group (YS), and Chenhang Island group (CH), with significant differences among the three groups (P＜0.05). Gene functional prediction results showed a high proportion of metabolism-related functional genes, and the utilization of the three types of carbon sources was consistent with that of carbon sources in culturable intestinal bacteria. The intestinal bacterial community of G. aurolineatus has a high metabolic capacity for carbon sources. Therefore, we plan to isolate high enzymeproducing strains from the intestines of this species in the future.

Abstract:Sea cucumber (Apostichopus japonicus), an important economic mariculture species in China, has high nutritional and medicinal values. In recent years, with the expansion of the breeding scale, new pathogens causing diseases often appear. In November 2020, a large-scale epidemic of skin ulcers was recorded in cultured A. japonicus in the Xiapu area of Fujian Province. In order to explore the pathogens causing diseases in A. japonicus, the potentially pathogenic bacteria were isolated, and the physicochemical properties, virulence factors, and drug sensitivity of the isolated bacteria were studied. The artificial regression infection results showed that the dominant strain isolated from the lesions on the body surface (XP-11) was the main pathogen causing the skin rot syndrome in A. japonicus, with the same symptoms of skin ulcers as the natural disease. The results showed that the dominant strain XP-11 isolated from the lesions on the body surface was the main pathogen causing the skin rot syndrome in A. japonicus. The strain XP-11 was identified as Photobacterium damselae subsp. damselae based on morphological characteristics, Biolog’s automatic microbial identification system, as well as 16S rRNA, housekeeping gene (gyrB), and urease C (ureC) gene sequence analyses. The results of virulence gene detection showed that the strain XP-11 contains two typical virulence genes of the hemolysin gene (hlyAch) and phospholipase activity gene (plpV). The results of antimicrobial susceptibility analysis showed that the strain XP-11 was sensitive to tetracycline, enrofloxacin, and trimethoprim/sulfamethoxazole. The minimum inhibitory concentrations of the strain XP-11 to Enrofloxacin, Neomycin sulfate, Thiamphenicol, Florfenicol, Doxycycline hydrochloride, Flumequine, sodium Sulfamethoxine, Sulfamethoxazole + Trimethoprim were 0.08, 2, 1, 1, 0.06, 0.125, 4, and 1.2/0.06 μg/mL, respectively. This is the first report regarding the diseases caused by P. damselae in sea cucumbers. In summary, P. damselae subsp. damselae was the causative agent of the skin ulceration syndrome of cultured A. japonicus, and the median lethal dose (LD₅₀) value was 1.08×10⁵ CFU/g body weight. The results of this study provided valuable references for further prevention and control of diseases caused by P. damselae in the sea cucumber aquaculture industry.