Abstract:In order to understand the grain-size structure characteristics of fish communities in Daya Bay, we constructed the biomass particle-size spectrum of fish in Daya Bay based on the data from two bottom trawl surveys in 2016. The heterogeneity of the characteristic parameters of the fish biomass particle-size spectrum from different parts of the bay in two seasons was compared and analyzed. The results showed that the pattern of the Sheldon-type biomass particle-size spectrum of fish in Daya Bay was unimodal; the fish particle size ranged from -2 to 10 and the highest peak was at a grain size of 3-4. The reduction in the curvature of the biomass particle-size spectrum of fish was mainly caused by the reduced size range from the emergence of a small number of large perennial settlers, , and seasonal migratory fish, . From the three areas of the bay (coastal, central, and bayou), the curvatures in the spring were the largest in the coastal area, followed by the central area, and they were the smallest in the bayou. The curvatures in autumn were the largest in the bayou, followed by the coastal area, and they were the smallest in the central area of the bay. The decrease in the curvature of the coastal area was mainly caused by the presence of a large number of small particle juveniles. The decrease in the curvature of the central area was due to the emergence of a small number of large , which reduced the size range. The increase in the curvature in the bayou was mainly caused by the emergence of a small number of large . It can be seen that the number of supplemental groups such perennial settler fish, migratory fish, and perennial juveniles, and the size ranges have a significant impact on the peak shape and curvature of the fish biomass particle-size spectrum. The ABC curve showed that the biomass particle-size spectrum of fish in spring and autumn were in a seriously disturbed state.

Abstract:Chlorophyll a (Chl a) concentrations and primary productivity were investigated in the surface water of the Nan'ao-Dongshan coastal area in September (autumn) and December (winter) of 2014, April (spring) of 2015, and July (summer) of 2017. The seasonal and spatial distribution patterns of Chl a and primary productivity were analyzed. The Chl a concentration varied from 0.37 μg/L to 14.9 μg/L. The average Chl a concentration in the surface water were summer (8.2 μg/L) > autumn (4.9 μg/L) > winter (1.52 μg/L) > spring (1.47 μg/L). The primary productivity varied from 0.6 to 45 mg(C)/(m³·h), and the average values were autumn[20.3 mg(C)/(m³·h)] > summer[18.2 mg(C)/(m³·h)] > spring[14.4 mg(C)/(m³·h)] > winter[5.6 mg(C)/(m³·h)]. The depth-integrated primary productivity varied from 14.1 mg(C)/(m²·d) to 3066.6 mg(C)/(m²·d), and the average values were autumn[1034.2 mg(C)/(m²·d)] > summer[715.5 mg(C)/(m²·d)] > spring[453.4 mg(C)/(m²·d)] > winter[133.8 mg(C)/(m²·d)]. The Chl a concentration generally decreased from the northwest inshore region to the southeast offshore region during the four seasons. However, there was no clear pattern for the distribution of primary productivity. Significant correlations between Chl a, primary productivity, and nutrients were found only in spring. Nitrogen may be a relatively important limiting nutrition factor in the Nan'ao-Dongshan coastal region. In general, the water quality was healthy and the concentrations of Chl a and nutrients were relatively low. For the sustainable utilization of fishery resources, a reasonable plan regarding stocking densities is needed for the cultured species according to the primary productivity in the Nan'ao-Dongshan costal region.

Abstract:To understand the attractive effect of artificial reefs, the activity traits of fishes, and the feasibility of ultrasonic telemetry for fish research in artificial reef areas, 5 species of 9 common rock fishes (22.0 cm±3.5 cm; 314 g±186 g) in the Beibu Gulf were tagged and tracked within an artificial reef area between July 7 and September 8, 2017, using the Vemco position system(VPS). Eleven receivers (VR2Tx, Vemco, 69 kHz) were launched in the artificial reef area of Fangchenggang inshore and the transmitters (V9P-2x, Vemco, 69 kHz) were tied to the backs of fishes. Not all fishes had good position results, and only 3 fishes had data available for analysis of home range size using 95% minimum convex polygons (MCPs). Home ranges were between 12687.6 m² and 17123.2 m², and the MCPs showed the activity of fishes in the small ranges. The other 6 fishes had poor position results (between 0 and 14 locations), and although the signal could not be received by 3 or more receivers, the data still indicated that the fishes were moving near the reef area because the range of signal reception was only approximately 200 m in the artificial reef area. Three fishes with poor position results left the area during this study between 28 to 51 days and then retured. This indicated that the fishes preferred the environment of the artificial reef area. During the study, the activity of fishes showed certain depth change rules. The fish activity in the shallower layer was between 15:00-22:00, and fish activity occurred above the reefs during this time, and perhaps it is the optimum time frame to determine the quantity of resources of these fish species in this area. To ensure the accuracy of the results, we eliminated the effect of tide before the calculation of depth results. The method of ultrasonic biotelemetry has an intuitive feeling for fish activity, but the method is in an experimental stage in China. The high cost is one reason why it cannot be widely promoted; furthermore, in the current experiment it was difficult to achieve the desired effects. We hope to analyze effectiveness for fish attraction and daily activities of fishes to provide a reference for subsequent research, and accumulate experience for subsequent application of this method.

Abstract:To assess the effect of enhancement of black porgy () in Daya Bay. Plastic oval tags (POTs) were used to study marking technology in juvenile black porgys. The results of experiment on tag retention rate and growth showed that the back muscles, approximately 5 mm below the 4^th-6^th spine at the base of the dorsal fin, were the optimal tagging position; after 90 days, the POTs retention rate was 81.76%. There was no significant difference in growth between the tagged group and the control group after 45 days (>0.05), but the growth of the tagged group was significantly slower than that of the control group after 90 days (<0.05). Based on this technique, the release experiment in Daya Bay was carried out once a year from 2014 to 2016. The reward-recapture method was used to collect the tagged fish, and the body length and body weight of each recaptured fish was measured. Information such as the recapture date and place, and how the fish were tagged was gathered, and the relevant data were subsequently analyzed. In the period of 3 years, a total of 60115 tagged black porgy juveniles were released, and the tagged fish were mainly recaptured by set-nets, drift-nets, and through angling, with a total number of 2758 (total recapture rate of 4.59%) recaptured individuals. The recapture rate of the larger juveniles was higher than that of the smaller juveniles. The tagged fish that were recaptured through angling accounted for 62.08% of the total recaptured fish. An analysis of the gathered information showed that the released tagged fish juveniles primarily migrated radially to the inner and outer areas of the bay; the maximum migration distance was over 70 km from the release site. In 1-2 months after released, the growth of black porgys were relatively slow and then relatively accelerated. After 5 to 7 months, the body length and body weight of the black porgys increased by 59.51%-127.20% and 322.75%-989.83%, respectively. The results indicated that, POT was a potential choice for juvenile black porgy. In the study area, tagged black porgy were easier to be recaptured by angling after released. The abundant food and the space available to avoid the enemy were the factors which influenced their distribution and growth.

Abstract:Based on the data obtained from four cruises in November (autumn) 2014, May (spring) and August (summer) 2015, and January (winter) 2016, the structure of zooplankton community in Lingshui Bay, including species composition, abundance, dominant species, and species diversity, was studied. A total of 94 zooplankton species and 21 types of pelagic larvae were identified. The most dominant group of zooplankton was copepods (38 species), followed by hydromedusae (11 species), and Chaetognatha (8 species), accounting for 40.43%, 11.70%, and 8.51% of the total species, respectively. The remaining groups were represented by 1 to 6 species per group. Based on species composition and ecological distribution, the zooplankton community in Lingshui Bay mainly comprised three ecological groups, including eurythermal euryhaline group, warm water coastal group, and warm water pelagic group; the dominant species were distributed mainly in the former two groups. No dominant species was widespread throughout all the seasons. Appendiculata was the only dominant group all year-round. Pelagic larvae formed an important group in Lingshui Bay. Their abundance in winter (lower water temperature) was higher than in spring (higher water temperature), which was different from that in subtropical waters. This suggests that in Lingshui Bay, lower seawater temperature was no longer the main factor determining zooplankton abundance. The abundance and biomass of zooplankton were highest in autumn, followed by winter, summer, and finally, spring. Both the species diversity indices were consistent in seasonal and horizontal variation, being higher in spring and summer than in autumn and winter, and higher in the outer bay than the inner bay. Two communities, from the inner and outer bays, were identified by clustering analysis, which can be mainly attributed to the barrier caused by the terrain. Furthermore, we measured temperature, salinity, concentration of chlorophyll a, phytoplankton abundance, and concentration of dissolved oxygen and determined the responses of the zooplankton community to these factors. Salinity was the primary factor influencing zooplankton community structure in Lingshui Bay, based on Pearson's correlation analysis. Based on the annual biomass of zoo-plankton in Lingshui Bay, potential productivity of zooplankton was estimated to be 2.24×10⁴ kg. The abundance of zooplankton in Lingshui Bay has changed dramatically with different seasons. Thus, it is necessary to continuously monitor zooplankton abundance in Lingshui Bay over a long period to better understand the actual prey situation.

Abstract:Samples of were collected from the northern South China Sea from July 2014 to May 2015. Biocharacters such as fork length (FL), body weight (BW), maturity stage, and otolith daily incrementation were measured and compared to understand the differences between the two species. Differences in the FL and BW of between females and males were significant (K, and were 109-310 mm and 117-283 mm, 13-358 g and 20-297 g, 76-558 d and 73-526 d, 278 mm and 276 mm, 1.30 and 1.30, -0.07 a and -0.08 a, respectively. The youngest age group of female at maturity stage Ⅲ was 350-400 d, and the hatching of female and male samples primarily occurred in March, July, and September to October. The FL range, BW range, otolith age, S. undosquamis were 105-269 mm and 95-264 mm, 11-220 g and 8-228 g, 79-486 d and 84-488 d, 269 mm and 265 mm, 1.29 and 1.29, -0.06 a and -0.06 a, respectively. The youngest age group of female at maturity stage Ⅲ was 200-250 d, and the hatching of female and male samples primarily occurred from June to November. For decades, the size and age of maturity of have been decreasing. Taken together, a policy that decreases fishing pressure could help to achieve the sustained development of the fishery resources of in the South China Sea.

Abstract:The jack mackerel () is one of the main catches in the northern South China Sea, and its spatial distribution is non-uniform. According to the two cycles of bottom trawl survey data in the northern South China Sea from 2014 to 2017 (2014-2015 is the first cycle, 2016-2017 is the second cycle), resource density is characterized by the catch per unit effort (CPUE). The Kolmogorov-Smirnov test (K-S test) was used to explore 11 probability distribution features. The results showed that the continental shelf area of the northern South China Sea had no obvious probability distribution, while the jack mackerel resource density in the Beibu Gulf obeys the lognormal distribution pattern, and the second cycle is more significant than the first cycle. At the same time, using a lognormal theory model (lognormal model and delta model) and an investigative design method (arithmetic method) to compare the estimation of the resource density within a certain area, we found that the lognormal model is more fit to describe the distribution characteristics of the density structure of jack mackerel, and the delta model is more suitable to estimate the jack mackerel resource density.

Abstract:Seaweeds are the major primary producers, and play a vital role in coastal ecosystems. Since 2000, large-scale cultivation of has rapidly developed along the Chinese coast. Nan'ao island is an important base for cultivation in Guangdong. In order to study the effects of large-scale seaweed cultivation on the aquatic environment and phytoplankton, monthly surveys were carried out in the cultivation area of Shen'ao Bay in Nan'ao island from March to June 2016. In this study, fish culture area (F), Gracilaria culture area (G), and control area (C) without cultivation activities were selected for sampling. There were three sampling points per area, marked as F₁, F₂, F₃, G₁, G₂, G₃, C₁, C₂, and C₃, respectively. Four surveys were undertaken on March 25, April 24, May 23, and June 22, 2016. March and April were the cultivation periods, while May was the harvest period, and in June, no was cultured. Dissolved oxygen (DO), pH, total nitrogen (TN), total phosphorus (TP), inorganic nitrogen (DIN), inorganic phosphorus (DIP), phytoplankton density, and chlorophyll a (Chl a) contents were measured. Moreover, the amount of N, P, and C removed from seawater and the amount of O₂ released to seawater by were estimated based on the statistical data from Nan'ao in 2016. The results showed that pH and DO in the culture area were significantly higher than those in other regions (>0.05) between the sampling areas after seaweed harvest (June). The contents of TN, TP, DIN, and DIP in the Gracilaria culture area were lower than those in other areas (<0.05) from March to April. Similarly, phytoplankton densities and Chl a contents were significantly lower in the <0.05). The total produce of in Nan'ao island for 2016 was 49729 t, removing 2212 t of N, 174 t of P, and 13000 t of C from seawater while releasing 34700 t of O₂ to seawater. Our results show that large-scale cultivation of could effectively remove N and P, improve pH and DO, and inhibit phytoplankton growth. This has the potential to control seawater eutrophication, mitigate the impacts of ocean acidification and hypoxia, and prevent harmful algal blooms.

Abstract:Leizhou Bay, located on the eastern side of Leizhou Peninsula in Guangdong province, is the primary habitat of Chinese white dolphin (), besides being a reserve for juvenile fish and shrimp. However, the ecological state of this coastal ecosystem remains largely unknown. To understand the fish community structure and its physical drivers in Leizhou Bay, seasonal bottom trawl along with environment monitoring surveys were conducted from 2016 to 2017. The relationships of fish community structure with environmental factors were analyzed using K-means cluster analysis, similarity percentage analysis, and redundancy analysis. These analyses led to the identification of 256 fish species, comprising mainly demersal fish and warm-water fish. The study sites for each season could be divided into two groups:group I, with water depth of less than 10 m, and group Ⅱ, with water depth between 10 m and 20 m. Group I showed an average similarity of 38.48%-47.44% across seasons in terms of fish community structure (which was shown as matrixes of sites by species biomass). Three species, Plotosus lineatus contributed greatly to the average similarity within Group I in summer, fall and winter. Furthermore, Group Ⅱ showed an average similarity of 41.38%-52.59% across seasons. The contributed mostly to the average similarity within Group Ⅱ in spring, summer and winter. The average dissimilarity between group I and group Ⅱ in seasons was 57.74%-76.25%. Six ecological factors, i.e. depth, dissolved oxygen, water temperature, salinity, pH, and chlorophyll a, explained 41.76%-47.11% of variation in fish biomass, with depth being the dominant environmental factor affecting fish community structure in each season. Moreover, the fish species richness in Leizhou Bay was obviously higher than in other bays of China. This study provides preliminary data on fish community structure and its relationship with environmental factors in Leizhou Bay, and provides clues for stocking enhancement in the waters.

Abstract:The summer fishing moratorium system, the main fishing management system in China, has been continuously adjusted and perfected in practice. In order to evaluate the conservation effects of prolonging the trawl net summer fishing moratorium period, which is contained in the new summer fishing moratorium system and promulgated in 2017, on the fishery resources, the data from the bottom trawl surveys in May during 2015-2017 and the dynamic integrated Ricker model were used to quantitatively analyze the structural characteristics of trawl catches and the dynamics of fish species such as the hairtail (). The results showed that the hairtail and the small yellow croaker () were the main organisms that were trawled in May, and their sex maturity ratios were 92.04%-95.57% and 13.82%-29.55%, respectively, while the proportion of juvenile fish for the two species were 74.94%-88.90% and 0.03%-4.19%, respectively. Compared with that from the previous 3.5 month fishing moratorium period, the biomass per recruit, yield per recruit, and the average catch weight of hairtail increased 7.04%, 8.96%, and 20.78%, respectively, after the newly enforced 4.5 month fishing moratorium period. According to our study, advancing and prolonging the trawl net moratorium period could further protect the spawning groups and juveniles of the hairtail and the small yellow croaker, which were the main economic fishery resources in the East China Sea and the Yellow Sea. The resource enhancement effect was more significant with the longer moratorium period, so the time setting of the new summer fishing moratorium system was reasonable. However, after the newly enforced summer fishing moratorium period, the main hairtail and little yellow croaker catch were still dominated by 1-year-old fish. Thus, it is necessary to support the implementation of other fishery resource management measures in addition to the new summer fishing moratorium system, such as the minimum mesh size and the open capture standard, to ensure that the conservation effects are firmly established and that the population structure of the fishery resources can continuously improve.

Abstract:The Yangtze finless porpoise, (YFP) is the flagship of aquatic protection species in the Yangtze River in China. The number of Yangtze finless porpoises is continuously decreasing because their living conditions are affected by human factors. Determining the distribution of the finless porpoises is necessary to protect them; however, surveys all along the Yangtze River are time-consuming and expensive. Environmental DNA (eDNA) technology used for the detection of organisms is economical, efficient, accurate, sensitive, and non-invasive and can narrow the scope of investigation, which allows limited conservation funds to be used more efficiently. It has already been applied to detect and estimate the distribution of endangered or invasive aquatic species. Environmental DNA technology often deals with a small amount of degraded and short DNA fragments, which implies that maximizing the eDNA yield is required to improve the accurate detection of the target organism from turbid stream systems. In this study, we compared the effects of four different pore-sized filters (10 μm, 5 μm, 1 μm, 0.45 μm) on the filtration time of eDNA during its extraction from stream water. Also, we compared the eDNA yield from water samples stored under two different conditions (room temperature 20℃, refrigerated 4℃) over a 14 day period. Results showed that the target eDNA was detected from the four different pore-sized filters; however, the filtration time was negatively correlated with the pore sizes of the filters. Considering the filtration time, the combination of a large pore-sized filter (5 μm) and a high volume of water (1 L) from the samples is a good choice to extract eDNA from the Yangtze River. Different storage methods and times significantly affected the eDNA yield. Thus, our results also support the recommendation that the water samples from the Yangtze River should be filtered within 6 hours of collection at room temperature or be stored at 4℃ for a short period of time (i.e., 48 hours). The eDNA concentration in the water samples dropped below the threshold for detection when they were stored at room temperature for 10 days or at 4℃ for 14 days; thus, the eDNA in the water samples is not suited for long-term preservation. Compared with traditional field investigations, the eDNA survey exhibited a 100% detection rate from the Yangtze river in the Jiangsu Province where the finless porpoise has emerged. Three positive results were also detected from 10 survey points where the finless porpoise has not yet been observed. The fitted curve between the number of finless porpoises and the eDNA yield was built to estimate the biomass of the porpoises within an area of water. Although eDNA production and degradation is affected by many environmental factors such as temperature, pH, and microbial communities, the technology was still more sensitive than traditional field investigations for the detection of the Yangtze finless porpoise in the Yangtze River.

Abstract:In the present study, the population differentiation of the purpleback flying squid () in the South China Sea was examined based on mitochondrial ND2, COI, and 16S rDNA sequences, using samples collected between September 2012 and September 2015. Phylogenetic analysis revealed two significantly divergent monophyletic groups corresponding to the "medium form" and the "dwarf form, " but no geographical lineages corresponding to the sampling localities or seasonal groups were found. The Analysis of Molecular Variance also revealed significant genetic differentiation between the "medium form" and the "dwarf form" (<0.0001), while no genetic variance between either geographic populations or seasonal groups was found. The genetic diversity analysis showed that both the "medium form" and the "dwarf form" of in the South China Sea were characterized by high haplotype diversity (0.9465 and 0.8545) and low nucleotide diversity (0.0051 and 0.0021). The genetic distance between the ‘medium form’ and the "dwarf form" based on ND2, COI, and 16S sequences were 14.0%, 9.6%, and 8.8%, respectively. The genetic distances between the two forms were considerably larger than the genetic distances within each of the two forms (<1%). It was demonstrated that two divergent populations of were sympatrically distributed in the South China Sea, i.e. the "medium form" and the "dwarf form." The genetic differentiation between these two populations was similar to that among separate species within Ommastrephidae, which indicated that the two morphologically distinct forms of the purpleback flying squid, namely the "medium form" (middle sized, with a photophore) and the "dwarf form" (small sized, without a photophore), are two distinct species.

Abstract:Based on the samples collected from bottom trawl surveys in Haizhou Bay and adjacent waters during spring and autumn in 2011 and 2013-2016, the composition of and variation in the trophic guilds of the fish community were studied. The results showed that the fish community comprised 5 trophic guilds, including shrimp predators, benthivores, shrimp/fish predators, zooplanktivores, and piscivores. The fish communities in Haizhou Bay and adjacent areas were dominated by the benthivore functional group in spring, and the proportion of Fang's gunnel () was higher than other species. In autumn, shrimp predators were the dominant trophic guild, with red gurnard () being the dominant species. From the perspective of biomass composition, the proportions of functional groups of the fish community in Haizhou Bay showed significant differences. The main functional groups were shrimp predators and benthivores, followed by shrimp/fish predators, while the zooplanktivores and piscivores functional groups were relatively sparse. The dominant species of these trophic guilds were 6 fish species:Fang's gunnel, red gurnard, lizardfish (), lionfish (). The trophic guilds and dominant species of the fish communities in Haizhou Bay in spring and autumn of each year varied greatly, mainly due to the impacts of environmental variations and fish migrations in this area.

Abstract:The Pearl River, the largest river in southern China, historically harbors abundant fishery resources. However, the fishery resources have severely declined in recent decades owning to dam cascade development, overfishing, water pollution, and so on. Therefore, it is necessary to evaluate fishery resource utilization and exploitation, which provides scientific guidance for fishery resource conservation in the Pearl River. Generally, the per recruitment model has been widely applied to the dynamics of single fish populations. The per recruitment models mainly consist of the yield per recruitment model (YPR) and the spawning biomass per recruitment models (SBR). The YPR model prevents overgrowth overfishing and is usually used to determine the fishery management parameters (e.g. mesh size and catch rate). This model could provide management guidance for the development and utilization of fish stocks. The spawning biomass per recruitment model prevents supplemental overfishing. This model is utilized to assess whether parental biological residues and spawning stock are sufficient to maintain the stock of larvae supplementation, and then it estimates the status of resource utilization. The barbel chub () is an important economic fish inhabiting the middle and lower reaches of the Pearl River. An assessment of the current status of utilization is important for reasonable resource exploitation and maintenance. The data of the present study were collected in the Zhaoqing section of the Xijiang River (an important stem of the Pearl River) between 2009 and 2014. We analyzed the growth and mortality characteristic parameters and evaluated the resource exploitation status by the YPR model, SBR model, and biological reference points. The relationship between standard length and weight was expressed as:=0.9595, =2346). The von Bertalanffy growth equation was selected as the optimal growth model and was expressed as ]. The present fishing intensity (=0.86) have far exceeded the level of sustainable population development. The stock of was overfished in its vegetative form. We suggest to increase the catch age to 3 years old (or to a standard length of 238 mm) for the stock conservation of in the Xijiang River; the yield per recruitment could thus be increased by 175%. The protective efficacy could increase with a fishing moratorium in the Pearl River, and relevant fishery management measurements should be improved at the same time.

Abstract:is native to the northern waters from the Pacific West Coast to Sonora, Mexico. Since its introduction to China from Hawaii in 1998, its area and product have increased every year and have become one of the most widely produced shrimp species in China. It is suitable for growth at temperatures of 25-35℃; below 18℃, it stops feeding. Low temperature limits the farming season and area of , thus affecting the economic benefits. In order to explore the genes related to the low temperature tolerance of , hepatopancreases were chosen from the low temperature stress group (18℃) and the normal temperature group (24℃) of three families to conduct Illumina HiSeq 2500 sequencing. The analysis of the sequencing data via splicing, annotation, and differential expression revealed that a total of 214.6 million clean reads were obtained and assembled into 50921 final unigenes with an average length of 828 bp (N50=1534 bp). The assembled unigenes contained 14329 significant unigenes (28.13% of all unigenes) after BLASTX against the Nr database (E-value cut-off of 10^-5). Seven databases, Nr, Nt, GO, KEGG, Swiss-prot, KOG, and Pfam, were used to annotate 1573 unigenes, accounting for 3.08% of all unigenes. The results comparing the digital gene expression data between the challenged and control shrimp showed that under low temperature stress, the expression of 641 genes was up-regulated and 1036 genes were down-regulated in family 1; 630 genes were up-regulated and 1343 genes were down-regulated in family 2; and 212 genes were up-regulated and 475 genes were down-regulated in family 3. Furthermore, 243 genes were differentially expressed in all three families, including 89 and 154 genes whose expressions were up- and down-regulated, respectively, under low temperature stress. The functional enrichment analysis revealed that the differentially expressed genes were more abundant during binding, catalytic activity, the biosynthesis of amino acids, and peroxisome, lysosome, arginine, and proline metabolism. According to the Q-value, three of the top 10 genes included the ATP-binding cassette subfamily B member 6 (ABCB6), C-type lectin, and glutamine synthetase (GS). The ABCB6 gene encodes the ABC transporter and participates in the ABC transport mechanism. It has been found that the ABC transporter is involved in many abiotic stresses in plants. C-type lectin, as an immunological factor, plays an important role in the innate immune defense, and it has been demonstrated that temperature can affect its expression in both . Glutamine synthase (GS) is involved in the regulation of ammonia nitrogen metabolism in crustaceans. Studies have shown that temperature can affect the metabolism of ammonia nitrogen in . C-type lectin and GS are both down-regulated under low temperature stress, so they may participate in the low temperature response mechanisms of , but further verification is needed. In this study, we selected 10 genes from 243 differentially expressed genes; five of the genes were up-regulated and five were down-regulated. Real time RT-PCR was used to verify the transcriptome sequencing results. The results showed that RNA-seq and real time RT-PCR produced similar expression patterns for the 10 different genes, which indicates that the differential gene expression results based on the transcriptome sequencing were credible. This study laid the foundation for the discovery of low temperature-related genes and molecular markers. It also provides a theoretical basis for in-depth discussion on the molecular determinant mechanism of low temperature resistance in in future studies.

Abstract:The yellowtail kingfish, , is a globally distributed marine economic pelagic fish species. It is a popular table fish all over the world for its tasty flesh and high nutritional content. As the consumption demand has increased and natural resources have declined in recent years, an increasing number of countries including China have begun to artificially culture this species due to its fast growth and market value. It is particularly suitable for the deep sea net cage culture method and is thus a promising candidate for the deep sea farming industry in China. Studying the morphometrics and physiology of embryos, larvae, juveniles, and young fish to obtain information about their early life history is the first step and key to the successful aquaculture of a fish species. Thus, we observed, recorded, and described the morphometric characteristics of the embryonic and postembryonic development of in order to provide basic knowledge for the artificial breeding and seedling production of this species. The fertilized eggs obtained by natural spawning were spherically shaped and buoyant. The fertilized eggs were transparent and had one oil globule in the yolk, with an egg diameter of (1.48±0.04) mm and an oil globule diameter of (0.37±0.02) mm. The fertilized eggs hatched 73 h 40 min after fertilization in (21.5±0.5)℃ water with a salinity of 32 and a pH of 8.0-8.2. The total length (TL) of the newly hatched larva was (4.23±0.39) mm and consisted of a long oval yolk sac, which accounted for one third of the TL. The larvae opened their mouths and exhibited blackened eyes at 3 days after hatching (DAH) with a TL of (4.61±0.43) mm. At this time, the yolk sac decreased in volume by approximately 95%, and the swim bladder primordium formed. Larvae at 4 DAH were (4.57±0.88) mm in TL and began to feed on rotifers, thus entering the mixed feeding stage. Five DAH, the larvae with a TL of (4.68±0.25) mm exhausted the yolk sac and the swim bladder began to inflate with air. The oil globule was absorbed at 8 DAH, and the larvae (TL 5.14 mm±0.358 mm) completely entered the exogenous nutritional stage. The swim bladder of the larvae at 7 DAH (TL of 4.79± 0.36 mm) became a bright vesicle after inflation with air, which exists through their life history. The intestine of the newly hatched larvae was thin, short, and straight, but became long, curled, and complicated with development. The first intestinal physiological curve formed at 10 DAH when the larvae were (5.19±0.37) mm in TL and the second formed at 15 DAH when the larvae reached (5.71±0.50) mm in TL. Flexion of the notochord started at 15 DAH and was completed at 25 DAH when the larvae were (8.66±1.06) mm in TL. The development of the dorsal fin, pectoral fin, anal fin, and caudal fin was completed by the time the juveniles were (20.04±1.56) mm in TL. At 60 DAH (TL 65.06 mm±1.94 mm), the scales on the body surface formed. At 80 DAH, when the young fish achieved (134.05±3.25) mm in TL, their appearance was similar to that of the adults.

Abstract:In order to study the response and survival mechanism of spermatozoa in the external environment, the contents of energy substances, the activities of key glycolipid metabolizing enzymes in the spermatophore, and sperm motility after a 36-h preservation were examined under different temperatures (16℃, 20℃, 24℃) and dissolved oxygen levels (1 mg/L, 3 mg/L, 6 mg/L). The results showed that the glycogen and triglyceride contents in the spermatophore after the 36-h treatment were significantly lower than those before the 36-h treatment, but the protein content showed no significant differences before and after the 36-h treatment. When the water temperature increased from 16℃ to 24℃, the glycogen content decreased, while the triglyceride content first decreased and then stabilized. The activities of hexokinase (HK), lactate dehydrogenase (LDH), pyruvate dehydrogenase (PDH), and succinate dehydrogenase (SDH) increased when the water temperature increased, while the activity of lipase (LIP) first increased and then stabilized. The initial velocity and immotile rate after activation had no significant changes, but the progressive motility rate was first stable and then decreased when the water temperature increased. When the dissolved oxygen content increased from 1 mg/L to 6 mg/L, the glycogen content decreased, while the triglyceride content was first stable and then decreased. The activities of HK, PDH, and SDH increased, while the activity of LDH first increased and then decreased when the dissolved oxygen content increased. The activity of LIP was first stable and then increased, while the initial velocity and progressive motility rate after activation first increased and then stabilized, while the immotile rate first decreased and then stabilized. These results suggested that glycogen and triglycerides in the spermatophore were the main energy substances of the spermatozoa. Low energy substance consumption was the foundation for the long-term survival of the sperm. Low temperature and hypoxia, which reduced the energy consumption of the spermatozoa, were beneficial for its long-term survival.

Abstract:The golden cuttlefish () is a rising aquaculture species with high economic value in China. A disease with necrosis symptoms in golden cuttlefish larvae emerged in a hatchery in Huangdao District, Qingdao. In this study, the pathogen was isolated and identified, the histopathology was investigated, and its route of transmission and sensitivity to different antibiotics were tested. The symptoms included anorexia, slow growth, and a dark body. In addition, the skin, muscles, oral arm, tentacular arm, and the internal organs were extensively ulcerated, and the mortality reached as high as 90%. Histopathological analysis showed that the chromatophore and the gill filament structure were disintegrated, the myofilament was broken, a large number of hepatic lobule epithelial cells were necrotized, and the microvilli of intestinal epithelial cells were shed off. Three dominant bacteria (SE-A, SE-B, SE-C) were isolated from the diseased golden cuttlefish larvae. Artificial infection experiments illustrated that the strains of SE-B and SE-C were the causative pathogens with a median lethal dose of 3.98×10⁶ CFU/mL and 8.91×10⁵ CFU/mL, respectively. Based on morphological observations, and physiological, biochemical, and molecular analyses (16S rDNA), SE-B was identified as . The analysis of the transmission route demonstrated that the two pathogens present during golden cuttlefish breeding were mainly carried by . The chemotherapeutant sensitivity tests illustrated that SE-B was sensitive to doxycycline and florfenicol, etc., while it was insensitive to streptomycin and gentamicin, etc. SE-C was sensitive to florfenicol and lomefloxacin, etc., while it was insensitive to neomycin and clarithromycin, etc.

Abstract:White-gill disease emerged among cage-cultured in Zhoushan in 2017. Systematic etiological methods such as polymerase chain reaction, histopathological sections, and electron microscopy in sick fish with clinical symptoms were performed to characterize the pathogen. Histopathological results showed that tissue necrosis was present in the spleen, liver, and kidney of sick fish. Moreover, the erythrocytes in the tissues underwent obvious degenerative changes, and a decreased number of red blood cells was observed in the blood. Ultrathin sections used in the electron microscopy showed the presence of microspore-like shapes with diameters from 300 to 600 nanometre. Total DNA extracted from the pathological tissue was used to amplify the 18S ribosomal RNA gene (SSU rDNA). One specific gene was identified to be homologous to that in sp. with 89% amino acid sequence homology. Our study results showed that the recent pandemic of white-gill disease that affected , was different from the previous white-gill disease. A specific and sensitive detection of the pathogen was developed by using nested PCR, which only requires a minimum amount of 0.5 pg of template DNA and produces 10⁴ more copies than the number of copies produced in single PCR amplifications.

Abstract:Viral hemorrhagic septicemia virus (VHSV) is one of the most serious pathogens of finfish that affects over 80 marine and freshwater species in North America, Europe, and Asia. The genome of VHSV is a negative-sense, single stranded RNA containing approximately 12000 base pairs that encode six proteins, which are the nucleoprotein (N), phosphoprotein (P), matrix protein (M), glycoprotein (G), non-virion protein (NV), and RNA polymerase protein (L) in order from 3' to 5'. The M protein functions in a variety of rhabdovirus infection processes such as assembly and budding, inhibiting host-cell directed transcription and gene expression, inducing apoptosis of the host cell, et al., which were all thoroughly investigated in other rhabdoviruses such as vesicular stomatitis virus and rabies virus, while less so in VHSV. In order to investigate the function of the M protein of VHSV, the M gene was amplified by PCR and cloned into the prokaryotic expression vector pET-32a(+), which was transformed into Rosetta (DE3) competent cells. The recombinant protein was induced by IPTG, and the polyclonal antibody was prepared by immunizing BALB/c mice with purified recombinant protein. The titer of the antibody was detected by an indirect ELISA, and the antibody specificity was tested by western blot and indirect immunofluorescence. The results showed that the full-length M gene was 606 bp. The fusion protein induced by IPTG mainly existed in the form of an inclusion body, and the size was about 36 kDa, which was slightly smaller than expected. The indirect ELISA assay showed that the titer of the antibody was greater than 1:102400. The western blot showed that the antibody could specifically identify the purified fusion protein and M protein in VHSV infected (EPC) cells. The indirect immunofluorescence showed that the M protein antibody can recognize the M protein in VHSV infected EPC cells, and the M protein was mainly localized in the cytoplasm and cell membrane. These results suggest that the prepared polyclonal antibody can be used as an effective tool to study the function of the M protein and for the diagnosis of VHSV.