In this study, the gonadal soma derived factor (gsdf) and anti-Müllerian hormone (amh) were cloned from Larimichthys crocea, and their expression patterns were analysed by qRT-PCR. The results shows that the open reading frame (ORF) of gsdf gene spaned a region of 618 bp and coded 205 amino acids with a signal peptide and a conserved domain of the TGF-β superfamily. Sequence alignment analysis reveals that the gsdf of L.crocea and Dicentrarchus labrax shared the highest homology. Phylogenetic analysis shows that the fish Gsdf proteins had a clade separated from the rest members of the TGF-β superfamily. The ORF of amh gene spaned a region of 1 563 bp and coded 520 amino acids that contained a signal peptide, an AMH-N domain and a TGF-β conserved domain. Phylogenetic analysis shows that Amh proteins of L.crocea and D.labrax had the nearest relationship. The qPCR analysis reveals that gsdf and amh genes were expressed mainly in gonad, and the expression levels in testis were significantly higher than that in ovary (P < 0.05). Before the gonad differentiation, gsdf and amh genes had already expressed, and the expression levels of two genes showed an increase-decrease trend in testis whereas the expression levels were very low in ovaries. Besides, compared with normal females, the expressions of two genes had more significant expression in gonad of pseudo-males (genetic females). It is indicated that gsdf and amh genes play a very important role in the process of L.crocea gonad differentiation.

We cloned the alpha-amylase gene cDNA of Haliotis diversicolor supertexta by rapid amplification of cDNA ends method (RACE) and reverse transcription polymerase chain reaction (RT-PCR) to analyze its tissue expression and correlation with growth traits. The results show that the full length of alpha-amylase gene cDNA was 2 260 bp with an open reading frame (ORF) of 2 088 bp encoding 695 amino acids. The alpha-amylase contained a signal peptide with 18 amino acid residues (MWAQYGIVSALLVLSASA). Two functional structure domains (domain A, domain C) were found in the protein of alpha-amylase. Domain A contained one catalytic center between 28^th and 396^th amino acids. The alpha-amylase mRNA expression in seven tissues (adductor muscle, intestine, digestive gland, stomach, mantle, rostral, foot) was observed, highest in stomach (326.803) and lowest in mantle (0.35). Significant difference was found in the expression of alpha-amylase between digestive and non-digestible tissues (P < 0.05). Significant positive correlation existed between alpha-amylase gene expression and growth traits (P < 0.05).

Ameson portunus is one of the common pathogens of the swimming crab (Portunus trituberculatus). In this study, a SYBR Green I real time qPCR method whose amplification efficiency reached up to 101.45% with a detection limit as low as 2.0×10¹ copies·μL^-1 was established by targeting A.portunus SSU rRNA gene. The method was A.portunus-specific with good repeatability within and between groups. Then the qPCR method was used to detect farmed swimming crabs from a "toothpaste disease" epidemic area, and the detection rate of A.portunus was 82.35%. The results show that the average muscle load per milligram of the live crabs was lower than that of the dead crabs significantly, which indicates that the death of crabs in the region is related with infection of A.portunus closely. When the load of A.portunus was 1.0×10⁹ copies·mg^-1 in the muscle tissue, P.trituberculatus had a risk of illness or even death. Besides, the detection rate for the same samples by a previously established nested-PCR method was only 64.71%, showing that the qPCR method in the present study had higher sensitivity and can provide good technical support for the early diagnosis and prevention of "toothpaste disease".

We cloned three grass carp (Ctenopharyngodon idellus) gcjam-a genes (gcjam-a1, gcjam-a2 and gcjam-a3) and used qRT-PCR to analyze their expression pattern in nine tissues of grass carp, as well as their expression after grass carp reovirus-GD108 strain infection. The three gcjam-a genes had 294~295 amino acids and two immunoglobulin Ig domains, including typical receptor binding domain D1 and transmembrane domain D2. The D2 domains of gcjam-a genes were identical while D1 domains were slightly different. In nine tissues of healthy grass carps, gcjam-a1 was mainly expressed in blood and brain, and gcjam-a2 was mainly expressed in the gills, but gcjam-a3 could not be detected in all tested tissues. After the virus infection, gcjam-a1, gcjam-a2 and gcjam-a3 increased in gills significantly; only gcjam-a1 increased in liver, spleen, intestine, kidney and brain. The gcjam-a1, expressed highest in healthy grass carps tissues among the three gcjam-a genes, increased in all six tissues after the virus infection, which suggests that it might be the main receptor of GCRV-GD108.

In present, genetic quality monitoring method of hatchery-reared fingerlings for stock enhancement has not been established in China, which leads to neglection of genetic quality of fry in screening process of releasing project. With the expansion of scale of releasing, this blind spot is genetically threating to natural populations day by day. In order to establish the method, we compared the fingerlings of a Lutjanus erythopterus stock and an L.erythopterus natural stock from four aspects (genetic divergence, genetic diversity, inbreeding and genetic information retention), and evaluated their genetic quality. The results show that faint genetic divergence existed between the two stocks (F_ST=0.016 1), and their genetic diversity level and effective population size of the fingerling stock were lower than those of the natural stock, with higher average inbreeding coefficients and F_IS values. It is proved that for genetic diversity, this fingerling stock is inferior to the natural stock, and the genetic quality of the fingerling stock fails to meet the requirement of stock enhancement, so releasing the stock may produce negative genetic effects. Since the deviation rate of effective population size was the highest (-35.34%), the effective population size is considered to be the major genetic quality defect.

The stable nitrogen isotope and biomass of zooplankton based on size fractionation were studied in the northern South China Sea during summer and winter, 2015. The zooplankton was divided into three groups according to size structure, i.e., micro-zooplankton (180~380 μm), meso-zooplankton (380~500 μm) and macro-zooplankton (>500 μm). The results show that significant spatial difference exist between zooplankton biomass and stable nitrogen isotope. And high values appeared around the Pearl River estuary, Dongsha Islands and south Taiwan Strait. The mean δ¹⁵N value of zooplankton in summer was higher than that in winter, especially that of the micro-zooplankton (P < 0.01), and the δ¹⁵N value of size-fractioned zooplankton generally increased from small to large size zooplankton. The correlation analysis shows that both the δ¹⁵N value of micro-and meso-zooplankton are closely related to zooplankton biomass, while the δ¹⁵N value of macro-zooplankton is not.

To estimate the carbon content of marine organisms in Zhelin Bay marine ranch of the South China Sea and determine their carbon storage, we measured the carbon content of different tissues from the marine organisms in Zhelin Bay before and after ashing by elemental analysis method. The results show that:1) Before ashing, the average carbon concentrations of meat, bones(shell) and viscera were 37.72%~47.41%, 11.23%~34.91% and 27.58%~33.95%, respectively, among which Osteichihyes, Crustacea (shrimp), Gastropoda and Bivalvia had better carbon fixation ability, but except Cephalopoda, and the other species difference was not obvious. After ashing, the average carbon contents were 1.83%~8.28%, 1.90%~12.54% and 0.62%~8.29%, respectively, and the carbon fixation ability of Gastropoda was the highest, followed by that of Bivalvia. 2) The amount of fixed carbon by organisms was about 6.728×10⁴ t in Zhelin Bay marine ranch in 2013, in which 0.155×10⁴ t carbon was removed from the sea by harvests, accounting for 2.31% of the total carbon storage, and about 0.11×10⁴ t carbon was deposited on the seabed, accounting for 1.7%. In addition, about 6.46×10⁴t carbon was stored in the sea and may re-enter the carbon cycle, accounting for 95.98%. The features of marine organism carbon sinks are different, and marine ranching can increase carbon sink effectively.

We studied the morphological characteristics and parameters of otolith of 207 Myctophum asperum collected in the continental shelf slope of the northern South China Sea during June to July, 2015. Results show that the otolith length (L₁), otolith width (L₂), otolith perimeter (P) and otolith area (A) had significant sex difference. The otolith width, otolith perimeter and otolith area were best described by logarithmic function with standard length (P < 0.05). The otolith length was best described by power function with standard length (P < 0.05). The otolith length and otolith width were best described by power function with body mass (P < 0.05). The otolith perimeter and otolith area were best described by logarithmic function with body mass (P < 0.05). The absolute size and relative size of otolith increased and remained stable with increasing standard length, respectively. Rostrum and antirostrum had linear relationship.

To study the effects of different modes of abalone mariculture on phytoplankton community structure and water environment, we carried out six surveys on the phytoplankton community and environmental factors in four mariculture areas (abalone culture area, Gracilaria lemaneiformis-abalone polyculture area, transition area and control area) in Shen′ao Bay, Nan′ao Island of Shantou City, from May to June, 2016. Altogether 84 species belonging to 45 genera of 4 phyla were recorded. The diatoms were the most dominant population with 37 genera and 71 species. For all culture areas, the average density of phytoplankton in after-harvest-period was higher than that in before-seaweed-harvest-period significantly (P < 0.05).The average density of phytoplankton in abalone culture area in before-harvest-period was higher than that in G.lemaneiformis-abalone polyculture area in after-harvest-period significantly (P < 0.05).In before-harvest-period, the concentrations of total nitrogen (TN), total phosphorus (TP), ammonia nitrogen (NH₄⁺-N) and chlorophyll-a (Chl-a) in G.lemaneiformis-abalone polyculture area were the lowest, while the values of Shannon-Wiener index and Pielou′s were the highest. No significant difference was found in different culture areas in after-harvest-period. The phytoplankton community structure was affected by TN, TP, water temperature (T) and chlorophyll a significantly. It is indicated that G.lemaneiformis-ablone polyculture system can reduce the concentrations of nitrogen and phosphorus, maintaining relative stable community structure of phytoplankton.

To determine the effects of dietary Bio100 level on growth performance, digestive enzyme activity, serum immune and biochemical indices of juvenile hybrid groupers (Epinephelus fuscoguttatus♀×E.lanceolatus♂), we prepared six experimental feeds with Bio100 contents of 0% (control), 0.05% (T1), 0.10% (T2), 0.15% (T3), 0.20% (T4) and 0.25% (T5). The fish [(23.33±0.33) g] were randomly assigned to six groups with three replicates per group and 20 fish per replicate, and were fed in indoor fiberglass fiber barrel (500 L) twice a day for eight weeks. The results show that the weight gain rate and the specific growth rate increased first and then decreased with increase of dietary Bio100 level, and those of T3 and T4 groups were significantly higher than those of the control group (P < 0.05). The feed coefficient rates of the experiment groups were significantly lower than that of the control group (P < 0.05). The muscle ash content of the experiment group increased with increase of dietary Bio100 level, and that of T5 group was significantly higher than those of T1 group and the control group (P < 0.05).The pepsin activity increased first and then decreased, and that of T3 group was significantly higher than those of T1, T5 groups and the control group (P < 0.05). The intestinal lipase activity increased first and then decreased, and that of T4 group was significantly higher than those of T1, T2 groups and the control group (P < 0.05). There was no significant difference in intestinal amylase activity among the groups (P>0.05). The lysozyme activity, alkaline phosphatase activity and C3 content of the experiment group were higher than those of the control group but with no significant difference (P>0.05). The Bio100 level in feed affected the cholesterol content and alanine aminotransferase activity of serum significantly. It is showed that the suitable adding amount of Bio100 in the feed of juvenile hybrid groupers was 0.15%.

In the present study, we investigated the effects of starvation on morphological development, growth and survival of Plectropomus leopardus larvae using experimental ecological method, and determined the initial feeding rate and point of no return (PNR) of the starved larvae. The results show that the larvae began to eat on 2.5 days post hatch (DPH) following by disappearance of yolk sac and oil globule on 3.0 DPH at water temperature of 23~24 ℃. Therefore, the larvae were vulnerable to starvation stress with only 0.5-day mixed vegetative period. The highest initial feeding rate was 65% on 3.5 DPH. The PNR was detected on 4.5~5.0 DPH, with only 2.0~2.5 d of initial feeding. The average total length in the starved group was not significantly different from that of control group before 3.5 DPH (P > 0.05), but after then it decreased significantly compared with the control group because of physiological atrophy (P  < 0.05). After endogenous nutrients being absorbed completely, a series of hunger-induced morphological characteristics appeared in starved group and all larvae died on 6.5 DPH. In conclusion, the optimum initial feeding time for P.leopardus is 2.5~3.5 DPH.

To discuss the difference in antioxidant activity among different algal polysaccharides, we analyzed the free radical-scavenging and anti-lipid peroxidation capacity of crude polysaccharides extracted from Betaphycus gelatinae, Ulva lactuca, Sargassum polycystum, Padina australis and Caulerpa sertularioides in vitro. The results indicate that five algal polysaccharides were significantly different in antioxidant activity. The polysaccharides of S.polycystum and P.australis showed strong reducing power and free radical-scavenging capacity for superoxide anion and hydroxyl radical. The scavenging capacity for superoxide anion of P.australis polysaccharide [IC₅₀=(262.00±24.60) μg·mL^-1] was significantly higher than that of S.polycystum [IC₅₀=(458.00±18.70) μg·mL^-1], and the scavenging capacity for hydroxyl radical of P.australis polysaccharide [IC₅₀=(388.00±45.29) μg·mL^-1] was similar with that of S.polycystum [IC₅₀=(312.04±37.42) μg·mL^-1].The scavenging capacity for DPPH of S.polycystum polysaccharide [IC₅₀=(95.80±7.48) μg·mL^-1] was significantly higher than the other algal polysaccharides, while the scavenging ability for DPPH of P.australis polysaccharide was not good enough [IC₅₀=(726.00±54.90) μg·mL^-1].According to the anti-lipid peroxidation analysis in vitro, P.australis polysaccharide had higher inhibitory capacity for liver cell membrane lipid peroxidation [IC₅₀=(283.67±44.14) μg·mL^-1], and certain ability to protect red cell lysis which was induced by hydrogen peroxide [IC₅₀=(335.50±22.47) μg·mL^-1].

To design a fast brining technology for low-salinity tilapia (Oreochromis mossambicus) fillets, we compared four brining methods (standing brining, saline injection, vacuum brining, ultrasonic-assisted brining) on tilapia fillets quality (salt content, water content, weight changing rate, pH, proteolysis index, texture property). Besides, on the basis of single factor experiment of saline injection and with response surface methodology, we studied the effects of salt concentration, brining time and ratio of fillet mass (g) to brining liquid volume (mL) on the salt content of the saline injection fillets, and then optimized the process. The results show that the saline injection fillets had the best brining effect with high salt permeation rate, good product quality and high product yield rate. The single factor experiment indicates that salt concentration, brining time and ratio of fillet mass (g) to brining liquid volume (mL) were the main influencing factors. The conditions optimized by Box-Behnken design are as follows:salt concentration of 2.26 mol·L^-1, brining time of 2.5 h, ratio of fillet mass (g) to brining liquid volume (mL) of 1:3.4. Under these conditions, the actual salt content was 2.93%, and the relative error of the target prediction value was 2.39%, showing feasibility of this optimization.

We carried out an investigation during 2012-2015 to analyze the structural characteristics and catch composition of one-beam trawl and two-beam trawl in the fishing grounds of the northern South China Sea. The index of relative importance (IRI) was used to evaluate the catch composition. The ratio of by-catch to shrimp by mass and the percentage of un-matured fish were also calculated. The results indicate that major difference of structural characteristics existed between one-beam trawl and two-beam trawl. The average ratio of by-catch to shrimp by mass was 12.68±14.52 and 1.79±1.02 for one-beam trawl and two-beam trawl, respectively. For both shrimp beam trawls, the dominant target species were Metapenaeus ensis,  M.joyneri, Marsupenaeus japonicus and M.affinis; the dominant by-catch species were Cynoglossus trigrammus, Saurida tumbil,  Sillago japonica, Caranx (Atule) kalla, Siganus oramin, Thrissa dussumieri, Portunus sanguinolentus, P.trituberculatus and P.pelagicus. The percentages of un-matured fish were high for both shrimp beam trawls. Furthermore, the potential impact of shrimp beam trawl on fishery resources is discussed.