This study aimed to investigate the effect and mechanism of immune enhancer chitosan oligosaccharides (COS) on non-specific immunity of E.sinensis. A total of 45 crabs (20±2) g with intact appendages and uniform individuals were selected for the experiments, and they were randomly divided into three groups, with fifteen crabs in each group. Each crab was injected with 0.1 mL of COS at concentrations of 0 (control group), 50 and 200 μg·mL^-1, respectively. Serum and blood lymphocytes were collected 24 hours later to analyze the changes in immune enzyme activity and immune genes, etc. The results showed that compared with the control group, COS treatment significantly increased the activities of superoxide dismutase, catalase, glutathione peroxidase and lysozyme in the serum of crab, significantly increased the content of nitric oxide, and decreased the content of malondialdehyde in serum. Quantitative real-time PCR results showed that compared with the control group, COS significantly increased the expression of EsToll1, EsToll2, EsMyD88, EsTube, EsPelle and EsDorsal in the Toll signaling pathway, and up-regulated the expression of anti-lipopolysaccharide factors EsALF and EsALF3. These results suggested that COS could improve the non-specific immunity and antioxidant capacity of E.sinensis, activate the Toll signaling pathway, and promote the expression of anti-lipopolysaccharide factors. This study provided theoretical support for the application of COS in E.sinensis.

Understanding the distribution characteristics of X.gladius can provide scientific basis for studying the habitat ecology of X.gladius,resource conservation and improving longline fishing gear.This paper highlights the results of domestic and international research on factors influencing the distribution and longline catch per unit effort (CPUE) of X.gladius,as well as the problems and proposes countermeasures to be taken for further research in the future.The results show that:1) X.gladius perform diurnal vertical movements,with a U-shaped movement pattern according to the changes of dissolved oxygen content in water layer,and generally distribute in the corresponding depth of 8.5-13.3 °C during the day and 23.6-26.2 °C during the night;2) X.gladius migrate to tropical waters for spawning and overwintering,and migrate to temperate waters for feeding; 3) X.gladius congregate in frontal areas and eddy fields;4) moonlight illumination affects the vertical movements of X.gladius,and moon phase may also be related to X.gladius spawning behavior;5) the catch rate of X.gladius in monofilament longline fishing is higher than that in polyfilament longline fishing,and the soaking time is positively correlated with the CPUE of X.gladius; 6) fluorescent rods in fishing gear can improve X.gladius CPUE,and the soaking time of fluorescent rods is positively correlated with X.gladius CPUE.The main shortcomings of the previous studies include:1) insufficient research on the relationship between climatic changes and the habitat change of X.gladius;2) less quantitative research on the effect of lunar illumination on X.gladius activity and the results are not robust;3) insufficient research on the effects of different hook types,hook offset and baits on X.gladius CPUE.The following issues are suggested for future research:1) increasing the testing experiments of TDR and CTD to study the effects of temperature,salinity,chlorophyll a and dissolved oxygen concentrations in different water layers on X.gladius distribution;2) using historical catch statistics and satellite remote sensing data to study the relationship between X.gladius distribution and marine environment in combination with changes in ocean monsoon and trade winds to find out the specific effects of climate change on X.gladius distribution;3) using illuminance meters to measure the illuminance of moonlight and quantitatively study the effects of monthly illuminance of moonlight on the vertical movements of X.gladius and their bait organisms and the spawning behavior of X.gladius; 4) further studying the effects of different hook types,hook offset and different baits on X.gladius CPUE.

Chemokine receptor is a kind of transmembrane receptor (GPCR) which includes seven hydrophobic transmembrane structures.Studies have shown that chemokine and their receptors play an important role in inflammatory reaction, pathogen infection, wound repair, tumor formation and metastasis and so on.But, the role of chemokine receptors in teleost fish, especially in fish antiviral remains unclear.In this study, the ORF sequence of CC chemokine receptor 6a (CCR6a) gene was cloned from tissue of orange-spotted grouper, and its sequence and evolutionary relationship were analyzed.At the same time, tissue distribution, subcellular localization and antiviral function of this gene were studied.The results showed that the full length of ORF sequence of CCR6a gene in oblique grouper was 1 131 bp, encoding 376 amino acids.Evolutionary tree analysis showed that orange-spotted grouper CCR6a was the closest relative between giant grouper.Quantitative real-time PCR (RT-qPCR) detection of CCR6a tissue distribution found that CCR6a was high expression in immune tissue like kidney, gill, and skin.Subcellular localization showed that CCR6a was distributed in membrane.Overexpression of CCR6a in GS cells could significantly inhibit the replication of red-spotted grouper nervous necrosis virus (RGNN).These results would help to understand the role of fish chemokines in viral infections.