Effect Of Low Salinity Stress On Salinity-related Characteristics In Portunus Trituberculatus "Ningxiang-1"

Both the parental and filial generation of Portunus trituberculatus were screened by low salinitystress, and the survival crabs of filial generation were collected as the low salinity tolerant groupwhich was named “Ningxiang-1”. In this study, combining the “one crab in one cage” aquaculturemode, growth parameters of “Ningxiang-1” was recorded, and physiological and biochemicalindexes of “Ningxiang-1” and wild crabs under low salinity were tested and comparativelyanalyzed. Specific results are as follows.(1) Growth parameters analysisThe molt cycle and body weight (BW), body height (BH), body length (BL), full carapacewidth (FCW), carapace width (CW), meropodit length of the claw (MLC), meropodit length of thefirst peraeopod (MLFP), fixed finger length of the claw (FFLC) of “Ningxiang-1” were measuredand recorded. Each trait was increased in varying degree within different molting period. Elevenmolting times were measured in this study, and the molting cycle was gradually lengthened alongwith the increase of the individual size.(2) Immune indexes analysis under low salinity stressActivities of THC, PP, PI, ACP, AKP, CAT, POD, T-SOD and hemocyanin in haemolymphwere tested in wild crabs and “Ningxiang-1” during which exposed to low salinity stress (salinity4)for72h. The results showed that, all indicators in the two groups of P. trituberculatus were changedafter low salinity stress. Different changing tendency of PP, PI, ACP, CAT, POD was determined intwo groups of crabs, while no apparent difference was detected in THC, AKP, T-SOD betweenwild crabs and “Ningxiang-1”.(3) Activity and expression of Na+/K+-ATPaseActivity and transcripts of Na+/K+-ATPase in gills were tested respectively. After the suddendecrease of salinity, the Na+/K+-ATPase expression level increased so that to increase theNa+/K+-ATPase protein activity, which may contribute to regulate the osmotic pressure of theorganism to adapt to the low salinity environment. However, after long-time exposed to the lowsalinity, the gill Na+/K+-ATPase mRNA expression and protein activity reduced.(4) Expression of HSPsThe quantitative real-time PCR (qRT-PCR) was employed to investigate the expressionprofiles of4HSP genes (HSP60, HSP70, HSP90-1, HSP90-2) in the hepatopancreas and hemocyteof wild crabs and “Ningxiang-1” exposed to low salinity (4ppt). The results showed that HSP60 gene exhibited similarly down-regulated expression profile between the two groups of P.trituberculatus after being subjected to low salinity condition. HSP70gene in the hemocyte of“Ningxiang-1” had been a state of high expression level after challenged to the low salinity so thatto resist the low salinity environment, and in the hepatopancreas, expression level in the“Ningxiang-1” was more stable than the wild group at the late stage of stress. HSP90-1andHSP90-2were highly expressed at12h in the hepatopancreas and24h in the hemocyte after lowsalinity challenge in the “Ningxiang-1”, but no to the wild crabs.In conclusion, the growth characteristics, survival rate, immune indicators, metabolismindicator and the expression of HSP reflected that “Ningxiang-1” has a normal growth rate and astronger low salt toletance than the wild crab.