Study On Strontium Marking And Wild Training Techniques Of Takifugu Obscurus

Takifugu obscurus,commonly known as bubble fish,belongs to Tetraodontiformes and Tetraodontidae.T.obscurus is a short migratory fish species widely distributed in the coastal areas of China,the Korean Peninsula and Japan.It has high economic value in food and medicine,with important edible and medicinal value.However,due to overfishing and water pollution,wild resources of T.obscurus have declined.stock enhancement and releasing are important measures to restore aquatic living resources.As two key technologies,marking and wild training are helpful to improve the survival rate and to evaluate the effect of releasing,which are less studied.Based on Strontium marking technology,this study demonstrated the feasibility and safety of large-scale strontium marking of T.obscurus.In addition,based on the analysis of physiological and biochemical characteristics of T.obscurus and the changes of swimming ability,the appropriate intensity and time of two sports training modes were determined.This study could provide guidance for large-scale strontium marking,optimization of rewilding training technology before releasing and provided a new approach to evaluate the stock enhancement and releasing efficiency of T.obscurus in the Yangtze Estuary.1、Analysis of the effect of strontium marking on otolith of T.obscurusAs one of the main releasing species in the Yangtze River estuary,there are few studies on the evaluation of releasing efficiency of T.obscurus.Mark recapture is the main method to evaluate the change of releasing species resources.As a marking method,Strontium marking of otolith has the advantages of high efficiency,high survival rate,low cost and easy operation.In this study,T.obscurus were immersed for 7 days using SrCl2·6H2O,and then were reared in non-additive water for 25 days.The results showed that proper concentration of strontium had no negative effect on the survival and growth of T.obscurus,and the growth of 18 mg/L group was the best.After immersing in strontium-rich water for 7 days,the strontium-calcium ratio in otolith of 18 mg/L group could reach 2.29 ± 0.02 mmol/mol,1.97 times of the detection limit(1.16 mmol/L),and the success rate of marking reached 100%.Notably,the strontium content in muscle,gill and liver of fish dropped to the safety threshold after 25 days,which was not enough to cause food safety risks of high strontium poisoning.This study verified the feasibility and safety of strontium marking on the application of T.obscurus,which provided reference materials for large-scale marking of T.obscurus in the future.2、Effects of exercise training on swimming ability and metabolic characteristics of T.obscurusProper exercise training can improve the survival rate of fish in the wild.In this study,different training intensities(0,0.75 and 1.5 BL/s)and time(1 week,2 weeks and 4 weeks)were set to analyze the changes of physiological and biochemical characteristics and swimming ability of T.obscurus under different training mechanisms.The results showed that the lysozyme and critical swimming speed of 0.75 BL/s group were significantly higher than the control group after 2 weeks,which increased by 78.85%and 22.79%,respectively,while the levels of cortisol,superoxide dismutase,lactic dehydrogenase and glycogen had no significant changes.The results of this study indicate that appropriate exercise training can effectively improve the immunity level and swimming ability of T.obscurus,which can provide guidance for optimization of rewilding training technology before releasing of T.obscurus in the Yangtze Estuary.3、Effects of chasing training on swimming ability and metabolic characteristics of T.obscurusProper chase training can improve the perception ability of fish to external risks.In this study,the changes of physiological and biochemical characteristics and swimming ability of T.obscurus under different training mechanisms were analyzed by setting up a catch-up experiment of T.obscurus once a day group,twice a day group and a control group.The training lasted for 2 weeks and then stopped for 1 week.The results showed that the lysozyme and critical swimming speed of once a day group were higher than the control group after training for 2 weeks,which was still higher than that of the control group after 1 week of suspension,but the levels of cortisol,superoxide dismutase,lactate dehydrogenase and glycogen had no significant changes.The levels of cortisol and lactate dehydrogenase of twice a day group were significantly higher than the control group after 2 weeks.The results of comprehensive indexes showed that the immunity level and exercise ability of once a day group were effectively improved after 2 weeks,and the training effect was better.Some training effects can still be maintained to a certain extent after 1 week of suspension,so it is suggested that the releasing activities should be carried out within 1 week of suspension.This study provides theoretical basis and technical support for the development of rewilding training technology before releasing and the improvement of adaptability after releasing of T.obscurus in the Yangtze Estuary.