Physiological And Behavioral Responses To Environmental Stress Of Several Endangered Fish Species Inthe Yangtze River

The survival,growth and reproduction are significantly affected by various environmental factors.In this study,four series of experiments were conducted using the juveniles of three endangered fish species habituated in the Yangtze River,i.e.,Spinibarbussinensis,Procyprisrabaudiand Myxocyprinusasiaticus.The experiment 1aimed to investigate the effects of acclmation temperature（25 and 15°C,21d）on thermal tolerance,hypoxia tolerance and swimming ability of Procyprisrabaudi and Myxocyprinusasiaticus;The experiment 2 aimed to examinethe effects of exhaustive chasing training（once or twice per day,20 days training with subsequently10 days of detraining）on the hypoxia tolerance,swimming ability and anti-predatory ability of juvenile Myxocyprinusasiaticus;Theexperiment 3 aimed to examine the effects of short-term fasting（14d）on the swimming behavior,stressresponses and immunity Spinibarbussinensis and Myxocyprinusasiaticus;The experiment 4 aimed to investigate the effects of predation stress on swimming behavior,stress responses and immunity of Spinibarbussinensis and Myxocyprinusasiaticus.The present thesis underpinned the physiological and behavioral mechanisms of fish in response to several important biotic and biotic environmental factors,and provided important theoretical support and valuabledata for their artificial breeding and wild population resource protection.The main results of present study as follows:（1）The thermal indicators of both species increased with temperature,and their valuesat both acclimation temperatures were similar to those of fish living in the Yangtze River.However,both species showedpoor hypoxia tolerance compared to most fish species in the Yangtze River,according to previousstudies.Inparticular,Chinese sucker acclimated at a low temperature exhibited an unusually strong decrease in hypoxia tolerance with decreasingtemperature（fish usually showed high hypoxia tolerance due to decreased oxygen demand and high environmental oxygentension at low temperature）.Furthermore,Chinese sucker exhibited poorer swimming performance than rock carp（whichis also a relatively poor swimmer among the fish species in the Yangtze River）when maintained at a high temperature dueto low swimming efficiency,possibly as a consequence of its deep body shape.The difference incritical swimming speed(U_crit)was magnified at lowtemperature due to the more profound decrease in metabolic scope in Chinese sucker than in rock carp（55%vs20%）,but Chinese sucker showed a higher resting metabolic rate than rock carp at a low temperature,which is difficult to explain.（2）Training showed nosignificant effect on anaerobic swimming performance.The fishfrom both training groups showed lower hypoxia tolerance and alower survival rate under predation.（3）Qingbo showed stronger swimming capacity,more active spontaneous behavior,higher plasma cortisol and Ig M levels as well as more profound response of both plasma cortisol and Ig M level to predation acclimation,compared to those of Chinese sucker;predation acclimation elicited higher plasma cortisol and Ig M levels and higher plasma lysosome activity,especially in qingbo;acute predator exposure resulted in higher plasma cortisol and shorter inter-individual distance whereas the later only manifested in non-acclimated groups.（4）Qingbo showed higher swimming capacity,more active spontaneous behavior,higher plasma Ig M level as well as more profound response of both plasma cortisol and Ig M to food deprivation,thus showed more profound body loss during fasting but higher weight gain in fed group;Chinese sucker showed higher SOD level compared to qingbo;and lysosome activity increased in fasted Chinese sucker but not changed in fasted qingbo compared to normally fed conspecies.The main conclusion as follows:（1）Low hypoxia tolerance and poor swimming performance due to the low cardiores piratory capacity and（or）non-streamlined body shape of both fish species,especially Chinese sucker,reared at low temperature might be two ofthe reasons why they are not well adjusted to the change in their natural habitat and have thus decline in recent decades.The underlying physiological and biochemical mechanisms involved in the unusual adjustment of the physiological functionof Chinese sucker and its ecological relevance must be investigated further.especially Chinese sucker,reared at low temperature might be two ofthe reasons why they are not well adjusted to the change in their natural habitat and have thus declined in recent decades.（2）Exercise training showed little effect or even a negativeeffect on physiological function in Chinese sucker,and the forcedtraining might not be the proper protocol to apply for improving thestocking enhancement of Chinese sucker..（3）Both non-specific and specific immune function up-regulated after predation acclimation possible via the increased release of cortisol which might evolved with purpose to a fast recovery after possible non-lethal hunting.These adjustmentsindicate that predation training might act as a potential training process for fisheries releasing in the Yangtze River water system.（4）Qingbo showed relatively high status of physiological performance possibly due to the fast-life style in their natural fast-flow habitat,which eventually resulted in poor adaptation to fluctuation of food resources;the immuneand antioxidant systems showed different responses to short-term fasting which might frequently happen in their natural habitats nowadays,suggesting these two fish species might have different fate in near future due to the unpredictable change in environmental factor such as food availability.