Study On Artificial Reproduction Of Schizothorax Irregularis And Effects Of Environmental Factors On The Growth Performance Of Juvenile Fish

Due to over-exploitation of water resources and intensification of human activities,the ecological environment of the Kizil River has been damaged and the survival environment of Schizothorax irregularis has deteriorated dramatically;the construction of water conservancy and hydropower projects has blocked the migratory routes of fish,making the survival and reproduction environment of S.irregularis,which has migratory breeding habits,extremely difficult.In recent years,the number of wild populations of S.irregularis has declined sharply and is now in an endangered state.In view of this,it is necessary to grasp the environmental characteristics of S.irregularis habitat,gonadal tissue development cycle,artificial reproduction and breeding method.In this experiment,S.irregularis population in Kizil River was selected as the research object,its habitat was identified,and two aquatic ecological surveys were conducted in its habitat in May（High water period）and September（Low water period）in 2020,and the main influencing factors of planktonic functional groups were analyzed by combining RDA and Pearson correlation analysis.The developmental morphology of S.irregularis gonads was observed by conventional biological measurements and histological methods;the changes of S.irregularis sex hormone secretion were analyzed by enzyme-linked immunoassay;S.irregularis artificial reproduction experiments were carried out to observe and record the embryonic development and the developmental characteristics of the early fry;the effects of water temperature,photoperiod and light intensity on the survival of juvenile fish were studied by significance test and RSM.The acute tolerance of S.irregularis to Na Cl and Na HCO₃was analyzed by the acute toxicity test,which provides a scientific basis for the rational development and utilization of S.irregularis resources and the establishment and protection of its germplasm resources.The main results of the study are as follows:1.The results showed that 28 species,4 phyla were in the phytoplankton community,in which diatoms and green algae accounted for the large part,taking up 71.43%and 14.29%respectively.There were 14 species,3 phyla in zooplankton community,including 7 rotifiers,4protozoans and 3 copedods.In May,an abundant water season,the dominant species in the Kizil River were Spirogyra communis,Arcella sp.and Rotaria tardigrada,while Spirogyra communis,Navicula oblonga,Navicula simplex,Nebela barbata and Arcella sp.were competitive in September,a drought season with a lower water level.Meanwhile it was proved that the density and the diversity of these two plankton communities in the dry season were higher and richer than those in the wet season,the species of both communities,however,were less diversified.The values of Shannon-Weiner Species Diversity Index（H’）in May and December were 1.825 6 and2.271 2 that indicated a moderate and mild pollution occurred there.Based on a further redundancy analysis,the p H,transparency and the load of nitrate and ammonium were considered as important environmental factors to monitor the habitat quality of plankton community.Specifically,the p H,TP and TN were the key factors to the zooplankton community.The negative evidence showing here,to some extent,was attributed to humans inappropriate activities.Giving the above,this study could provide an enlightenment to the ecological restoration,resource conservation and development of the Kizil River.2.Spermatophore and ovary development of S.irregularis was divided into six periods;the spawning period of S.irregularis was from March to May,and the number percentage of egg grains peaked at 2.9～3.0 mm in diameter,and very few mature egg grains were present in the ovary during the VI period after spawning.The presence of very few mature grains in the ovaries at post-spawning stage VI led to the conclusion that the spawning type of S.irregularis was fully synchronized;the serum concentrations of estradiol and testosterone in both females and males reached their highest levels at stage V.3.The reproductive period of S.irregularis was mainly concentrated from late April to mid-May in the southern Xinjiang region,and S.irregularis spawned micro-mucilaginous eggs with a diameter of（2.95±0.15）mm and swelling up to（3.53±0.12）mm after water absorption.The embryos underwent seven stages of development,including embryonic disc,oogenesis,blastocyst,protointestine,neuroembryo,organ formation and emergence of membrane.(At a water temperature of（17.14±0.01）℃,the fertilized eggs were incubated for 147 h 31 min,with a total accumulation temperature of 2 513.01℃·h.The first hatchlings were（8.72±0.26）mm in length,with heartbeat and blood circulation,and spent most of the time lying on the bottom of the water,with occasional movement;the early hatchlings were divided into four periods:the emergence of eye pigment,the emergence of body pigment,the inflation of the swim bladder and the complete absorption of the yolk sac.The whole length of the pups was（21.51±0.75）mm at432 h after the emergence of the membrane.4.The results of the single-factor test showed that the survival rate of juvenile fish was highest at（94.44±0.58）%when the water temperature was 10℃;the survival rate of juvenile fish reached the highest when the daily light time was 16 h;the survival rate of juvenile fish was lower when the light intensity was lower than 10 lx;the feeding rate and specific growth rate of juvenile fish in the test group with the water temperature of 5～15℃increased with the increase of temperature,and when the water temperature exceeded When the water temperature exceeded20℃,the feeding activity of juvenile fish decreased and the growth slowed down;the feeding rate and specific growth rate of juvenile fish reached the maximum when the daily light time was 16 h;the feeding rate and specific growth rate of juvenile fish reached the maximum under the light intensity of 1 000 lx,and the light intensity above or below 1 000 lx had a negative effect on the feeding and growth of juvenile fish.The response surface optimization model showed that the maximum theoretical survival rate of S.irregularis was 92.96%and the theoretical specific growth rate was 1.73%/day for the combination of temperature of 10.45°C,light duration of 15.86h and light intensity of 1 166.28 lx5.The LC₅₀of S.irregularis under acute stress of Na Cl at 24,48,72,and 96 h were 12.8,10.6,9.5,and 8.6 g/L,respectively,and its safe mass concentration was calculated to be 0.9 g/L.The LC₅₀of S.irregularis under acute stress of Na HCO₃at 24,48,72,and 96 h were 107.2,97.6,88.8,81.3 mmol/L,and the calculated safe mass concentration was 8.1 mmo/L.