The growth performance is often influenced by environmental factors during aquaculture practice.An appropriate culture environment enhances fish growth and promotes muscular quality by regulating physiological and biochemical processes.The intensive aquaculture model is frequently applied in fish farms.Some concerns about the intensive aquaculture model are issued.Crowding stress caused by high stocking density and nitrite poisoning often occurred in the intensive aquaculture practice.Temperature regulates fish growth as a key environmental factor.Muscular quality forms paralleled with fish growth.Facing alterations in stocking density,water quality,temperature,and other varieties,fish strive to adapt to the environmental changes and maintain homeostasis for normal growth.This dissertation investigated growth rate,food conversion efficiency,muscular histology,physiological condition,and biochemical profiles in gibel carp（Carassius gibelio）suffered from thermal stress,crowding stress,and nitrite exposure.The main results are as follows.The effect of thermal stress on physiological,biochemica,and transcriptome characteristicsGibel carps（initial body weight:110.06±10.36 g,body length:14.85±0.57 cm）.In this experiment,three temperature treatments were applied at room temperature（20.7±1.9°C）,26°C（±0.30°C）,and 32°C（±0.49°C）,respectively.We used heating rods with a power of 500 watts to control the water temperature,and the heating rate was0.5°C per hour.The fish in 9 tanks were all collected at 0h,1h,12h,24h,72h,and 168h after water temperatures reached 26°C or 32°C,respectively.Serum T4 levels did not change significantly throughout the experimental period.Serum T3 in the 26°C groups was significantly increased at 24h but FT3 and FT4 were significantly decreased（P＜0.05）.Serum T3 and FT3 in the 32°C groups reached the lowest value at 72h,it was always lower than that in the room temperature group.32°C and 26°C groups serum cortisol levels increased significantly after 1h of heat stress and reached the highest point after12h（P＜0.05）.The serum cortisol levels of each treatment group showed a trend of rapid increase at first and then slow decrease,but the 32°C groups were always higher than the other two groups.The plasma levels of biochemical parameters were significantly changed（P＜0.05）.The antioxidant capacity of 26°C and 32°C groups liver were affected by heat stress,CAT,T-SOD,GSH,and GSH-PX showed a trend of increasing first and then decreasing,but there was no significant change in T-AOC in each treatment group,and each period time.The structures of myofiber and myocommata in white and red muscles were significantly changed by thermal stress.The elevated temperature caused changes in the structure of the gill over time in secondary lamellae,degraded gill lamellae,and cartilage in the primary lamellae.The acute temperature elevation damaged the intestine tissue.The injures in goblet cells,microvilli,and enterocytes were observed at 12h,24h,and 72h after exposure to thermal stress.The relative expression of m RNA in the liver and white muscle of gibel carp was affected by both temperature and duration.The m RNA relative expression in the liver of hsp70 and hsp90 in the 32°C groups increased with time and reached the highest value at 168h.There was no significant change in the room temperature group.Myog and myod m RNA levels rose significantly in26°C and 32°C groups,while the expression of mrf4,mstn-1 and mstn-2 did not significantly rise but still increase comparing to the room temperature group.The expression levels of psma2 and psmc1 in the white muscle were significantly increased at1h in the 26°C treatment group.At 168h,the expression levels of psmc1 were positively correlated among temperature groups,but the differences were not significant.The expression of the murf1 gene was significantly increased at 1h and 12h in both the 26°C and 32°C treatment groups,and the expression of mafbx at 168h increased significantly with the increase in temperature.The following results were obtained by transcriptome analysis:Wherein 1743 genes were up-regulated and 2417 genes were down-regulated in the 26°C groups,4942 genes were up-regulated and 6710 genes were down-regulated in the 32°C groups,5123 genes were up-regulated and 6576 genes were down-regulated in room temperature group.A total of 7956 and 4678 DEGs was identified in the 26°C and32°C groups,respectively,compared to the room temperature group.These include 4073genes that were up-regulated and 3883 genes being down-regulated in the 26°C groups,2787 genes being up-regulated and 1891 genes being down-regulated in the 32°C groups.In addition,compared to the 26°C groups,a total of 6201 DEGs were obtained in the32°C groups,includinge 2995 up-DEGs and 3206 down-DEGs.In the top 20 pathways significantly enriched by the 26°C vs 32°C groups,phagosome,neuroactive ligand-receptor interaction,staphylococcus aureus infection,terpenoid backbone biosynthesis,and complement and coagulation cascades were the most significantly enriched.The influences of different stocking densities on fish growth,blood biochemical characteristics,antioxidative capacity,and muscular qualityGibel carps（initial body weight 57.04±1.89 g,body length:12.83±1.87 cm）were cultured at three stocking densities,high stocking density(HSD,10.85 kg m-3),medium stocking density(MSD,5.06 kg m-3),and low stocking density(LSD,1.47 kg m-3),for 60days.The highest growth rate was found in the fish reared in the LSD group.High stocking density inhibited fish growth significantly（P＜0.05）.The content of either crude fat or crude ash of fish muscle was significantly altered by stocking densities（P＜0.05）.The crude protein content,however,did not change significantly.Significant differences in plasma biochemical profiles,such as the concentrations of plasma glucose,alanine aminotransferase,aspartate aminotransferase,cholesterol,and creatinine,were found among groups.The fish reared in the LSD group exhibited the highest activities of superoxide dismutase（SOD）,glutathione peroxidase（GSH-Px）,and catalase（CAT）in the liver（P＜0.05）.The content of glutathione（GSH）and the level of total antioxidant capacity（T-AOC）declined significantly in the HSD group（P＜0.05）.Compared to the LSD and MSD groups,plasma cortisol levels increased significantly in the HSD group（P＜0.05）.The highest levels of triiodothyronine and thyroxine were found in the LSD group.Muscle texture profiles were affected significantly by stocking density.The muscle of fish reared in the LSD group showed a significantly highest level of either resilience or springiness.The results showed that high stocking density exerted a negative impact on growth,antioxidative capacity,and muscle quality in gibel carp.The influence of nitrite exposure on the physiological,biochemical,and transcriptomeGibel carps（initial body weight:107.81±7.11g,body length:15.56±0.56 cm）were exposure to 5 concentrations levels of nitrite（NO2-）at 0 mg l-1,20 mg l-1,40 mg l-1,60mg l-1,and 80 mg l-1,respectively,for 4 days.The fish were sampled at 0h,1h,3h,12h,24h,48h,and 96h after nitrite exposure.The fish suffered from stress during the nitrite exposure.Acute nitrite exposure led to significant histopathological changes in liver,white and red muscle,gill,and intestine within 96h exposure.Detachments on myocommata,inflammation,and fatty degeneration were observed in the nitrite-exposed fish.Thyroid hormone metabolism was disturbed by nitrite exposure.The declines in T3and T4 occurred in the nitrite-exposed fish（P＜0.05）.The enzyme activities of GSH-Px,SOD,and CAT were decreased in white muscle and liver by nitrite exposure（P＜0.05）.The content of GSH and total antioxidative capability also declined in the nitrite-exposed fish（P＜0.05）.The activity of either GSH-Px or CAT recovered to the control level at 96h after exposure.The content of the carbonyl protein in white muscle elevated with the increase of the concentration of nitrite and exposed time.A significant elevation in ubiquitinated protein content was demonstrated in either the white muscle or red muscle of fish exposed to nitrite.The expressions of myog,and mrf4 in muscle were significantly increased in the 24h group,and there were no significant differences in myog and mrf4after 96h treatment.The treatment groups in myod compared to the control group after96h showed no significant differences.The patterns of mstn-1 and mstn-2 were different from myog,myod and mrf4.The mstn-1 and mstn-2 rosed significantly in a high concentration of nitrite at sampling time points,especially at 24h,while mstn-1 m RNA expression level no significant change between control groups and treatment groups.The expression of psma2 in the white muscle was significantly increased in the 60 mg/L concentration group at 1h（P＜0.05）,and there was no significant difference in other periods.In the 60 mg/L exposure group,the expression of psmc1 was significantly increased at 1h（P＜0.05）.In the 60 mg/L concentration group,the expression levels of murf1 and mafbx were significantly increased at 1h（P＜0.05）,and the expression levels at96h had the same trend.The expression levels were the highest in the 60 mg/L concentration group（P＜0.05）.The difference is that murf1 only has significant differences in the 60 mg/L concentration group,no significant differences were found between the other treatment groups and the control group,and mafbx was significantly increased in expression compared with the control group at 20 mg/L,40 mg/L and 60mg/L concentrations（P＜0.05）.The transcriptome results include 4073 genes were up-regulated and 3883 genes were down-regulated in CK-40,2787 genes were up-regulated and 1891 genes were down-regulated in CK-60,2787 genes were up-regulated and 1891genes were down-regulated in CK-80.Furthermore,a total of 577 and 1536 DEGs were identified in CK-60 and CK-80,respectively,compared to CK-40.Among them were 278genes up-regulated and 299 genes down-regulated in CK-60,900 genes up-regulated and630 genes down-regulated in CK-80.In addition,compared to CK-60,a total of 892DEGs were obtained in the CK-80,including 378 up-DEGs and 514 down-DEGs.The classification of all DEGs enrichment functions mainly includes cellular process,biological regulation,metabolic process,binding,catalytic activity,and cellular anatomical entity.A significantly different gene expression is contained in the immune system,nitrogen metabolism,and glutathione metabolic pathways under high nitrite stress.The main DEGs contained within the immune system including hsp90 and hsp90aa1were up-regulated at CK-0 and turned down-regulated with increasing nitrite concentration.Nfkbia,IL-1b,fos,fosb,fosl1,and usp28 were down-regulated at low nitrite concentrations and later significantly up-regulated at CK-80.In the nitrogen metabolism and glutathione metabolic pathways,mgst1,mgst2,gpx1 and chac1 were down-regulated at CK-0,CK-20,CK-40,and CK-60,and later significantly up-regulated at CK-80.gpx3,odc1,orf1,ca4,and gln A were up-regulated at CK-0 and CK-20,then down-regulated with increasing nitrite concentration.In summary,Appropriate culture density enhanced fish growth and improved muscular quality by regulating physiological and biochemical processes.Thermal stress could change muscular construction,decrease antioxidant capacity,reduce MRFs family genes and ubiquitin protein in white muscle expression level in white muscle,and increase the expression level of hepatic heat shock protein.Nitrite exposure exerted a detrimental impact on muscle and gill histology,hormonal metabolism,and antioxidative capacity.High concentrations of nitrite increase the expression levels of MRFs family and ubiquitin proteins in white muscle.Suitable temperature and minimizing nitrite content would keep fish in good condition and improve the benefit of fish culture.Fish could exhibit normal or faster growth in reasonable accommodations.