| Spotted sea bass(Lateolabrax maculatus)is an essential economic fish along the coast of China which has been widely cultivated in coastal and inland areas of China.Spotted sea bass has the advantages of strong adaptability to the environment,high yield,delicious meat,and rich in high-quality amino acids,and consumers deeply love it because of its high nutritional value and delicious taste.In aquaculture,temperature is one of the most critical environmental factors.Temperature affects almost all biological processes of fish,including physiological metabolism,behavior,stress response,immune function and species distribution.Fish are ectothermic animals,and their body temperature depends on the water environment and is often affected by changes in environmental temperature.It is of great significance to explore the low temperature tolerance of spotted sea bass for its culture in high latitude and low temperature environment in China.This study used histology,physiology,molecular biology,and cell biology methods to analyze the behavior changes,histological changes,liver glycolipid metabolism enzyme activities,and glycolipid metabolism-related gene expression levels of spotted sea bass under low-temperature conditions.In addition,the c DNA sequence of the YB-1 gene of spotted sea bass was obtained by gene cloning.The role and function of the YB-1 gene in fish under low-temperature stress conditions were explored by combining with molecular biology methods such as over-expression experiments,double luciferase gene reporting experiments,tissue YB-1 specific expression,and YB-1transcription level of different tissues under different low-temperature conditions.The study on the response mechanism of spotted sea bass to low temperatures is conducive to screening or developing low temperature-tolerant varieties,studying the stress resistance of spotted sea bass,and promoting aquaculture.The main results are as follows:(1)During the short-term cooling process,it was observed that fish died(food intake decreased)until 12℃.With continuous cooling,the mortality rate gradually increased,with a higher mortality rate(50 %)at 7-1 gene in fish under low-temperature stres4 ℃.The mortality rate of fish under long-term low-temperature stress at 8 ℃ is about 30 %.With the decrease in water temperature,the swimming speed of fish becomes slower,and the number of swimming fish decreases with the decrease in temperature.(2)At low temperatures,the histological morphology of gill filaments of spotted sea bass changed,mainly including lamellar curling,epithelial cell proliferation,and vacuolation.The liver of spotted sea bass mainly showed nuclear swelling,cell damage,and vacuolation after low-temperature stress.(3)Under continuous low-temperature stress(4 ss.s mainly showed nuclear swelling,cell damage,and vacge,and vac mainly including lamellar curling,epithelial cell proliferation,and ity rate of fish under long-term lowcreased with long-term exposure to the low temperature of 8 ℃ for 4 days.SOD activity in the long-term low-temperature stress group showed a downward trend.The genes PPAR-α,PPAR-γ,eif4ebp1,eif4ebp2,G6 Pase,and mlst8 related to glucose and lipid metabolism are up-regulated after lowtemperature stress.However,the degree of up-regulation of each gene depends on the temperature and duration of stress.(4)After 4 days of long-term exposure to low temperature stress,myristic acid(C14:0)and palmitic acid(C16:0)in muscle tissue decreased significantly.At the same time,compared with the control group,the content of eicosapentaenoic acid(EPA)in all experimental groups increased.(5)The c DNA sequence of spotted sea bass YB-1 was cloned..The full-length c DNA sequence of YB-1 was 1454 bp,including 151 bp 5′ untranslated region(UTR),900 bp open reading frame(ORF)and 402 bp 3′ UTR.qRT-PCR was used to quantify the transcription levels of the YB-1 gene in 8 tissues.The YB-1 m RNA was the most abundant in the liver,and its expression in gill and muscle was low. |
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