Research On Tolerance Of Juvenile Coregonus Ussuriensis Under Sodium Bicarbonate Stress

Carbonate alkalinity is considered to be one of the main stressors of fish,and it is also one of the current research hotspots to explore the influence of alkalinity stress on fish.Because of its tender meat and important nutritional and economic value,Ussuri cisco（Coregonus ussuriensis Berg）is a special economic fish in Heilongjiang Province,and it also has a certain tolerance to carbonate alkalinity.In this study,the effects of Ussuri cisco on acute and chronic experiments were studied under the sodium bicarbonate stress.The results are as follows:1.Ussuri cisco had some tolerance to sodium bicarbonate alkalinity stress,and the semi-lethal concentrations（LC50）of sodium bicarbonate alkalinity for Ussuri cisco at24 h,48 h,72 h and 96 h were 51.697,47.721,44.297 and 42.317 mmol/L,respectively.And the Safe Concentration（SC）was 12.199 mmol/L.2.In the growth experiment,the effect of 42 d chronic alkalinity stress on Ussuri cisco had a dose effect,specifically,low concentration promoted growth and development,while high concentration inhibited it.20 and 30 mmol/L groups of Ussuri cisco were inhibited in length and body weight to some extent,and growth performance was significantly reduced（p<0.05）.The growth performance（ADG,SGR,FCR,WGR）of Ussuri cisco exposed to low Na HCO₃alkalinity（5 mmol/L,10 mmol/L）was better than that of the control group,with the highest growth performance of this fish in the 10mmol/L,with ADG,SGR and WGR 1.34,1.30 and 1.25 times higher than that of the control group,respectively.While the feed conversion rate（FCR）was only 81%of that of the control group（p<0.05）.3.In the 96 h acute stress experiment and 30 d chronic stress experiment,high alkalinity stress caused oxidative damage within the tissues of Ussuri cisco,and the activities of three antioxidant enzymes（Superoxide dismutase（SOD）,Catalase（CAT）and Glutathione peroxidase（GSH））in gill and liver tissues were significantly increased（p<0.05）.In the low alkalinity group（5 mmol/L and 10 mmol/L）,the malondialdehyde（MDA）content remained at the control level,but the highest MDA content in the 30mmol/L alkalinity group was found in the gill and liver tissues of Ussuri cisco,which were 1.45 and 1.83 times higher than the control group,respectively（p<0.05）.The MDA content in gill and liver tissues of Ussuri cisco was the highest in the 30 mmol/L alkalinity group,which was 1.45 and 1.83 times higher than the control group,respectively（p<0.05）.4.HE staining was performed on gill and liver tissues of Ussuri cisco.In acute stress experiments,no damage was observed in the gill and liver tissues of Ussuri cisco at the beginning of the stress period,and lamellar edema began to appear in the gill tissues after 12 h.Oxidative damage and vacuolization of cells were found in the liver tissues after 24 h.In chronic stress experiments,the damage in gill and liver tissues of Ussuri cisco increased with the increase of alkalinity,and the most severe lesions were observed in the 30 mmol/L group（p<0.05）.5.The expression of NKA-α,CA,AQP,IL-1βand TNF-αincreased and then decreased with the time of stress in the acute experiment,reached the peak at 12-24 h,and then returned to the control level.Under chronic stress,the expressions of NKA-α,CA and AQP in low alkalinity（5,10 mmol/L）were slightly up-regulated but not significant（p>0.05）,and those in high alkalinity（20,30 mmol/L）were significantly higher than those in control group（p<0.05）.The expressions of IL-1βand TNF-αin 30mmol/L group were the highest,8.6 and 10.1 times of those in control group,respectively（p<0.05）.In chronic stress,IGF-1/GH expression decreased with increasing concentration（p<0.05）.In conclusion,Ussuri cisco has a certain alkaline tolerance and can maintain high growth performance in 10 mmol/L.Long-term high alkalinity stress not only inhibits growth but also leads to oxidative damage in fish tissues.Under high alkalinity stress,gill,liver,kidney and other tissues in Ursuline salmon are involved in acid-base regulation and osmoregulation to help the fish adapt to the environment and overcome the osmotic pressure imbalance,but the molecular regulation of Ursuline salmon under alkalinity stress needs to be further investigated.