Performance Evaluation Of The 4^th,5^th Salinity-Alkalinity Selected Generations And Effects Of Salinity Stress On Fatty Acid Contents Of Nile Tilapia

To cultivate the new aquaculture strain for large salinity and alkalinity waters in north China,a selection program for salinity and alkalinity tolerant tilapia has been carried out by Shanghai Ocean University at Huanghua,Hubei Province since 2012.In2017,2018,the 4^th,5^th salinity-alkalinity selected generation was obtained,respectively.Here,the tolerance index and growth performance of the 4^th and 5^thselected generations were evaluated.Meantime,the effects of salinity stress on the content of fatty acids in liver and expression level of some genes related to lipid metabolism were studied.The major results were as follows:?1?Acute lethal test of salinity,alkalinity and salinity-alkalinity was used to determine the tolerance index of the 3^rd,4^th and 5^th salinity-alkalinity selected generations of Nile tilapia fry.The results showed that the semi-lethal concentration of salinity was 22.473 g/L,24.468 g/L and 23.833g/L,and the semi-lethal concentration of alkalinity was 8.256 g/L,8.443 g/L and 8.453 g/L of 3^rd,4^th and 5^th selected generations at 96 h,respectively.In the salinity-alkalinity experiment,no death occurred when the salinity was 10 g/L,the 96h alkalinity semi-lethal concentration were 4.612 g/L,4.538 g/L and 4.883 g/L when the salinity was 15 g/L,while the 96 h alkalinity semi-lethal concentration at were 1.861 g/L,1.875 g/L and 1.782 g/L at the20 g/L salinity.There was no significant difference between 4^th and 5^th selected generations in semi-lethal concentration of salinity,alkalinity and salinity-alkalinity?P>0.05?,when acute salinity test,the salinity lethal concentration of the 4^th and 5^thselected generations salinity was significantly higher than that of the 3^rdselected generation?P<0.05?.The acute alkalinity test and salinity-alkalinity test showed no significant difference between 3^rd,4^th and 5^thselected generations of semi-lethal concentration?P>0.05?.The results showed salinity-alkalinity tolerance of the 4^th,5^thselected generations of Nile tilapia was improved and tended to stable.?2?Respectively in fresh water?S0A0?,salinity water?S10A0?and saline-alkaline?Na HCO₃?waters?S10A2,S10A4,S10A6?,growth comparison on the 4^th of salinity-alkalinity selected generation of Nile tilapia and the control group?not breeding group?was carries on for 60 days,their salinity and alkalinity tolerance was compared through chronic stress tests.The results showed that the semi-lethal salinity and alkalinity concentration of the 4^th selected generation was 55.730±1.34g/L and16.31±1.37g/L,respectively,which was significantly higher than those of the control group?46.47±1.64g/L and 12.27±1.08g/L??P<0.05?.Daily weight gain in the S0A0group was significantly higher than that in other salinity and alkalinity groups.With the alkalinity increased the daily weight gain of each group decreased.In test group S10A0,S10A2,S10A4 and S10A6,the average daily weight gain of the 4^thgeneration was significantly higher than that of the control group.Growth of the 4^th and 5^th selection generations of Nile tilapia was carried out in S10A2 water for 60 days.The results showed that the average daily gain was 1.99 g/d for the control group,2.16 g/d for the 4^th generation and 2.26 g/d for the 5^th generation.the growth performance of the 4^th and 5^th generation was higher than the control group,and the growth performance of the 5^th generation was higher than that of the 4^thgeneration.?3?To investigate the effects of salinity on the metabolism of fatty acids in the liver of Nile tilapia,this study compared the changes of fatty acid composition and the m RNA expressions of lipoprotein lipase?LPL?,malic enzyme?ME?and peroxisome proliferator-activated receptor-alpha?PPAR-??in the liver of Nile tilapia in the salinity water?8 and 16?during two week salinity stress.The results showed that the plasma osmolality in the salinity group rose to the highest level at 12 h,and the plasma osmolality in the 16 salinity group was significantly higher than that in the 8 salinity group,the plasma osmolality gradually decreased and tended to be stable in the late stage of treatments.Before 96h,the content of saturated fatty acids?SFA?of in the liver of the salinity groups was significantly lower than the freshwater group?P<0.05?,they gradually recovered to the initial level after 96h.The content of monounsaturated fatty acid?MUFA?in the liver of the salinity group was significantly lower than the freshwater group?P<0.05?.The content of long-chain polyunsaturated fatty acids?mainly DHA,EPA and ARA?in the liver of the salinity groups was significantly higher than the freshwater group?P<0.05?.The m RNA expressions of LPL,ME and PPAR-?in the liver of the salinity group was significantly higher than the freshwater group?P<0.05?.These results showed that the composition of fatty acids in the liver and lipid metabolism could be impacted by salinity stress,which provide basic information for lipid energy utilization in fish osmoregulation.