Effects Of Dietary Protein Levels On Growth,Serum Biochemical Index And Histological Structure Of Gift Under Ammonia-nitrogen Stress

To investigate the influence of chronic ammonia-nitrogen stress on the growth performance,body composition,serum biochemical markers,and non-specific hepatic immune indices of Oreochromis niloticus,the protein levels were formulated as 22.64%,27.26%,31.04%,35.63%,38.47%,and 42.66%of the six isoenergetic test feeds were cultured with A₀（0.02 mg/L）and A₁（35.0±5.0 mg/L）at 2 ammonia concentrations.Feeds of three protein levels（22.64%,31.04%and 38.47%）were fed in A₀ level,and 6 protein levels were fed in A₁ level.A total of 9experimental groups were fed with satiation for 8 weeks.The results showed that:Compared with A₀ level,A₁ level weight gain rate（WGR）,specific growth rate（SGR）,lactate dehydrogenase（LD）,whole fish water,crude ash,muscle crude fat content,alanine aminotransferase（ALT）),aspartate aminotransferase（AST）,glutathione peroxidase（GSH-Px）,serum catalase（CAT）and gill Na⁺/K⁺-ATPase activity were reduced significantly,protein efficiency（FER）,liver to body ratio（HSI）increased significantly（P<0.05）,and feed efficiency（FE）,superoxide dismutase（SOD）,and whole fish crude protein content did not change significantly（P>0.05）.When the protein level was 22.64%,the VSI and SR of the A₁level were significantly lower than the A₀ level（P<0.05）.With the increase of protein levels,the final body weight,WGR,SGR,FE,ALT,GSH-Px,SOD,and Na⁺/K⁺-ATPase activity,total fish water and crude protein content of G.tilapia were increased significantly（P<0.05）,while FER,VSI decreased significantly（P<0.05）,muscle moisture and crude protein content had no significant difference（P>0.05）.The change trends of RBC（red blood cell）and HCT（hematocrit）in A₀ and A₁ groups were similar,they all increased with the increase of protein levels,and there was a significant difference among the groups（P<0.05）.In group A₁,the number of red blood cells of tilapia increased first and then decreased with the increase of protein levels,and the difference between the groups was significant（P<0.05）.At the same protein level,the number of RBCs and HCT in A₁ tilapia group were significantly lower than those in group A₀.At the level of A₁,the activity of PER,GSH-Px,ALT and CAT reached a level consistent with A₀ level of 31.04%at a protein level of38.64%.HSI and VSI remained stable at a protein level of 35.63%or higher.FE,TP The content and gill Na⁺/K⁺-ATPase activity reached a level consistent with the A₀ level at 31.04%protein level.Increasing the level of protein in feed,to a certain extent,slowing down the damage of ammonia and nitrogen stress on tilapia and kidney tissue of tilapia,and raising the level of feed protein,to a certain extent can restore the damage of ammonia nitrogen stress to tilapia.The results showed that under the condition of feed fat level of 7%,according to the comprehensive analysis of the indicators of growth indicators,serum biochemical indicators and non-specific immunity indicators against ammonia nitrogen stress,the protein level in G.tilapia feed reached or exceeded31.04%.Effectively improve anti-stress and anti-oxidation capabilities,thereby enhancing the body’s resistance to environmental stress.